ALBERT

Description: Abstract The research aims to evaluate the output of biogas and the concentration of CH4 and gaseous impurities such as CO2 and H2S in the process of digesting chicken manure without additives (experiment A) and with 10% of biochar additive (by mass of the dry load) (experiment B) under anaerobic and mesophilic conditions. It has been found that the average output of biogas from a particular amount of chicken manure (experiments A and B) obtained in the 45‐day experimental research is similar in both cases and reaches 12.88 l d–1 and 12.36 l d–1, respectively. However, the biochar additive increases CH4 concentration in biogas and reduces the concentration of gaseous impurities (CO2 and H2S) in biogas. The maximum concentration of CH4 in biogas obtained from a load of manure with biochar additive is higher than that in biogas obtained by using a load without a biochar additive, and reaches 72.0% and 68.5%, respectively. The average CO2 concentration, reaching 33.09% and 47.5%, respectively, in biogas obtained from the load with 10% of biochar additive is lower than that in biogas obtained from the manure load without an additive. The average concentration of H2S in the biogas obtained in experiment B is lower than that in experiment A and reaches 95.9 mg m–3 and 195.5 mg m–3, respectively. The biochar additive adsorbs gaseous impurities (CO2 and H2S) from biogas without adsorbing CH4. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Reliable estimation of the volume and timing of snowmelt runoff is vital for water supply and flood forecasting in snow‐dominated regions. Snowmelt is often simulated using temperature‐index (TI) models due to their applicability in data‐sparse environments. Previous research has shown that a modified‐TI model, which uses a radiation‐derived proxy temperature instead of air temperature as its surrogate for available energy, can produce more accurate snow covered area (SCA) maps than a traditional TI model. However, it is unclear whether the improved SCA maps are associated with improved snow water equivalent (SWE) estimation across the watershed or improved snowmelt‐derived streamflow simulation. This paper evaluates whether a modified‐TI model produces better streamflow estimates than a TI model when they are used within a fully‐distributed hydrologic model. It further evaluates the performance of the two models when they are calibrated using either point SWE measurements or SCA maps. The Senator Beck Basin in Colorado is used as the study site because its surface is largely bedrock, which reduces the role of infiltration and emphasizes the role of the SWE pattern on streamflow generation. Streamflow is simulated using both models for six years. The modified‐TI model produces more accurate streamflow estimates (including flow volume and peak flow rate) than the TI model, likely because the modified‐TI model better reproduces the SWE pattern across the watershed. Both models also produce better performance when calibrated with SCA maps instead of point SWE data, likely because the SCA maps better constrain the space‐time pattern of SWE.

Description: Abstract Inorganic membranes can operate under harsh conditions. However, successful synthesis of inorganic membranes is still challenging, and its performance depends on many factors. This work reports the effect of dip‐coating duration, inlet pressure, and inlet flow rate on the flux, permeability, and selectivity of silica membranes. A silica membrane was prepared by the deposition of silica sol onto porous alumina support. The permeability test was conducted at 100 °C using a single gas of CO2 and CH4. The highest flux was observed at the maximum inlet pressure and inlet flow rate for the membrane prepared at the minimum dip‐coating duration. The neural network modeling of the membrane predicted permeabilities showed a considerably high validity regression (R ≈ 0.99) of the predicted data linked to the experimental sets. The separation factor (α) was the highest at the maximum dip‐coating duration. The synthesized silica membrane has potential for CO2/CH4 separation under harsh operating conditions. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract The concentration of greenhouse gases (GHG)s and specifically CO2 continue to rise in the global environment including the atmosphere and the oceans. Oil and gas exploration in oceans and the increased probability of CO2 being destined for ocean storage have made the oceans much vulnerable to acidification and hence detrimental to the entire marine ecosystem. Offshore wind energy, along with other renewables, have the potential to lower the rate of CO2 absorption in the global eco system. Distant offshore wind farms are faced with the problem of dispatch of surplus wind power. Power‐to‐gas technology can be used to convert the offshore wind power into synthetic natural gas that can be transported through the existing network of offshore gas pipelines. The novel method has the capability to significantly reduce GHG emissions, solve the power dispatch problems of offshore wind farms, as well as reduce the oceanic environmental degradation. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Groundwater transit time is an essential hydrologic metric for groundwater resources management. However, especially in tropical environments studies on the transit time distribution (TTD) of groundwater infiltration and its corresponding mean transit time (mTT) have been extremely limited due to data sparsity. In this study, we primarily use stable isotopes to examine the TTDs and their mTTs of both vertical and horizontal infiltration at a riverbank infiltration area in the Vietnamese Mekong Delta (VMD), representative of the tropical climate in Asian Monsoon regions. Precipitation, river water, groundwater, and local ponding surface water were sampled for three to nine years and analyzed for stable isotopes (δ18O and δ2H), providing a unique data set of stable isotope records for a tropical region. We quantified the contribution that the two sources contributed to the local shallow groundwater by a novel concept of two‐component lumped parameter models (LPMs) that are solved using δ18O records. The study illustrates that two‐component LPMs, in conjunction with hydrological and isotopic measurements, are able to identify subsurface flow conditions and water mixing at riverbank infiltration systems. However, the predictive skill and the reliability of the models decrease for locations farther from the river, where recharge by precipitation dominates, and a low‐permeable aquitard layer above the highly permeable aquifer is present. This specific setting impairs the identifiability of model parameters. For river infiltration short mTTs (〈40 weeks) were determined for sites closer to the river (〈200 m), whereas for the precipitation infiltration the mTTs were longer (〉80 weeks) and independent of the distance to the river. The results not only enhance the understanding of the groundwater recharge dynamics in the VMD but also suggest that the highly complex mechanisms of surface‐groundwater interaction can be conceptualized by exploiting two‐component LPMs in general. The model concept could thus be a powerful tool for better understanding both the hydrological functioning of mixing processes and the movement of different water components in riverbank infiltration systems.

Description: Abstract Physically‐based models are useful frameworks for testing intervention strategies designed to reduce elevated sediment loads in agricultural catchments. Evaluating the success of these strategies depends on model accuracy, generally established by a calibration and evaluation process. In this contribution, the physically‐based SHETRAN model was assessed in two similar UK agricultural catchments. The model was calibrated on the Blackwater catchment (18 km2) and evaluated in the adjacent Kit Brook catchment (22 km2) using 4‐years of 15‐minute discharge and suspended sediment flux data. Model sensitivity to changes in single and multiple combinations of parameters as well as sensitivity to changes in Digital Elevation Model (DEM) resolution were assessed. Model flow performance was reasonably accurate; with a Nash‐Sutcliffe efficiency coefficient (NSE) of 0.78 in Blackwater and 0.60 in Kit Brook. In terms of event prediction, the mean of the absolute percentage of difference (μAbsdiff) between measured and simulated flow volume (Qv), peak discharge (Qp), sediment yield (Sy) and peak sediment flux (Sp) showed larger values in Kit Brook (48% [Qv], 66% [Qp], 298% [Sy], 438% [Sp]) compared to the Blackwater catchment (30% [Qv], 41% [Qp], 106% [Sy], 86% [Sp]). Results indicate that SHETRAN can produce reasonable flow prediction but performs less well in estimation of sediment flux, despite reasonably similar hydro‐sedimentary behaviour between catchments. The sensitivity index showed flow volume sensitive to saturated hydraulic conductivity and peak discharge to the Strickler coefficient; sediment yield was sensitive to the overland flow erodibility coefficient and peak sediment flux to raindrop/leaf soil erodibility coefficient. The multi‐parameter sensitivity analysis showed that different combinations of parameters produced similar model responses. Model sensitivity to grid resolution presented similar flow volumes for different DEM resolutions, whereas event peak and duration (for both flow and sediment flux) were highly sensitive to changes in grid size.

Description: Abstract High‐frequency stable isotope data are useful for validating atmospheric moisture circulation models and provide improved understanding of the mechanisms controlling isotopic compositions in tropical rainfall. Here we present a near‐continuous 6‐month record of O‐ and H‐isotope compositions in both water vapour and daily rainfall from Northeast Australia measured by laser spectroscopy. The data set spans both Wet and Dry Seasons to help address a significant data and knowledge gap in the southern hemisphere tropics. We interpret the isotopic records for water vapour and rainfall in the context of contemporaneous meteorological observations. Surface air moisture provided near‐continuous tracking of the links between isotopic variations and meteorological events on local to regional spatial scales. Power spectrum analysis of the isotopic variation showed a range of significant periodicities, from hourly to monthly scales and cross‐wavelet analysis identified significant regions of common power for hourly‐averaged water vapour isotopic composition and relative humidity, wind direction and solar radiation. Relative humidity had the greatest sub‐diurnal influence on isotopic composition. On longer timescales (weeks to months) isotope variability was strongly correlated with both wind direction and relative humidity. The high‐frequency records showed diurnal isotopic variations in O‐ and H‐isotope compositions due to local dew formation and, for deuterium excess, as a result of evapotranspiration. Several significant negative isotope anomalies on a daily scale were associated with the activity of regional mesoscale convective systems and the occurrence of two tropical cyclones. Calculated air parcel back‐trajectories identified the predominant moisture transport paths from the Southwest Pacific Ocean while moisture transport from northerly directions occurred mainly during the Wet Season monsoonal air flow. Water vapour isotope compositions reflected the same meteorological events as recorded in rainfall isotopes but provided much more detailed and continuous information on atmospheric moisture cycling than the intermittent isotopic record provided by rainfall. Improved global coverage of stable isotope data for atmospheric water vapour is likely to improve simulations of future changes to climate drivers of the hydrological cycle.

Description: Hydrological Processes, Volume 33, Issue 19, Page 2499-2501, 15 September 2019.

Description: Abstract Controlled release of carbon dioxide (CO2) into the soil and atmosphere is performed to test detection and monitoring tools, for which several field laboratories were established by a number of institutions worldwide. Numerical simulations of CO2 behavior in the shallow subsurface region are other forms of validation and verification of the leakage pathways and destinations. These studies aim to improve monitoring and verification of CO2 in case of unexpected leakages for public assurance. In this work, we present the results of a numerical modeling study conducted to simulate the injection of CO2 as carried out during a field test in Viamão, southern Brazil, where 20 kg day–1 of CO2 was pumped for 30 days through a vertical well 3 m below ground in an altered granitic soil. Multiphase flow simulations were performed with the TOUGH2/EOS7CA software for unsaturated porous media, using field data and injection parameters, including sensitivity tests to permeability direction, diffusivity, and boundary conditions. Results with increased horizontal permeabilities are in better agreement with the field observations. In this condition, mass balance calculations indicate approximately 90% of injected CO2 (20 kg day–1 during 30 days) remains in the soil after 180 days from injection start, consistent with the measured flow through the soil–atmosphere interface. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Monitoring and estimation of snow depth in alpine catchments is needed for a proper assessment of management alternatives for water supply in these water resources systems. The distribution of snowpack thickness is usually approached by using field data that come from snow samples collected at a given number of locations that constitute the monitoring network. Optimal design of this network is required to obtain the best possible estimates. Assuming that there is an existing monitoring network, its optimization may imply the selection of an optimal network as a subset of the existing one (if there are not funds to maintain them) or enlarging the existing network by one or more stations (optimal augmentation problem). We propose an optimization procedure that minimizes the total variance in the estimate of snowpack thickness. The novelty of this work is to treat, for the first time, the problem of snow observation network optimization for an entire mountain range rather than for small catchments as done in previous studies. Taking into account the reduced data available, which is a common problem in many mountain ranges, the importance of a proper design of these observation networks is even larger. Snowpack thickness is estimated by combining regression models to approach the effect of the explanatory variables and kriging techniques to consider the influence of the stakes location. We solve the optimization problems under different hypotheses, studying the impacts of augmentation and reduction, both, one by one and in pairs. We also analyse the sensitivity of results to non‐snow measurements deduced from satellite information. Finally, we design a new optimal network by combining the reduction and augmentation methods. The methodology has been applied to the Sierra Nevada mountain range (southern Spain), where very limited resources are employed to monitor snowfall and where an optimal snow network design could prove critical. An optimal snow observation network is defined by relocating some observation points. It would reduce the estimation variance by around 600 cm2 (15%).

Description: Abstract The effects of root systems on soil detachment by overland flow are closely related to vegetation types. The objective of this study was to quantify the effects of two gramineous roots (Paspalum mandiocanum with shallow roots and Pennisetum giganteum with deep roots) on soil detachment capacity, rill erodibility and critical shear stress on alluvial fans of benggang in southeast China. A 4 m long and 0.12 m wide flume was used. Slope steepness ranged from 9% to 27%, and unit flow discharge ranged from 1.39×10‐3 to 4.19×10‐3 m2 s‐1. The mean detachment capacities of Paspalum mandiocanum and Pennisetum giganteum lands were 18% and 38% lower than that of bare land, respectively, and the effects of root on reducing soil detachment were mainly reflected in the 0‐5 cm soil layer. The most important factors in characterizing soil detachment capacity were root length density and soil cohesion, and soil detachment capacity of the two grass lands could be estimated using flow shear stress, soil cohesion, and root length density (NSE=0.90). With the increase in soil depth, rill erodibility increased, while shear stress decreased. The mean rill erodibilities of Paspalum mandiocanum and Pennisetum giganteum lands were 81% and 61% as much as that of bare land, respectively. Additionally, rill erodibilities of the two grass lands could be estimated as an exponential function by root length density and soil cohesion (NSE=0.88). The mean critical shear stress of Paspalum mandiocanum and Pennisetum giganteum lands were 1.29 and 1.39 times that of bare land, respectively, and it could be estimated with a linear function by root length density (NSE=0.76). This study demonstrated that planting of the two grasses Paspalum mandiocanum and Pennisetum giganteum could effectively reduce soil detachment and enhance soil resistance to erosion on alluvial fans, with the deep roots of Pennisetum giganteum being more effective than the shallow roots of Paspalum mandiocanum. The results are helpful for understanding the influencing mechanism of root systems on soil detachment process.

Description: Abstract In order to utilize as much of the pore space for CO2 storage in high permeability thick saline aquifers, it is vital to investigate the interactions of injected CO2 with formation brine and rock. In order to quantify the displacement process, we investigate the dynamic storage efficiency factor (DSEF) for saline aquifers where pressure increase is minimal during the injection phase. Dimensionless numbers are derived from basic governing equations, constitutive equations, initial and boundary conditions using the inspection analysis. Then using the Hammersley sequence sampling, 178 numerical experiments are designed, and a compositional reservoir simulator is used to perform these simulations. In the next step, response surface regression analysis is used to establish a relationship between DSEF obtained from the numerical simulations and the corresponding dimensionless numbers. The simulation results show that for the studied conditions the underground dynamics is mostly influenced by the gravity number, followed by effective aspect ratio and dip numbers. The results from the response surface regression analysis are used to develop a correlation, which can be used to estimate the dynamic CO2 storage capacity of relevant zones. This study provides quantitative measures for the different competing mechanisms involved in underground displacement of fluids in CO2 geological storage, which can serve as a useful tool during planning phase of storage projects. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract The aim of this study was to investigate how the spatial distribution of grass influenced runoff and erosion from a hillslope with loess and cinnamon soils in the rocky area of Northern China. We set up a trial to test the two soils with different treatments, including bare soil (BS), grass strips on the upper (UGS) and lower (DGS) parts of the slope, grass cover over the entire slope (GS), and a grass carpet on the lower part of the slope (GC), under simulated rainfall conditions. The results showed that the runoff coefficients for the loess and cinnamon soils decreased by between 4% and 20% and by between 2% and 37%, respectively, when covered with grass. Grass spatial distribution had little effect on the runoff, but more effect on erosion than vegetation coverage degree. The most effective location of grass cover for decreasing hillslope erosion was at the foot, and the high efficiency was mainly due to controlling of rill formation and sediment deposition. The soil loss from GS, DGS, and GC on the loess and cinnamon soils was between 77% and 93% less and 55% and 80% less, respectively, compared to the loss from BS. However, the soil characteristics had little effect on soil erosion for well‐vegetated slopes. The results highlight the importance of vegetation re‐establishment at the foot of hillslope in controlling soil erosion.

Description: Greenhouse Gases: Science and Technology, Volume 9, Issue 4, Page 610-612, August 2019.

Description: Abstract The phase equilibria with the confinement effect could shift in nano‐pores, which could have a great impact on the recovery mechanisms of CO2 injection in tight oil reservoirs; this has not been systematically studied. In this paper, the confinement effect with property shift and capillarity effect is introduced into the flash calculation of confined fluids. The Soave modification of the Redlich–Kwong equation of state is extended by the molecular‐wall collision parameter to describe the shifted pressure–volume–temperature properties of confined fluid, and the Young–Laplace equation is applied to evaluate the capillary pressure. This developed model could effectively be applied for phase equilibrium calculation in tight porous media because of the verification of experimental results. A binary mixture is investigated to study the different effect of capillary pressure and property shift on phase equilibria. Subsequently, a typical hydrocarbon fluid from Middle Bakken tight oil reservoirs is studied with CO2 injection. Results illustrate that the confinement effect could play an increasingly important part in the phase equilibrium state. The CO2 solubility and mass transfer driving force in tiny pores would be greater than those in large pores under the same conditions. The gas phase saturation would be smaller with the same compositions, which could extend the single‐phase region of fluid flow in porous media. Furthermore, bubble‐point pressure, the minimum miscible pressure of CO2/hydrocarbon, and the viscosity of tight oil dissolved with CO2 both decrease with the pore size, which has a good influence on tight oil recovery. In general, the confinement effect could effectively reinforce the recovery mechanisms of CO2 injection, which is conducive to the enhancement of tight oil recovery. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Recent field experiments in Iceland and Washington State (USA) show that basalt formations may be favorable targets for carbon capture and sequestration (CCS) because CO2 mineralization reactions proceed rapidly. These results imply that there is tremendous opportunity for implementing CCS in large igneous provinces. However, the magnitude of this opportunity comprises commensurate levels of uncertainty because basalt reservoirs are characterized by highly heterogeneous, fracture‐controlled hydraulic properties. This geologic uncertainty is propagated as parametric uncertainty in quantitative risk models, thus limiting the efficacy of models to predict CCS performance attributes, such as reservoir integrity and storage potential. To overcome these limitations, this study presents a stochastic approach for quantifying the geomechanical performance attributes of CCS operations in a highly heterogeneous basalt reservoir. We utilize geostatistical reservoir characterization to develop an ensemble of equally probable permeability distributions in a flood basalt reservoir with characteristics of the Wallula Basalt Pilot Project. We then simulate industrial‐scale CO2 injections within the ensemble and calculate the mean and variance of fluid pressure over a 1‐year injection period. These calculations are combined with the state of stress in southeast Washington State to constrain the spatial extent at which shear failure, fracture initiation, and borehole breakdown may occur. Results from this study show that (i) permeability uncertainty alone causes injection pressure to vary over 25 MPa, (ii) shear failure is likely to occur at 7 times greater distances from the injection than the CO2 migrates, and (iii) joint initiation pressures are localized within the volume comprising the CO2 plume. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Despite political turmoil and intrigue, along with the inevitable financial uncertainty, the desire to overcome the obstacles that could hold back the innovation and implementation of technologies and projects to tackle climate change remains active. The recent climate change protests by school children are an indicator of not only the level of concern over climate issues, but what is also at stake if these obstacles allow progress to be derailed. The good news is that in the area of carbon capture utilisation and storage (CCUS), considered to be among the costliest, but necessary, weapons in the climate change mitigation arsenal, progress continues to be made. In this article, GHGS&T's Muriel Cozier rounds up some of the most recent developments. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: The manuscript analyses links between flood spatial arrangement and soil water balance in a plain watershed, and, with that purpose, landscape metrics are calculated in maps obtain by remote sensed data in different hydrological scenarios. In contrast with previous works that investigate connectivity, we applied landscape metrics focusing on flooding pattern, their spatial and temporal variability, and their relationship with soil water balance. In addition, the analysis of patterns allows highlighting the internal heterogeneity that plain landscapes usually exhibit. Abstract In areas with very mild relief, water drains in a disordered way due to the lack of a developed drainage network, as it occurs in extremely flat sedimentary regions like the Argentine Pampas. The study analysed the flood spatial arrangements in 2014 by calculating landscape metrics and relating them to soil water balance. The study area is located at Del Azul creek lower basin (Pampa Ecoregion, Argentina). Daily soil water balances were obtained, and seven landscape metrics were calculated in 15 windows in five LandSat images, all along 2014, to explore the relationship between hydrological scenarios and spatial pattern summarized with principal component analysis. Water excess concentrated in winter (June and August); deficits were in late spring and summer (January and November), whereas the beginning of autumn (March) was an intermediate situation. Principal component 1 (44.7%) reflected area and shape metrics and correlated positively with water table level; principal component 2 (32.3%) summarized aggregation ones and was negatively associated with accumulated water excesses or deficits in previous 30 days and useful reserve. Both exhibited possible threshold‐driven behaviour. Internal heterogeneity between NW and SE zones within the study area coincided with the existence of ancient alluvial fans. The results highlight the peculiarities of the flood spatial patterns in regions with very mild relief, where landforms usually determine water flows.

Description: Abstract To investigate the flow field near fracture entrance and promote the development of sand fracturing with carbon dioxide as the working fluid, numerical simulation of multiphase flow was conducted with a 3D geological model considering the compressibility of carbon dioxide. The flow field of carbon dioxide alone was firstly investigated to lay the foundation for the analysis of multiphase flow, and then comparative analysis was conducted on the flow field of both the injecting sand from the pipe and the annulus. The results show that jet fracture with carbon dioxide can achieve a 4.46 MPa pressure boost at the fracture tip compared to the annulus pressure, which theoretically validates the feasibility of the mentioned technology. Sand fracturing can achieve a higher pressure boost in the cavity, while it needs greater pump pressure at the surface. Injecting sand from the annulus could decrease the need for pump pressure by 6.62 MPa at the condition of injecting 25% carbon dioxide from the annulus simultaneously, while the pressure difference between the cavity tip and the annulus decreases as a result. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract This work introduces water–air two‐phase flow into integrated surface–subsurface flow by simulating rainfall infiltration and run‐off production on a soil slope with the finite element method. The numerical model is formulated by partial differential equations for hydrostatic shallow flow and water–air two‐phase flow in the shallow subsurface. Finite element computing formats and solution strategies are presented to obtain a numerical solution for the coupled model. An unsaturated seepage flow process is first simulated by water–air two‐phase flow under the atmospheric pressure boundary condition to obtain the rainfall infiltration rate. Then, the rainfall infiltration rate is used as an input parameter to solve the surface run‐off equations and determine the value of the surface run‐off depth. In the next iteration, the pressure boundary condition of unsaturated seepage flow is adjusted by the surface run‐off depth. The coupling process is achieved by updating the rainfall infiltration rate and surface run‐off depth sequentially until the convergence criteria are reached in a time step. A well‐conducted surface run‐off experiment and traditional surface–subsurface model are used to validate the new model. Comparisons with the traditional surface–subsurface model show that the initiation time of surface run‐off calculated by the proposed model is earlier and that the water depth is larger, thus providing values that are closer to the experimental results.

Description: Scaling issues in snow hydrology persist due to limitations in instrumentation and inability to measure physical properties and processes at spatiotemporal scales required for analysis. Snow depth and water equivalent (SWE) across scale estimated using time‐lapse photos, transects, and model grids (Canadian Meteorological Centre depth, GlobSnow SWE) were found to represent different physical processes and have substantially different statistical moments. Findings have implications for understanding limitations of distributing snowpack measurements, data assimilation, and validation of remotely sensed estimates. Abstract This study investigates scaling issues by evaluating snow processes and quantifying bias in snowpack properties across scale in a northern Great Lakes–St. Lawrence forest. Snow depth and density were measured along transects stratified by land cover over the 2015/2016 and 2016/2017 winters. Daily snow depth was measured using a time‐lapse (TL) camera at each transect. Semivariogram analysis of the transect data was conducted, and no autocorrelation was found, indicating little spatial structure along the transects. Pairwise differences in snow depth and snow water equivalent (SWE) between land covers were calculated and compared across scales. Differences in snowpack between forested sites at the TL points corresponded to differences in canopy cover, but this relationship was not evident at the transect scale, indicating a difference in observed process across scale. TL and transect estimates had substantial bias, but consistency in error was observed, which indicates that scaling coefficients may be derived to improve point scale estimates. TL and transect measurements were upscaled to estimate grid scale means. Upscaled estimates were compared and found to be consistent, indicating that appropriately stratified point scale measurements can be used to approximate a grid scale mean when transect data are not available. These findings are important in remote regions such as the study area, where frequent transect data may be difficult to obtain. TL, transect, and upscaled means were compared with modelled depth and SWE. Model comparisons with TL and transect data indicated that bias was dependent on land cover, measurement scale, and seasonality. Modelled means compared well with upscaled estimates, but model SWE was underestimated during spring melt. These findings highlight the importance of understanding the spatial representativeness of in situ measurements and the processes those measurements represent when validating gridded snow products or assimilating data into models.

Description: Abstract Global warming and the greenhouse effect are two of the most important environmental problems. Carbon dioxide, methane, and nitrous oxide emissions are the main greenhouse gas emissions in wastewater treatment plants. In this study, the greenhouse gas emission sources in a wastewater treatment plant were determined. Direct (from fossil fuel combustion, methane emissions, and process emissions of the other greenhouse gases) and indirect emissions (primarily from electricity use) in the plant were monitored. The optimum influent characteristics and operating conditions have been defined by using Monte Carlo simulation to minimize the emissions. The results revealed that the highest direct greenhouse gas emission was observed in August with the value of 23.328 kg CO2‐eq d–1 and the lowest emission was 7.56 kg CO2‐eq d–1 measured in January. The aeration tank is a major source of greenhouse gas emissions. Indirect emission has occurred because of the anaerobic digester but the biogas has been cogenerated in the plant, so it has been ignored for the calculation. According to the simulation study, if the plant is operated under optimum operating conditions, it can emit the lowest amount of greenhouse gas emissions. The optimum removal values required for the minimum greenhouse gas emissions are 79% for chemical oxygen demand, 75% for biochemical oxygen demand, and 82% for total suspended solid. The optimum operating conditions for the aeration tank, which is the major source of emission, are 5.33 h of hydraulic retention time, 0.215 d of solid retention time, and 0.999 for food/microorganisms. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Greenhouse Gases: Science and Technology, Volume 9, Issue 4, Page 607-609, August 2019.

Description: The cover image is based on the Review Renewable absorbents for CO2 capture: from biomass to nature by Qingyao He et al., https://doi.org/10.1002/ghg.1902. Cover image © Feihong Liang.

Description: Abstract Forest canopies present irregular surfaces that alter both the quantity and spatiotemporal variability of precipitation inputs. The drop size distribution (DSD) of rainfall varies with rainfall event characteristics and is altered substantially by the forest stand properties. Yet, the influence of two major European tree species, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst), on throughfall DSD is largely unknown. In order to assess the impact of these two species with differing canopy structures on throughfall DSD, two optical disdrometers, one above and one below the canopy of each European beech and Norway spruce, measured DSD of both incident rainfall and throughfall over two months at a 10 second resolution. Fractions of different throughfall categories were analysed for single precipitation events of different intensities. While penetrating the canopies, clear shifts in drop size and temporal distributions of incoming rainfall were observed. Beech and spruce, however, had different DSD, behaved differently in their effect on diameter volume percentiles as well as width of drop spectrum. The maximum drop sizes under beech were higher than under spruce. The mean ± standard deviation of the median volume drops size (D50) over all rain events was 2.7 ± 0.28 mm for beech and 0.80 ± 0.04 mm for spruce, respectively. In general, there was a high DSD variability within events indicating varying amounts of the different throughfall fractions. These findings help to better understand the effects of different tree species on rainfall partitioning processes and small scale variations in subcanopy rainfall inputs, thereby demonstrating the need for further research in high resolution spatial and temporal properties of rainfall and throughfall.

Description: A recently theoretically deduced rill flow resistance equation, based on a power‐velocity profile, was tested experimentally on plots of varying slopes (ranging from 9% to 26%) in which mobile and fixed bed rills were incised. The measurements carried out in both conditions confirmed that the Darcy–Weisbach friction factor can be accurately estimated using the proposed theoretical approach. For the investigated conditions, the effect of sediment transport on the flow resistance law is negligible respect to the grain roughness effect. Abstract Rills caused by run‐off concentration on erodible hillslopes have very irregular profiles and cross‐section shapes. Rill erosion directly depends on the hydraulics of flow in the rills, which may differ greatly from hydraulics of flow in larger and regular channels. In this paper, a recently theoretically deduced rill flow resistance equation, based on a power–velocity profile, was tested experimentally on plots of varying slopes (ranging from 9% to 26%) in which mobile and fixed bed rills were incised. Initially, measurements of flow velocity, water depth, cross‐section area, wetted perimeter, and bed slope, carried out in 320 reaches of mobile bed rills and in 165 reaches of fixed rills, were used for calibrating the theoretical flow resistance equation. Then the relationship between the velocity profile parameter Γ, the channel slope, and the flow Froude number was separately calibrated for the mobile bed rills and for the fixed ones. The measurements carried out in both conditions (fixed and mobile bed rills) confirmed that the Darcy–Weisbach friction factor can be accurately estimated using the proposed theoretical approach. For mobile bed rills, the data were supportive of the slope independence hypothesis of velocity, due to the feedback mechanism, stated by Govers. The feedback mechanism was able to produce quasicritical flow conditions. For fixed bed rills, obtained by fixing the rill channel, by a glue, at the end of the experimental run with a mobile bed rill, the slope independence of the flow velocity measurements was also detected. Therefore, an experimental run carried out by a rill bed fixed after modelling flow action is useful to detect the feedback mechanism. Finally, the analysis showed that, for the investigated conditions, the effect of sediment transport on the flow resistance law can be considered negligible respect to the grain roughness effect.

Description: Analyses of stem water stable isotope composition were used to identify water taken up by plants. The Populus trees and Shepherdia and Symphoricarpos shrubs had contrasting functional rooting depths as illustrated by the different seasonal patterns of change in deuterium excess values, which indicated greater shallow soil water use by the shrub species. Abstract Riparian cottonwood forests in dry regions of western North America do not typically receive sufficient growing season precipitation to completely support their relatively high transpiration requirements. Water used in transpiration by riparian ecosystems must include alluvial groundwater or water stored in the potentially large reservoir of the unsaturated soil zone. We used the stable oxygen and hydrogen isotope composition of stem xylem water to evaluate water sources used by the dominant riparian cottonwood (Populus spp.) trees and shrubs (Shepherdia argentea and Symphoricarpos occidentalis) in Lethbridge, Alberta, during 3 years of contrasting environmental conditions. Cottonwoods did not exclusively take up alluvial groundwater but made extensive use of water sourced from the unsaturated soil zone. The oxygen and hydrogen isotope compositions of cottonwood stem water did not strongly overlap with those of alluvial groundwater, which were closely associated with the local meteoric water line. Instead, cottonwood stem water δ18O and δ2H values were located below the local meteoric water line, forming a line with a low slope that was indicative of water exposed to evaporative enrichment of heavy isotopes. In addition, cottonwood xylem water isotope compositions had negative values of deuterium excess (d‐excess) and line‐conditioned (deuterium) excess (lc‐excess), both of which provided evidence that water taken up by the cottonwoods had been exposed to fractionation during evaporation. The shrub species had lower values of d‐excess and lc‐excess than had the cottonwood trees due to shallower rooting depths, and the d‐excess values declined during the growing season, as shallow soil water that was taken up by the plants was exposed to increasing, cumulative evaporative enrichment. The apparent differences in functional rooting pattern between cottonwoods and the shrub species, strongly influenced the ratio of net photosynthesis to stomatal conductance (intrinsic water‐use efficiency), as shown by variation among species in the δ13C values of leaf tissue.

Description: Hydrological Processes, Volume 33, Issue 17, Page 2263-2265, 15 August 2019.

Description: Abstract The economic feasibility of carbon dioxide (CO2) enhanced oil recovery (EOR) to offset CO2 capture costs from a coal‐fired power plant are evaluated for 36 source‐sink scenarios in Ohio; one of the top ten states for fossil‐fuel use and CO2 emissions in the United States. Six capture scenarios are examined for a representative 550 megawatt (MW) coal‐fired power plant, and three CO2‐EOR injection scenarios are evaluated for both East Canton oil field and Gore consolidated oil field. The potential costs and credits associated with CO2 storage related tax incentives are also considered. Power plant capture performance and costs integrated with field‐scale CO2‐EOR techno‐economics suggest that there are potentially feasible scenarios for capture, transport, and CO2‐EOR storage of 25%, 50%, and 90% of CO2 emissions, respectively, from a 550 MW power plant. Economically feasible outcomes exhibiting net present values of $2191, $1380, and $1940 million are estimated for the 25%, 50%, and 90% capture scenarios, respectively. On average, the 45Q tax credit for CO2 storage affords a $3–$7 per barrel decrease in the minimum oil price required to break‐even on the project. In all source‐sink scenarios qualifying as feasible, the CO2 capture costs incurred by the power plant are offset by revenue from CO2‐EOR and are not passed on to ratepayers during the 30‐year analysis time frame. The most economical outcome for supporting a commercial carbon capture, utilization, and storage project in Ohio is also identified, and the potential impact of CO2‐EOR operational strategy on source‐sink feasibility is discussed. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract A dynamically coupled mass, momentum, and heat transfer model was developed, which demonstrated the unstable behavior of CO2 movement inside porous sediment during high pressure injection and its transformation into solid hydrates. The presented mathematical model was solved using the implicit finite difference method, and through ordering the set of model equations, a complex integrated methodology could be established to analyze the CO2 hydrate nucleation procedure within P‐T equilibrium conditions. The results showed that the intrinsic permeability factor of the porous sediment had great influence on the pressure distribution. At 10−13 m2 intrinsic permeability, the formation pressure distribution became stable at an early stage of the hydrate growth process and remained stable afterwards. The overall hydrate covered length was 320 m due to the massive hydrate growth rate. When intrinsic permeability was reduced to 10−14 m2, it showed delay in pressure distribution and the overall hydrate covered length shifts to up to 310 m due to the delay in pressure distribution. Whereas at a 10−15 m2 intrinsic permeability factor, there was significant delay in pressure distribution so the injection pressure was not fully distributed even after 30 days of the induction process, which squeezed the hydrate covered length to 130 m. This pressure distribution had direct correlation with other parameter variations during the hydrate growth process, such as temperature distribution, hydrate growth rate, CO2 velocity, CO2 density, CO2 and H2O saturation, CO2 permeability, and interface boundary movement speed. Hence, the pressure distribution inside hydrate‐bearing sediment is the most dominant factor to enhance CO2 storage capacity but it does not give satisfactory results in extended formations. © 2019 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract As a water‐less fracturing mining technology, supercritical CO2 fracturing has attracted increasing attention in the mining industry. Based on detailed analysis of CO2 phase behavior in the whole process of supercritical CO2 fracturing, the whole cycle of supercritical CO2 fracturing was divided into the supercritical CO2 fracturing stage and the CO2 phase transition–induced fracturing stage, and according to the characteristics of each fracturing stage, the fracturing mechanism of supercritical CO2 was analyzed in stages, and the roles of the two stages in the life cycle of the entire supercritical CO2 fracturing process were obtained. Through the laboratory test of supercritical CO2 fracturing coal mass, the pressure–time curves during the whole process of supercritical CO2 fluid fracturing were analyzed, and the rationality and correctness of the supercritical CO2 fracturing staged analysis method proposed in this paper were verified. Based on the energy conservation theory and the state function equation of classical thermodynamics, the burst energy of the CO2 phase transition–induced fracturing stage was estimated. By comparing the trinitrotoluene equivalent of phase‐transition energy with the trinitrotoluene amount of explosive explosion, it was proved that the CO2 phase transition–induced fracturing stage was not negligible. The research results of this paper are of considerable significance for the full understanding of the supercritical CO2 fracturing mechanism. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract CO2 capture and storage (CCS) can be an important feature of a decarbonization strategy involving electricity generation. According to the recently revised Section 45Q tax credits, said credits will be provided for implementing CCS, which is motivating some United States (US) electricity generation companies to revisit their business strategies for CCS. This paper discusses alternative business models being considered by companies for undertaking CCS, including providing a ‘template’ for evaluating the cost‐effectiveness of CCS with Section 45Q tax credits and storage in saline reservoirs. Using stylized illustrative examples, the paper indicates how use of Section 45Q tax credits should be expected to change dispatch at an electricity generating unit. For situations similar to the examples, the paper suggests that Section 45Q tax credits may need to be modified to achieve its intended impact. Modifications can include extending the time period of tax credit availability beyond the current 12 years. In addition, continued R&D investments in CCS and specific support for first‐of‐a‐kind CCS demonstrations would be valuable complements for the deployment of the Section 45Q tax credit. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Hydrological Processes, Volume 0, Issue ja, -Not available-.

Description: Abstract Meltwater from glaciers is not only a stable source of water but also affects downstream streamflow dynamics. One of these dynamics is the interannual variability of streamflow. Glaciers can moderate streamflow variability, because the runoff in the glacierised part, driven by temperature, correlates negatively with the runoff in the non‐glacierised part of a catchment, driven by precipitation, thereby counterbalancing each other. This is also called the glacier compensation effect (GCE) and the effect is assumed to depend on relative glacier cover. Previous studies found a convex relationship between streamflow variability and glacier cover of different glacierised catchments, with lowest streamflow variability at a certain optimum glacier cover. In this study we aim to revisit these previously found curves to find out if a universal relationship between interannual streamflow variability and glacier cover exists, which could potentially be used in a space‐for‐time substitution analysis. Moreover, we test the hypothesis that the dominant climate drivers (here precipitation and temperature) switch around the suggested optimum of the curve. First a set of virtual nested catchments, with the same absolute glacier area but varying non‐glacierised area, were modelled to isolate the effect of glacier cover on streamflow variability. The modelled relationship was then compared to a multi‐catchment dataset of gauged glacierised catchments in the European Alps. In a third step, changes of the GCE curve over time were analysed. Model results showed a convex relationship and the optimum in the simulated curve aligned with a switch in the dominant climate driver. However, the multi‐catchment data and the time change analyses did not suggest the existence of a universal convex relationship. Overall, we conclude that GCE is complex due to entangled controls and changes over time in glacierised catchments. Therefore, care should be taken to use a GCE curve for estimating and/or predicting interannual streamflow variability in glacierised catchments.

Description: Abstract Base flows are important for tropical regions with pronounced dry seasons which are facing increasing water demands. Base flow generation, however, is one of the most challenging hydrological processes to characterize in the tropics. In many years during the May‐December wet season in the Panama Canal Watershed (PCW), base flows in rivers abruptly increase. This increase persists until the start of the December‐April dry season. Understanding this unusual base flow jump (BFJ) behavior is critical to improve water provisioning in seasonal tropics, especially during droughts and extended dry seasons. This study developed an integrated approach combining piecewise regression on cumulative average base flow and sensitivity analysis to calculate the timing and magnitude of BFJ. Rainfall, forest cover, mean land surface slope, catchment area and estimated subsurface storage were tested as predictors for the occurrence and magnitude of the BFJs in seven sub‐catchments of the PCW. Sensitivity analysis on correlated predictors allowed ranking of predictor contributions due to isolated and cross correlation effects. Correlations between observed BFJs and BFJs predicted by watershed and rainfall‐related predictors were 0.92 and 0.65 for BFJ timing and magnitude, respectively. Forest cover was the second most significant predictor after cumulative rainfall for jump magnitude, owing to larger subsurface storage and groundwater recharge in forests than pastures. Catchments in the mountainous eastern PCW always generated larger jumps due to their higher rainfall and greater forest cover than the western PCW catchments. The cross‐correlations between predictors contributed to more than 50% of the jump variances. The results demonstrate the importance of rainfall gradient and catchment characteristics in affecting the sudden and sustained BFJs, which can help inform land management decisions intended to enhance water supplies in tropics. This study underscores the need for more research to further understand the hydrological processes involved in the BFJ phenomenon, including better BFJ models and field characterizations, to help improve tropical ecosystem services under a changing environment.

Description: Melting seasonal ground ice reduces potential evapotranspiration and may be a mechanism for peatland persistence in the Western Boreal Plain Abstract Peatlands in the Western Boreal Plains act as important water sources in the landscape. Their persistence, despite potential evapotranspiration (PET) often exceeding annual precipitation, is attributed to various water storage mechanisms. One storage element that has been understudied is seasonal ground ice (SGI). This study characterized spring SGI conditions and explored its impacts on available energy, actual evapotranspiration, water table, and near surface soil moisture in a western boreal plains peatland. The majority of SGI melt took place over May 2017. Microtopography had limited impact on melt rates due to wet conditions. SGI melt released 139mm in ice water equivalent (IWE) within the top 30cm of the peat, and weak significant relationships with water table and surface moisture suggest that SGI could be important for maintaining vegetation transpiration during dry springs. Melting SGI decreased available energy causing small reductions in PET (〈10mm over the melt period) and appeared to reduce actual evapotranspiration variability but not mean rates, likely due to slow melt rates. This suggests that melting SGI supplies water, allowing evapotranspiration to occur at near potential rates, but reduces the overall rate at which evapotranspiration could occur (PET). The role of SGI may help peatlands in headwater catchments act as a conveyor of water to downstream landscapes during the spring while acting as a supply of water for the peatland. Future work should investigate SGI influences on evapotranspiration under differing peatland types, wet and dry spring conditions, and if the spatial variability of SGI melt leads to spatial variability in evapotranspiration.

Description: Abstract In urban areas, the presence of impervious surfaces limits natural drainage and routes water to stormwater infrastructure with finite capacity, making these areas especially prone to flooding. Though large floods are responsible for endangering lives and causing extensive damage, there is growing evidence that more frequent floods with shallow water depths, termed nuisance flooding, can have a high cumulative cost and many direct and indirect damages. To determine whether locations of nuisance flooding may be linked to topography, we took a parsimonious, spatially distributed approach to explore whether high topographic index values co‐occur with citizen‐reported nuisance flooding. We obtained nuisance flood reports from the municipal data service 311 for several watersheds in New York City and Baltimore, USA. Our analysis tested two topographic indices (TI)—topographic wetness index (TWI) and sink depth—both calculated from high‐resolution (~1 m) digital elevation models. Generally, our findings suggest that not all but many locations of reported flooding tend to coincide with deep sinks or large TWI. However, nuisance flooding reports most commonly coincided with deep sinks and high TWI when using a maximum, instead of coincident, TI value extracted around each reported location of flooding, an approach we used due to the uncertainty in location accuracy of flooding reports. Overall, our results show promise for application of topographic indices, typically applied in more natural settings, as indicators of nuisance flooding areas in urbanized environments. Although limitations to this approach exist, the application of TIs and crowd‐sourced reporting in tandem could provide a useful starting point for mapping flood‐prone areas in many cities with technologically adept community members and ample geospatial data.

Description: 1 There was a poor correlation between the flow intensity indices of velocity category and nondimensional sediment transport capacity.2 Ignoring the partition phenomenon of the relation curves, stream power can be used to predict sediment transport capacity, with a coefficient of determination of 0.85.3 An empirical formula for predicting sediment transport with a coefficient of determination of 0.90 was established by multiple regression analysis based on the general flow intensity index. Abstract Soil erosion is a major contributor to land degradation in the Loess Plateau in China. To clarify the sediment transport capacity of overland flow influenced by hydraulic parameters, such as shear stress, sand shear stress (hydraulic gradient partition method and hydraulic radius partition method), mean flow velocity, Froude number, stream power, and unit stream power, indoor experiments with eight‐unit‐width flow discharges from 0.0667 × 10−3 to 0.3333 × 10−3 m2·s−1, six slope gradients from 3.49 to 20.79%, and two kinds of sand soils (d50 = 0.17 and 0.53 mm) were systematically investigated. A nondimensional method was adopted in data processing. Results showed that there was a partition phenomenon of relation curves because of the different median grain diameters. The correlation between the nondimensional stream power and nondimensional sediment transport capacity was the highest, followed by the correlation between the nondimensional unit stream power and nondimensional sediment transport capacity. However, there was a poor correlation between the flow intensity indices of velocity category and nondimensional sediment transport capacity. Nondimensional stream power, nondimensional unit stream power, and nondimensional shear stress could predict sediment transport capacity well. Ignoring the partition phenomenon of the relation curves, stream power could be used to predict sediment transport capacity, with a coefficient of determination of .85. Furthermore, a general flow intensity index was obtained to predict sediment transport capacity of overland flow. Finally, an empirical formula for predicting sediment transport capacity with a coefficient of determination of .90 was established by multiple regression analyses based on the general flow intensity index. During the analysis between measured sediment transport capacities in present study and predicted values based on Zhang model, Mahmoodabadi model, and Wu model, it was found that these three models could not accurately predict sediment transport capacities of this study because different models are estimated on the basis of different experimental conditions.

Description: Abstract Growing interest in offshore geologic carbon sequestration (GCS) motivates evaluation of the consequences of subsea CO2 well blowouts. We have simulated a hypothetical major CO2 well blowout in shallow water of the Texas Gulf Coast. We use a coupled reservoir‐well model (T2Well) to simulate the subsea blowout flow rate for input to an integral model (TAMOC) for modeling CO2 transport in the water column. Bubble sizes are estimated for the blowout scenario for input to TAMOC. Results suggest that a major CO2 blowout in ≥50 m of water will be almost entirely attenuated by the water column due to CO2 dissolution into seawater during upward rise. In contrast, the same blowout in 10 m of water will hardly be attenuated at all. Results also show that the size of the orifice of the leak strongly controls the CO2 blowout rate. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract A few relatively large reservoirs, hundreds of small reservoirs and numerous farm dams were built in the upper Gan River Basin, China. The operation of such a reservoir network can serve as a significant source of variability in the local hydrological regime and should be included in research to better understand the interaction between multiple hydrological processes and watershed management. In this study, a reservoir network module that included reservoirs of multiple sizes was developed and fully integrated into a coupled land surface and distributed hydrologic model, CLHMS, for a detailed description of the hydrological impact of a reservoir network. A generalized release scheme was employed to determine the outflow of both large and small reservoirs. The integrated model was then evaluated against observations and reanalysis data, which indicate that the model can reasonably reconstruct the reservoir operation, streamflow and other hydrological variables. Results quantitatively demonstrate that a reservoir network can result in an increased streamflow in dry seasons, a decreased streamflow in wet seasons, a generally larger groundwater discharge, higher groundwater level, a slightly damper soil condition and a larger amount of evapotranspiration at the basin level. With the integrated model, it is feasible to achieve more sustainable watershed planning and management.

Description: Abstract Seasonal snowpacks in marginal snow environments are typically warm and nearly isothermal, exhibiting high inter‐ and intra‐annual variability. Measurements of snow depth and snow water equivalent were made across a small subalpine catchment in the Australian Alps over two snow seasons in order to investigate the extent and implications of snowpack spatial variability in this marginal setting. The distribution and dynamics of the snowpack were found to be influenced by upwind terrain, vegetation, solar radiation and slope. The role of upwind vegetation was quantified using a novel parameter based on gridded vegetation height. The elevation range of the catchment was relatively modest (185 m), and elevation impacted distribution but not dynamics. Two characteristic features of marginal snowpack behaviour are presented. Firstly, the evolution of the snowpack is described in terms of a relatively unstable accumulation state and a highly stable ablation state, as revealed by temporal variations in the mean and standard deviation of snow water equivalent. Secondly, the validity of partitioning the snow season into distinct accumulation and ablation phases is shown to be compromised in such a setting. Snow at the most marginal locations may undergo complete melt several times during a season and, even where snow cover is more persistent, ablation processes begin to have an effect on the distribution of the snowpack early in the season. Our results are consistent with previous research showing that individual point measurements are unable to fully represent the variability in the snowpack across a catchment, and we show that recognising and addressing this variability is particularly important for studies in marginal snow environments.

Description: Abstract Spatiotemporal heterogeneity in soil water content is recognized as a common phenomenon, but heterogeneity in the hydrogen and oxygen isotope composition of soil water, which can reveal processes of water cycling within soils, has not been well studied. New advances are being driven by measurement approaches allowing sampling with high density in both space and time. Using in situ soil water vapor probe techniques, combined with conventional soil and plant water vacuum distillation extraction, we monitored the hydrogen and oxygen stable isotopic composition of soil and plant waters at paired sites dominated by grasses and Gambel's oak (Quercus gambelli) within a semi‐arid montane ecosystem over the course of a growing season. We found that sites spaced only 20 m apart had profoundly different soil water isotopic and volumetric conditions. We document patterns of depth‐ and time‐explicit variation in soil water isotopic conditions at these sites, and consider mechanisms for the observed heterogeneity. We found that soil water content and isotopic variability was damped under Quercus gambelli, perhaps due in part to hydraulic redistribution of deep soil water or groundwater by Quercus gambelli in these soils relative to the grass‐dominated site. We also found some support for H isotope discrimination effects during water uptake by Quercus gambelli. In this ecosystem, the soil water content was higher than that at the neighboring grass site, and thus 25% more water was available for transpiration by Quercus gambelli compared to the grass site. This work highlights the role of plants in governing soil water variation and demonstrates that they can also strongly influence the isotope ratios of soil water. The resulting fine‐scale heterogeneity has implications for the use of isotope tracers to study soil hydrology and evaporation and transpiration fluxes to improve understanding of water cycling through the soil‐plant‐atmosphere continuum.

Description: Abstract Novel Mn‐doped CaO was prepared by the combustion method. The CO2 capture performance of Mn‐doped CaO, carbonated in the presence of steam and under severe calcination conditions (950°C and 70% CO2/30% N2) during calcium looping cycles, was investigated in a dual fixed‐bed reactor. The intercoupling effects of Mn and steam on CO2 capture by CaO were also studied. Doping of Mn in CaO by the combustion method greatly improved the CO2 capture capacity of CaO. The carbonation conversions of Mn‐doped CaO increased with increasing steam concentration from 0 to 15%. When the molar ratio of Mn/Ca was 0.75 : 100, Mn‐doped CaO achieved the highest CO2 capture capacity. Under severe calcination conditions, the carbonation conversion of Mn‐doped CaO, where the molar ratio of Mn to Ca = 0.75 : 100 in the presence of 15% steam, was about 0.4 after ten cycles (carbonation for 5 min at 650°C under 15% CO2/15% steam/N2), which was 4.38 times as high as that of the original CaO in the absence of steam. The cyclic CO2 capture capacities of CaO were improved by Mn and steam. Synergistic enhancement effects of Mn and steam on the CO2 capture capacities of CaO were also found. The effect of steam on the carbonation conversion of Mn‐doped CaO was stronger than that of the original CaO. Mn in the presence of steam showed a more positive effect on CO2 capture by CaO. X‐ray photoelectron spectroscopy analysis showed that doping of Mn in CaO enhanced the transport of electrons in the carbonation of CaO, which helped to increase the carbonation rate. When steam was present in the carbonation, Mn‐doped CaO possessed a more porous structure and smaller CaO grains than the original CaO during the cycles. Simulation calculations using periodic density functional theory (DFT) showed that CO2 molecules were easier to absorb on CaO owing to the doping of Mn and the presence of steam. The synergistic enhancement effects of Mn and steam on CO2 captured the performance of CaO. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract While we know that rainfall interception (the rain caught, stored, and evaporated from aboveground vegetative surfaces and ground litter) is affected by rain and throughfall drop size, what was unknown until now is the relative proportion of each throughfall type (free throughfall, splash throughfall, canopy drip) beneath coniferous and broadleaved trees. Based on a multi‐national dataset of 〉 120 million throughfall drops, we found that the type, number, and volume of throughfall drops are different between coniferous and broadleaved tree species, leaf states, and timing within rain events. Compared to leafed broadleaved trees, conifers had a lower percentage of canopy drip (51% vs. 69% with respect to total throughfall volume) and slightly smaller diameter splash throughfall and canopy drip. Canopy drip from leafless broadleaved trees consisted of fewer and smaller diameter drops (D50_DR, fiftieth cumulative drop volume percentile for canopy drip, of 2.24 mm) than leafed broadleaved trees (D50_DR of 4.32 mm). Canopy drip was much larger in diameter under woody drip points (D50_DR of 5.92 mm) than leafed broadleaved trees. Based on throughfall volume, the percentage of canopy drip was significantly different between conifers, leafed broadleaved trees, leafless broadleaved trees, and woody surface drip points (p ranged from 〈 0.001 to 0.005). These findings are partly attributable to differences in canopy structure and plant surface characteristics between plant functional types and canopy state (leaf, leafless), among other factors. Hence, our results demonstrating the importance of drop‐size dependent partitioning between coniferous and broadleaved tree species could be useful to those requiring more detailed information on throughfall fluxes to the forest floor.

Description: Abstract High‐elevation tropical grassland systems, called Páramo, provide essential ecosystem services such as water storage and supply for surrounding and lowland areas. Páramo systems are threatened by climate and land use changes. Rainfall generation processes and moisture transport pathways influencing precipitation in the Páramo are poorly understood but needed to estimate the impact of these changes, particularly during El Niño conditions which largely affect hydrometeorological conditions in tropical regions. To fill this knowledge gap, we present a stable isotope analysis of rainfall samples collected on a daily to weekly basis between January 2015 and May 2016 during the strongest El Niño event recorded in history (2014‐2016) in two Páramo regions of Central America (Chirripó, Costa Rica) and the northern Andes (Cajas, south Ecuador). Isotopic compositions were used to identify how rainfall generation processes (convective and orographic) change seasonally at each study site. HYSPLIT air mass back trajectory analysis was used to identify preferential moisture transport pathways to each Páramo site. Our results show the strong influence of northeast trade winds to transport moisture from the Caribbean Sea to Chirripó and the South American low‐level jet to transport moisture from the Amazon forest to Cajas. These moisture contributions were also related to the formation of convective rainfall associated with the passage of the Intertropical Convergence Zone over Costa Rica and Ecuador during the wetter seasons and to orographic precipitation during the transition and drier seasons. Our findings provide essential baseline information for further research applications of water stable isotopes as tracers of rainfall generation processes and transport in the Páramo and other montane ecosystems in the tropics.

Description: Abstract Seasonal snow cover in mountainous regions will affect local climate and hydrology. In this study, we assessed the role of altitude in determining the relative importance of temperature and precipitation in snow cover variability in the Central Tianshan Mountains. The results show that: (1) in the study area, temperature has a greater influence on snow cover than precipitation during most of the time period studied and in most altitudes. (2) In the high‐elevation area, there is a threshold altitude of 3900±400 m, below which temperature is negatively while precipitation is positively correlated to snow cover, above which the situation is the opposite. Besides, this threshold altitude decreases from snow accumulated period to snow stable period and then increases from snowmelt period to snow‐free period. (3) Below 2000 m, there is another threshold altitude of 1400±100 m during the snow stable period, below (above) which precipitation (temperature) is the main driver of snow cover.

Description: Hydrological Processes, Volume 33, Issue 6, Page 889-891, 15 March 2019.

Description: Abstract Low flow events can cause significant impacts to river ecosystems and water‐use sectors; as such it is important to understand their variability and drivers. In this study, we characterize the variability and timing of annual total frequency of low streamflow days across a range of headwater streams within the continental United States (US). To quantify this, we use a metric that counts the annual number of low flow days below a given threshold, defined as the Cumulative Dry days Occurrence (CDO). First, we identify three large clusters of streamgauge locations using a Partitioning Around Medoids (PAM) clustering algorithm. In terms of timing, results reveal that for most clusters, the majority of low streamflow days occur from the middle of summer until early fall, though several locations in Central and Western US also experience low flow days in cold seasons. Further, we aim to identify the regional climate and larger‐scale drivers for these low streamflow days. Regionally, we find that precipitation deficits largely associate with low streamflow days in the western US, while within the central and eastern US clusters, high temperature indicators are also linked to low streamflow days. In terms of larger‐scale, we examine sea surface temperature (SST) anomalies, finding that extreme dry years exhibit a high degree of co‐occurrence with different patterns of warmer SST anomalies across the Pacific and northern Atlantic Oceans. The linkages identified with regional climate and SSTs offer promise towards regional prediction of changing conditions of low streamflow events.

Description: Abstract Plant transpiration depends on environmental conditions, and soil water availability is its primary control under water deficit conditions. In this study, we improve a simplified process‐based model proposed by Buckley, Turnbull & Adams (2012) (hereafter "BTA") by including soil water potential (ψsoil) to explicitly represent the dependence of plant transpiration on root‐zone moisture conditions. The improved model is denoted as the BTA‐ψ model. We assessed the performance of the BTA and BTA‐ψ models in a subtropical monsoon climate and a Mediterranean climate with different levels of water stress. The BTA model performed reasonably in estimating daily and hourly transpiration under sufficient water conditions, but it failed during dry periods. Overall, the BTA‐ψ model provided a significant improvement for estimating transpiration under a wide range of soil moisture conditions. Although both models could estimate transpiration (sap flow) at night, BTA‐ψ was superior to BTA in this regard. Species differences in the calibrated parameters of both models were consistent with leaf‐level photosynthetic measurements on each species, as expected given the physiological basis of these parameters. By combining a simplified representation of physiological regulation with reasonable performance across a range of soil moisture conditions, the BTA‐ψ model provides a useful alternative to strictly empirical models for modeling transpiration.

Description: Abstract Characterization of spatial and temporal variability of stable isotopes (δ18O & δ2H) of surface waters is essential to interpret hydrological processes and establish modern isotope‐elevation gradients across mountainous terrains. Here, we present stable isotope data for river waters across Kyrgyzstan. River water isotopes exhibit substantial spatial heterogeneity among different watersheds in Kyrgyzstan. Higher river water isotope values were found mainly in the Issyk–Kul Lake watershed, whereas waters in the Son–Kul Lake watershed display lower values. Results show a close δ18O–δ2H relation between river water and the LMWL (Local Meteoric Water Line), implying that river water experiences little evaporative enrichment. River water from the high elevation regions (e.g., Naryn and Son–Kul Lake watershed) had the most negative isotope values, implying that river water is dominated by snowmelt. Higher d‐excess (average d=13.9‰) in river water probably represents the isotopic signature of combined contributions from direct precipitation and glacier melt in stream discharge across Kyrgyzstan. A significant relationship between river water δ18O and elevation was observed with a vertical lapse rate of 0.13 ‰/100 m. These findings provide crucial information about hydrological processes across Kyrgyzstan and contribute to a better understanding of the paleoclimate/elevation reconstruction of this region.

Description: Abstract Evaporative flux is a key component of hydrological budgets. Water loss through evapotranspiration reduces volumes available for runoff. The transition from liquid to water vapour on open water surfaces requires heat. Consequently, evaporation act as a cooling mechanism during summer. Both river discharge and water temperature simulations are thus influenced by the methods used to model evaporation. In this paper, the impact of evapotranspiration estimation methods on simulated discharge is assessed using a semi‐distributed model on two Canadian watersheds. The impact of evaporation estimation methods on water temperature simulations is also evaluated. Finally, the validity of using the same formulation to simulate both of these processes is verified. Five well known evapotranspiration models and five evaporation models with different wind functions were tested. Results show a large disparity (18‐22% of mean annual total evapotranspiration) among the evapotranspiration methods, leading to important differences in simulated discharge (3‐25% of observed discharge). Larger differences results from evaporation estimation methods with mean annual divergences of 34‐48%. This translates into a difference in mean summer water temperature of 1‐15%. Results also show that the choice of model parameter has less influence than the choice of evapotranspiration method in discharge simulations. However, the parameter values influence thermal simulations in the same order of magnitude as the choice of evaporation estimation method. Overall, the results of this study suggest that evapotranspiration and open water evaporation should be represented separately in a hydrological modelling framework, especially when water temperature simulations are required.

Description: Abstract Dissolved organic carbon (DOC) originating in peatlands can be mineralized to carbon dioxide (CO2) and methane (CH4), two potent greenhouse gases. Knowledge of the dynamics of DOC export via runoff is needed for a more robust quantification of C cycling in peatland ecosystems, a prerequisite for realistic predictions of future climate change. We studied dispersion pathways of DOC in a mountain‐top peat bog in the Czech Republic (Central Europe), using a dual isotope approach. While δ13CDOC values made it possible to link exported DOC with its within‐bog source, δ18OH2O values of precipitation and runoff helped to understand runoff generation. Our two‐year DOC‐H2O isotope monitoring was complemented by a laboratory peat incubation study generating an experimental time‐series of δ13CDOC values. DOC concentrations in runoff during high‐flow periods were 20‐30 mg L‐1. The top 2 cm of the peat profile, composed of decaying green moss, contained isotopically lighter C than deeper peat, and this isotopically light C was present in runoff in high‐flow periods. In contrast, baseflow contained only 2‐10 mg DOC L‐1, and its more variable C isotope composition intermittently fingerprinted deeper peat. DOC in runoff occasionally contained isotopically extremely light C whose source in solid peat substrate was not identified. Pre‐event water made up on average 60 % of the water runoff flux, while direct precipitation contributed 40 %. Runoff response to precipitation was relatively fast. A highly leached horizon was identified in shallow catotelm. This peat layer was likely affected by a lateral influx of precipitation. Within 36 days of laboratory incubation, isotopically heavy DOC that had been initially released from the peat was replaced by isotopically lighter DOC, whose δ13C values converged to the solid substrate and natural runoff. We suggest that δ13C systematics can be useful in identification of vertically stratified within‐bog DOC sources for peatland runoff.

Description: Abstract Oil wells that intersect a potential CO2 storage zone in a depleted oil and gas field may provide leakage pathways. It is essential to estimate the field‐scale leakage risk associated with these wells. In this study, a risk‐based approach is used to estimate the risk of leakage. Existing reduced‐order models for well leakage are used to quantitatively estimate well leakage rates for cased‐cemented, cased‐uncemented, and open wellbores. For each existing well that intersects the storage zone, we introduce the well leakage index (WLI), which accounts for wellbore geometry, distance from the injection well, buffer layers between the storage zone and underground sources of drinking water, and the nature of storage zone boundary type. For an initial injection well location, the total site well leakage index (SWLI) is calculated, which is the summation of the WLI for all of the wells. Next, the injector location is varied areally and SWLI is calculated for a specified number of potential injector well locations in the storage zone area. Small values for the SWLI correspond to low well leakage potential, indicating where injection well locations can be considered. The developed criterion provides a means to systemically find the areas with highest and lowest well leakage potential for a storage zone. Due to the reduced order nature of the developed method, it should be a useful tool in the planning and execution phase of the CO2 geological sequestration process. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Geological carbon storage (GCS) refers to the technology of capturing man‐made carbon dioxide (CO2) emissions, typically from stationary power sources, and storing such emissions in deep underground reservoirs. GCS is an approach being explored globally as a defense mechanism against climate change projections, although it is not without its critics. An important focus has been recently placed on understanding the coupling between rock–fluid geochemical alterations and mechanical changes for CO2 storage schemes in saline aquifers. This article presents a review of the current state of knowledge regarding CO2‐induced geochemical reactions in subsurface reservoirs, and their potential impact on mechanical properties and microseismic events at CO2 storage sites. This review focuses, in particular, on the current state of the art in fluid–rock interactions within the GCS context. Key issues to be addressed include geochemical reactions and the alteration of transport and mechanical properties. Specific review topics include the swelling of clays, the prediction of dissolution and precipitation reaction rates, CO2‐induced changes in porosity and permeability, constitutive models of chemo–mechanical interactions in rock, and correlations between geochemical reactions and induced seismicity. The open questions in the field are emphasized, and new research needs are highlighted. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract An audit is not always something that an organisation looks forward to. Having procedures or expenditures critiqued by an independent body has the potential to be nerve‐wracking. But the scrutiny can often lead to better decisions for the future. In this article, GHGS&T's Muriel Cozier looks at the findings from the audit of the past 10 years of European Union's climate action. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Reservoir tillage (RT) improves the soil rainwater harvesting capacity and reduces soil erosion on cropland, but there is some debate regarding its effectiveness. The objective of this study was to further verify the effect of RT on soil erosion and explore the reasons for this effect by analysing microrelief changes during rainfall. Rainfall intensities of 60, 90 and 120 mm/h and three slope degrees (5°, 15° and 25°, representing gentle, medium and steep slopes) were considered. A smooth surface (SS) served as the control. The microrelief changes were determined based on digital elevation models (DEMs), which were measured using a laser scanner with a 2‐cm grid before and after rainfall events. The results showed that compared to the values for the SS, RT reduced both the runoff and sediment by approximately 10‐20% on the gentle slope; on the medium slope, although RT also reduced the runoff in the 90 and 120 mm/h intensity rainfall events, the sediment increased by 158.90% and 246.08%; on the steep slope, the sediment increased by 92.33 to 296.47%. Overall, when the runoff control benefit of RT was lower than 5%, there was no sediment control benefit. RT was effective at controlling soil loss on the gentle slopes but was not effective on the medium and steep slopes. This is because the surface depressions created by RT were filled in with sediment that eroded from the upslopes, and the surface microrelief became smoother, which then caused greater soil and water loss than that on an SS at the later rainfall stage.

Description: Abstract Hydrological studies focused on Hortonian rainfall‐runoff scaling have found that the runoff depth generally declines with the plot length in power‐law scaling. Both the power‐law proportional coefficient and the scaling exponent show great variability for specific conditions, but why and how they vary remain unclear. In the present study, the scaling of hillslope Hortonian rainfall‐runoff processes is investigated for different rainfall, soil infiltration, and hillslope surface characteristics using the physically based Cell‐based Rainfall‐Infiltration‐Runoff Model (CeRIRM). The results show that both temporally intermittent and steady rainfalls can result in prominent power‐law scaling at the initial stage of runoff generation. Then, the magnitude of the power‐law scaling decreases gradually due to the decreasing run‐on effect. The power‐law scaling is most sensitive to the rainfall and soil infiltration parameters. When the ratio of rainfall to infiltration exceeds a critical value, the magnitude of the power‐law scaling tends to decrease notably. For different intermittent rainfall patterns, the power‐law exponent varies in the range of ‐1.0 to ‐0.113, which shows an approximately logarithmic increasing trend for the proportional coefficient as a function of the runoff coefficient. The scaling is also sensitive to the surface roughness, soil sealing, slope angle, and hillslope geometry because these factors control the runoff routing and run‐on infiltration processes. These results provide insights into the variable scaling of the Hortonian rainfall‐runoff process, which are expected to benefit modeling of large‐scale hydrological and ecological processes.

Description: Abstract Catchments consist of distinct landforms that affect the storage and release of subsurface water. Certain landforms may be the main contributors to streamflow during extended dry periods and these may vary for different catchments in a given region. We present a unique dataset from snapshot field campaigns during low‐flow conditions in eleven catchments across Switzerland to illustrate this. The catchments differed in size (10 to 110 km2), varied from predominantly agricultural lowlands to Alpine areas, and covered a range of physical characteristics. During each snapshot campaign, we jointly measured streamflow and collected water samples for the analysis of major ions and stable water isotopes. For every sampling location (basin), we determined several landscape characteristics from national geo‐datasets, including drainage area, elevation, slope, flowpath length, dominant land use, and geological and geomorphological characteristics, such as the lithology and fraction of Quaternary deposits. The results demonstrate very large spatial variability in specific low‐flow discharge and water chemistry: neighboring sampling locations could differ significantly in their specific discharge, isotopic composition and ion concentrations, indicating that different sources contribute to streamflow during extended dry periods. However, none of the landscape characteristics that we analyzed could explain the spatial variability in specific discharge or stream water chemistry in multiple catchments. This suggests that local features determine the spatial differences in discharge and water chemistry during low‐flow conditions and that this variability cannot be assessed a priori from available geodata and statistical relations to landscape characteristics. The results furthermore suggest that measurements at the catchment outlet during low‐flow conditions do not reflect the heterogeneity of the different source areas in the catchment that contribute to streamflow.

Description: Abstract In headwater catchments, streamflow recedes between periods of rainfall at a predictable rate generally defined by a power‐law relationship relating streamflow decay to streamflow. Research over the last four decades has applied this relationship to predictions of water resource availability as well as estimations of basin‐wide physiographic characteristics and ecohydrologic conditions. However, the interaction of biophysical processes giving rise to the form of these power‐law relationships remain poorly understood, and recent investigations into the variability of streamflow recession characteristics between discrete events have alternatively suggested evapotranspiration, water table elevation, and stream network contraction as dominant factors, without consensus. To assess potential temporal variability and interactions in the mechanism(s) driving streamflow recession, we combine long‐term observational data from a headwater stream in the southern Appalachian Mountains with state and flux conditions from a process‐based ecohydrologic model. Streamflow recession characteristics are non‐unique, and vary systematically with seasonal fluctuations in both rates of transpiration and watershed wetness conditions, such that transpiration dominates recession signals in the early growing season and diminishes in effect as the water table elevation progressively drops below and decouples with the root zone with topographic position. As a result of this decoupling, there exists a seasonal hysteretic relationship between streamflow decay and both evapotranspiration and watershed wetness conditions. Results indicate that for portions of the year, forest transpiration may actively compete with subsurface drainage for the same water resource that supplies streamflow, though for extended time periods these processes exploit distinct water stores. Our analysis raises concerns about the efficacy of assessing humid headwater systems using traditional recession analysis, with recession curve parameters treated as static features of the watershed, and we provide novel alternatives for evaluating interacting biological and geophysical drivers of streamflow recession.

Description: Abstract The study on the hydraulic properties of coastal aquifers has significant implications both in hydrological sciences and environmental engineering. Although many analytical solutions are available, most of them are based on the same basic assumption that assumes aquifers extend landward semi‐infinitely which does not necessarily reflect the reality. In this study, the general solutions for a leaky confined coastal aquifer have been developed that consider both finitely landward constant‐head and no‐flow boundaries. The newly developed solutions were then used to examine theoretically the joint effects of leakage and aquifer length on hydraulic head fluctuations within the leaky confined aquifer, and the validity of using the simplified solution that assumes the aquifer is semi‐infinite. The results illustrated that the use of the simplified solution may cause significant errors, depending on joint effects of leakage and aquifer length. A dimensionless characteristic parameter was then proposed as an index for judging the applicability of the simplified solution. In addition, practical application of the general solution for the constant‐head inland boundary was used to characterize the hydraulic properties of a leaky confined aquifer using the data collected from a field site at the Seine River estuary, France, and the versatility of the general solution was further justified.

Description: Abstract Sequence SO2/CO2 capture technology will be more attractive as the control on secondary pollution is strengthened and the operating cost is decreased. The sulfation, pore, and fractal characteristics of a spent CaO‐based adsorbent are studied. The spent modified CaO/Ca12Al14O33 is used in this study. The effect of cyclic numbers in the calcium‐looping process on sulfation conversion and the pore characteristics of spent adsorbents is investigated. A model between the fractal dimension and the Brunner–Emmet–Teller (BET) specific surface area (SBET) of the spent CaO/Ca12Al14O33 is established. The sulfation reaction characteristic of spent adsorbents is also interpreted by the fractal mechanism. Results show that the sulfation conversions of spent CaO/Ca12Al14O33 are almost 10% higher than those of spent CaO at the same cyclic number. The sulfation reaction rate in the product layer diffusion‐controlled stage is much lower than that in the chemical reaction‐controlled stage. The spent CaO/Ca12Al14O33 adsorbents are mainly composed of meso‐ and macropores. The pore size distributions show that there are two peaks in the curves. The surface fractal dimension (D1) and the pore fractal dimension values of spent adsorbents show a trend that is similar to those of SBET and total pore volume, respectively. The relation between the D1 values of four different CaO‐based adsorbents and their SBET values is a quadratic function, and a higher D1 indicates an irregular surface of disordered fractals, which significantly affects the efficiency of the sulfation reaction. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract The global warming and change in climatic conditions due to rising concentration of CO2 in atmosphere are the most important challenges of 21st century. Catalytic conversion of CO2 to methanol will not only check global warming but also provide an alternative source of fuel. The phase purity of solid catalysts has a considerable influence on the desired product selectivity. Reduction temperature is one of the most important parameters responsible for catalyst phase formation. Herein, the effect of a range of reduction temperatures between 100 and 600°C on the phase composition of Pd–Ga bimetallic catalyst and CO2 hydrogenation to methanol activity was investigated. X‐ray diffraction (XRD) analysis revealed the formation of different phases at different reduction temperatures. The variation in catalyst structure was also analyzed using field emission scanning electron microscope‐energy dispersive X‐ray spectroscopy (FESEM‐EDS), Brunaue–Emmett–Teller, H2 chemisorption, and transmission electron microscopy techniques. The influence of reduction temperature, pressure (1–25 bar), H2/CO2 ratio (3–9), and reaction temperature (150–250°C) on methanol and CO selectivity from CO2 hydrogenation at atmospheric pressure was also studied. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract In the context of geologic carbon dioxide (CO2) sequestration, the storage effectiveness of a caprock–reservoir system is a function of the properties of both the caprock and reservoir – namely, the ability of the caprock to prevent upward leakage of CO2 (caprock sealing capability), the mechanical response of the reservoir and caprock (by evaluating in situ stress changes), and the extent and degree to which CO2 can be trapped over long periods of time. In this work, all three parameters were considered to evaluate the storage effectiveness of the Cambrian–Ordovician sequence of the Northern Appalachian Basin. We constructed a series of hydro‐mechanical models to investigate interactions between CO2 flow and geomechanical processes and to evaluate the three aspects of storage performance. Models were built to evaluate two scenarios: (1) single reservoirs with a single overlying caprock, and (2) systems comprising multiple reservoirs and multiple intermediate caprock units in addition to the primary (uppermost) caprock unit. The overall conclusion of the work is that focusing only on one aspect of storage effectiveness might not necessarily warrant long‐term CO2 storage. Results of the sensitivity analysis for the single caprock–reservoir system show that each storage effectiveness metric has its own control parameters. A comparison among three stacked caprock–reservoir systems in different parts of the study area shows that each location in the study area could be appropriate for one of the storage effectiveness metrics. Therefore, we conclude that the screening process to select the best site for CO2 sequestration should be based on an evaluation of all three metrics. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract The hybrid process of carbonated low salinity waterflood (CLSWF) integrating low salinity waterflood (LSWF) and carbonated waterflood (CWF) is proposed as enhanced oil recovery (EOR) incorporating CO2 storage. Based on the understanding of the mechanisms of LSWF and CWF, the hybrid technology is simulated with a fully‐coupled model of fluid flow, geochemical reactions, and equation of state, which describes chemical interactions in the oil/brine/rock system. The comprehensive simulations confirm the synergetic effects of the hybrid CLSWF when compared to waterflooding (WF) and LSWF. In addition, optimum designs of cost‐efficient CLSWF securing CO2 storage are drawn via optimization and sensitivity studies. First, CLSWF enhances wettability modification effect, when compared to LSWF. In CLSWF, extensive mineral dissolution causes more cation exchange. Following the multicomponent ion exchange theory of the wettability modification mechanism, CLSWF produces more residual oil than LSWF with an increasing equivalent fraction of cation. Consequently, it enhances oil recovery by 6.9% and 2.5%, compared with WF and LSWF. Second, the interphase transport of CO2 introduces the oil viscosity reduction effect, which improves the injectivity of CLSWF. Lastly, it sequestrates 25% of the injected CO2 in the depleted reservoir via the solubility‐trapping mechanism. In optimization and sensitivity studies, the optimum design of CLSWF is determined to produce more oil recovery by 9.9% and more net present value by 35% over WF. In addition, 33% of the injected CO2 becomes sequestrated in the reservoirs. This study clarifies that hybrid CLSWF improves EOR, injectivity, and CO2 storage. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Fertilizer management and straw returning are effective measures to regulate greenhouse gas emissions and increase crop yields, which have attracted wide attention in agricultural production. To clarify the effect of Chinese milk vetch returning with nitrogen fertilizer on rice yield and greenhouse gas emissions in paddy field, field experiments were conducted during 2017–2018 and four treatments were proposed in this study, including the treatments with Chinese milk vetch returning plus different nitrogen fertilizer application amount, namely RA, RB, RC, and control CK (winter fallow without Chinese milk vetch returning). The results showed that treatments RA, RB, and RC significantly increased the early rice yield by 15.35%, 12.94%, and 15.35%, respectively (P〈0.05), and treatment RA had the best effect on the annual yield (P〈0.05) compared with control CK. Meanwhile, all the treatments with Chinese milk vetch returning plus nitrogen fertilizer increased the global warming potential, but the difference between RA, RB, and control CK was not significant (P〉0.05); the greenhouse gas intensity produced by RA was 11.76% lower than control CK. In summary, treatment RA, followed by RB, had the best effect in increasing rice production and reducing greenhouse gas emissions in paddy fields. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Two parameters that play the most important role in the appraisal of environmental risk performance at carbon dioxide (CO2) storage sites are the prospective impact of the pore pressure increase and CO2 saturation. In this context, this study investigates the spatiotemporal evolution of pressure buildup and CO2 saturation as a function of flow region's size, average porosity and permeability, and heterogeneity, as well as the injection rate and total volume of injected fluid. The practical importance of this study is to investigate the factors that affect the extent of pressure buildup and areal extent of CO2 plume both during and after injection, which will impact risk assessment as well as influence effective monitoring operations. This study pursues the above objective using two risk metrics that are based on numerical simulations and illustrated using representative models of three realistic storage sites with varying volumetric storage potential and geological settings, all with open geologic systems. The two metrics (the spatiotemporal extent of pressure buildup and CO2 saturation plume, respectively) used in this study are able to capture the geologic (structural and petrophysical) and operational complexities that cannot be incorporated into analytical or semianalytical solutions. The results of this study suggest that in addition to the average permeability, the areal extent of the pressure buildup during the injection period is strongly related to the injection rate, whereas the postinjection period may be more strongly influenced by the reservoir heterogeneity. The areal extent of the saturation plume during active injection is highly correlated to the mass of injected fluid, and the postinjection behavior is impacted by the shape of the reservoir–seal interface. These findings are consistent with other recent studies by the National Risk Assessment Partnership (NRAP) on characteristic reservoir behavior. The results have been used to generate pressure and saturation plume profiles (over time) that can be used to support risk‐based decision making. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract The stable isotopes of water (δ2H and δ18O) are useful conservative tracers for tracking the movement of water in soil. But while the tracking of water infiltrating through the soil profile and its movement as runoff and groundwater recharge are well developed, water movement through the soil can also include evaporative fractionation. Soil water fractionation factors have, until now, been largely empirical. Unlike open water evaporation where temperature, humidity and vapor pressure gradient define fractionation, soil water evaporation includes fractionation by soil matrix effects. These effects are still poorly characterized. Here we present preliminary results from a simple laboratory experiment with four soil admixtures with grain sizes that range from sand to silt and clay. Our results show that soil tension seems to control the isotope fractionation of resident soil water. The relationship between soil tension and equilibrium fractionation appears to be independent of soil texture and appears well supported by thermodynamic theory. While these results are preliminary, they suggest that future work should go after soil tension effects as a possible explanatory factor of soil water and water vapor fractionation.

Description: Abstract Surface water flooding (SWF) is a recurrent hazard that affects lives and livelihoods. Climate change is projected to change the frequency of extreme rainfall events that can lead to SWF. Increasingly, data from Regional Climate Models (RCMs) are being used to investigate the potential water‐related impacts of climate change; such assessments often focus on broad‐scale fluvial flooding and the use of coarse resolution (〉12km) RCMs. However, high‐resolution (〈4km) convection‐permitting RCMs are now becoming available that allow impact assessments of more localised SWF to be made. At the same time, there has been an increasing demand for more robust and timely real‐time forecast and alert information on SWF. In the UK, a real‐time SWF Hazard Impact Model framework has been developed. The system uses 1km gridded surface runoff estimates from a hydrological model to simulate the SWF hazard. These are linked to detailed inundation model outputs through an Impact Library to assess impacts on property, people, transport and infrastructure for four severity levels. Here, a set of high‐resolution (1.5km and 12km) RCM data has been used as input to a grid‐based hydrological model over southern Britain to simulate Current (1996‐2009) and Future (~2100s; RCP8.5) surface runoff. Counts of threshold‐exceedance for surface runoff and precipitation (at 1‐, 3‐ and 6‐hour durations) are analysed. Results show that the percentage increases in surface runoff extremes, are less than those of precipitation extremes. The higher‐resolution RCM simulates the largest percentage increases, which occur in winter, and the winter exceedance counts are greater than summer exceedance counts. For property impacts the largest percentage increases are also in winter however, it is the 12km RCM output that leads to the largest percentage increase in impacts. The added‐value of high‐resolution climate model data for hydrological modelling is from capturing the more intense convective storms in surface runoff estimates.

Description: Abstract Investigating the performance that can be achieved with different hydrological models across catchments with varying characteristics is a requirement for identifying an adequate model for any catchment, gauged or ungauged, just based on information about its climate and catchment properties. As parameter uncertainty increases with the number of model parameters, it is important to identify not only a model achieving good results, but to aim at the simplest model still able to provide acceptable results. The main objective of this study is to identify the climate and catchment properties determining the minimal required complexity of a hydrological model. As previous studies indicate that the required model complexity varies with the temporal scale, the study considers the performance at the daily, monthly and annual timescales. In agreement with previous studies, the results show that catchments located in arid areas tend to be more difficult to model. They therefore require more complex models for achieving an acceptable performance. For determing which other factors influence model performance an analysis was carried out for four catchment groups (snowy, arid, eastern and western catchments). The results show that the baseflow and aridity indices are the most consistent predictors of model performance across catchment groups and timescales. Both properties are negatively correlated with model performance. Other relevant predictors are the fraction of snow in the annual precipitation (negative correlation with model performance), soil depth (negative correlation with model performance) and some other soil properties. It was observed that the sign of the correlation between the catchment characteristics and model performance varies beetween clusters in some cases, stressing the difficulties encountered in large sample analyses. Regarding the impact of the timescale, the study confirmed previous results indicating that more complex models are needed for shorter timescales.

Description: Abstract The paper presents oxygen and hydrogen isotopes of 284 precipitation event samples systematically collected in Irkutsk, in the Baikal region (southeast Siberia), between June 2011 and April 2017. This is the first high‐resolution dataset of stable isotopes of precipitation from this poorly studied region of continental Asia, which has a high potential for isotope‐based paleoclimate research. The dataset revealed distinct seasonal variations: relatively high δ18O (up to –4‰) and δD (up to –40‰) values characterise summer air masses, while lighter isotope composition (–41‰ for δ18O and –322‰ for δD) is characteristic of winter precipitation. Our results show that air temperature mainly affects the isotope composition of precipitation, while no significant correlations were obtained for precipitation amount and relative humidity. A new temperature dependence was established for weighted mean monthly precipitation: +0.50‰/°C (r2 = 0.83; p 〈 0.01; n = 55) for δ18O and +3.8‰/°C (r2 = 0.83, p 〈 0.01; n = 55) for δD. Secondary fractionation processes (e.g. contribution of recycled moisture) were identified mainly in summer from low d excess. Backward trajectories assessed with the HYSPLIT model indicate that precipitation with the lowest mean δ18O and δD values reaches Irkutsk in winter related to moisture transport from the Arctic. Precipitation originating from the west/southwest with the heaviest mean isotope composition reaches Irkutsk in summer, thus representing moisture transport across Eurasia. Generally, moisture transport from the west i.e. the Atlantic Ocean predominates throughout the year. A comparison of our new isotope dataset with simulation results using the ECHAM5‐wiso climate model reveals a good agreement of variations in δ18O (r2 = 0.87; p 〈 0.01; n = 55) and air temperature (r2 = 0.99; p 〈 0.01; n = 71). However, the ECHAM5‐wiso model fails to capture observed variations in d excess (r2 = 0.14; p 〈 0.01; n = 55). This disagreement can be partly explained by a model deficit of capturing regional hydrological processes associated with secondary moisture supply in summer.

Description: Abstract Mapping of Groundwater‐Dependant Ecosystems (GDEs) relies largely on assumption‐laden evaporation models and few global, direct, and real‐time monitoring techniques exist. We propose a new Synthetic Aperture Radar imagery‐derived index, SARGDE, to identify and monitor these ecosystems across Australia. The index captures vegetation reliance on groundwater during dry periods by estimating the relative stability of foliage and branch structure from the Vertical/Horizontal cross‐polarized band and InSAR coherence. SARGDE is tested over two contrasting study sites in Australia. To build and verify the index, a total of 90 Sentinel‐1 Interferometric Wide images are processed. GDE response to the SAR signal is explored using a non‐linear dimension reduction algorithm. Relevant statistical parameters are derived from data‐cubes and combined to form the index. As the index relies on a one‐year time‐series of globally, freely available, and cloud‐insensitive SAR imagery, SARGDE offers unprecedented capabilities for large‐scale, annual monitoring of GDEs. Such monitoring will aid reconciliation of human and ecosystem groundwater needs by acting as a systematic monitoring tool, helping policy makers to assure ecosystem sustainability where impacts related to mining, agriculture, or climate change may occur.

Description: Hydrological Processes, EarlyView.

Description: An integrated hydrologic model is used to simulate watershed hydrodynamics following land cover changes due to a wildfire. Differences between present‐day and postwildfire groundwater pressure show nonlinear increases and decreases that are not spatially limited to burn scar areas. Abstract In recent years, wildfires in the western United States have occurred with increasing frequency and scale. Climate change scenarios in California predict prolonged periods of droughts with even greater potential for conditions amenable to wildfires. The Sierra Nevada Mountains provide 70% of water resources in California, yet how wildfires will impact watershed‐scale hydrology is highly uncertain. In this work, we assess the impacts of wildfires perturbations on watershed hydrodynamics using a physically based integrated hydrologic model in a high‐performance‐computing framework. A representative Californian watershed, the Cosumnes River, is used to demonstrate how postwildfire conditions impact the water and energy balance. Results from the high‐resolution model show counterintuitive feedbacks that occur following a wildfire and allow us to identify the regions most sensitive to wildfires conditions, as well as the hydrologic processes that are most affected. For example, whereas evapotranspiration generally decreases in the postfire simulations, some regions experience an increase due to changes in surface water run‐off patterns in and near burn scars. Postfire conditions also yield greater winter snowpack and subsequently greater summer run‐off as well as groundwater storage in the postfire simulations. Comparisons between dry and wet water years show that climate is the main factor controlling the timing at which some hydrologic processes occur (such as snow accumulation) whereas postwildfire changes to other metrics (such as streamflow) show seasonally dependent impacts primarily due to the timing of snowmelt, illustrative of the integrative nature of hydrologic processes across the Sierra Nevada‐Central Valley interface.

Description: Abstract Rainfall simulators can enhance our understanding of the hydrologic processes affecting the total runoff to urban drainage systems. This knowledge can be used to improve urban drainage designs. In this study, a rainfall simulator is developed to simulate rainfall on urban green surfaces. The rainfall simulator is controlled by a microcomputer programmed to replicate the temporal variations in rainfall intensity of both historical and synthetic rainfall events with constant rainfall intensity on an area of one square metre. The performance of the rainfall simulator is tested under laboratory conditions with regard to spatial uniformity of the rainfall, the kinetic energy of the raindrops, and the ability to replicate historical and synthetic rainfall events with temporally varying intensity. The rainfall simulator is applied in the field to evaluate its functionality under field conditions and the influence of wind on simulated rainfall. Finally, a field study is carried out on the relationship between runoff, soil volumetric water content, and surface slope. Performance and field tests show that the simulated rainfall has a uniform spatial distribution while the kinetic energy of the raindrops is slightly higher than that of other comparable rainfall simulators. The rainfall simulator performs best in low wind speed conditions. The simulator performs well in replicating historical and synthetic rainfall events by matching both intensity variations and accumulated rainfall depth. The field study shows good correlation between rainfall, runoff, infiltration, soil water content, and surface slope.

Description: Hydrological Processes, Volume 33, Issue 18, Page 2381-2383, 30 August 2019.

Description: Municipalities may alter their storm water management focus depending on the most relevant processes (left); the analytical framework developed in this study can be used with measured soil properties to estimate the propensity of urban versus predeveloped reference soil profiles towards saturation‐excess overland flow (SEOF) or infiltration‐excess overland flow (IEOF), with 11 cities in the United States analysed (right). Abstract Uncontrolled overland flow drives flooding, erosion, and contaminant transport, with the severity of these outcomes often amplified in urban areas. In pervious media such as urban soils, overland flow is initiated via either infiltration‐excess (where precipitation rate exceeds infiltration capacity) or saturation‐excess (when precipitation volume exceeds soil profile storage) mechanisms. These processes call for different management strategies, making it important for municipalities to discern between them. In this study, we derived a generalized one‐dimensional model that distinguishes between infiltration‐excess overland flow (IEOF) and saturation‐excess overland flow (SEOF) using Green–Ampt infiltration concepts. Next, we applied this model to estimate overland flow generation from pervious areas in 11 U.S. cities. We used rainfall forcing that represented low‐ and high‐intensity events and compared responses among measured urban versus predevelopment reference soil hydraulic properties. The derivation showed that the propensity for IEOF versus SEOF is related to the equivalence between two nondimensional ratios: (a) precipitation rate to depth‐weighted hydraulic conductivity and (b) depth of soil profile restrictive layer to soil capillary potential. Across all cities, reference soil profiles were associated with greater IEOF for the high‐intensity set of storms, and urbanized soil profiles tended towards production of SEOF during the lower intensity set of storms. Urban soils produced more cumulative overland flow as a fraction of cumulative precipitation than did reference soils, particularly under conditions associated with SEOF. These results will assist cities in identifying the type and extent of interventions needed to manage storm water produced from pervious areas.

Description: Abstract Regional heterogeneity during low‐carbon economy development among provinces in China should be considered with more concerns by central government. Spatial coordination can bring more opportunities for underdeveloped provinces. Under this background, provincial low‐carbon economy transformation performance is evaluated during 2000–2016 and spatial characters are analyzed to supply detailed development information. Based on parametric input–output evaluation model and linear programming method, provincial low‐carbon economy transformation performance is evaluated. Spatial analysis methods such as Moran index, Moran scatter diagram, and Markov chain are implemented to analyze their spatial characters and dynamic trends. Main results are as follows: First, linear programing supplies reliable parameter results to evaluate the transformation performance. Mean value rises during 2000−2011 and there is a slight downward trend during 2013−2016. Economy transformation performance is still at lower medium level for most provinces nowadays and there is a long way to go further. Second, according to Markov chain results, more than 90% provinces exist as state self‐locking and less than 10% may exist as state jumping. Third, spatial correlation exists among provinces and ‘lower−lower’ type dominates with respect to low‐carbon economy transformation performance. They are mainly underdeveloped provinces in northwestern China. Absorbing greener production technology is the best choice for them. Yangtze River Delta provinces such as Shanghai, Jiangsu, and Zhejiang are of ‘higher–higher’ type. Regional cooperatives can exert lots of potentials and are beneficial to stimulate transformation performance. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Permeability reduction of infiltration media due to suspended solid (SS) clogging is the bane of groundwater artificial recharge (GAR). To overcome the clogging problem and advance the understanding of the process‐based spatial‐temporal evolution of SS clogging, a 1D laboratory column simulation was carried out, followed by numerical modelling of the experimental data in this study. It was found that clogging caused a reduction in the hydraulic conductivity (K) in the upper layer at the beginning and extended deeper to approximately 50 cm, and no reduction in K was detected below 52 cm throughout the experimental period of 129 h. The most clogged layer spanned from the surface to a depth of 11 cm, and the middle 11‐52 cm was characterized by a slight decrease in K. The clogging rates of the different layers decreased with the depth, which was based on data analysis, with the largest value of 0.038 h‐1 in the upper 1 cm. The overall K began to decrease from the surface layer and was increasingly affected by clogging with time. A mathematical model was established to simulate the SS clogging process evolution based on considerations of the attachments and detachments of particles. Then, the model was applied to perform several scenario analyses after calibration and validation using the data obtained in the experiment. The simulation results indicated that the SS concentration was much more sensitive than the groundwater depth (GD) below the land surface, and 10 days of constant recharge is recommended as the disposal cycle of the clogged layer under the given conditions.

Description: Abstract During the last decades, increasing exports of both dissolved organic carbon (DOC) and iron were observed from peat catchments in North America and Europe with potential consequences for water quality of streamwater and carbon storages of soils. As mobilisation and transport processes of DOC and iron in peat catchments are only partly understood, the purpose of this study was to elucidate these processes in an intensively monitored and studied system. Specifically, it was hypothesised that dissimilatory iron reduction in riparian peatland soils mobilises DOC initially adsorbed to iron minerals. During stormflow conditions, both DOC and iron will be transported into the stream network. Ferrous iron may be reoxidised at redox interfaces on its way to the stream and subsequently ferric iron could be transported together with DOC as complexes. To test these hypotheses, generalised additive models (GAM) were applied to 14 years of weekly time series of discharge and concentrations of selected solutes measured in a German headwater stream called Lehstenbach. This stream drains a 4.19 km2 forested mountain catchment, one third of which is covered by riparian peatland soils. We interpreted results of different types of GAM in the way that (a) iron reduction drove the mobilisation of DOC from peatland soils and that (b) both iron and DOC were transported as complexes after their joint mobilisation to and within the steam. It was speculated that low nitrate availability in the uppermost wetland soil layer, particularly during the growing season, promoted iron reduction and thus the mobilisation of DOC. However, the influence of nitrate on the DOC mobilisation remains relatively uncertain. This influence could be further investigated using methods similar to the GAM analysis conducted here for other catchments with long‐term data as well as detailed measurements of the relevant species in riparian wetland soils and the adjacent stream network.

Description: Abstract The chemical absorption process for carbon dioxide (CO2) capture is a promising method to reduce greenhouse gas emissions in the energy industry. Worldwide applications of the CO2 chemical absorption process will consume plenty of chemical absorbents and have hazardous impacts on the environment. The development of renewable absorbents from biomass can not only fill the gap of absorbent production, but also provide a novel green approach to recycle the used absorbents into nature without additional pollution. In this review, we summarized several renewable absorbents available from biomass such as biomass ash slurries, alkanolamines, aqueous ammonia, and amino acid salts. The preparations, CO2 absorption capacities, advanced treatments, and applications of the renewable absorbents were also reviewed. Moreover, the advantages and challenges in the preparation of the renewable absorbents were discussed, as well as their CO2 absorption performance improvement. Finally, future research avenues into degradation and utilization of renewable absorbents in nature were suggested. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Hydrological Processes, Volume 33, Issue 16, Page 2157-2159, 30 July 2019.

Description: Abstract Synchronously and accurately estimating the flood discharges and dynamic changes in the fluid density is essential for hydraulic analysis and forecasting of flash floods, as well as for risk assessment. However, such information is rare for steep mountain catchments, especially in regions that are hotspots for earthquakes. Therefore, six hydrological monitoring sites were established in mainstream and tributaries of the 78.3 km2 Longxi River catchment, an affected region of the Wenchuan earthquake region in China. Direct real‐time monitoring equipment was installed to measure the flow depths, velocities and fluid total pressures of the flood hydrographs. Based on field measurements, real‐time mean cross‐sectional velocities during the flood hydrographs could be derived from easily obtainable parameters: cross‐sectional maximum velocities and the calibrated dimensionless parameter Kh. Real‐time discharges were determined based on this non‐contact method to establish the effective rating curves of this mountainous stream, ranging from 1.46 m3/s to 386.34 m3/s with the RMSEs of ≤10.22 m3/s. Compared to the traditional point‐velocity method and empirical Manning's formula, the proposed non‐contact method was reliable and safe for monitoring whole flood hydrographs. Additionally, the real‐time fluid density during the flood hydrographs was calculated based on the direct monitoring parameters for fluid total pressures and water depths. During the flood hydrograph, transient flow behaviour with higher fluid density generally occurred downstream during the flood peak periods when the flow was in the supercritical flow regime. The observed behaviour greatly increased the threat of damage to infrastructure and human life near the river. Thus, it is important to accurately estimate flood discharge and identify for fluid densities so that people at risk from an impending flash flood are given reliable, advanced warning.

Description: Abstract We develop plume migration metrics based on spatial moment analysis methods that quantify the spatio‐temporal evolution of plumes at geologic CO2 storage sites. The metrics are generalized to handle any 3‐D scalar attribute field values. Within the geologic CO2 storage context, these can be parameters such as CO2 saturation, effective pressure, overpressure, dissolved CO2 concentration, total dissolved solids, pH, and other attributes that are critical for assessing risks. The metrics are comprehensive in that they can effectively handle and account for complex continuous and discontinuous plumes and intra‐plume migration. We demonstrate the metrics on simulated CO2 plumes injected into flat and tilted reservoirs with homogeneous and heterogeneous permeability fields. Using these idealized reservoir scenarios, we demonstrate the information that the metrics extract, showing that the metrics elucidate nuances in plume migration not apparent by standard approaches to the scalar fields values. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

Description: Abstract Porous carbon fibers (PCFs) were prepared from porous polyacrylonitrile fibers by cross‐linking, oxidation, and carbonization. X‐ray diffraction patterns revealed that graphite structures as well as disordered carbon coexisted in the PCFs. Nitrogen content was more than 15.3 wt% with the variation of oxidation temperature, and a maximum value was obtained at 275°C. Nitrogen was quickly released with carbonization temperature. Compared with the fiber prepared at elevated carbonization temperatures, those owning high nitrogen contents deserved better carbon dioxide (CO2) adsorption performance in the simulated flue gas environment (10% CO2/90% N2). The CO2 adsorption had a better relationship with nitrogen content rather than specific surface area and pore volumes. Especially, nitrogen was very useful to enhance the CO2 adsorption of the fibers with low microporosity. The heat of CO2 adsorption was in the range of 39.8–54.6 kJ mol−1, which indicated good selectivity of CO2 adsorption. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Sulfur dioxide (SO2) and carbon dioxide (CO2) removals are of great significance for fossil fuel combustion, where they can be simultaneously captured by calcium‐based absorbents. Nevertheless, the CO2 uptake capacity declines with SO2 partial pressures. This paper aims at explaining the mechanisms of steam‐declined sulfation and steam‐enhanced carbonation by density functional theory calculations. CaO(001) surface is chosen as the absorbent, and the transition state is calculated to obtain the desorption barrier energy of the adsorbates. By analyzing the desorption of the adsorbate on pristine CaO(001) surface and the CaO(001) surface that has adsorbed other adsorbate, it can be concluded that SO2 adsorption inhibits CO2 adsorption since the barrier energy of CO2 desorption on SO2‐CaO(001) surface (24.15 kJ mol–1) is less than CO2 desorption on CaO(001) surface (129.52 kJ mol–1). By comparing the coadsorption energy of the two adsorbates with the sum of the adsorption energy of each adsorbate, it is practical that the H2O adsorption inhibits SO2 adsorption because the calculated coadsorption energy (−221.27 kJ mol–1) is larger than the sum of H2O adsorption energy (–100.00 kJ mol–1) and SO2 adsorption energy (−194.37 kJ mol–1). However, the calculated coadsorption energy of H2O and CO2 adsorption (−254.89 kJ mol–1) is less than the sum of CO2 adsorption energy (−144.23 kJ mol–1) and H2O adsorption energy (−100.00 kJ mol–1), indicating the promotion of CO2 adsorption. Steam in the adsorption process plays the roles of sulfation suppression and carbonation enhancement. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract CO2 storage in different geological formations has been recognized as one of the promising mitigation approaches to reduce the emission of CO2 into the atmosphere. There are many complex hydro‐chemo‐mechanical interactions (effective stress changes, water acidification, and mineral dissolution) that may take place in a storage site during or after injection, reducing the integrity of formations in the short or long term. Although there have been several studies carried out in the past to assess the feasibility of sandstones and limestone formations as a safe CO2 storage site, the effect of hydrological, mechanical, and chemical processes on the storage site integrity has not been deeply addressed. The aim of this study is to couple thermo‐hydro‐chemo‐mechanical processes upon CO2 injection and assess their impact on the key storage aspects of quartz‐rich sandstone and calcite‐rich limestone. A numerical model was built to simulate CO2 flooding into a saline aquifer with sandstone and limestone composition for 500 years. The results obtained indicated that geochemical activity and CO2 dissolution are significantly higher in limestone and may increase the porosity by ∼16%. During injection, a decrease in the reservoir strength was observed in both rock types upon exposure to CO2. A remarkable variation in the geomechanical characteristics was also revealed in the sandstone after injection. However, ground displacements (subsidence) of 0.0017 and 0.033 m were, respectively, observed in sandstone and limestone aquifers, at the end of 500 years. It is recommended to consider a high‐strength reservoir for carbon capture and storage (CCS) projects in order to reduce the likelihood of compaction. It was also found that both rock types have a good storage capacity, injectivity, and trapping potentials (the structural and dissolution trappings) to capture and hold CO2 in place. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Hydrological Processes, Volume 33, Issue 15, Page 2045-2047, 15 July 2019.

Description: A numerical model coupling flow conditions with biochemical reactions is developed. A method for delineating the zones of nitrification and denitrification is proposed. Genetic programming is used to optimize simulation and realize real‐time forecasts. Abstract The hyporheic zone (HZ) plays a vital role in the stream ecosystem. Reactions in the HZ such as denitrification and nitrification have been examined in previous studies. However, no numerical model has yet been developed that can accurately simulate nitrogen concentration changes in the HZ, because the zones for the two reactions can change throughout the reactions. This study proposes a method of evaluating the nitrogen removal rate in the HZ through numerical modelling. First, a basic two‐dimensional numerical model coupling flow conditions with biochemical reactions is proposed to consider both nitrification and denitrification. The zones for different reactions are determined under the assumption that related environmental variables (i.e., the dissolved oxygen) will not change throughout the reactions. Next, to examine changes in environmental variables throughout the reactions, an improved model is proposed, and a method is developed for delineating the boundary between nitrification and denitrification zones and identifying a transition zone where either reaction might take place. However, more information about biochemical reactions in the HZ is required to use the improved model. To overcome this shortcoming, a new model that couples the basic model and genetic programming (GP) is proposed to optimize the simulation results of the basic model and allow for real‐time forecasting. The results show that the basic model obtains acceptable simulation results for nitrate concentration distribution in the HZ. The improved model performs better than the basic model, but the model coupling the basic model with GP performs best. In addition, the function of the HZ in nitrogen removal is examined through a case study of four scenarios, leading to the conclusion that the HZ has a higher nitrogen removal rate when water quality is neither too poor nor too good. Overall, this study enhances our understanding of the HZ and can benefit the restoration and management of HZs and streams in the face of the continual degradation caused by human activity.

Description: Abstract The environmental problems caused by global warming have attracted close attention of governments and scientists all over the world. As the source and sink of atmospheric carbon dioxide, cropland soil plays an important role in the global carbon cycle. Paddy soil is a major component of global cropland, and there is growing research on its carbon sequestration potential. Based on the dynamic characteristics of soil carbon sequestration in cropland, this paper reviews and synthesizes the process and mechanism of soil carbon sequestration in cropland, discusses the driving factors of soil carbon sequestration in cropland from the perspective of crop management practices, and emphatically discusses the knowledge of soil carbon sequestration potential in paddy fields in China. The main conclusions are as follows: (1) The organic carbon content of cropland soil in China is obviously lower than the global average, and the current sequestration rate of paddy soil in China is obviously lower than the potential sequestration rate, which has great potential for carbon sequestration. Since the mid‐1980s, China's agricultural soil organic carbon (SOC) has been gradually increasing, especially the carbon sink effect of rice soil in southern China. (2) Soil and crop management practices such as conservation agriculture, irrigation, integrated nutrition management, straw returning, and crop rotation can improve input efficiency, increase SOC content in the soil carbon pool, and reduce greenhouse gas emissions. (3) The research on SOC fixation mechanism has entered the micro level of soil particles. The chemical protection mechanism of clay, the physical protection mechanism of aggregates, and the biological mechanism interact and influence each other. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract Using a solid Na‐based sorbent is one potential option to decrease CO2 emission in coal‐fired power plants, and the CO2 sorption reactivity of Na2CO3/γ‐Al2O3 sorbent was improved by mechanically doping MgO into Na2CO3/γ‐Al2O3 in our previous study while the mechanism was not clear. In this paper, the CO2 sorption/desorption mechanisms of the promising MgO‐doped Na‐based sorbent prepared by the two‐step incipient wetness impregnation method were studied using a fixed‐bed reactor, together with characterizations of X‐ray fluorescence, nitrogen adsorption apparatus, field emission scanning electron microscopy, X‐ray diffraction, and thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG‐FTIR). Also, the sorption behaviors were well described with Avrami's fractional‐order kinetic model. Results demonstrated that MgO not only dispersed on γ‐Al2O3 but entered γ‐Al2O3’s lattice, leading to the formation of Mg‐Al mixed oxides for CO2 sorption. In addition, a new phase Mg6Al2CO3(OH)16·4H2O was produced during the CO2 sorption process, which plays a crucial role in facilitating the conversion of Na2CO3 to NaHCO3. The CO2 sorption capacity of MgO‐doped Na‐based sorbents is presumably determined by the trade‐off between microstructure and active component dispersion. The knowledge gained about the promotion mechanism of MgO provides fundamental direction for the synthesis of Mg–Al mixed oxides, supported with the developed microstructure for CO2 sorption enhancement of Na‐based sorbents. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Description: Abstract An automated disk infiltrometer was developed to improve the measurements of soil hydraulic properties (saturated hydraulic conductivity and sorptivity) of soils affected by wildfire. Guideline are given for interpreting curves showing cumulative infiltration as a function of time measured by the autodisk. The autodisk was used to measure the variability of these soil hydraulic properties in three different sample sets: (1) a reference soil consisting of a non‐repellent, uniform, fine sand; (2) soils with the same soil‐textural classification derived from the same bedrock geology but having different initial burn severities; and (3) soils from different bedrock geology but having the same burn severity. The autodisk infiltrometer had greater sampling rates and volume resolution when compared to the visual mini‐disk infiltrometer from previous studies. There was no statistical difference in the mean values measured using the autodisk and visual mini‐disk, but the variability of the autodisk measurements was significantly less than the visual mini‐disk for a given set of samples. The greatest variability of soil hydraulic properties in reference samples with uniform particle size was attributed to different pore geometries (coefficient of variation, COV = 0.28‐0.34). Unburned field samples (same soil type) with heterogeneous particle sizes had greater variability (COV=0.57‐0.78) than the reference samples. However, this basic variability decreased or remained constant in these field samples as burn severity increased. Additional sources of variability (COV=0.53‐1.99) were attributed to multiple‐layers resulting from ash or sediment deposition. Results indicate that resolving differences in soil hydraulic properties from different sites requires more than the common 10 random samples because of the multiple sources of variability.

Description: Abstract Planning soil conservation strategies requires predictive techniques at event scale because a large percentage of soil loss over a long‐time period is due to relatively few large storms. Considering runoff is expected to improve soil loss predictions and allows relation of the process‐oriented approach with the empirical one, furthermore, the effects of detachment and transport on soil erosion processes can be distinguished by a runoff component. In this paper, the empirical model USLE‐MB (USLE‐M based), including a rainfall‐runoff erosivity factor in which the event rainfall erosivity index EI30 of the Universal Soil Loss Equation (USLE) multiplies the runoff coefficient QR raised to an exponent b1 〉 1 is tested by the measurements carried out for the Masse (10 plots) and Sparacia (22 plots) experimental stations in Italy. For the Masse experimental station, an exponent b1 〉 1 was also estimated by tests carried out by a nozzle‐type rainfall simulator. For each experimental site in fallow conditions, the effect of the sample size of the plot soil loss measurements on the estimate of the b1 coefficient was also studied by the extraction of a fixed number N of randomly obtained pairs of the normalized soil loss and runoff coefficient. The analysis showed that the variability of b1 with N is low and that 350 pairs are sufficient to obtain a stable estimate of b1. A total of 1,262 soil loss data were used to parameterize the model both locally and considering the two sites simultaneously. The b1 exponent varied between the two sites (1.298–1.520), but using a common exponent (1.386) was possible. Using a common b1 exponent for the two experimental areas increases the practical interest for the model and allows the estimation of a baseline component of the soil erodibility factor, which is representative of the at‐site soil intrinsic and quasi‐static properties. Development of a single USLE‐MB model appears possible, and sampling other sites is advisable to develop a single USLE‐MB model for general use.

Description: Hydrological Processes, Volume 33, Issue 13, Page 1781-1783, 30 June 2019.

Description: Abstract The root‐zone moisture replenishment mechanisms are key unknowns required to understand soil hydrological processes and water sources used by plants. Temporal patterns of root‐zone moisture replenishment reflect wetting events that contribute to plant growth and survival and to catchment water yield. In this study, stable oxygen and hydrogen isotopes of twigs and throughfall were continuously monitored to characterize the seasonal variations of the root‐zone moisture replenishment in a native vegetated catchment under Mediterranean climate in South Australia. The two studied hillslopes (the north‐facing slope [NFS] and the south‐facing slope [SFS]) had different environmental conditions with opposite aspects. The twig and throughfall samples were collected every ~20 days over 1 year on both hillslopes. The root‐zone moisture replenishment, defined as percentage of newly replenished root‐zone moisture as a complement to antecedent moisture for plant use, calculated by an isotope balance model, was about zero (±25% for the NFS and ± 15% for the SFS) at the end of the wet season (October), increased to almost 100% (±26% for the NFS and ± 29% for the SFS) after the dry season (April and May), then decreased close to zero (±24% for the NFS and ± 28% for the SFS) in the middle of the following wet season (August). This seasonal pattern of root‐zone moisture replenishment suggests that the very first rainfall events of the wet season were significant for soil moisture replenishment and supported the plants over wet and subsequent dry seasons, and that NFS completed replenishment over a longer time than SFS in the wet season and depleted the root zone moisture quicker in the dry season. The stable oxygen isotope composition of the intraevent samples and twigs further confirms that rain water in the late wet season contributed little to root‐zone moisture. This study highlights the significant role of the very first rain events in the early wet season for ecosystem and provides insights to understanding ecohydrological separation, catchment water yield, and vegetation response to climate changes.

Description: Abstract Preferential flowpaths transport phosphorus (P) to agricultural tile drains. However, if and to what extent this may vary with soil texture, moisture conditions, and P placement is poorly understood. This study investigated (a) interactions between soil texture, antecedent moisture conditions, and the relative contributions of matrix and preferential flow and (b) associated P distributions through the soil profile when fertilizers were applied to the surface or subsurface. Brilliant blue dye was used to stain subsurface flowpaths in clay and silt loam plots during simulated rainfall events under wet and dry conditions. Fertilizer P was applied to the surface or via subsurface placement to plots of different soil texture and moisture condition. Photographs of dye stains were analysed to classify the flow patterns as matrix dominated or macropore dominated, and soils within plots were analysed for their water‐extractable P (WEP) content. Preferential flow occurred under all soil texture and moisture conditions. Dye penetrated deeper into clay soils via macropores and had lower interaction with the soil matrix, compared with silt loam soil. Moisture conditions influenced preferential flowpaths in clay, with dry clay having deeper infiltration (92 ± 7.6 cm) and less dye–matrix interaction than wet clay (77 ± 4.7 cm). Depth of staining did not differ between wet (56 ± 7.2 cm) and dry (50 ± 6.6 cm) silt loam, nor did dominant flowpaths. WEP distribution in the top 10 cm of the soil profile differed with fertilizer placement, but no differences in soil WEP were observed at depth. These results demonstrate that large rainfall events following drought conditions in clay soil may be prone to rapid P transport to tile drains due to increased preferential flow, whereas flow in silt loams is less affected by antecedent moisture. Subsurface placement of fertilizer may minimize the risk of subsurface P transport, particularily in clay.

Description: Abstract Flood irrigation is globally one of the most used irrigation methods. Typically, not all water that is applied during flood irrigation is consumed by plants or lost to evaporation. Return flow, the portion of applied water from flood irrigation that returns back to streams either via surface or subsurface flow, can constitute a large part of the water balance. Few studies have addressed the connection between vertical and lateral subsurface flows and its potential role in determining return flow pathways due to the difficulty in observing and quantifying these processes at plot or field scale. We employed a novel approach, combining induced polarization, time‐lapse electrical resistivity tomography, and time‐lapse borehole nuclear magnetic resonance, to identify flow paths and quantify changes in soil hydrological conditions under nonuniform application of flood irrigation water. We developed and tested a new method to track the wetting front in the subsurface using the full range of inverted resistivity values. Antecedent soil moisture conditions did not play an important role in preferential flow path activation. More importantly, boundaries between lithological zones in the soil profile were observed to control preferential flow pathways with subsurface run‐off occurring at these boundaries when saturation occurred. Using the new method to analyse time‐lapse resistivity measurements, we were able to track the wetting front and identify subsurface flow paths. Both uniform infiltration and preferential lateral flows were observed. Combining three geophysical methods, we documented the influence of lithology on subsurface flow processes. This study highlights the importance of characterizing the subsurface when the objective is to identify and quantify subsurface return flow pathways under flood irrigation.

Description: Abstract Evapotranspiration (ET) is an essential component of the hydrological cycle and plays a critical role in water resource management. However, ET is often overlooked in order to transform rainfall to runoff for better streamflow simulation. Hydrological models are commonly used to estimate areal actual evapotranspiration (AET) after calibration against observed discharge. However, classical approaches are often inadequate to appropriately simulate other hydrologic components. Hence, it is important to introduce natural heterogeneity to enhance hydrological processes and reduce water balance errors. In this study, the effectiveness of introducing a constant crop coefficient (Kc), flux tower‐based Kc, and leaf area index (LAI) to three hydrological models (Three‐Parametric Hydrologic Model [TPHM], Génie Rural à 4 paramètres Journalier [GR4J], and Catchment hydrologic cycle Assessment Tool [CAT]) is assessed for the simulation of daily streamflow and AET in a mountainous mixed forest watershed (8.54 km2) in South Korea. The results show that the streamflow simulations after introduction of Kc and LAI to the original models are quite similar. However, the effectiveness of the AET estimation was significantly enhanced after introduction of the flux tower‐based Kc and LAI. The information criterion computed to compare the models reveals that the flux tower‐based Kc‐simulated AET demonstrated better agreement with the observed AET. The Pearson's correlation coefficients (R2) of the TPHM (8%), GR4J (55%), and CAT (55%) models also showed improvements that were greater than the constant based Kc simulation. Similarly, the limitations of the three models with respect to capturing seasonal variation as well as high and low flows were enhanced after the introduction of the flux tower‐based Kc, which adequately reproduced hydrological processes with minimum water balance errors and bias. A regression analysis revealed the potential of estimating Kc as a linear function of LAI (R2 = 0.84). The results of this study indicate that introduction of Kc and LAI to the conceptual rainfall–runoff models can be considered an effective approach to reduce water balance errors and uncertainties in hydrological models and improve the reliability of climate change studies and water resource management.