ALBERT

Description: The oxidative ratio (OR) of the biosphere is the stoichiometric ratio (O 2 /CO 2 ) of gas exchange by photosynthesis and respiration—a key parameter in budgeting calculations of the land and ocean carbon sinks. Carbon cycle-climate feedbacks could alter the OR of the biosphere by affecting the quantity and quality of organic matter in plant biomass and soil carbon pools. This study considers the effect of elevated atmospheric carbon dioxide concentrations ([CO 2 ]) on the OR of a hardwood forest after 9 growing seasons of free-air CO 2 -enrichment (FACE). We measured changes in the carbon oxidation state (C ox ) of biomass and soil carbon pools as a proxy for the ecosystem OR. The OR of net primary production, 1.039, was not affected by elevated [CO 2 ]. However, the C ox of the soil carbon pool was 40% higher at elevated [CO 2 ], and the estimated OR values for soil respiration increased from 1.006 at ambient [CO 2 ] to 1.054 at elevated [CO 2 ]. A biochemical inventory of the soil organic matter ascribed the increases in C ox and OR to faster turnover of reduced substrates, lignin and lipids, at elevated [CO 2 ]. This implicates the heterotrophic soil community response to elevated [CO 2 ] as a driver of disequilibrium in the ecosystem OR. The oxidation of soil carbon pool constitutes an unexpected terrestrial O 2 sink. Carbon budgets constructed under the assumption of OR equilibrium would equate such a terrestrial O 2 sink to CO 2 uptake by the ocean. The potential for climate-driven disequilibrium in the cycling of O 2 and CO 2 in the terrestrial biosphere warrants further investigation.

Description: Impact of climate change and land use on watershed runoff involves multiattribute ecohydrologic interactions. This information is critical to development of comprehensive stormwater management policies. Watersheds in the continental United States have diverse temperatures and precipitation regimes and varying hydrogeomorphic features that influence runoff. This study investigates watershed-scale runoff using statistical modeling for stormwater policy optimization. Multivariate statistical modeling show that vegetative activity, annual evaporation, precipitation, temperature and soil moisture significantly influenced watershed runoff. Soil moisture has a strong influence on runoff with each percent increase causing five percent increase in runoff. Nonlinear modeling with quadratic and interaction effects shows a significant interaction between soil moisture and other climatic variables in influencing annual runoff patterns. Changes in climate affect ecohydrologic characters by altering available soil moisture, evaporation, precipitation patterns and runoff. Optimization of green infrastructure design can be a successful management tool for runoff with an understanding that changes to multiple attributes in ecohydrologic variables affects runoff. Multi-attribute based green infrastructure and incentive policies can result in comprehensive stormwater policies that incorporate climatic and ecohydrologic conditions of watershed systems.

Description: Previous studies investigating organic-rich tundra have reported that increasing biodegradation of Arctic tundra soil organic carbon (SOC) under warming climate regimes will cause increasing CO 2 and CH 4 emissions. Organic-poor, mineral cryosols, which comprise 87% of Arctic tundra, are not as well characterized. This study examined biogeochemical processes of one-meter-long intact mineral cryosol cores (1-6% SOC) collected in the Canadian high Arctic. Vertical profiles of gaseous and aqueous chemistry and microbial composition were related to surface CO 2 and CH 4 fluxes during a simulated spring/summer thaw under light versus dark and in situ versus water saturated treatments. CO 2 fluxes attained 0.8±0.4 mmol CO 2 m -2 hr -1 for in situ treatments, of which 85±11% was produced by aerobic SOC oxidation, consistent with field observations and metagenomic analyses indicating aerobic heterotrophs were the dominant phylotypes. The Q 10 values of CO 2 emissions ranged from 2-4 over the course of thawing. CH 4 degassing occurred during initial thaw, however all cores were CH 4 sinks at atmospheric concentration CH 4 . Atmospheric CH 4 uptake rates ranged from -126±77 to -207±7 nmol CH 4 m -2 hr -1 with CH 4 consumed between 0-35 cm depth. Metagenomic and gas chemistry analyses revealed that high-affinity Type II methanotrophic sequence abundance and activity were highest between 0- 35 cm depth. Microbial sulfate reduction dominated the anaerobic processes, outcompeting methanogenesis for H 2 and acetate. Fluxes, microbial community composition, and biogeochemical rates indicate that mineral cryosols of Axel Heiberg Island act as net CO 2 sources and atmospheric CH 4 sinks during summertime thaw under both in situ and water saturated states.

Description: Boreal lake sediments are important sites of organic carbon (OC) storage, which have accumulated substantial amounts of OC over the Holocene epoch; the temporal evolution and the strength of this Holocene carbon (C) sink is, however, not well constrained. In this study we investigated the temporal record of carbon mass accumulation rates (CMARs), and assessed qualitative changes of terrestrially derived OC in the sediment profiles of seven Swedish boreal lakes, in order to evaluate the variability of boreal lake sediments as a C sink over time. CMARs were resolved on a short-term (centennial) and long-term (i.e. over millennia of the Holocene) time scale, using radioactive lead ( 210 Pb) and carbon ( 14 C) isotope dating. Sources and degradation state of terrestrially derived OC were identified and characterized by molecular analyses of lignin phenols. We found that CMARs varied substantially on both short-term and long-term scales, and that the variability was mostly attributed to sedimentation rates and uncoupled from the OC content in the sediment profiles. The lignin phenol analyses revealed that woody material from gymnosperms was a dominant and constant OC source to the sediments over the Holocene. Furthermore, lignin-based degradation indices, such as acid-to-aldehyde ratios, indicated that post-depositional degradation in the sediments was very limited on longer time scales, implying that terrestrial OC is stabilized in the sediments on a permanent basis.

Description: We investigate the benefits of assimilating in situ and satellite data of the fraction of photosynthetically active radiation (FAPAR) relative to eddy-covariance flux measurements for the optimization of parameters of the ORCHIDEE biosphere model. We focus on model parameters related to carbon fixation, respiration and phenology. The study relies on two sites – Fontainebleau (deciduous broadleaf forest) and Puechabon (Mediterranean broadleaf evergreen forest) – where measurements of net carbon exchange (NEE) and latent heat (LE) fluxes are available at the same time as FAPAR products derived from ground measurements or derived from spaceborne observations at high (SPOT) and medium (MERIS) spatial resolutions. We compare the different FAPAR products, analyze their consistency with the in situ fluxes, and then evaluate the potential benefits of jointly assimilating flux and FAPAR data. The assimilation of FAPAR data leads to a degradation of the model-data agreement with respect to NEE at the two sites. It is caused by the change in leaf area required to fit the magnitude of the various FAPAR products. Assimilating daily NEE and LE fluxes however has a marginal impact on the simulated FAPAR. The results suggest that the main advantage of including FAPAR data is the ability to constrain the timing of leaf onset and senescence for deciduous ecosystems, which is best achieved by normalizing FAPAR time series. The joint assimilation of flux and FAPAR data lead to a similar model-data improvement across all variables than when each data-stream is used independently, corresponding however to different and likely improved parameter values.

Description: In order to investigate the importance of biogenic silica associated biopolymers on the scavenging of radionuclides, the diatom Phaeodactylum tricornutum was incubated together with the radionuclides 234 Th, 233 Pa, 210 Pb, and 7 Be during their growth phase. Normalized affinity coefficients were determined for the radionuclides bound with different organic compound classes (i.e., proteins, total carbohydrates, uronic acids) in extracellular (non-attached and attached exopolymeric substances, EPS), intracellular (ethylene diamine tetraacetic acid, EDTA and sodium dodecyl sulfate, SDS extractable), and frustule embedded biopolymeric fractions (BF). Results indicated that radionuclides were mostly concentrated in frustule BF. Among three measured organic components, URA showed the strongest affinities to all tested radionuclides. Confirmed by spectrophotometry and 2-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance (2D HSQC-NMR) analyses, the frustule BF were mainly composed of carboxyl-rich, aliphatic-phosphoproteins, which were likely responsible for the strong binding of many of the radionuclides. Results from this study provide evidence for selective absorption of radionuclides with different kinds of diatom-associated biopolymers acting in concert rather than as a single compound. This clearly indicates the importance of these diatom related biopolymers, especially frustule biopolymers, in the scavenging and fractionation of radionuclides used as particle tracers in the ocean.

Description: Plant phenology is one of the preferred indicators of climate change, and its variation potentially impacts community dynamics and ecosystem functions. To better understand the responses of plants’ flowering phenology to rising temperatures, we investigated the temperature sensitivity (expressed as the date of changes in phenology per change in temperature in degree Celsius, days °C −1 ) of flowering phenology for more than 220 plant species at 59 sites in China during the period 1963–1988. Our results indicated that most flowerings in China were significantly sensitive to the temperature in the two months (60 days) prior to the flowering dates. Plants in warmer regions showed larger sensitivities to increased temperatures. Species flowering in the late spring and early summer were generally less sensitive to changing temperature than species flowering at other times of the year. For plants flowering in the spring, species that flower earlier showed higher temperature sensitivity; however, for plants flowering in the summer and autumn, species that flower earlier showed lower temperature sensitivity. The responses of the first and last flowering times to changing temperature were mostly consistent, so flowering durations were rarely (6.1%) sensitive to changing temperature. We hypothesize that plants in cold regions may have adapted to the more variable temperatures and thus showed lower temperature sensitivities than plants in warm regions. Overall, the responses of flowering phenology to temperature varied significantly among temperature zones and plant species, so it should be considered carefully when estimating the impacts of climate warming on the terrestrial biosphere.

Description: Northern peatlands have accumulated a large amount of organic carbon (C) in their thick peat profile. Climate change and associated variations in soil environments are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is still highly uncertain. Verifying and understanding the influences of changes in environmental factors on C gas fluxes in biogeochemical models are essential for forecasting feedbacks between C gas fluxes and climate change. In this study, we applied a biogeochemical model, DeNitrification-DeComposition (DNDC), to assess impacts of air temperature (T A ) and water table (WT) on C gas fluxes in an Alaskan peatland. DNDC was validated against field measurements of net ecosystem exchange of CO 2 (NEE) and CH 4 fluxes under manipulated surface soil temperature and WT conditions in a moderate rich fen. The validation demonstrates that DNDC was able to capture the observed impacts of the manipulations in soil environments on C gas fluxes. To investigate responses of C gas fluxes to changes in T A and soil water condition, we conducted a series of simulations with varying T A and WT. The results demonstrate that: 1) uptake rates of CO 2 at the site were reduced by either too colder or warmer temperatures, and generally increased with increasing soil moisture; 2) CH 4 emissions showed an increasing trend as T A increased or WT rose toward the peat surface; and 3) the site could shift from a net GHG sink into a net GHG source under some warm and/or dry conditions. A sensitivity analysis evaluated the relative importance of T A and WT to C gas fluxes. The results indicate that both T A and WT played important roles in regulating NEE and CH 4 emissions, and that within the investigated ranges of the variations in T A and WT, changes in WT showed a greater impact than changes in T A on NEE, CH 4 fluxes, and net C gas fluxes at the study fen.

Description: To clarify the effect of differences in hydrophyte life forms on methane (CH 4 ) production and its carbon stable isotopic signature (δ 13 C-CH 4 ), we analyzed CH 4 and carbon dioxide (CO 2 ) concentrations, their stable carbon isotope values, and chemical constituents dissolved in porewater in a small floating peat bog in Japan. Because eutrophication has modified the surrounding water quality the bog vegetation on the mat has been, in part, replaced by fen-type vegetation. We hypothesized that differences in hydrophyte habitats affect redox conditions, including dissolved oxygen (DO) in water and therefore the amounts and carbon isotopic values of CH 4 and CO 2 dissolved in porewater. Between the habitats of two Sphagnum species, DO was considerably higher and CH 4 concentrations were significantly lower in Sphagnum cuspidatum Ehrh. habitats in hollow (DO; 0.62 ± 0.20 mg/L (SE) and CH 4 ; 0.18 ± 0.02 mmol/L) than in Sphagnum palustre L. habitats in hummock (DO; 0.29 ±0.08 and CH 4 ; 0.82 ±0.06) in porewater (10 cm depth). Both DO and CH 4 concentrations in three vascular plant habitats ( Rhynchospora fauriei Franch., Phragmites australis [reed], and Menyanthes trifoliata L.) in porewater (10 cm depth) were intermediate relative to the two Sphagnum species. However, CH 4 flux in M. trifoliata site was significantly higher than that at both Sphagnum sites, suggesting that the type of gas transport (diffusive or convective via root and stem) affected the depth profile of CH 4 concentrations and its flux. δ 13 C-CH 4 values in porewater also varied among the vegetation types, even within Sphagnum species (e.g., at 10-cm depth, δ 13 C-CH 4 : R. fauriei , −55.3 ± 1.8‰ [SE]; P. australis , −57.5 ± 1.6‰; M. trifoliata , −56.7 ± 1.5‰; S. cuspidatum , −71.2 ± 1.4‰; and S. palustre , −60.4 ± 0.6‰). Our results suggests that significant differences arise in CH 4 concentration and δ 13 C-CH 4 values among the hydrophyte habitats even within a small peat bog and that change in vegetation relative to trophic conditions can affect CH 4 emissions and associated δ 13 C-CH 4 values.

Description: Dynamics of carbon dioxide and energy exchange over a small boreal lake were investigated. Flux measurements have been carried out by the eddy covariance technique during two open water periods (June-October) at Lake Kuivajärvi in Finland. Sensible heat ( H ) flux peaked in the early morning and upward sensible heat flux at night results in unstable stratification over the lake. Minimum H was measured in the late afternoon, often resulting in adiabatic conditions or slightly stable stratification over the lake. The latent heat flux ( LE ) showed a different pattern, peaking in the afternoon, and having a minimum at night. High correlation (r 2 =0.75) between H and water-air temperature difference multiplied by wind speed ( U ) was found, while LE strongly correlated with the water vapour pressure deficit multiplied by U (r 2 =0.78). Monthly average values of energy balance closure ranged between 70 and 99%. The lake acted as net source of carbon dioxide, and the measured flux ( F CO2 ) averaged over the two open-water periods (0.7 µmol m −2 s −1 ) was up to three times higher than those reported in other studies. Furthermore, it was found that, during period of high wind speed (〉3 m s −1 ) shear induced water turbulence controls the water-air gas transfer efficiency. However, under calm night-time conditions, F CO2 was poorly correlated with the difference between the water and the equilibrium CO 2 concentrations multiplied by U . Night-time cooling of surface water enhances the gas transfer efficiency through buoyancy-driven turbulent mixing, and simple wind speed based transfer velocity models strongly underestimate F CO2 .