ALBERT

Description: No abstract is available for this article.

Description: Ebullition is an important pathway for methane emission from inland waters. However, the mechanisms controlling methane bubble formation and release in aquatic sediments remain unclear. A laboratory incubation experiment was conducted to investigate the dynamics of methane bubble formation, storage and release in response to hydrostatic head drops in three different types of natural sediment. Homogenized clayey, silty and sandy sediments (initially quasi-uniform through the depth of the columns) were incubated in chambers for three weeks. We observed three distinct stages of methane bubble formation and release: Stage I – formation of micro bubbles, displacing mobile water from sediment pores with negligible ebullition; Stage II – formation of large bubbles, displacing the surrounding sediment with concurrent increasing in ebullition; Stage III – formation of conduits, with relatively steady ebullition. The maximum depth-averaged volumetric gas content at steady state varied from 18.8% in clayey to 12.0% in silty and 13.2% in sandy sediment. Gas storage in the sediment columns showed a strong vertical stratification: most of the free gas was stored in an upper layer, whose thickness varied with sediment grain size. The magnitude of individual ebullition episodes was linearly correlated to hydrostatic head drop and decreased from clayey to sandy to silty sediment, and was in excess of that estimated from expansion alone indicating the release of porewater methane. These findings combined with a hydrodynamic model capable of determining dominant sediment type and depositional zones could help resolve spatial heterogeneities in methane ebullition at medium to larger scales in inland waters.

Description: Research on the subterranean CO 2 dynamics has focused individually on either surface soils or bedrock cavities, neglecting the interaction of both systems as a whole. In this regard, the vadose-zone contains CO 2 -enriched air ( ca. 5% by volume) in the first meters, and its exchange with the atmosphere can represent from 10 to 90% of total ecosystem CO 2 emissions. Despite its importance, to date still lacking are reliable and robust databases of vadose-zone CO 2 contents that would improve knowledge of seasonal-annual above-belowground CO 2 balances. Here we study two and a half years of vadose-zone CO 2 dynamics in a semi-arid ecosystem. The experimental design includes an integrative approach to continuously measure CO 2 in: vertical and horizontal soil profiles, following gradients from surface to deep horizons and from areas of net biological CO 2 production (under plants) to areas of lowest CO 2 production (bare soil), as well as a bedrock borehole representing karst cavities and ecosystem-scale exchanges. We found that CO 2 followed similar seasonal patterns for the different layers, with the maximum seasonal values of CO 2 delayed with depth (deeper more delayed). However, the behavior of CO 2 transport differed markedly among layers. Advective transport driven by wind induced CO 2 emission both in surface soil and bedrock, but with negligible effect on subsurface soil, which appear to act as a buffer impeding rapid CO 2 exchanges. Our study provides the first evidence of enrichment of CO 2 under plant, hypothesizing that CO 2 -rich air could come from root zone or by transport from deepest layers through cracks and fissures.

Description: Forest ecosystems play an important role in the global cycling of mercury (Hg). In this study, we characterized the Hg cycling at a remote evergreen broadleaf (EB) forest site in southwest China (Mt. Ailao). The annual Hg input via litterfall is estimated to be 75.0 ± 24.2 µg m -2 yr -1 at Mt. Ailao. Such a quantity is up to one order of magnitude greater than those observed at remote temperate/boreal (T/B) forest sites. Production of litter biomass is found to be the most influential factor causing the high Hg input to the EB forest. Given their large areal coverage, Hg deposition through litterfall in EB forests is appropriately 9 ± 5 Mg yr -1 in China and 1086 ± 775 Mg yr -1 globally. The observed wet Hg deposition at Mt. Ailao is 4.9 ± 4.5 µg m -2 yr -1 , falling in the lower range of those observed at 49 T/B forest sites in North America and Europe. Given the data, the Hg deposition flux through litterfall is approximately 15 times higher than the wet Hg deposition at Mt. Ailao. Steady Hg accumulation in decomposing litter biomass and Hg uptake from the environment were observed during a 25-month litter decomposition. The size of the Hg pool in the organic horizon of EB forest floors is estimated to be up to 2-10 times the typical pool size in T/B forests. This study highlights the importance of EB forest ecosystems in global Hg cycling, which requires further assessment when more data become available in tropical forests.

Description: Salt marshes provide numerous valuable ecological services. In particular, nitrogen (N) removal in salt marsh sediments alleviates N loading to the coastal ocean. N removal reduces the threat of eutrophication caused by increased N inputs from anthropogenic sources. It is unclear, however, whether chronic nutrient over-enrichment alters the capacity of salt marshes to remove anthropogenic N. To assess the effect of nutrient enrichment on N cycling in salt marsh sediments, we examined important N cycle pathways in experimental fertilization plots in a New England salt marsh. We determined rates of nitrification, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) using sediment slurry incubations with 15 N labeled ammonium or nitrate tracers under oxic headspace (20% oxygen / 80% helium). Nitrification and denitrification rates were more than ten-fold higher in fertilized plots compared to control plots. By contrast, DNRA, which retains N in the system, was high in control plots but not detected in fertilized plots. The relative contribution of DNRA to total nitrate reduction largely depends on the carbon/nitrate ratio in the sediment. These results suggest that long-term fertilization shifts N cycling in salt marsh sediments from predominantly retention to removal.

Description: Understanding how tropical rainforests respond to elevated atmospheric CO 2 concentration (eCO 2 ) is essential for predicting Earth's carbon, water and energy budgets under future climate change. Here we use long-term (1982-2010) precipitation ( P ) and runoff ( Q ) measurements to infer runoff coefficient ( Q / P ) and evapotranspiration ( E ) trends across 18 unimpaired tropical rainforest catchments. We complement that analysis by using satellite observations coupled with ecosystem process modelling (using both ‘top-down’ and ‘bottom-up’ perspectives) to examine trends in carbon uptake and relate that to the observed changes in Q / P and E . Our results show there have been only minor changes in the satellite-observed canopy leaf area over 1982-2010, suggesting that eCO 2 has not increased vegetation leaf area in tropical rainforests and therefore any plant response to eCO 2 occurs at the leaf-level. Meanwhile, observed Q / P and E also remained relatively constant in the 18 catchments, implying an unchanged hydrological partitioning and thus approximately conserved transpiration under eCO 2 . For the same period, using a ‘top-down’ model based on gas-exchange theory, we predict increases in plant assimilation ( A ) and light-use efficiency ( ε ) at the leaf-level under eCO 2 , the magnitude of which is essentially that of eCO 2 ( i.e ., ~12% over 1982-2010). Simulations from ten state-of-the-art ‘bottom-up’ ecosystem models over the same catchments also show the direct effect of eCO 2 is to mostly increase A and ε with little impact on E . Our findings add to the current limited pool of knowledge regarding the long-term eCO 2 impacts in tropical rainforests.

Description: The savanna vegetation of Brazil (Cerrado) accounts for 20-25% of the land cover of Brazil and is the second largest ecosystem following Amazonian forest; however, Cerrado mass and energy exchange is still highly uncertain. We used eddy covariance to measure the net ecosystem CO 2 exchange (NEE) of grass-dominated Cerrado ( campo sujo ) over three years. We hypothesized that soil water availability would be a key control over the seasonal and interannual variations in NEE. Multiple regression indicated that gross primary production (GPP) was positively correlated (Pearson's r = 0.69; p 〈 0.001) with soil water content, radiation, and the MODIS-derived Enhanced Vegetation Index (EVI), but negatively correlated with the vapor pressure deficit (VPD), indicating that drier conditions increased water limitations on GPP. Similarly, ecosystem respiration (Reco) was positively correlated (Pearson's r = 0.78; p 〈 0.001) with the EVI, radiation, soil water content, and temperature but slightly negatively correlated with rainfall and the VPD. While the NEE responded rapidly to temporal variations in soil water availability, the grass-dominated Cerrado stand was a net source of CO 2 to the atmosphere during the study period, which was drier compared to the long-term average rainfall. Cumulative NEE was approximately 842 gC m -2 , varying from 357 gC m -2 in 2011 to 242 gC m -2 in 2012. Our results indicate that grass-dominated Cerrado may be an important regional CO 2 source in response to the warming and drying that is expected to occur in the southern Amazon Basin under climate change.

Description: Large fires account for a disproportionally high percentage of area burned with potentially severe environmental and socioeconomic impacts. This study characterizes extremely large fires (ELF, 2500–24,843 ha) in Portugal (1998–2013) and the concomitant fuel and weather conditions, analyzing the response of ELF size to their variation. ELF burned less shrubland-grassland (33% of the total ELF area) than forest (59% of total), the latter primarily composed by pine and pine-eucalypt. High fuel hazard was the norm, as indicated by median values of 0.98 for fuel load as a fraction of potential (maximum) load, and time since fire 〉14 years over 91% of the burned area. ELF occurred under anticyclonic circulation patterns, especially ridging, and 78% of them coincided with extreme fire danger days (corresponding to infrequent conditions) in conjunction with unstable atmosphere. Containment time, fire growth rate and energy release metrics varied by one more order of magnitude than ELF size, hence indicating that size alone is insufficient to describe extreme fires. Distinct combinations between ambient weather conditions, atmospheric instability and drought defined three categories of ELF as defined by size. Quantile regression indicated that increasingly larger fires showed gradually stronger responses to fire weather severity, highlighting the difficulty in restraining fire spread in flammable landscapes in the absence of extensive fuel treatments. Data limitations inherent to the methods used are discussed, and improvements to further advance the understanding of extreme fires are suggested.

Description: The aim of this work was to couple physical-chemical approaches with photocatalysis to reduce by a simple, inexpensive way the organic load of olive mill wastewater (OMW), mandatorily prior to the final discharge. Before irradiation, different sorbents were tested to remove part of the organic fraction, monitored by measuring chemical oxygen demand (COD) and polyphenols (PP). Different low-cost, safe materials were tested, that is, Y zeolite (ZY), montmorillonite, and sepiolite. Considerable decrease of organic load was obtained, with the highest abatement (40%) provided by ZY (10 g L−1 in 1 : 10 OMW). Use of the three sorbents, in particular ZY, was convenient compared to commercial activated carbons. UV light photocatalytic tests, performed using P25 TiO2 on ZY-treated OMW, yielded quantitative remediation (ca. 90%). Also solar light provided significative results, PP being lowered by 74% and COD by 56%. Sol-gel anatase TiO2 and N-doped anatase TiO2 were also tested, obtaining good results, around 80% PP and 40% COD. Finally, an integrated approach was experimented by ZY-supported anatase TiO2 (TiO2@ZY). This photoreactive sorbent allowed one-pot treatment of OMW significative abatements of PP (77%) and COD (39%) with only 1 g L−1 material, under solar light.

Description: Molybdenum (Mo) thin films are widely used as rear electrodes in copper indium gallium diselenide (CIGS) solar cells. The challenge in Mo deposition by magnetron sputtering lies in simultaneously achieving good adhesion to the substrates while retaining the electrical and optical properties. Bilayer Mo films, comprising five different thickness ratios of a high pressure (HP) deposited bottom layer and a low pressure (LP) deposited top layer, were deposited on 40 cm × 30 cm soda-lime glass substrates by DC magnetron sputtering. We focus on understanding the effects of the individual layer properties on the resulting bilayer Mo films, such as microstructure, surface morphology, and surface oxidation. We show that the thickness of the bottom HP Mo layer plays a major role in determining the micromechanical and physical properties of the bilayer Mo stack. Our studies reveal that a thicker HP Mo bottom layer not only improves the adhesion of the bilayer Mo, but also helps to improve the film crystallinity along the preferred [] direction. However, the surface roughness and the porosity of the bilayer Mo films are found to increase with increasing bottom layer thickness, which leads to lower optical reflectance and a higher probability for oxidation at the Mo surface.

Description: Lakes are highly relevant players in the global carbon cycle as they can store large amounts of organic carbon (OC) in sediments, thereby removing OC from the actively cycling pool. However, sediment OC can be released to pore water under anoxic conditions and diffuse into the water column. In carbon budgets of lake ecosystems, this potential OC loss pathway from sediments is generally disregarded. Combining field observations and incubation experiments, we quantitatively investigated dissolved OC (DOC) diffusion from sediments into anoxic water of a boreal lake. We observed substantial increases of bottom-water DOC (26% in situ, 16% incubation), translating into a DOC flux from the sediment that was comparable to anoxic sediment respiration (3.3 vs. 5.1 mmol m –2 d –1 ). Optical characterization indicated that colored and aromatic DOC was preferentially released. Reactivity assays showed that DOC released from anoxic sediment enhanced water column respiration and flocculation in re-oxygenated water. Upon water oxygenation, flocculation was the most important loss pathway removing ~77% of released DOC, but the remaining ~23% was mineralized, constituting a pathway of permanent loss of sediment OC. DOC diffusion from lake sediment during anoxia and subsequent mineralization in oxic water during mixing increases overall OC loss from anoxic sediments by ~15%. This study enlarges our understanding of lake ecosystems by showing that under anoxic conditions, significant amounts of DOC can be released from OC stored in sediments and enter the active aquatic carbon cycle again.

Description: Boreal lakes can be ice-covered for a substantial portion of the year at which time methane (CH 4 ) can accumulate below ice. The amount of CH 4 emitted at ice-melt is partially determined by the interplay between CH 4 production and CH 4 oxidation, performed by methane-oxidizing bacteria (MOB). Yet, the balance between oxidation and emission and the potential for CH 4 oxidation in various lakes during winter is largely unknown. To address this we performed incubations at 2 °C to screen for wintertime CH 4 oxidation potential in seven lakes. Results showed that CH 4 oxidation was restricted to three lakes, where the phosphate concentrations were highest. Molecular analyses revealed that MOB were initially detected in all lakes, although an increase in type I MOB only occurred in the three lake water incubations where oxidation could be observed. Accordingly, the increase in CO 2 was on average five times higher in these three lake water incubations. For one lake where no oxidation was measured, we tested if temperature and CH 4 availability could trigger CH 4 oxidation. However, regardless of incubation temperatures and CH 4 concentrations, ranging from 2-20 °C and 1-500 μM respectively, no oxidation was observed. Our study indicates that some lakes with active wintertime CH 4 oxidation may have low emissions during ice-melt, while other and particularly nutrient poor lakes may accumulate large amounts of CH 4 below ice that, in the absence of CH 4 oxidation, will be emitted following ice-melt. This variability in CH 4 oxidation rates between lakes needs to be accounted for in large-scale CH 4 emission estimates.

Description: Rivers play a major role in the transport and processing of dissolved organic matter (DOM). Disturbances that impact DOM dynamics, such as river impoundments and flow regulation have consequences for biogeochemical cycling and aquatic ecosystems. In this study we examined how river impoundments and hydrologic regulation impact DOM quantity and quality by tracking spatial and seasonal patterns of DOM in a large, regulated river (Klamath River, USA). Dissolved organic carbon (DOC) concentrations decreased downstream and longitudinal patterns in DOC load varied by season. Export of DOM (as DOC) was largely driven by river flow, while DOM composition was strongly influenced by impoundments. Seasonal algal blooms in upstream lentic reaches provided a steady source of algal DOM that was processed in downstream reaches. DOM at upstream sites had an average spectral slope ratio (S R ) 〉 1, indicating algal-derived material, but decreased downstream to an average S R 〈1, more indicative of terrestrial-derived material. The increasingly terrestrial nature of DOM exported from reservoirs likely reflects degraded algal material that becomes increasingly more recalcitrant with distance from upstream source and additional processing. As a result, DOM delivered to free-flowing river reaches below impoundments was less variable in composition. Downstream of impoundments, tributary influences resulted in increasing contributions of terrestrial DOM from the surrounding watershed. Removal of the four lower dams on the Klamath River is scheduled to proceed in the next decade. These results suggest that management should consider the role of impoundments on altering DOM dynamics, particularly in the context of dam removal.

Description: Steep vegetation-free talus slopes in high mountain environments are prone to superficial slope failures and surface erosion. Eco-engineering measures can reduce slope instabilities and thus contribute to risk mitigation. In a field experiment, we established mycorrhizal and non-mycorrhizal research plots and determined their biophysical contribution to small scale soil fixation. Mycorrhizal inoculation impact on plant survival, aggregate stability and fine root development was analyzed. Here, we present plant survival (n total  = 1248) and soil core (n total  = 108) analyses of three consecutive years in the Swiss Alps. Soil cores were assayed for their aggregate stability coefficient (ASC), root-length density (RLD) and mean root diameter (MRD). Inoculation improved plant survival significantly, but it delayed aggregate stabilization relative to the non-inoculated site. Higher aggregate stability occurred only after three growing seasons. Then also RLD tended to be higher and MRD increased significantly at the mycorrhizal treated site. There was a positive correlation between RLD, ASC and roots 〈 0.5 mm, which had the strongest impact on soil aggregation. Our results revealed a temporal offset between inoculation effects tested in laboratory and field experiments. Consequently, we recommend to establish an intermediate to long-term field-experimental monitoring before transferring laboratory results to the field.

Description: This manuscript details investigations of a productive, mountain freshwater lake and examines the dynamic relationship between the chemical, stable isotope and microbial composition of lake-bed sediments with the geochemistry of the lake water column. A multi-disciplinary approach was used in order to better understand the lake water-sediment interactions including quantification and sequencing of microbial 16S rRNA genes in a sediment core as well as stable isotope analysis of C, S, N. One visit included the use of a pore water sampler to gain insight into the composition of dissolved solutes within the sediment matrix. Sediment cores showed a general decrease in total C with depth which included a decrease in the fraction of organic C combined with an increase in the fraction of inorganic C. One sediment core showed a maximum concentration of dissolved organic C, dissolved inorganic C and dissolved methane in pore water at the 4 cm depth which corresponded with a sharp increase in the abundance of 16S rRNA templates as a proxy for the microbial population size as well as the peak abundance of a sequence affiliated with a putative methanotroph. The isotopic separation between dissolved inorganic and dissolved organic carbon is consistent with largely aerobic microbial processes dominating the upper water column while anaerobic microbial activity dominates the sediment bed. Using sediment core carbon concentrations, predictions were made regarding the breakdown and return of stored carbon per year from this temperate climate lake with as much as 1.3 Gg C yr -1 being released in the form of CO 2 and CH 4 .

Description: To determine the availability of atmospheric NO 3 − deposition on forested ecosystems and to understand the interaction between the nitrogen cycle in a forest ecosystem and atmospheric nitrogen input/output, we quantitatively evaluated the atmospheric NO 3 − passing through forested watersheds by measuring δ 18 O NO3 leaching during rainfall events in two forest ecosystems (Su-A and Ab-S). Atmospheric NO 3 − leaching in rainfall events was clearly higher in Ab-S than in Su-A, even for a similar amount of rainfall, which demonstrated that atmospheric NO 3 − leaching differs among forested watersheds. Our observations suggest that a large part of the atmospheric NO 3 − leached from the watersheds was derived from surface soil, which was deposited before rainfall events occurred; however, direct atmospheric NO 3 − leaching via throughfall discharge also contributed, especially at the beginning of rainfall events. In Ab-S, 2.9–37.8% (average = 15.5%) of atmospheric NO 3 − deposition passed through the watershed, accounting for 3.1–49.8% (average, 26.4%) of the total NO 3 − leached during rainfall events. The NO 3 − input was not large, and the NO 3 − pool and net nitrification rate were small; therefore, nitrogen was not saturated in the soil at Ab-S. Nevertheless, some of the atmospheric NO 3 − deposition was not assimilated and was leached immediately. Moreover, our observations suggest that the hydrological characteristics of the watersheds, which control the ease of rainwater discharge, strongly influenced the rate of atmospheric NO 3 − leaching. This suggests that the hydrological characteristics of watersheds influence the availability of atmospheric NO 3 − deposition in forested ecosystems and the progression of nitrogen saturation.

Description: Key Points Regional differences in d13C and d18O from earlywood and latewood were observed, which reflect a gradient in seasonal monsoon development. Tree WUE inferred from latewood d13C exhibited greater sensitivity to moisture variation near the North limit of the monsoon system. Summer air humidity has a significant latitudinal influence on the relative d13C and d18O values in cellulose of earlywood and latewood.

Description: Aerobic respiration is an important component of in-stream metabolism. The larger part occurs in the streambed, where it is difficult to directly determine actual respiration rates. Existing methods for determining respiration are based on indirect estimates from whole-stream metabolism or provide time invariant results estimated from oxygen consumption measurements in enclosed chambers that do not account for the influence of hydrological changes. In this study we demonstrate a simple method for determining time-variable hyporheic respiration. We use a windowed cross-correlation approach for deriving time-variable travel times from the naturally changing electrical conductivity signal that is transferred into the sediment. By combining the results with continuous in situ dissolved oxygen measurements, variable oxygen consumption rate coefficients in the streambed are obtained. An empirical temperature relationship is derived and used for standardizing the respiration rate coefficients to isothermal conditions. For demonstrating the method, we compare two independent measurement spots in the streambed, which were located upstream and downstream of an in-stream gravel bar and thus exposed strongly diverse travel times. The derived respiration rate results are in accordance with findings of other stream studies. By comparing the travel time and respiration rate coefficient (i.e. Damköhler number) we estimate the contribution of each to the oxygen consumption in the streambed.

Description: Three hydrocalumite-like compounds in a Ca/Al ratio of 2 containing nitrate and acetate anions in the interlaminar region were prepared by a simple, economic, and environmentally friendly method. The solids were characterized by X-ray powder diffraction (XRD), thermogravimetric (TG) analysis, nitrogen adsorption-desorption at −196°C, scanning electron microscopy (SEM), infrared spectroscopy (FTIR), and UV-Vis Diffuse Reflectance Spectroscopy (DRS). The catalytic activity of the calcined solids at 700°C was tested in the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) where 57% degradation of 2,4-D (40 ppm) and a mineralization percentage of 60% were accomplished within 150 minutes. The photocatalytic properties were attributed to mayenite hydration, since the oxide ions in the cages are capable of reacting with water to form hydroxide anions capable of breaking down the 2,4-D molecules.

Description: This study uses an integrated modeling framework that couples the dynamics of hydrology, soil thermal regime, and ecosystem carbon and nitrogen to quantify the long-term peat carbon accumulation in Alaska during the Holocene. Modeled hydrology, soil thermal regime, carbon pools and fluxes and methane emissions are evaluated using observation data at several peatland sites in Minnesota, Alaska, and Canada. The model is then applied for a 10,000-year (15 ka to 5 ka; 1 ka = 1000 cal yr before present) simulation at four peatland sites. We find that model simulations match the observed carbon accumulation rates at fen sites during the Holocene ( R 2  = 0.88, 0.87, 0.38 and -0.05 using comparisons in 500-year bins). The simulated (2.04 m) and observed peat depths (on average 1.98 m) also compared well ( R 2  = 0.91). The early Holocene carbon accumulation rates, especially during the Holocene thermal maximum (HTM) (35.9 gCM –2 yr –1 ), are estimated up to 6-times higher than the rest of the Holocene (6.5 gCM –2 yr –1 ). Our analysis suggests that high summer temperature and the lengthened growing season resulted from the elevated insolation seasonality, along with wetter-than-before conditions might be major factors causing the rapid carbon accumulation in Alaska during the HTM. Our sensitivity tests indicate that, apart from climate, initial water-table depth and vegetation canopy are major drivers to the estimated peat carbon accumulation. When the modeling framework is evaluated for various peatland types in the Arctic, it can quantify peatland carbon accumulation at regional scales.

Description: Key Points Inflowing warm Atlantic water increases the net sea-air exchange in Siberian shelf seas. The increased volume transport has a larger impact on the CO2 flux than the warming of the water. The sea-air flux of CH4 is mainly affected by the increase in water temperature.

Description: Gross primary productivity (GPP) has been reported to increase with the fraction of diffuse solar radiation, for a given total irradiance. The correlation between GPP and diffuse radiation suggests effects of diffuse radiation on canopy light-use efficiency, but potentially confounding effects of vegetation phenology have not been fully explored. We applied several approaches to control for phenology, using 8 years of eddy-covariance measurements of winter wheat in the U.S. Southern Great Plains. The apparent enhancement of daily GPP due to diffuse radiation was reduced from 260% to 75%, after subsampling over the peak growing season or by subtracting a 15-day moving average of GPP, suggesting a role of phenology. The diffuse radiation effect was further reduced to 22% after normalizing GPP by a spectral reflectance index to account for phenological variations in LAI and canopy photosynthetic capacity. Canopy photosynthetic capacity covaries with diffuse fraction at a given solar irradiance at this site because both factors are dependent on day of year, or solar zenith angle. Using a two-leaf sun-shaded canopy radiative transfer model, we confirmed that the effects of phenological variations in photosynthetic capacity can appear qualitatively similar to the effects of diffuse radiation on GPP, and therefore can be difficult to distinguish using observations. The importance of controlling for phenology when inferring diffuse radiation effects on GPP raises new challenges and opportunities for using radiation measurements to improve carbon cycle models.

Description: Photovoltaic (PV) energy is one of the most important energy sources since it is clean and inexhaustible. It is important to operate PV energy conversion systems in the maximum power point (MPP) to maximize the output energy of PV arrays. An MPPT control is necessary to extract maximum power from the PV arrays. In recent years, a large number of techniques have been proposed for tracking the maximum power point. This paper presents a comparison of different MPPT methods and proposes one which used a power estimator and also analyses their suitability for systems which experience a wide range of operating conditions. The classic analysed methods, the incremental conductance (IncCond), perturbation and observation (P&O), ripple correlation (RC) algorithms, are suitable and practical. Simulation results of a single phase NPC grid connected PV system operating with the aforementioned methods are presented to confirm effectiveness of the scheme and algorithms. Simulation results verify the correct operation of the different MPPT and the proposed algorithm.

Description: Concentrated sunlight that is transmitted by fiber optics has been used for generating electricity, heat, and daylight. On the other hand, multijunction photovoltaic cells provide high efficiency for generating electricity from highly concentrated sunlight. This study deals with designing and simulating a high-efficiency coupler, employing a mathematical model to connect sunlight with fiber optics for multiple applications. The coupler concentrates and distributes irradiated light from a primary concentrator. In this study, a parabolic dish was used as the primary concentrator, a coupler that contains nine components called a compound truncated pyramid and a cone (CTPC), all of which were mounted on a plate. The material of both the CTPC and the plate was BK7 optical glass. Fiber optics cables and multijunction photovoltaic cells were connected to the cylindrical part of the CTPC. The fibers would transmit the light to the building to provide heat and daylight, whereas multijunction photovoltaic cells generate electricity. Theoretical and simulation results showed high performance of the designed coupler. The efficiency of the coupler was as high as , whereas the rim angle of the dish increased to an optimum angle. Distributed sunlight in the coupler increased the flexibility and simplicity of the design, resulting in a system that provided concentrated electricity, heat, and lighting for residential buildings.

Description: Water-soluble graphitic hollow carbon nanorods (wsCNRs) are exploited for their light-driven photochemical activities under outdoor sunlight. wsCNRs were synthesized by a simple pyrolysis method from castor seed oil, without using any metal catalyst or template. wsCNRs exhibited the light-induced photochemical degradation of methylene blue used as a model pollutant by the generation of singlet oxygen species. Herein, we described a possible degradation mechanism of methylene blue under the irradiation of visible photons via the singlet oxygen-superoxide anion pathway.

Description: The Finite-difference Ecosystem-scale Tree-Crown Hydrodynamics model version 2 (FETCH2) is a tree-scale hydrodynamic model of transpiration. The FETCH2 model employs a finite difference numerical methodology and a simplified single-beam conduit system to explicitly resolve xylem water potentials throughout the vertical extent of a tree. Empirical equations relate water potential within the stem to stomatal conductance of the leaves at each height throughout the crown. While highly simplified, this approach brings additional realism to the simulation of transpiration by linking stomatal responses to stem water potential rather than directly to soil moisture, as is currently the case in the majority of land-surface models. FETCH2 accounts for plant hydraulic traits, such as the degree of anisohydric/isohydric response of stomata, maximal xylem conductivity, vertical distribution of leaf area, and maximal and minimal xylem water content. We used FETCH2 along with sap flow and eddy covariance data sets collected from a mixed plot of two genera (oak/pine) in Silas Little Experimental Forest, NJ, USA, to conduct an analysis of the intergeneric variation of hydraulic strategies and their effects on diurnal and seasonal transpiration dynamics. We define these strategies through the parameters that describe the genus-level transpiration and xylem conductivity responses to changes in stem water potential. Our evaluation revealed that FETCH2 considerably improved the simulation of ecosystem transpiration and latent heat flux than more conventional models. A virtual experiment showed that the model was able to capture the effect of hydraulic strategies such as isohydric/anisohydric behavior on stomatal conductance under different soil-water availability conditions.

Description: Although many studies have considered the carbon or greenhouse gas budgets of peat ecosystems, only a few have considered the nutrient budget of peat soils and this, in turn, has limited the ability of studies to consider the impact of changes in climate and atmospheric deposition on the phosphorus budget of a peat soil. This study considered the total phosphorus (P) budget of an upland peat-covered catchment over the period 1993 to 2012. The study has shown: Total atmospheric deposition of phosphorus varied from 62 to 175 kg P/km 2 /yr; The carbon:phosphorus ratio of the peat profile declines significantly from values in the litter layer (C:P = 1326) to approximately constant at 30 cm depth (C:P = 4240); The total fluvial flux of phosphorus varied from 49 to 111 kg P/km 2 /yr, of which between 45 and 77% was dissolved P. The total phosphorus sink varied from -5.6 to +71.7 kg P/km 2 /yr with a median of +29.4 kg P/km 2 /yr, which is within the range of the estimated long-term accumulation rate of phosphorus in the peat profile of between 3 and 32 kg P/km 2 /yr. The phosphorus budget of the peat ecosystem relies on rapid recycling near the soil surface and this means that any vegetation management may critically deprive the ecosystem of this nutrient.

Description: Permafrost collapse, known as thermokarst, can alter soil properties and carbon emissions. However, little is known regarding the effects of permafrost collapse in upland landscapes on the biogeochemical processes that affect carbon balance. In this study, we measured soil carbon and physiochemical properties at a large thermokarst feature on a hillslope in the northeastern Tibetan Plateau. We categorized surfaces into three different micro-relief patches based on type and extent of collapse (control, drape and exposed areas). Permafrost collapse resulted in substantial decreases of surface soil carbon and nitrogen stocks, with losses of 29.6 ± 5.9% and 26.7 ± 8.8% for carbon and nitrogen, respectively, in the 0-10 cm soil layer. Laboratory incubation experiments indicated that control soil had significantly higher CO 2 production rates than that of drapes. The results from Fourier transform infrared (FTIR) spectroscopy analysis showed that exposed soils accumulated some organic matter due to their low position within the feature, which was accompanied by substantial changes in the chemical structure and characteristics of the soil carbon. Exposed soils had higher hydrocarbon and lignin/phenol backbone content than in control and drape soils in the 0-10 cm layer. This study demonstrates that permafrost collapse can cause abundant carbon and nitrogen loss, potentially from mineralization, leaching, photo-degradation and lateral displacement. These results demonstrate that permafrost collapse redistributes the soil organic matter, changes its chemical characteristics, and leads to losses of organic carbon due to the greenhouse gas emission.

Description: The discovery of anaerobic ammonium oxidation (anammox) highlighted the importance of alternative metabolic pathways to inorganic nitrogen removal in natural environments, particularly in those subjected to increased nitrate inputs, such as estuaries. Laboratory enrichment experiments were used to test the effect of increasing loads of nitrate (NO 3 - ), nitrite (NO 2 - ), and ammonium (NH 4 + ) on the anammox process. Three Atlantic temperate estuaries (NW Portugal) were investigated along a salinity gradient, and anammox activity was measured under different NO 3 - , NO 2 - and NH 4 + treatments, using the isotope pairing technique. Obtained results showed that NO 3 - stimulated denitrification but not anammox, whereas NO 2 - additions had a positive effect on anammox activity, confirming its role as a key environmental control. On the other hand, increasing NH 4 + concentrations seemed to inhibit anammox for low salinity sites. Our findings suggested an important role of the natural availability of nitrogen compounds in regulating anammox and the magnitude of anammox versus denitrification in estuarine environments.

Description: Understanding stream carbon export dynamics is needed to accurately predict how the carbon balance of peatland catchments will respond to climatic and environmental change. We used a twelve year record (2003-2014) of continuous streamflow and manual spot measurements of total organic carbon (TOC), dissolved inorganic carbon (DIC), methane (CH 4 ) and organic carbon quality (SUVA 254 ) to assess interannual and seasonal variability in stream carbon export for a peatland catchment (70% mire and 30% forest cover) in northern Sweden. Mean annual total carbon export for the twelve year period was 12.2 g C m −2  yr −1 , but individual years ranged between 6 and 18 g C m −2  yr −1 . TOC, which was primarily composed of dissolved organic carbon (〉99%), was the dominant form of carbon being exported, comprising 63% to 79% of total annual exports, and DIC contributed between 19% and 33%. CH 4 made up less than 5% of total export. When compared to previously published annual net ecosystem exchange (NEE) for the studied peatland system, stream carbon export typically accounted for 12 to 50% of NEE for most years. However, in 2006 stream carbon export accounted for 63 to 90% (estimated uncertainty range) of NEE due to a dry summer which suppressed NEE, followed by a wet autumn that resulted in considerable stream export. Runoff exerted a primary control on stream carbon export from this catchment; however, our findings suggest that seasonal variations in biologic and hydrologic processes responsible for production and transport of carbon within the peatland were secondary influences on stream carbon export. Consideration of these seasonal dynamics is needed when predicting stream carbon export response to environmental change.

Description: Solar panels have become attractive in order to generate and supply electricity in commercial and residential applications. Their increased module efficiencies have caused not only a massive production but also a sensible drop on sale prices. Methods of characterization, instrumentation for in situ measurements, defect monitoring, process control, and performance are required. A temperature characterization method by means of thermograph analysis is exposed in this paper. The method was applied to multicrystalline modules, and the characterization was made with respect to two different variables, first a thermal transient and second a characterization with respect to the current. The method is useful in order to detect hot spots caused by mismatch conditions in electrical parameters. The description, results, and limitations of the proposed method are discussed.

Description: Streambed substrates harbor a rich biome responsible for biogeochemical processing in riverine waters. Beyond their biological role, the presence of benthic and hyporheic biofilms can play an important role in influencing large scale transport of solutes, even for conservative tracers. As biofilms grow and accumulate biomass, they actively interact with and influence surface and sub-surface flow patterns. To explore this effect we conducted experiments at the Notre Dame Linked Ecosystems Experimental Facility (ND-LEEF) in four outdoor streams, each with different gravel beds. Over the course of 20 weeks we conducted transport experiments in each of these streams and observed different patterns in breakthrough curves as biofilms grew on the substrate. Biofilms played a major role in shaping the observed conservative transport patterns. Overall, while the presence of biofilms led to a decreased exchange rate between the fast (mobile) and slow (immobile) parts of the flow domain, water that was exchanged tended to be stored in the slow regions for longer times once biofilms had established. More specifically, we observed enhanced longitudinal dispersion in breakthrough curves as well as broader residence time distributions when biofilms were present. Biofilm colonization over time homogenized transport patterns across the four streams that were originally very distinct. These results indicate that stream biofilms exert a strong control on conservative solute transport in streams, a role that to date has not received enough attention.

Description: Fe-doped TiO2 (Fe/TiO2) film photocatalyst was prepared by sol-gel and dip-coating process to extend its photoresponsivity to the visible spectrum. To promote the CO2 reduction performance with the photocatalyst, some types of base materials used for coating Fe/TiO2, which were netlike glass fiber and Cu disc, were investigated. The characterization of prepared Fe/TiO2 film coated on netlike glass fiber and Cu disc was analyzed by SEM and EPMA. In addition, the CO2 reduction performance of Fe/TiO2 film coated on netlike glass disc, Cu disc, and their overlap was tested under a Xe lamp with or without ultraviolet (UV) light, respectively. The results show that the concentration of produced CO increases by Fe doping irrespective of base material used under the illumination condition with UV light as well as that without UV light. Since the electron transfer between two overlapped photocatalysts is promoted, the peak concentration of CO for the Fe/TiO2 double overlapping is approximately 1.5 times as large as the Fe/TiO2 single overlapping under the illumination condition with UV light, while the promotion ratio is approximately 1.1 times under that without UV light.

Description: Significant climate fluctuations in the Arctic over the recent past, and additional predicted future temperature changes, highlight the need for high-resolution Arctic paleoclimate records. Arctic coastal environments supplied with terrigenous sediment from Arctic rivers have the potential to provide annual to sub-decadal resolution records of climate variability over the last few millennia. A potential tool for paleotemperature reconstructions in these marine sediments is the MBT’/CBT proxy based on branched glycerol dialkyl glycerol tetraethers (brGDGTs). In this study, we examine the source of brGDGTs in the Colville River, Alaska and the adjacent Simpson Lagoon, and reconstruct temperatures from Simpson Lagoon sediments to evaluate the applicability of this proxy in Arctic estuarine environments. The Colville catchment soils, fluvial sediments, and estuarine sediments contain statistically similar brGDGT distributions, indicating that the brGDGTs throughout the system are soil-derived with little alteration from in situ brGDGT production in the river or coastal waters. Temperatures reconstructed from the MBT’/CBT indices for surface samples show good agreement with regional summer (June through September; JJAS) temperatures, suggesting a seasonal bias in Arctic temperature reconstructions from the Colville system. In addition, we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 y, revealing an overall warming trend in the 20 th century that is consistent with trends observed in regional instrumental records. These results support the application of this brGDGT-based paleotemperature proxy for sub-decadal scale summer temperature reconstructions in Arctic estuaries containing organic material derived from sediment-laden, episodic rivers.

Description: Global warming is expected to raise temperatures in freshwater lakes, which have been acknowledged to contribute up to 10% of the atmospheric methane concentrations. Increasing temperature enhances methane production and oxidation rates, but few studies have considered the balance between both processes at experimentally higher temperatures within lake sediments. The temperature dependence of methane concentrations, methane production rates and methanogenic ( mcrA ) and methanotrophic ( pmoA ) community size was investigated in intact sediment cores incubated with aerobic hypolimnion water at 4, 8 and 12 °C over three weeks. Sediment cores of 25 cm length were collected at two temperate lakes – Lake Stechlin (Germany) (meso-oligotrophic, maximum depth 69.5 m), and Lake Geneva (France/Switzerland) (mesotrophic, maximum depth 310 m). While methane production rates in Lake Stechlin sediments did not change with increasing temperatures, methane concentrations decreased significantly. In contrast, methane production rates increased in 20-25 cm in Lake Geneva sediments with increasing temperatures, but methane concentrations did not differ. Real-time PCR demonstrated the methanogenic and methanotrophic community size remained stable independently of the incubation temperature. Methane concentrations as well as community sizes were one to two magnitudes higher in Lake Stechlin than in Lake Geneva, while potential methane production rates after 24 h were similar in both lakes, with on average 2.5 and 1.9 nmol g -1 DW h -1 , respectively. Our results suggest that at higher temperatures methane oxidation could balance, and even exceed, methane production. This suggests anaerobic methane oxidation could be involved in the methane balance at a more important rate than previously anticipated.

Description: It is important to clarify the quantity and composition of hydrologic N export from terrestrial ecosystem and its primary controlling factors, because it affected N availability, productivity and C storage in natural ecosystems. The most previous investigations were focused on the effects of N deposition and human disturbance on the composition of hydrologic N export. However, few studies were aware of whether there were significant differences in the concentrations and composition of hydrologic N export from natural ecosystems in different climate zones, and what is the primary controlling factor. In the present study, three natural forest ecosystems and one natural grassland ecosystem that were located in different climate zones and with different soil pH range were selected. The concentrations of total dissolved N, DON, NH 4 + , NO 3 − in soil solution and stream water, soil properties, and soil gross N transformation rates were measured to answer above questions. Our results showed that NO 3 - concentrations and the composition pattern of hydrologic N export from natural ecosystems varied greatly in the different climate zones. The NO 3 - concentrations in stream water varied largely, ranging from 0.1 mg N L -1 to 1.6 mg N L -1 . While, DON concentration in stream water, ranging from 0.1 to 0.9 mg N L -1 , did not differ significantly and the concentrations of NH 4 + were uniformly low (average 0.1 mg N L -1 ) in all studied sites. There was a trade-off relationship between the proportions of NO 3 - and DON to total dissolved N in stream water. In subtropical strongly acidic forests soil site, DON was the dominance in total dissolved N in stream water. While, NO 3 - -N became dominance in temperate acidic forests soil site, subtropical alkaline forests soil region, and the alpine meadow sites on the Tibetan Plateau. The proportions of NO 3 - to total dissolved N in both soil solution and stream water significantly increased with the increasing of the gross autotrophic nitrification rates (p 〈 0.01). Our results indicated that the characteristics of soil N transformations were the most primary factor regulating the composition of hydrologic N losses from ecosystems. The nitrification was the central soil N transformation processes regulating N composition in soil solution and hydrologic N losses. These results provided important information on understanding easily the composition of hydrologic N export from terrestrial ecosystem.

Description: The internal impedances of different dye-sensitized solar cell (DSSC) models were analyzed by electrochemical impedance spectrometer (EIS) with an equivalent circuit model. The Nyquist plot was built to simulate the redox reaction of internal device at the heterojunction. It was useful to analyze the component structure and promote photovoltaic conversion efficiency of DSSC. The impedance of DSSC was investigated and the externally connected module assembly was constructed utilizing single cells on the scaled-up module. According to the experiment results, the impedance was increased with increasing cells connected in series. On the contrary, the impedance was decreased with increasing cells connected in parallel.

Description: Dissolved organic matter (DOM) composition may be an important determinant of its fate in freshwaters, but little is known about temporal variability in DOM composition and the biodegradability of DOM in northern temperate watersheds. We measured biodegradable dissolved organic carbon (BDOC) via incubation assays and DOM composition using optical indices on eleven dates in three Lake Superior tributaries. Percent BDOC (%BDOC) and BDOC concentrations were seasonally synchronous across these watersheds, despite that they vary in size by orders of magnitude (1.7 to 3400 km 2 ). Relative to %BDOC, BDOC concentrations were more tightly constrained among sites on any given date. BDOC also varied within seasons; for example, %BDOC on two different dates in winter were among the highest (29% and 54%) and lowest (0%) values observed for each site (overall %BDOC range: 0 to 72%). DOM composition varied the most among tributaries during a summer storm event when BDOC (both as % and concentration) was elevated, but was remarkably similar among tributaries during fall, spring and winter. Multivariate models identified humic-like and tryptophan-like fluorophores as predictors of %BDOC, but DOM composition only described 21% of the overall variation in %BDOC. Collectively, these three rivers exported ~18 Gg C yr -1 as DOC and ~2Gg C yr -1 as BDOC, which corresponded to 9 to 17% of annual DOC exported in biodegradable form. Our results suggest much of the C exported from these northern temperate watersheds may be biodegradable within 28 days, and that large pulses of labile DOM can be exported during storm events and spring snowmelt.

Description: The predicted increase in the frequency and intensity of climate extremes is expected to impact terrestrial carbon fluxes to the atmosphere, potentially changing ecosystems from carbon sinks to sources, with positive feedbacks to climate change. As the second largest terrestrial carbon flux, soil CO 2 efflux or soil respiration (R s ), is strongly influenced by soil temperature and moisture. Thus, climate extremes such as heat waves and extreme drought should have substantial impacts on R s . We investigated the effects of such climate extremes on growing season R s in a mesic grassland by experimentally imposing two years of extreme drought combined with midsummer heat waves. After this two-year period, we continued to measure R s during a recovery year. Two consecutive drought years reduced R s by ~25% each growing season; however when normal rainfall returned during the recovery year, formerly droughted plots had higher rates of R s than control plots (up to +17%). The heat wave treatments had no effect on R s , alone or when combined with drought, and during the growing season, soil moisture was the primary driver of R s with little evidence for R s temperature sensitivity. When compared to aboveground net primary production, growing season R s was much less sensitive to drought, but was more responsive post-drought. These results are consistent with the hypothesis that ecosystems become sources of CO 2 during drought because carbon inputs (production) are decreased relatively more than outputs (respiration). Moreover, stimulation of R s post-drought may lengthen the time required for net carbon exchange to return to pre-drought levels.

Description: Global changes are altering many important drivers of ecosystem functioning, with precipitation amount and disturbance frequency being especially important. Carbon (C) and nitrogen (N) pools are key contemporary attributes of ecosystems that can also influence future C uptake via plant growth. Thus, understanding the impacts of altered precipitation amounts (through controls of primary production inputs) and disturbance regimes (through losses of C and N in biomass) is important to project how ecosystem services will respond to future global changes. A major difficulty inherent within this task is that drivers of ecosystem function and processes often interact, resulting in novel ecosystem responses. To examine how changes in precipitation affect grassland ecosystem responses under a frequent disturbance regime (annual fire), we assessed the biogeochemical and ecological consequences of more than two decades of irrigation in an annually burned mesic grassland in the central United States. In this experiment, precipitation amount was increased by 31% relative to ambient and 1 in 3 years were statistically extreme relative to the long-term historical record. Despite evidence that irrigation decreased root:shoot ratios and increased rates of N cycling – each expected to reduce soil C and N with annual burning – we detected no changes in these biogeochemical pools. This surprising biogeochemical resistance highlights the need to explore additional mechanisms within long-term experiments concerning the consequences of global change impacts on ecosystems.

Description: Foliage/atmosphere exchange is an important pathway of deposition and loss in the biogeochemical mercury (Hg) cycle of terrestrial ecosystems. The foliage/atmosphere fluxes of Hg 0 were observed over four seasons in a Masson pine (Pinus massoniana) forest in south China. Hg 0 exchange showed a bi-directional process, but without clear compensation point. Hg 0 emissions peaked mid-day in all four seasons, probably associated with Hg photoreduction on needle surface. Peaks in Hg 0 adsorption/deposition often occurred in the morning, especially in spring and autumn. Although current-year needles accumulated Hg at a rate of 19.4 µg · m -2  · yr -1 , they were a net Hg 0 source of 1.7 µg · m -2  · yr -1 to the atmosphere as their release of Hg exceeded inputs. In addition, previous-year needles emitted Hg 0 at an average rate of 9.2 µg · m -2  · yr -1 . Based on the mass balance of Hg in the forest canopy, the dry deposition of Hg was estimated 52.5 µg · m -2  · yr -1 , much higher than the wet deposition (to 14.4 µg · m -2  · yr -1 ). Although Hg in the atmosphere is considered the main source of Hg in folia, soil water may contribute to Hg 0 emission by plant transpiration. These processes should be further studied in the future.

Description: This paper identifies the partial shading problem of a PV module using the one-diode model and simulating the characteristics exhibiting multiple-peak power output condition that is similar to a PV array. A modified particle swarm optimization (PSO) algorithm based on the suggested search-agent deployment, retracking condition, and multicore operation is proposed in order to continuously locate the global maximum power point for the PV system. Partial shading simulation results for up to 16 modules in series/parallel formats are presented. A distributed PV system consisting of up to 8 a-silicon thin film PV panels and also having a dedicated DC/DC buck converter on each of the modules is tested. The converter reaches its steady state voltage output in 10 ms. However for MPPT operation, voltage, and current measurement interval is set to 20 ms to avoid unnecessary noise from the entire electric circuit. Based on the simulation and experiment results, each core of the proposed PSO operation should control no more than 4 PV modules in order to have the maximum tracking accuracy and minimum overall tracking time. Tracking for the global maximum power point of a distributed PV system under various partial shading conditions can be done within 1.3 seconds.

Description: This paper discusses the utilisation of PV systems for electric vehicles charging for transportation requirements of smart cities. The gap between PV power output and vehicles charging demand is highly variable. Therefore, there is a need for additional support from a public distribution grid or a storage device in order to handle the residual power. Long term measurement data retrieved from a charging station for 15 vehicles equipped with a PV system were used in the research. Low and high irradiation seasons influenced the PV output. The charging demand of electric vehicles varied over the course of a year and was correlated to weather conditions. Therefore, the sizing and performance of a supportive storage device should be evaluated in a statistical manner using long period observations.

Description: The performance of a solar assisted heat pump dryer integrated with biomass furnace has been designed and evaluated for drying red chillies, and drying kinetics of red chillies were evaluated. The red chillies were dried from 22 kg with moisture content of 4.26 db to moisture content of 0.08 db which needed 11 hours, with the average drying chamber temperature, drying chamber relative humidity, and an air mass flow rate of 70.5°C, 10.1%, and 0.124 kg/s, respectively, while the open sun drying needed 62 hours. Compared to open sun drying, this dryer yielded 82% saving in drying time. The drying rate, the specific moisture extraction rate, and thermal efficiency of the dryer were estimated in average to be about 1.57 kg/h, 0.14 kg/kWh, and 9.03%, respectively. Three mathematical models, the Newton, Henderson-Pabis, and Page models, were fitted to the experimental data on red chillies dried by solar assisted heat pump dryer integrated with biomass furnace and open sun drying. The performance of these models was evaluated by comparing the coefficient of determination (), mean bias error (MBE), and root mean-square error (RMSE). The Page model gave the best results for representing drying kinetics of red chillies.

Description: Hyporheic flow in aquatic sediment controls solute and heat transport thereby mediating the fate of nutrients and contaminants, dissolved oxygen, and temperature in the hyporheic zone (HZ). We conducted a series of numerical simulations of hyporheic processes within a dune with different uniform temperatures, coupling turbulent open-channel fluid flow, porous fluid flow, and reactive solute transport, to study the temperature dependence of nitrogen source/sink functionality and its efficiency. Two cases were considered: a polluted and a pristine stream. Sensitivity analysis was performed to investigate the influence of stream water [NO 3 − ] /[NH 4 + ]. The simulations showed that in both cases warmer temperatures resulted in shallower denitrification zones and oxic-anoxic zone boundaries, but the trend of net denitrification rate and nitrate removal or production efficiency of the HZ for these two cases differed. For both cases, at high [NO 3 − ] /[NH 4 + ], the HZ functioned as a NO 3 − sink with the nitrate removal efficiency increasing with temperature. But at low [NO 3 − ] /[NH 4 + ] for the polluted stream, the HZ is a NO 3 − sink at low temperature, but then switches to a NO 3 − source at warmer temperatures. For the pristine stream case, the HZ was always a NO 3 − source, with the NO 3 − production efficiency increasing monotonically with temperature. In addition, although the interfacial fluid flux expectedly increased with increasing temperature due to decreasing fluid viscosity, the total nitrate flux into the HZ did not follow this trend. This is because when HZ nitrification is high, uniformly elevated [NO 3 − ] lowers dispersive fluxes into the HZ. We found that there are numerous confounding and interacting factors that combined to lead to the final temperature-dependence of N transformation reaction rates. Although the temperature effect on the rate constant can be considered as the dominant factor, simply using the Arrhenius equation to predict the reaction rate would lead to incomplete insight by ignoring the changes in interfacial fluid and solute fluxes and reaction zone areas. Our study shows that HZ temperature and stream [NO 3 − ] /[NH 4 + ] are key controls for HZ sink/source functions.

Description: We present six and a half years of eddy covariance measurements of fluxes of methane (F CH4 ) and carbon dioxide (F CO2 ) from a flooded rice paddy in Northern California, USA. A pronounced warming trend throughout the study associated with drought and record high temperatures strongly influenced carbon (C) budgets and provided insights into biophysical controls of F CO2 and F CH4 . Wavelet analysis indicated that photosynthesis (GEP) induced the diel pattern in F CH4 , but soil temperature ( T s ) modulated its amplitude. Forward stepwise linear models and neural networking modeling were used to assess the variables regulating seasonal F CH4. As expected due to their competence in modeling non-linear relationships, neural network models explained considerably more of the variance in daily average F CH4 than linear models. During the growing season, GEP and water levels typically explained most of the variance in daily average F CH4 . However, T s explained much of the interannual variability in annual and growing season CH 4 sums. Higher T s also increased the annual and growing season ratio of F CH4 to GEP. The observation that the F CH4 to GEP ratio scales predictably with T s may help improve global estimates of F CH4 from rice agriculture. Additionally, T s strongly influenced ecosystem respiration, resulting in large interannual variability in the net C budget at the paddy, emphasizing the need for long-term measurements particularly under changing climatic conditions.

Description: A novel modeling tool for calculation of central receiver concentrated flux distributions is presented, which takes into account drift effects. This tool is based on a drift model that includes different geometrical error sources in a rigorous manner and on a simple analytic approximation for the individual flux distribution of a heliostat. The model is applied to a group of heliostats of a real field to obtain the resulting flux distribution and its variation along the day. The distributions differ strongly from those obtained assuming the ideal case without drift or a case with a Gaussian tracking error function. The time evolution of peak flux is also calculated to demonstrate the capabilities of the model. The evolution of this parameter also shows strong differences in comparison to the case without drift.

Description: The upwelling area off North-West Africa is characterized by high export production, high nitrate and low oxygen concentration in bottom waters. The underlying sediment consists of sands that cover most of the continental shelf. Due to their permeability sands allow for fast advective porewater transport and can exhibit high rates of nitrogen (N) loss via denitrification as reported for anthropogenically eutrophied regions. However, N-loss from sands underlying naturally eutrophied waters is not well studied and in particular N-loss from the North-West African shelf is poorly constrained. During two research cruises in April/May 2010/11, sediment was sampled along the North-West African shelf and volumetric denitrification rates were measured in sediment layers down to 8 cm depth using slurry incubations with 15 N-labelled nitrate. Areal N-loss was calculated by integrating volumetric rates down to the nitrate penetration depth derived from porewater profiles. Areal N-loss was neither correlated with water depth nor with bottom-water concentrations of nitrate and oxygen, but was strongly dependent on sediment grain size and permeability. The derived empirical relation between benthic N-loss and grains size suggests that porewater advection is an important regulating parameter for benthic denitrification in sands and further allowed extrapolating rates to an area of 53,000 km 2 using detailed sediment maps. Denitrification from this region amounts to 995 kt per year (average 3.6 mmol m -2 d -1 ) which is 4 times higher than previous estimates based on diffusive porewater transport. Sandy sediments cover 50-60% of the continental shelf and thus may contribute significantly to the global benthic N-loss.

Description: Present-day serpentinization generates groundwaters with conditions (pH 〉 11, Eh 〈 -550 mV) favorable for the microbial and abiotic production of organic compounds from inorganic precursors. Elevated concentrations of methane, C 2 -C 6 alkanes, acetate, and formate were detected at these sites, but the microbial or abiotic origin of these compounds remains unclear. While geochemical data indicate that methane at most sites of present-day serpentinization is abiotic, the stable carbon, hydrogen, and clumped isotope data as well as the hydrocarbon gas composition from The Cedars, CA, USA are consistent with a microbial origin for methane. However, there is no direct evidence of methanogenesis at this site of serpentinization. We report on laboratory experiments in which the microbial communities in fluids and sediments from The Cedars were incubated with 13 C labeled substrates. Increasing methane concentrations and the incorporation of 13 C into methane in live experiments, but not in killed controls, demonstrated that methanogens converted methanol, formate, acetate (methyl group), and bicarbonate to methane. The apparent fractionation between methane and potential substrates (α 13 C CH4-CO2(g)  = 1.059 to 1.105, α 13 C CH4-acetate  = 1.042 to 1.119) indicated that methanogenesis was dominated by the carbonate reduction pathway. Increasing concentrations of volatile organic acid anions indicated microbial acetogenesis. α 13 C CO2(g)-acetate values (0.999 to 1.000), however, were inconsistent with autotrophic acetogenesis, thus suggesting that acetate was produced through fermentation. This is the first study to show direct evidence of microbial methanogenesis and acetogenesis by the native microbial community at a site of present-day serpentinization.

Description: Quantification and prediction of N 2 O emissions from croplands under different agricultural management practices are vital for sustainable agriculture and climate change mitigation. We simulated N 2 O emissions under tillage and no-tillage, and different nitrogen (N) fertilizer types and application methods (i.e. nitrification inhibitor, chicken manure and split applications) in a cornfield using the DeNitrification-DeComposition (DNDC) model. The model was parameterized with field experimental data collected in Nashville, Tennessee under various agricultural management treatments and run for a short term (3 yrs) and a long term (100 yrs). Results showed that the DNDC model could adequately simulate N 2 O emissions as well as soil properties under different agricultural management practices. The modeled emissions of N 2 O significantly increased by 35% with tillage, and decreased by 24% with the use of nitrification inhibitor, compared with no-tillage and normal N fertilization. Chicken manure amendment and split applications of N fertilizer had minor impact on N 2 O emission in a short term, but over a long term (100 yrs) the treatments significantly altered N 2 O emission (+35%, −10%, respectively). Sensitivity analysis showed that N 2 O emission was sensitive to mean annual precipitation, mean annual temperature, soil organic carbon, and the amount of total N fertilizer application. Our model results provide valuable information for determining agricultural best management practice to maintain highly productive corn yield while reducing greenhouse gas emissions.

Description: A key uncertainty concerning the effect of wildfire on carbon dynamics is the rate at which fire-killed biomass (e.g., dead trees) decays and emits carbon to the atmosphere. We used a ground-based approach to compute decomposition of forest biomass killed, but not combusted, in the Biscuit Fire of 2002, an exceptionally large wildfire that burned over 200,000 ha of mixed conifer forest in southwestern Oregon, USA. A combination of federal inventory data and supplementary ground measurements afforded the estimation of fire-caused mortality and subsequent 10-year decomposition for several functionally distinct carbon pools at 180 independent locations in the burn area. Decomposition was highest for fire-killed leaves and fine roots and lowest for large diameter wood. Decomposition rates varied somewhat among tree species and was only 35% lower for trees still standing than for trees fallen at the time of the fire. We estimate a total of 4.7 Tg C was killed but not combusted in the Biscuit Fire, 85% of which remains 10 years after. Biogenic carbon emissions from fire-killed necromass were estimated to be 1.0, 0.6, and 0.4 Mg C ha -1 yr -1 at 1, 10, and 50 years after the fire, respectively; compared to the one-time pyrogenic emission of nearly 17 Mg C ha -1 .

Description: Northern peatlands store ~500 Pg of carbon (C); however, controls on the spatial distribution of the stored C may differ regionally, owing to the complex interaction among climate, ecosystem processes, and geophysical controls. As a globally significant C sink, elucidation of controls on the distribution of C in the Hudson Bay Lowlands, Canada (HBL) is of particular importance. Although peat age is related to timing of land emergence and peat depth in the HBL, considerable variation in the total C mass (kg m -2 ) among sites of similar peat age suggests that other factors may explain spatial patterns in C storage (Pg) and sequestration. Here, we quantify the role of two key factors in explaining the spatial distribution the C mass in the HBL (n = 364 sites): (i) climate variability, and (ii) peat lithology, for two major peatland classes in the HBL (bogs and fens). We find that temperature, precipitation, and evapotranspiration each explained nearly half of the C mass variability. Regions characterized by warmer and wetter conditions stored the most C as peat. Our results show that bogs and fens store similar amounts of C within a given climate domain, although via distinct storage mechanisms. Namely, fen peats tend to be shallower and more C dense (kg m -3 ) compared to bogs. Following geophysical controls on the timing of peat initiation, our results reveal that both the widespread bog-fen patterning and variability in regional climate contribute to explaining the spatial distribution of the peat C mass in the HBL.

Description: Design, construction, and evaluation of a cylindrical-trough solar concentrator with 1.3 m aperture, 2.15 m length, and 0.54 m focal length, with heat-pipe or vacuum tube receiver and one axis tracking system, are presented. Design performance was tested under ASHRAE standard 93-1986 (RA 91). The concentrator system is lightweight and inexpensive since it was made of polymeric membranes and was pneumatically inflated to acquire its cylindrical shape achieving good optical quality. Further implementation of a flat and a cylindrical extension of the concentrating mirror as secondary mirrors was incorporated into the concentrator design in order to compensate for seasonal variations of collected radiation. Total initial investment of $163.30 or $58.5/m2 and efficiencies ranging from 33 to 25% for 25 up to 65°C show an excellent cost-performance ratio. Construction, costs, and efficiencies obtained by us and developed by other groups are compared to emphasize the high cost/benefit ratio and efficiencies of this approach.

Description: The biggest problems of our time are environmental pollution and the reduction of fossil fuel resources. In recent years, photovoltaic (PV) has started to be used efficiently in order to produce electrical energy from solar energy throughout the world. In this study, a wheat mover machine taking its energy with PV technology transformation from the sun was designed supported by smart sensors. The designed vehicle was tested in two wheat fields in Sivas in Turkey. It was seen that daily average sunshine rates were not lower than 700 Watt/m2 during the testing dates and time. The amounts of electrical charge used to mow 5 m2 and 50 m2 areas are obtained as 500 mAh and 3395 mAh, respectively. Also maximum power is calculated from used PV panel as 26.15 Watt during the day of the experiments. The range of solar radiation intensity is found 4.5 kWh/m2/day at the studied kWh which was 0.140 USD on the date of November 2015. This system is 94.5% more economic than conventional mowers over an area of 1000 m2.

Description: Permafrost soils currently store approximately 1672 Pg of carbon (C), but as high latitudes warm, this temperature-protected C reservoir will become vulnerable to higher rates of decomposition. In recent decades, air temperatures in the high latitudes have warmed more than any other region globally, particularly during the winter. Over the coming century, the arctic winter is also expected to experience the most warming of any region or season, yet it is notably understudied. Here we present non-summer season (NSS) CO 2 flux data from the Carbon in Permafrost Experimental Heating Research (CiPEHR) project, an ecosystem warming experiment of moist acidic tussock tundra in interior Alaska. Our goals were to quantify the relationship between environmental variables and winter CO 2 production, account for subnivean photosynthesis and late fall plant C uptake in our estimate of NSS CO 2 exchange, constrain NSS CO 2 loss estimates using multiple methods of measuring winter CO 2 flux, and quantify the effect of winter soil warming on total NSS CO 2 balance. We measured CO 2 flux using four methods: two chamber techniques (the snow pit method and one where a chamber is left under the snow for the entire season), eddy covariance, and soda lime adsorption, and found that NSS CO 2 loss varied up to 4 fold, depending on the method used. CO 2 production was dependent on soil temperature and day of season but atmospheric pressure and air temperature were also important in explaining CO 2 diffusion out of the soil. Warming stimulated both ecosystem respiration and productivity during the NSS and increased overall CO 2 loss during this period by 14% (this effect varied by year, ranging from 7 to 24%). When combined with the summertime CO 2 fluxes from the same site, our results suggest that this sub-arctic tundra ecosystem is shifting away from its historical function as a C sink to a C source.

Description: The mean cost price of electricity in Burkina Faso at the end of the last quarter of 2012 was 158 FCFA/kWh for a country where more than 46% of the population lives below the national poverty threshold. To look for solution to that problem, the resort to photovoltaic solar energy is justified for that country. The purpose of this study is to promote the integration of both technical and economical surveys in solar energy preliminary projects in Ouagadougou. To reach that, investigations were carried out in some households and attention was paid from the calibration of the domestic electric meters. Energy demands collected within each household allow us to design a corresponding solar kit through optimization rules. An estimate was edited and financial viability study for each household was also carried out thereafter. In this study, only households using the national electricity network calibration meter on their disadvantage favorably answered to all financial indicators and appear as the only one that could profit from such project. This work is helpful to note that photovoltaic solar energy still stays at a primitive level of competitiveness compared to conventional energy resources for small systems in Ouagadougou.

Description: Nitrogen (N) is an important nutrient as it often limits productivity, but in excess can impair water quality. Most studies on watershed N cycling have occurred in upland forested catchments where snowmelt dominates N export; fewer studies have focused on low-relief watersheds that lack snow. We examined watershed N cycling in three adjacent, low-relief watersheds in the Upper Coastal Plain of the southeastern United States to better understand the role of hydrological flowpaths and biological transformations of N at the watershed scale. Groundwater was the dominant source of nitrified N to stream water in 2 of the 3 watersheds, while atmospheric deposition comprised 28% of stream water nitrate in one watershed. The greater atmospheric contribution may have been due to the larger stream channel area relative to total watershed area or the dominance of shallow subsurface flowpaths contributing to stream flow in this watershed. There was a positive relationship between temperature and stream water ammonium concentrations and a negative relationship between temperature and stream water nitrate concentrations in each watershed suggesting that N cycling processes (i.e., nitrification, denitrification) varied seasonally. However, there were no clear patterns in the importance of denitrification in different water pools possibly because a variety of factors (i.e., assimilatory uptake, dissimilatory uptake, mixing) affected nitrate concentrations. Together, these results highlight the hydrological and biological controls on N cycling in low-gradient watersheds, and variability in N delivery flowpaths among adjacent watersheds with similar physical characteristics.

Description: Multiwall carbon nanotubes (MWCNTs) were modified by acids (H2SO4 : HNO3) for generating active groups on the nanotube surface. Unmodified- and modified-carbon nanotubes were coated on the conductive glass and conductive plastic substrates by a slurry paste method, and they were used as the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). Scanning electron microscopy reveals that carbon nanotubes are evenly deposited on the conductive glass. The efficiency of the glass based DSSCs of unmodified- and modified-carbon nanotubes and Pt CEs is ~4.73%, ~5.66%, and ~6.08%, respectively. The efficiency of the plastic based DSSCs of the unmodified- and modified-carbon nanotubes CEs is ~0.80% and ~2.11%, respectively. The voltammogram and electrochemical impedance spectroscopy results suggest that the superior performance of the modified-carbon nanotubes DSSCs is attributable to the high electrocatalytic activity and the low charge-transfer resistance of the modified-carbon nanotubes film over the unmodified-carbon nanotubes film.

Description: Projected changes in the seasonality of hydroclimatic regimes are likely to have important implications for water resources and terrestrial ecosystems in the U.S. Pacific Northwest. The tree-ring record, which has frequently been used to position recent changes in a longer-term context, typically relies on signals embedded in the total ring width of tree rings. Additional climatic inferences at a sub-annual temporal scale can be made using alternative tree-ring metrics such as earlywood and latewood widths and the density of tree-ring latewood. Here, we examine seasonal precipitation and temperature signals embedded in total ring width, earlywood width, adjusted latewood width, and blue intensity chronologies from a network of six Pinus ponderosa sites in and surrounding the upper Columbia River basin of the U.S. Pacific Northwest. We also evaluate the potential for combining multiple tree-ring metrics together in reconstructions of past cool- and warm-season precipitation. The common signal among all metrics and sites is related to warm-season precipitation. Earlywood and latewood widths differ primarily in their sensitivity to conditions in the year prior to growth. Total and earlywood widths from the lowest elevation sites also reflect cool-season moisture. Effective correlation analyses and composite-plus-scale tests suggest that combining multiple tree-ring metrics together may improve reconstructions of warm-season precipitation. For cool-season precipitation, total ring width alone explains more variance than any other individual metric or combination of metrics. The composite-plus-scale tests show that variance-scaled precipitation reconstructions in the upper Columbia River basin may be asymmetric in their ability to capture extreme events.

Description: The forest litter layer lies at the boundary between soil and atmosphere and is a major factor in biogeochemical cycles. While there are several studies on how the litter layer controls soil trace gas emissions, litter emissions itself are less well understood, and it is still unclear how important gases respond to changing temperature and moisture. In order to assess leaf litter gas exchange we conducted laboratory incubation experiments in which the full set of climate relevant gases, i.e. carbon dioxide (CO 2 ), nitrous oxide (N 2 O), methane (CH 4 ), and nitric oxide (NO) coming from deciduous and coniferous leaf litter were measured at 5 temperatures and 7 moisture contents. In addition, we compared litter and soil from different origin in terms of temperature / moisture responses of gas fluxes and investigated possible interactions between the two climate factors. Deciduous litter emitted more CO 2 (up to 335 mg CO 2 -C kg -1 h -1 ) than coniferous litter, whereas coniferous litter released maximum amounts of NO (207 µg NO-N kg -1 h -1 ). N 2 O was only emitted from litter under very moist and warm conditions (〉70 %wet weight, 〉10 °C). CH 4 emissions were close to zero. Temperature sensitivities of litter emissions were generally lower than for soil emissions. Nevertheless, wet and warm conditions always enhanced litter emissions, suggesting a strong feedback effect of the litter layer to predicted future climate change.

Description: In this study, an exergy analysis of two kinds of solar-driven cogeneration systems consisting of solar collectors and an organic Rankine cycle (ORC) is presented for series mode and parallel mode. Three kinds of solar collectors are considered: flat-plate collectors (FPC), evacuated tube collectors (ETC), and parabolic trough collectors (PTC). This study mainly compares the exergy output of the two kinds of solar cogeneration systems under different temperatures of the return heating water and different inlet temperatures of the solar collectors. This study shows that, from the perspective of or , the parallel mode is superior to the series mode. From the perspective of , the parallel mode is superior to the series mode when the solar collector is FPC; however, the series mode is superior to the parallel mode when the solar collector is PTC. When the solar collector is ETC, the result depends on the temperature of the return heating water. When the temperature of the return heating water is low (below 46°C), the series mode is better, and when the temperature of the return heating water is high (above 46°C), the parallel mode is better.

Description: Pharmaceuticals are present in an aquatic environment usually in low (ng/L) concentrations. Their continuous release can lead to unwanted effects on the nontarget organisms. The main points of their collection and release into the environment are wastewater treatment plants. The wastewater treatment plants should be upgraded by new technologies, like advanced oxidation processes (AOPs), to be able to degrade these new pollutants. In this study, the degradation of albendazole (ALB), a drug against parasitic helminths, was investigated using four UV-based AOPs: UV photolysis, UV photocatalysis (over TiO2 film), UV + O3, and UV + H2O2. The ranking of the degradation process degree of the ALB and its degradation products for studied processes is as follows: UV photolysis 

Description: The energy scenario today is focused on the development and usage of solar cells, especially in the paradigm of clean energy. To readily create electron and hole pairs, solar cells utilize either photoactive or photosensitive components. A bulk heterojunction (BHJ) is a nanolayer consisting of donor and acceptor components with a large interpenetrated acceptor and donor contact area. In this context, a mix of P3HT and PCBM offers novelty for its use as an acceptor as well as a donor. In the work presented here, we address the mechanism of modelling and characterization of a BHJ-based polymer solar cell. Here, a new design of BHJ polymer solar cells have been designed, modelled, using Silvaco TCAD in the Organic Solar module, and matched with an already assembled device having similar features. Using this model, we have been able to estimate key parameters for the modelled devices, such as the short-circuit current density, open-circuit voltage, and fill factor with less than 0.25 error index compared to the fabricated counterpart, paving the way for fabless polymer solar cell design and optimization.

Description: This work undertakes both simulation and experimental studies of a new design of a photovoltaic thermal solar air collector (PV/T). In order to improve the thermal and electrical performances for a specific application, the analytical expressions for thermal parameters and efficiency are derived by developing an energy balance equation for each component of the PV/T air collector. This type of hybrid collector can be applied in the facades of buildings. The electricity and heat produced will satisfy the energy needs of the buildings, while ensuring an aesthetic view of its facades. A typical prototype was designed, constructed, and implemented in the applied research unit on renewable energies in Ghardaia, situated in the south of Algeria. This region has semiarid characteristics. Results obtained by an experimental test are presented and compared to those predicted through simulation. Results include the temperature of each component of the PV/T collector and air temperature at the inlet and outlet of the channel. It has been found that the theoretical results predicted by the developed mathematical model, for instance, outlet temperature, agree with those found through experimental work.

Description: Mismatching operating conditions negatively affect the extracted energy in photovoltaic (PV) systems. They may also lead to dangerous localized heating phenomena (hot spots) that can cause, in turn, accelerated ageing and reduced reliability. Since the adoption of bypass diodes or smart active switches does not prevent the occurrence of hotspots, it is necessary to investigate alternative strategies. A promising solution is represented by the proper regulation of the operating point of the PV cells in the current vs. voltage (-) or power vs. voltage (-) planes when mismatching conditions occur. In particular, in this paper, the existence of operating points allowing a suitable compromise between maximization of the extracted power and minimization of thermal stresses, due to hot spots, is experimentally evidenced. Experimental results highlighting the link existing between the operating point in the - plane and the PV cell temperature distribution under uniform and mismatching operating conditions are presented and discussed. On the basis of the obtained experimental results, it is possible to state that, when mismatching conditions occur, it is mandatory to properly choose the operating point: the global maximum power point may not be the best operating point. Hence, it is crucial to gain information about the eventual occurrence of mismatching conditions in order to be able to properly choose the best operating point. Therefore, another crucial aspect that is evidenced in this paper is represented by the fact that the detection of the occurrence of mismatching conditions, based on the analysis of the shape of the - and/or - characteristics, is effective only if the analysis is carried out for both positive and negative voltages.

Description: Highly light scattering structures have been generated in a poly(ethylene terephthalate) (PET) film using a CO2 laser. The haze, and in some cases the transparency, of the PET films have been improved by varying the processing parameters of the laser (namely, scanning velocity, laser output power, and spacing between processed tracks). When compared with the unprocessed PET, the haze has improved from an average value of 3.26% to a peak of 55.42%, which equates to an absolute improvement of 52.16% or a 17-fold increase. In addition to the optical properties, the surfaces have been characterised using optical microscopy and mapped with an optical profilometer. Key surface parameters that equate to the amount and structure of surface roughness and features have been analysed. The CO2 laser generates microstructures at high speed, without affecting the bulk properties of the material, and is inherently a chemical-free process making it particularly applicable for use in industry, fitting well with the high-throughput, roll to roll processes associated with the production of flexible organic photovoltaic devices.

Description: This study is aimed at providing a comparison between fuzzy systems and convectional P&O for tracking MPP of a PV system. MATLAB/Simulink is used to investigate the response of both algorithms. Several weather conditions are simulated: (i) uniform irradiation, (ii) sudden changing, and (iii) partial shading. Under partial shading on a PV panel, multipeaks appeared in - characteristics of the panel. Simulation results showed that a fuzzy controller effectively finds MPP for all weather condition scenarios. Furthermore, simulation results obtained from the FLC are compared with those obtained from the P&O controller. The comparison shows that the fuzzy logic controller exhibits a much better behavior.

Description: Currently, standard semitransparent photovoltaic (PV) modules can largely replace architectural glass installed in the windows, skylights, and facade of a building. Their main features are power generation and transparency, as well as possessing a heat insulating effect. Through heat insulation solar glass (HISG) encapsulation technology, this study improved the structure of a typical semitransparent PV module and explored the use of three types of high-reflectivity heat insulation films to form the HISG building-integrated photovoltaics (BIPV) systems. Subsequently, the authors analyzed the influence of HISG structures on the optical, thermal, and power generation performance of the original semitransparent PV module and the degree to which enhanced performance is possible. The experimental results indicated that the heat insulation performance and power generation of HISGs were both improved. Selecting an appropriate heat insulation film so that a larger amount of reflective solar radiation is absorbed by the back side of the HISG can yield greater enhancement of power generation. The numerical results conducted in this study also indicated that HISG BIPV system not only provides the passive energy needed for power loading in a building, but also decreases the energy consumption of the HVAC system in subtropical and temperate regions.

Description: Photovoltaic (PV) generators suffer from fluctuating output power due to the highly fluctuating primary energy source. With significant PV penetration, these fluctuations can lead to power system instability and power quality problems. The use of energy storage systems as fluctuation compensators has been proposed as means to mitigate these problems. In this paper, the behavior of PV power fluctuations in Northern European climatic conditions and requirements for sizing the energy storage systems to compensate them have been investigated and compared to similar studies done in Southern European climate. These investigations have been performed through simulations that utilize measurements from the Tampere University of Technology solar PV power station research plant in Finland. An enhanced energy storage charging control strategy has been developed and tested. Energy storage capacity, power, and cycling requirements have been derived for different PV generator sizes and power ramp rate requirements. The developed control strategy leads to lesser performance requirements for the energy storage systems compared to the methods presented earlier. Further, some differences on the operation of PV generators in Northern and Southern European climates have been detected.

Description: Testing complex land surface models has often proceeded by asking the question: does the model prediction agree with the observation? Such an approach has yet led to high-performance terrestrial models that meet the challenges of climate and ecological studies. Here we test the Community Land Model (CLM) by asking the question: does the model behave like an ecosystem? We pursue its answer by testing CLM in the ecosystem functional space (EFS) at the Missouri Ozark AmeriFlux (MOFLUX) forest site in the central USA, focusing on carbon and water flux responses to precipitation regimes and associated stresses. In the observed EFS, precipitation regimes and associated water and heat stresses controlled seasonal and interannual variations of net ecosystem exchange (NEE) of CO 2 and evapotranspiration in this deciduous forest ecosystem. Such controls were exerted more strongly by precipitation variability than by the total precipitation amount per se. A few simply constructed climate variability indices captured these controls, suggesting a high degree of potential predictability. While the interannual fluctuation in NEE was large, a net carbon sink was maintained even during an extreme drought year. Although CLM predicted seasonal and interanual variations in evapotranspiration reasonably well, its predictions of net carbon uptake were too small across the observed range of climate variability. Also, the model systematically underestimated the sensitivities of NEE and evapotranspiration to climate variability and overestimated the coupling strength between carbon and water fluxes. We suspect that the modeled and observed trajectories of ecosystem fluxes did not overlap in the EFS and the model did not behave like the ecosystem it attempted to simulate. A definitive conclusion will require comprehensive parameter and structural sensitivity tests in a rigorous mathematical framework. We suggest that future model improvements should focus on better representation and parameterization of process responses to environmental stresses and on more complete and robust representations of carbon-specific processes so that adequate responses to climate variability and a proper degree of coupling between carbon and water exchanges are captured.

Description: Recent research and development of clean energy have become essential due to the global climate change problem, which is caused largely by fossil fuels burning. Therefore, biodiesel, a renewable and ecofriendly biofuel with less environmental impact than diesel, continues expanding worldwide. The process for biodiesel production involves a significant energy demand, specifically in the methanol recovery stage through a flash separator and a distillation column. Traditionally, the energy required for this process is supplied by fossil fuels. It represents an opportunity for the application of renewable energy. Hence, the current study presents a system of thermal energy storage modeled in TRNSYS® and supported by simulations performed in ASPEN PLUS®. The aim of this research was to supply solar energy for a methanol recovery stage in a biodiesel production process. The results highlighted that it is feasible to meet 91% of the energy demand with an array of 9 parabolic trough collectors. The array obtained from the simulation was 3 in series and 3 in parallel, with a total area of 118.8 m2. It represents an energy saving of 70 MWh per year.

Description: Exchange between wetland surface water and the atmosphere is driven by a variety of motions, ranging from rainfall impact to thermal convection and animal locomotion. Here, we examine the effect of wind-driven vegetation movement. Wind causes the stems of emergent vegetation to wave back and forth, stirring the water column and facilitating air-water exchange. To understand the magnitude of this effect, a gas transfer velocity ( k 600 -value) was measured via laboratory experiments. Vegetation-waving was studied in isolation by mechanically forcing a model canopy to oscillate at a range of frequencies and amplitudes matching those found in the field. The results show that stirring due to vegetation-waving produces k 600 -values from 0.55 cm/hr to 1.60 cm/hr. The dependence of k 600 on waving amplitude and frequency are evident from the laboratory data. These results indicate that vegetation-waving has a non-negligible effect on gas transport; thus it can contribute to a mechanistic understanding of the fluxes underpinning biogeochemical processes.

Description: Solar energy conversion is an object of continuous research, focusing on improving the energy efficiency as well as the structure of photovoltaic cells. With efficiencies continuously increasing, state-of-the-art PV cells offer a good solution to harvest solar energy. However, they are still lacking the flexibility and conformability to be integrated into common objects or clothing. Moreover, many sun-exposed surface areas are textile-based such as garments, tents, truck coverings, boat sails, and home or outdoor textiles. Here, we present a new textile-based dye-sensitized solar cell (DSC) which takes advantage from the properties inherent to fabrics: flexibility, low weight, and mechanical robustness. Due to the necessary thermostability during manufacturing, our DSC design is based on heat-resistant glass-fiber fabrics. After applying all needed layers, the overall structure was covered by a transparent and simultaneously conductive protective film. The light and still flexible large-area devices (up to 6 cm2 per individual unit) are working with efficiencies up to 1.8% at 1/5 of the sun. Stability tests assure no loss of photovoltaic activity over a period of at least seven weeks. Therefore, our technology has paved the way for a new generation of flexible photovoltaic devices, which can be used for the generation of power in the mentioned applications as well as in modern textile architecture.

Description: We partitioned the soil carbon dioxide flux (R s ) into its respective autotrophic and heterotrophic components in a mature temperate-boreal forest (Howland Forest in Maine, USA). We combined automated chamber measurements of R s with two different partitioning methods: (1) a classic root trenching experiment and (2) a radiocarbon ( 14 C) mass balance approach. With a model-data fusion approach, we used these data to constrain a parsimonious ecosystem model (FöBAAR), and we investigated differences in modeled C fluxes and pools under both current and future climate scenarios. The trenching experiment indicated that heterotrophic respiration accounted for 53 ± 11% of total R s . In comparison, using the 14 C method, the heterotrophic contribution was 42 ± 9%. For both current and future model runs, incorporating the partitioning data as constraints substantially reduced the uncertainties of autotrophic and heterotrophic respiration fluxes. Moreover, with best-fit model parameters, the two partitioning methods yielded fundamentally different estimates of the relative contributions of autotrophic and heterotrophic respiration to total R s , especially at the annual time scale. Surprisingly, however, modeled soil C and biomass C pool size trajectories did not differ significantly between model runs based on the different methods. Instead, model differences in partitioning were compensated for by changes in C allocation, resulting in similar, but still highly uncertain, soil C pool trajectories. Our findings show that incorporating constraints on the partitioning of R s can reduce model uncertainties of fluxes but not pools, and the results are sensitive to the partitioning method used.

Description: Uncertainty surrounding future climate makes it difficult to have confidence that current nutrient management strategies will remain effective. This study used monitoring and modelling to assess current effectiveness (% phosphorus reduction), and resilience (defined as continued effectiveness under a changing climate) of best management practices (BMPs) within 5 catchments of the Lake Simcoe watershed, Ontario. The model INCA-P was used, and monitoring data used to calibrate and validate a series of management scenarios. To assess current BMP effectiveness, models were run over a baseline period 1985-2014 with and without management scenarios. Climate simulations were run (2070-2099), and BMP resilience calculated as the % change in effectiveness between the baseline and future period. Results demonstrated that livestock removal from water courses was the most effective BMP, while manure storage adjustments were the least. Effectiveness varied between catchments, influenced by the dominant hydrological and nutrient transport pathways. Resilience of individual BMPs was associated with catchment sensitivity to climate change. BMPs were most resilient in catchments with high soil water storage capacity, and small projected changes in frozen-water availability and in soil moisture deficits. Conversely, BMPs were less resilient in catchments with larger changes in spring melt magnitude and in overland flow proportions. Results indicated that BMPs implemented are not always those most suited to catchment flow pathways, and a more site-specific approach would enhance prospects for maintaining P reduction targets. Furthermore, BMP resilience to climate change can be predicted from catchment physical properties and present day hydrochemical sensitivity to climate forcing.

Description: Biogeochemical processes driving the spatial variability of soil CO 2 production and flux are well studied, but little is known about the variability in the spatial distribution of the stable carbon isotopes that make up soil CO 2 , particularly in complex terrain. Spatial differences in stable isotopes of soil CO 2 could indicate fundamental differences in isotopic fractionation at the landscape level, and may be useful to inform modeling of carbon cycling over large areas. We measured the spatial and seasonal variability of the δ 13 C of soil CO 2 (δ S ) and the δ 13 C of soil CO 2 flux (δ P ) in a subalpine forest ecosystem located in the Rocky Mountains of Montana. We found consistently more isotopically depleted values of δ S and δ P in low and wet areas of the landscape relative to steep and dry areas. Our results suggest that the spatial patterns of δ S and δ P are strongly mediated by soil water and soil respiration rate. More interestingly, our analysis revealed different temporal trends in δ P across the landscape; in high landscape positions δ P became more positive whereas in low landscape positions δ P became more negative with time. These trends might be the result of differential dynamics in the seasonality of soil moisture and its effects on soil CO 2 production and flux. Our results suggest concomitant yet independent effects of water on physical (soil gas diffusivity) and biological (photosynthetic discrimination) processes that mediate δ S and δ P , and are important when evaluating the δ 13 C of CO 2 exchanged between soils and the atmosphere in complex terrain.

Description: The extent to which atmospheric nitrogen (N) deposition reflects land use differences and biogenic vs. fossil fuel reactive N sources remains unclear, yet represents a critical uncertainty in ecosystem N budgets. We compared N concentrations and isotopes in precipitation-event bulk (wet + dry) deposition across nearby valleys in northern Utah with contrasting land use (highly urban vs. intensive agriculture/low-density urban). We predicted greater nitrate (NO 3 - ) vs. ammonium (NH 4 + ) and higher δ 15 N of NO 3 - and NH 4 + in urban valley sites. Contrary to expectations, annual N deposition (3.5–5.1 kg N ha -1 y -1 ) and inorganic N concentrations were similar within and between valleys. Significant summertime decreases in δ 15 N of NO 3 - possibly reflected increasing biogenic emissions in the agricultural valley. Organic N was a relatively minor component of deposition (~13%). Nearby paired wildland sites had similar bulk deposition N concentrations as the urban and agricultural sites. Weighted bulk deposition δ 15 N was similar to natural ecosystems (-0.6 ± 0.7‰). Fine atmospheric particulate matter (PM 2.5 ) had consistently high values of bulk δ 15 N (15.6 ± 1.4‰), δ 15 N in NH 4 + (22.5 ± 1.6‰), and NO 3 - (8.8 ± 0.7‰), consistent with equilibrium fractionation with gaseous species. δ 15 N in bulk deposition NH 4 + varied by more than 40‰, and spatial variation in δ 15 N within storms exceeded 10‰. Sporadically high values of δ 15 N were thus consistent with increased particulate N contributions as well as potential N source variation. Despite large differences in reactive N sources, urban and agricultural landscapes are not always strongly reflected in the composition and fluxes of local N deposition—an important consideration for regional-scale ecosystem models.

Description: The magnitude of net soil nitrous oxide (N 2 O) production from a snow covered catchment in a northern temperate forest was investigated. There was considerable net soil N 2 O-N production and consumption through the snowpack, ranging from -6.6 to 26.2 g-N ha-1 d-1. There was no difference in net N 2 O production among topographic positions despite significant variation in soil moisture, reduction-oxidation conditions and pore water dissolved organic carbon and nitrate. Soil temperatures did not vary among topographic positions, suggesting that temperatures at or above the freezing point allow N 2 O production to proceed under the snowpack. Redox conditions were lower at wetland positions compared to lowlands and uplands, suggesting that the biogeochemical pathway of N 2 O production varies with topography. Over the entire non-growing season, 1.5 kg of N 2 O-N was exported to the atmosphere from the 6.33 ha catchment, representing 31% of the growing season N 2 O-N production. These results suggest winter is an active time for gaseous N production in these forests, and that N 2 O production under the snowpack represents an often unmonitored flux of N from catchments.

Description: We analyzed twenty years (1993-2013) of observations of dissolved inorganic macronutrients (nitrate, N; phosphate, P; silicate, Si) and chlorophyll a (Chl) at Palmer Station, Antarctica (64.8°S, 64.1°W) to elucidate how large-scale climate and local physical forcing affect the interannual variability in the seasonal phytoplankton bloom and associated drawdown of nutrients. The leading modes of nutrients (N, P, and Si Empirical Orthogonal Functions 1, EOF1) represent overall negative anomalies throughout growing seasons, showing a mixed signal of variability in the initial levels and drawdown thereafter (low-frequency dynamics). The second most common seasonal patterns of nitrate and phosphate (N, P EOF2) capture prolonged drawdown events during December-March, which are correlated to Chl EOF1. Si EOF2 captures a drawdown event during November-December, which is correlated to Chl EOF2. These different drawdown patterns are shaped by different sets of physical and climate forcing mechanisms. N and P drawdown events during December-March are influenced by the winter and spring Southern Annular Mode (SAM) phase, where nutrient utilization is enhanced in a stabilized upper water column as a consequence of SAM-driven winter sea ice and spring wind dynamics. Si drawdown during November-December is influenced by early sea ice retreat, where ice breakup may induce abrupt water column stratification and a subsequent diatom bloom or release of diatom cells from within the sea ice. Our findings underscore that seasonal nutrient dynamics in the coastal WAP are coupled to large-scale climate forcing and related physics, understanding of which may enable improved projections of biogeochemical responses to climate change.

Description: Shunting is one of the key issues in industrial silicon solar cells which degrade cell performance. This paper presents an approach for investigation of the performance degradation caused by the presence of ohmic extended shunts at various locations in industrial silicon solar cells. Location, nature, and area of the shunts existing in solar cells have been examined by lock-in infrared thermography (LIT). Based on LIT images and experimental dark I-V curves of solar cell, shunted cell has been modeled, from which loss in fill factor and efficiency due to the specific shunt has been obtained. Distributed diode modeling approach of solar cell has been exploited for obtaining simulation results which were supported by experimental measurements. The presented approach is useful to estimate performance reduction due to specific shunts and to quantify losses, which can help in improving the efficiency of solar cell during production by tackling the shunt related problems based on the level of severity and tolerance.

Description: Solar photovoltaic (PV) energy sources are rapidly gaining potential growth and popularity compared to conventional fossil fuel sources. As the merging of PV systems with existing power sources increases, reliable and accurate PV system identification is essential, to address the highly nonlinear change in PV system dynamic and operational characteristics. This paper deals with the identification of a PV system characteristic with a switch-mode power converter. Measured input-output data are collected from a real PV panel to be used for the identification. The data are divided into estimation and validation sets. The identification methodology is discussed. A Hammerstein-Wiener model is identified and selected due to its suitability to best capture the PV system dynamics, and results and discussion are provided to demonstrate the accuracy of the selected model structure.

Description: An atmospheric pressure chemical vapor deposition (AP-CVD) system has been newly developed for boron silicate glass (BSG) film deposition dedicating to solar cell manufacturing. Using the system, thermal boron diffusion from the BSG film is investigated and confirmed in terms of process stability for surface property before BSG deposition and BSG thickness. No degradation in carrier lifetime is also confirmed. A boron diffusion simulator has been newly developed and demonstrated for optimization of this process. Then, the boron thermal diffusion from AP-CVD BSG is considered to be the suitable method for N-type silicon solar cell manufacturing.

Description: Energy supply together with the data management is one of the key challenges of our century. Specifically, to decrease the climate change effects as energy requirement increases day by day poses a serious dilemma. It can be adequately reconciled with innovative data management in (renewable) energy technologies. The new environmental-friendly planning methods and investments that are discussed by researchers, governments, NGOs, and companies will give the basic and most important variables in shaping the future. We use modern data mining methods (SOM and -Means) and official governmental statistics for clustering cities according to their consumption similarities, the level of welfare, and growth rate and compare them with their potential of renewable resources with the help of Rapid Miner 5.1 and MATLAB software. The data mining was chosen to make the possible secret relations visible within the variables that can be unpredictable at first sight. Here, we aim to see the success level of the chosen algorithms in validation process simultaneously with the utilized software. Additionally, we aim to improve innovative approach for decision-makers and stakeholders about which renewable resource is the most suitable for an exact region by taking care of different variables at the same time.

Description: To quickly and precisely extract the parameters for solar cell models, inspired by simplified bird mating optimizer (SBMO), a new optimization technology referred to as population classification evolution (PCE) is proposed. PCE divides the population into two groups, elite and ordinary, to reach a better compromise between exploitation and exploration. For the evolution of elite individuals, we adopt the idea of parthenogenesis in nature to afford a fast exploitation. For the evolution of ordinary individuals, we adopt an effective differential evolution strategy and a random movement of small probability is added to strengthen the ability to jump out of a local optimum, which affords a fast exploration. The proposed PCE is first estimated on 13 classic benchmark functions. The experimental results demonstrate that PCE yields the best results on 11 functions by comparing it with six evolutional algorithms. Then, PCE is applied to extract the parameters for solar cell models, that is, the single diode and the double diode. The experimental analyses demonstrate that the proposed PCE is superior when comparing it with other optimization algorithms for parameter identification. Moreover, PCE is tested using three different sources of data with good accuracy.

Description: We have studied the p-type hydrogenated silicon oxide (:H) films prepared in the amorphous-to-microcrystalline transition region as a window layer in a-Si:H/a-:H multijunction solar cells. By increasing the -to- flow ratio () from 10 to 167, the :H(p) films remained amorphous and exhibited an increased hydrogen content from 10.2% to 12.2%. Compared to the amorphous :H(p) film prepared at low , the :H(p) film deposited at of 167 exhibited a higher bandgap of 2.04 eV and a higher conductivity of 1.15 × 10−5 S/cm. With the employment of :H(p) films prepared by increasing from 10 to 167 in a-Si:H single-junction cell, the FF improved from 65% to 70% and the efficiency increased from 7.4% to 8.7%, owing to the enhanced optoelectrical properties of :H(p) and the improved p/i interface. However, the cell that employed :H(p) film with over 175 degraded the p/i interface and degraded the cell performance, which were arising from the onset of crystallization in the window layer. Compared to the cell using standard a-:H(p), the a-Si:H/a-:H tandem cells employing :H(p) deposited with of 167 showed an improved efficiency from 9.3% to 10.3%, with of 1.60 V, of 9.3 mA/cm2, and FF of 68.9%.

Description: Subpicosecond transient absorption spectroscopy is a powerful tool used to clarify the exciton and carrier dynamics within the organic solar cells (OSCs). In this review article, we introduce a method to determine the absolute numbers of the excitons and carriers against delay time (t) only from the photoinduced absorption (PIA) and electrochemically induced absorption (EIA) spectra. Application of this method to rr-P3HT-, PTB7-, and SMDPPEH-based OSCs revealed common aspects of the carrier formation dynamics. First, the temporal evolution of the numbers of the excitons and carriers indicates that the late decay component of exciton does not contribute to the carrier formation process. This is probably because the late component has not enough excess energy to separate into the electron and hole across the donor/acceptor (D/A) interface. Secondly, the spectroscopy revealed that the exciton-to-carrier conversion process is insensitive to temperature. This observation, together with the fast carrier formation time in OSCs, is consistent with the hot exciton picture.

Description: Ecosystem models often perform poorly in reproducing interannual variability in carbon and water fluxes, resulting in considerable uncertainty when estimating the land-carbon sink. While many aggregated variables (growing season length, seasonal precipitation or temperature) have been suggested as predictors for interannual variability in carbon fluxes, their explanatory power is limited and uncertainties remain as to their relative contributions. Recent results show that the annual count of hours where evapotranspiration (ET) is larger than its 95th percentile is strongly correlated with the annual variability of ET and gross primary production (GPP) in an ecosystem model. This suggests that the occurrence of favorable conditions has a strong influence on the annual carbon budget. Here, we analyzed data from 8 forest sites of the AmeriFlux network with at least 7 years of continuous measurements. We show that for ET and the carbon fluxes GPP, ecosystem respiration (RE), and net ecosystem productivity, counting the “most active hours/days” (i.e., hours/days when the flux exceeds a high percentile) correlates well with the respective annual sums, with correlation coefficients generally larger than 0.8. Phenological transitions have much weaker explanatory power. By exploiting the relationship between most active hours and interannual variability, we classify hours as most active or less active and largely explain interannual variability in ET and carbon fluxes, particularly for GPP and RE. Our results suggest that a better understanding and modeling of the occurrence of large values in high-frequency ecosystem fluxes will result in a better understanding of interannual variability of these fluxes.

Description: Radiocarbon in CO 2 ( 14 CO 2 ) measurements can aid in discriminating between fast (〈1 year) and slower (〉5-10 years) cycling of C between the atmosphere and the terrestrial biosphere due to the 14 C disequilibrium between atmospheric and terrestrial C. However, 14 CO 2 in the atmosphere is typically much more strongly impacted by fossil fuel emissions of CO 2 , and, thus, observations often provide little additional constraints on respiratory flux estimates at regional scales. Here, we describe a dataset of 14 CO 2 observations from a tall tower in northern Wisconsin (USA) where fossil fuel influence is far enough removed that, during the summer months, the biospheric component of the 14 CO 2 budget dominates. We find that the terrestrial biosphere is responsible for a significant contribution to 14 CO 2 that is 2-3 times higher than predicted by the CASA terrestrial ecosystem model for observations made in 2010. This likely includes a substantial contribution from the North American Boreal ecoregion, but transported biospheric emissions from outside the model domain cannot be ruled out. The 14 CO 2 enhancement also appears somewhat decreased in observations made over subsequent years, suggesting that 2010 may be anomalous. With these caveats acknowledged, we discuss the implications of the observation/model comparison in terms of possible systematic biases in the model vs short-term anomalies in the observations. Going forward, this isotopic signal could be exploited as an important indicator to better constrain both the long-term carbon balance of terrestrial ecosystems and the short-term impact of disturbance-based loss of carbon to the atmosphere.

Description: The prolonged Millennium drought in southeast Australia (2001–2009) provides a unique opportunity to analyze the responses of a semi-arid ecosystem to severe droughts. In this paper, we analyzed vegetation dynamics in the Millennium drought using visible/infrared observations, passive microwave observations, and a simple ecohydrological model. The satellite observations indicated that the ecosystem maintained its greenness in the Millennium drought, although the total aboveground biomass was significantly decreased by water scarcity. The results of our numerical experiments suggested that the resilience of vegetation greenness to the drought could be explained by a carbon allocation strategy that was sensitive to light and water availability and by temporal changes in vegetation traits. Our numerical experiments successfully simulated the decrease of total aboveground biomass with unchanged vegetation greenness during the Millennium drought.

Description: To test the hypothesis that particle composition has a stronger influence on the community structure of particle-attached than free-living bacteria, elemental (C/N, δ 13 C, and δ 15 N) and chemical composition of particles and the size-fractionated bacterial community composition were examined along the particle density gradient from the Pearl River to the open basin in the South China Sea. Microbial communities were collected at the three size fractions of 0.2–0.8, 0.8–3, and 〉3 µm and the community composition was analyzed using high-throughput sequencing of the 16S rRNA gene (V3–V4 regions). Multivariate analysis evaluating the similarities of bacterial community composition and chemical composition of particles revealed their general consistent spatial variations along the particle density gradient from freshwater to the sea basin. However, compositions of particulate organic matter were more strongly related to the free-living than to the particle-attached bacterial community composition, which was composed of relatively abundant anaerobic bacteria and those taxa preferring low-oxygen conditions. This latter result might be caused by low-oxygen micro-zones in particles. Community network models further revealed tighter interactions within the particle-attached than in free-living bacterial communities, suggesting that a relatively confined space in particles is more favorable for interactions within the community. These analyses indicated that particle micro-niche properties might be important in shaping particle-attached community structure. In contrast, particulate organic matter compositions significantly influenced the free-living bacterial community probably through the release of labile or semi-labile organic matter from particles contributing to the bioavailability of dissolved organic carbon.

Description: No abstract is available for this article.

Description: Knowledge of what controls the activity of subsurface microbial communities is critical for assessing and managing biogenic methane resources. In this study, 19 formation water and 5 gas samples were collected at depths of 800 to 1900 m from Quaternary biogenic gas fields of the Qaidam Basin, China. The formation waters were brines with chloride (Cl) concentrations from 1200 to 2700 mM. Bacterial 16S rRNA gene copies ranged from 3.75 × 10 4 to 2.23 × 10 6 copies mL -1 of water, and those of archaea ranged from 2.44 × 10 3 to 4.66 × 10 7 copies mL -1 of water. Both bacterial and archaea 16s rRNA gene copies were negatively correlated with Cl concentration. The microbial community structure differed significantly depending on Cl concentrations. At high Cl waters (〉1800 mM), the microbial community showed a halophilic signature made up of several abundant taxonomic groups within Firmicules , γ-Proteobacteria and methylotrophic Methanosarcinales. At low Cl, Firmicules and hydrogenotrophic methanogens were dominant members. The proportion of inferred hydrogenotrophic methanogens decreased from 89% to 14% of total archaeal reads with increasing Cl concentration; in contrast, methylotrophic species increased from 11% to 85%. Given that the proportion of hydrogenotrophic species was positively correlated with the archaeal gene abundances, we suggest that Cl concentrations primarily constrain the activity of archaea catalyzing H 2 reduction of CO 2 . Our results show that dilution of formation waters is critical in the process of biogenic gas formation, suggesting that an engineered decrease in Cl concentrations may induce methanogenesis as a potential method to increase gas reserves in such areas in the future.

Description: Land surface phenology (LSP) in the Sahara Desert is poorly understood due to the difficulty in detecting subtle variations in vegetation greenness. This study examined the spatial and temporal patterns of LSP and its responses to rainfall seasonality in the Sahara Desert. We first generated daily two-band Enhanced Vegetation Index (EVI2) from half-hourly observations acquired by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board the METEOSAT Second Generation series of geostationary satellites from 2006 to 2012. The EVI2 time series was used to retrieve LSP based on the Hybrid Piecewise Logistic Model. We further investigated the associations of spatial and temporal patterns in LSP with those in rainfall seasonality derived from the daily rainfall time series of the Tropical Rainfall Measurement Mission. Results show that the spatial shifts in the start of the vegetation growing season generally follows the rainy season onset that is controlled by the summer rainfall regime in the southern Sahara Desert. In contrast, the end of the growing season significantly lags the end of the rainy season without any significant dependence. Vegetation growing season can unfold during the dry seasons after onset is triggered during rainy seasons. Vegetation growing season can be as long as 300 days or more in some areas and years. However, the EVI2 amplitude and accumulation across the Sahara region was very low indicating sparse vegetation as expected in desert regions. EVI2 amplitude and accumulated EVI2 strongly depended on rainfall received during the growing season and the preceding dormancy period.

Description: CH 4 is the second largest contributor to human-induced global warming. However, large uncertainties still exist regarding the magnitude and temporal variation of CH 4 exchanges in China's natural ecosystems, especially under climate changes. In this study, we assessed its uncertainty and temporal variation during 1979–2012, by integrating a biogeochemical model, extensive in situ measurements, and various sources of wetland maps. Uncertainty analyses suggested that previous studies might have underestimated CH 4 emissions, primarily due to bias in wetland extents in NE China. After that, 1 km resolution wetland maps were used to drive the model, together with a 0.1° resolution climate dataset. The model showed that China's natural wetlands emitted 4.56 ± 1.24 Tg CH 4 yr −1 during the 1980s, which decreased to 3.86 ± 1.09 Tg CH 4 yr −1 in the 2000s, mainly due to wetland drainage in NE China. However, recent glacier-melt-induced wetland expansion has enhanced CH 4 emissions by 28% on the Tibetan Plateau since the 1980s. The magnitude of CH 4 uptake by the natural ecosystems has remained relatively stable, e.g., −2.57 ± 0.18 and −2.70 ± 0.19 Tg CH 4 yr −1 in the 1980s and 2000s, respectively. In summary, the net CH 4 balance of China's natural ecosystems has shown a decreasing pattern, i.e., 1.99 ± 1.42 and 1.16 ± 1.28 Tg CH 4 yr −1 in the 1980s and 2000s, respectively, despite distinct regional differences between NE China and the Tibetan Plateau. Furthermore, this study emphasizes the correct representation of wetland extent and its dynamics, i.e., wetland drainage in populated regions and wetland expansion in glacier-fed regions, in driving the decadal CH 4 exchange magnitude.

Description: Knowledge of nitrogen (N) and phosphorus (P) stoichiometry is essential for understanding biogeochemical cycle and ecosystem functioning. However, large-scale patterns in soil stoichiometry are not yet fully understood along environmental gradients nor over the temporal scale. Using a comprehensive dataset and artificial neural network approach (ANN), we evaluated spatial and temporal patterns in topsoil N and P concentrations and N:P ratio across China's forests. Our results revealed that soil weathering stage, climatic factors ( i.e., temperature and precipitation) and forest types jointly explained approximately 34.1% and 30.4% of spatial variation in soil N and P, respectively. By contrast, only precipitation could explain the variation in N:P ratio, with soil N:P ratio exhibiting a trend of increase along theprecipitation gradient. The observed spatial patterns in soil N:P ratio were consistent with previous findings derived from plants and microbes, suggesting that variation in precipitation may induce the imbalance of N:P stoichiometry in forest ecosystems. Our results also indicated that topsoil N:P ratios exhibited a significant increase from the 1980s to 2000s. However, the associations of N:P dynamics with a single element largely depended on forest type. In evergreen forests, soil N:P dynamics were caused by increasing N and decreasing P. Conversely, N:P changes in deciduous broadleaf forests were triggered only by soil N accumulation. Overall, these results demonstrated a stoichiometric shift in soil N:P both spatially and temporally, implying that nutrient imbalance between soil N and P may be accelerated under global change scenarios.

Description: Here we report a facile, efficient, and catalyst-free method to realize C-C cross-coupling of aryl chlorides and inert arenes under UV light irradiation. The aryl radical upon homolytic cleavage of C-Cl bond initiated the nucleophilic substitution reaction with inert arenes to give biaryl products. This mild reaction mode can also be applied to other synthetic reactions, such as the construction of C-N bonds and trifluoromethylated compounds.

Description: Al doped SnO2 microspheres were prepared through hydrothermal method. As-prepared SnO2 microspheres were applied as photoanode materials in dye-sensitized solar cells (DSCs). The properties of the assembled DSCs were significantly improved, especially the open-circuit voltage. The reason for the enhancement was explored through the investigation of dark current curves and electrochemistry impedance spectra. These results showed that the Al doping significantly increased the reaction resistance of recombination reactions and restrained the dark current. The efficient lifetime of photoexcited electrons was also obviously lengthened.

Description: No abstract is available for this article.