B13A-0405
Water and energy budget under a manipulated water table of a wetland in interior Alaska
Wetlands are an important part of water and surface energy budgets in Boreal ecosystems. This study is located at the Bonanza Creek Long Term Ecological Research site 20 miles south west of Fairbanks. Measurements were taken at the Alaska Peatland Experiment, which is located in a fen within the Tanana river basin, and was setup to study the carbon balance in water table manipulation plots. These plots consist of a control, lowered, and raised water table. The water table influences carbon balance related processes which reflects the significance of the water budget of each plot. During the summer of 2008 we measured and logged all the components for creating the water and energy budget at the soil air interface including its water table manipulations. We also measured the thaw depth on a daily bases and the variability of the hydraulic conductivity in space and time. The water budget identifies the controls over the water table fluctuation in time, which affects the carbon balance. In addition we have data from frozen cores taken in spring of 2008 and analyzed them for their ice content. We verified the energy consumption due to thaw depth with the ground heat flux component of the surface energy balance. It was found that the manipulation of the water table has a strong effect on the water and energy budget of the system.
B13A-0406
Long-Term Monitoring of Sensible and Latent Heat Fluxes Using Eddy Covariance at a High-Arctic Permafrost Site on Svalbard, Norway
Land-atmosphere interactions are an important element in the energy and water budget in permafrost
regions. We present long-term measurements of sensible and latent heat fluxes at a high-arctic continuous
permafrost site on Svalbard, Norway, using the eddy covariance method. The site is situated in hilly tundra at
the foot of two major glaciers, and is characterized by sparse vegetation alternating with exposed soil and
rock fields. The study was performed from April to September in the years 2007 and 2008, thus covering a
period from late winter until the end of the summer season in both years.
The general pattern of the measured fluxes was largely similar in 2007 and 2008. During April, temperatures
ranged from -20°C to +5°C, with an average of -11°C both in 2007 and 2008. Sensible
heat fluxes were mostly negative, corresponding to an energy transfer from the atmosphere to the snow
pack. The latent heat flux was generally positive, but remained low most of the time. With a temperature
remaining rather constant between -5°C and +5°C and predominantly neutral atmospheric
exchange conditions during most of May and June, both measured fluxes were comparatively insignificant.
The appearance of large snow free patches around the end of June triggered a strong increase of sensible
and latent heat fluxes. Hereby, the latent heat flux was approx. twice as large as the sensible heat flux, most
likely due to very wet soil conditions directly after snow melt. This situation reversed during July, when the
tundra increasingly dried up in most of the potential fetch area of the eddy system. The immediate
surrounding of the measurement site could then be characterized as moderately moist tundra. Both sensible
and latent heat fluxes remained largely positive, and displayed a strong diurnal course, with peak fluxes
associated with maxima of solar radiation.
In relation with recordings of the radiative parts of the energy budget, eddy covariance measurements have
proven to be a valuable method to capture a more complete picture of energy fluxes at this maritime
permafrost site.
B13A-0407
Spatial and Temporal Dynamics in CO2 and CH4 in Open Water Pools in an Ombrotrophic Raised Bog and Possible Responses to Climate Change.
To test the hypothesis that the developmental stage of peatland pools is related to C cycling, we measured pool water column and sediment concentrations of dissolved CO2, CH4 and DOC over 2 years in 16 pools varying in size and depth, along with light, dissolved oxygen and temperature. Water column dissolved CO2 concentrations generally decreased with increasing pool depth from 0.3 to 0.75 m, with smaller differences for water column DOC and CH4. There was a distinct seasonal pattern, with larger concentrations observed during mid-summer, than either spring or fall. All pools were supersaturated at times of sampling, with average water column dissolved CH4 ten times greater and dissolved CO2 four times greater than atmospheric equivalents. Mid-summer water temperatures were 1 to 5 °C warmer in shallow pools (0.3, 0.35 m depth) than deep pools (0.7, 0.75 m depth) and between 0 and 30 cm, dissolved oxygen concentrations were significantly lower in shallow pools (p < 0.001). Light attenuation at 30 cm was also significantly lower in a 0.35 m pool (p = 0.02). In three pools with average depths of 0.4, 0.7 and 0.75 m, sediment dissolved CH4 concentrations were significantly different (p < 0.001) with the average concentration in the deepest six times greater than the shallow pool. There were small differences between sediment CO2, with the highest concentration observed in the 0.7 m deep pool, 1.4 times greater than the other two pools. Our results suggest that there may be greater decomposition in the sediments and greater water column activity in shallow pools supported by mid-summer warmer temperatures, higher DO and high DOC concentrations, whereas there is greater anaerobic decomposition in deeper pools, supported by colder water and sediment temperatures. Processes affected by climate driven environmental change will alter the C dynamics of pools changing their role in the peatland C balance.
B13A-0408
Twenty years of methane and carbon dioxide flux measurements from a temperate peatland
We have measured ecosystem respiration, net ecosystem CO2 exchange (NEE), CH4 flux, water table height, and meteorological data on a semi-continuous basis at Sallie's Fen, NH, USA, a nutrient poor fen located at the southern limit of boreal peatlands in North America, for nearly 20 years. Our major findings include: 1. Instantaneously measured CH4 fluxes show high interannual variability and reveal clear relationships between CH4 fluxes and environmental variables. 2. However, seasonally averaged CH4 fluxes show low interannual and spatial variability. 3. Species composition and environmental variables (air temperature, peat temperature, water table level) affect relationships between CH4 fluxes and measures of plant productivity (NEEmax, photosynthesismax, respiration. 4. Each year rates of photosynthesis and respiration increase throughout the season with increasing temperature. 5. Interannual variability is driven by changes in weather in a climate-determined landscape. 6. Measured dark chamber respiration rates have increased over the 20-year period. 7. Plant species composition in the peatland is transitioning to a more shrub-dominated ecosystem which may be driving increased respiration rates observed at this site. 8. Regional O3 events appear to impact respiration rates in autochamber measured CO2 exchange. Long-term datasets of trace gas exchange from peatlands like those presented here are essential in the development and validation of process based models for prediction of future climate impacts on these sensitive ecosystems.
B13A-0409
Title: Interannual variability in the temperature-responsiveness of CO2 flux from forest and peatland soils
Northern forests and peatlands store large amounts of carbon in soils. The development of robust predictions of carbon fluxes from these ecosystems is important to improving biogeochemical models, especially in the context of global environmental change. We measured fluxes of CO2 from upland forest and peatland soils in the Marcell Experimental Forest (northern Minnesota, USA) from 2005 through 2007. We compared fluxes from upland and peatland hydrologic settings and also used regression approaches to examine the effectiveness of soil temperature, soil moisture, and water table level in predicting CO2 flux. Differences between upland and peatland CO2 flux were sometimes apparent but were not consistent across sampling years. In 2005, the mean upland CO2 flux was significantly higher than the mean peatland flux; in both 2006 and 2007, peatland fluxes exceeded upland fluxes, though the difference was not significant. Soil temperature was generally a stronger predictor of CO2 flux than was soil moisture or water table, but its predictive strength varied by hydrologic setting and year. In 2005, these variables explained roughly 60 percent of the variation of CO2 flux in both uplands and peatlands, but the strength of these predictive relationships declined in 2006 and 2007. Our study highlights the potential role of soil temperature in feedbacks between climate and the carbon cycle, but also illustrates a strong need for understanding interannual variability in the temperature responsiveness of CO2 flux.
B13A-0410
Impact of Small-Scale Changes in Soil Moisture on Redox Dynamics and Trace gas Emissions in Mesocosms of fen and bog Peat
We analyzed the effects of short-term changes in soil moisture, as they occur during summer months, on the redox dynamics and trace gas emissions from peatland mesocosms. Using peat from an ombrotrophic northern bog and a minerotrophic, alpine fen, we determined water contents using the FDR technique, analyzed pore water chemistry in the unsaturated and saturated zone and quantified fluxes of CO2 and CH4 using the static chamber technique. In situ production and consumption of acetate, CO2, CH4 and terminal electron acceptors were quantified by mass balance. Concentrations and turnover of CO2, CH4 and electron acceptors were higher in the fen than in the bog peat, resulting in 4 times higher CO2 and 10 times higher CH4 emissions. Acetate partly accumulated to very high concentrations of 5.7 mmol L-1 and fermentation processes were thus partly decoupled from terminal respiration. Differences in hydrologic properties of the peats had a strong impact on redox dynamics. Reducing conditions prevailed up to 5 cm above the water table in the fen peat whereas such conditions were limited to the saturated zone in the bog peat. Drought periods resulted in a much stronger response of water table position in the fen peat, but had little impact on redox processes. Methane was mostly produced near the water table in the fen peat (> 50 nmol cm-3d-1) and was fairly insensitive to drought in comparison to the bog peat. After irrigation, methanogenesis restarted in both peats without appreciable time-lag. Methane emission was reduced during water table fluctuations in the fen peat and too low to be analyzed in the bog peat. CO2 production was dominated by the unsaturated zone that was enlarged due to water table fluctuations; but increased production rates did not result in altered fluxes. The results of the study suggest that short-term fluctuations in water table and soil moisture may alter redox process patterns but that trace gas fluxes are quite resilient in comparison.
B13A-0411
Nutrient Availability and Carbon Cycling in a Subarctic Wetland - a Pulse Labeling Experiment
Northern wetlands are important ecosystems in the context of biospheric feedbacks to climate change, due to the large storage of organic C in their soils. Nitrogen deposition and increased nutrient availability in soils following climate warming may cause changes in these ecosystems affecting greenhouse gas exchange. We have studied C cycling under controlled laboratory conditions using whole ecosystem monoliths with intact surface vegetation from a fertilization experiment in a north Swedish subarctic wetland. The experimental site has been fertilized with N and P since 2006, and during autumn 2007, three monoliths from fertilized plots and three monoliths from control plots were collected. The monoliths were installed in a growth chamber where temperature and radiation could be controlled to simulate natural conditions. The monoliths were isolated from the surroundings using transparent chambers connected to tubing with a constant inflow of atmospheric air. The outflowing air from all six chambers and a reference chamber were analyzed for CO2 and CH4. Each monolith was exposed to 14CO2 during an hour under daytime irradiation conditions allowing vegetation to assimilate labeled CO2. During more than 70 days after labeling, we monitored the amount of 14CO2 and 14CH4 in outflowing air, as well as the amount of 14C in soil water. Above and belowground plant biomass were analyzed for 14C after the experiment was terminated. We hypothesize that fertilization will lower 14C root to shoot ratio compared to control. This in turn will lead to decreased 14C root exudation rates in fertilized monoliths, which may lower substrate availability for methanogenesis. The results from this experiment will be presented and discussed at the conference.
B13A-0412
Impact of Long-Term Drying on Belowground Carbon Cycling in a Northern bog
Peatlands are important global sinks of carbon dioxide and sources of methane. Impacts of climate change on these functions are of great interest. To estimate the impact of long-term drying on belowground carbon cycling and peat decomposability we investigated a transect across a drainage ditch in the Mer Bleue peatland, Ontario, Canada. To this end we installed multi-level-piezometers and pore-water peepers in distances of 15, 30, 60 and 200 m from the ditch in an open and a forested part of the bog and obtained detailed concentration depth profiles of relevant decomposition products in the pore-water and potential respiration rates in incubations. Respiration rates were also derived from inverse pore-water modeling and related to their thermodynamic energy yields. Maximum concentrations ranged from 2-3.5 mmol L-1 (DIC) and up to 0.5 mmol L-1 (CH4) and differed primarily between the open and forested site of the transect but not in distance from the ditch. Calculated Gibbs free energy of key processes ranged from - 60.7 to +31.2 kJ mol-1 substrate-1. Potential respiration rates and rates derived from inverse pore- water modeling mostly peaked near the water table and were also higher at the forested site (up to 9.0 nmol cm-3d-1 for CO2) compared to 0.1-4.4 nmol cm-3d-1 at the bog site. In situ rates by inverse pore-water modeling were generally lower than results from incubations. Concentration profiles of relevant decomposition products were similar with depth at all sites and varied only in the upper parts of peat profiles. Changes in vegetation and plant community structure induced by drainage thus seemed to be the most important effect of long-term drainage with respect to belowground C cycling.
B13A-0413
Simulating the Carbon Cycling of an Ombrotrophic Peatland in Eastern Canada using a Coupled Land Surface Climate and Wetland Carbon Model
Northern peatlands represent one of the largest terrestrial soil carbon pools with between 20 and 30% of all soil carbon, despite covering only 3% of the land. Northern peatlands are located in regions where the climate has been projected to experience significant changes so the fate of this stored carbon is of concern. We have coupled a land surface climate, wetland-CLASS that simulates soil temperatures and water contents with a process-based wetland biogeochemical model, the McGill Wetland Model (MWM) to examine how climate influences the cycling of carbon in northern peatlands. We evaluate the coupled climate – wetland carbon model with multi-year eddy-covariance measurements of NEE ( Net Ecosystem Exchange), GPP (Gross Primary Production) and TER( Terrestrial Ecosystem Respiration) from a raised, ombrotrophic bog, Mer Bleue, located in the cool temperate ecoclimatic zone, near Ottawa, Canada (45°25'N, 75°40'W). The measurements record used is continuous from 1999 to 2002. The root mean square error (RMSE) for daily GPP, TER and NEE is ~0.60, 0.51, and 0.49 g C m-2 d-1, respectively.. The systematic RMSE and unsystematic – i.e. random RSME for daily GPP, TER and NEE are ~0.19, 0.08, and 0.31 g C m-2 d-1, and ~0.57, 0.50, and 0.38 g C m-2 d-1, respectively. The index of agreement between modeled and observed GPP, TER and NEE is 98%, 96% and 84%, respectively. The performance of the coupled wetland-CLASS MWM is statistical similar to the performance of MWM when measured soil temperatures and moisture conditions are used. The results show that the coupled wetland- CLASS MWM captures adequately the magnitude and direction, and the inter-annual and seasonal variability of the CO2 fluxes reasonably well. These results provide us with confidence to use the coupled model to examine the sensitivity of the storage and fluxes of peatland carbon to various future climate scenarios
B13A-0414
Variability of Carbon Exchanges Between Two Contrasting Northern Peatlands
Northern peatland contain about one quarter of the world's terrestrial carbon. It appears that many peatlands still remains a small, but persistent sinks of carbon dioxide and sources of methane. The sink strength is small compared to actively growing boreal forests but equal to the Holocene average peatland carbon accumulation. This suggests that the function of northern peatlands, with regard to C sequestration, has not change relative to the Holocene average uptake. In contrast to forested ecosystems there have been few long-term continuous measurements of the components of the C balance of peatlands ecosystems. In addition to measurements of net ecosystem exchange and net methane emission (or uptake), the C balance of peatlands requires accurate estimates of the loss of carbon dissolved in runoff. Multi-year measurements of these three major exchanges have been made in contrasting northern peatlands: Mer Bleue, a raised ombrotrophic bog located at the boreal - temperate boundary in eastern Canada, and Degero Stormyr, a mineral poor, oligotrophic fen located in northern Sweden. Despite very different plant communities and moisture regimes the long-term average NEE, methane exchange and net loss of carbon dissolved in water are surprisingly similar in these two systems. However, Mer Bleue has a much greater inter-annual variability in the exchanges than does Degero Stormyr peatland. The difference in exchanges appears related to differences in the variability in moisture supply to the vegetation layer and water storage in the peat. In the early 1990s, the eminent peatland ecologist, Eville Gorham estimated, with few observations, the relative importance of the C balance components of northern peatlands. The multi-year records indicate that these early estimates with reasonable good within an order of magnitude.
B13A-0415
The Closed Chamber Method Overestimates CO2 Respiration Fluxes in Low-Turbulence Nighttime Conditions
Knowledge about ecosystem respiration is required for accurate estimates of daily, seasonal and annual carbon exchange between ecosystems and the atmosphere. Ecosystem respiration differs from photosynthesis in its diurnal and seasonal regime and its response to environmental controls. Contrary to photosynthesis, ecosystem respiration persists during nighttime. Measurements by the closed chamber technique were often used for the calculation of nighttime respiration fluxes during low-turbulence nighttime conditions, where the use of the eddy covariance method is problematic. The goal of this study is to investigate if also the closed chamber measurements could be biased during atmospheric low-turbulence conditions. This study presents CO2 flux observations (n = 602) measured at night at a boreal peatland in eastern Finland for two investigation periods during the years 2005 and 2006. We have used the closed chamber technique for measurements at flark, lawn and hummock microsites. Threshold for screening data into either well-developed or low-turbulence conditions were made using the friction velocity (u*), with u* <0.1 ms-1 indicating low turbulence conditions. During chamber experiments in low-turbulence nighttime conditions, the CO2 concentration within the chamber headspace was observed to increase extremely fast at the start of the closure period which we consider an artefact of the chamber method under low-turbulence nighttime conditions, but which leads to an overestimation of CO2 fluxes. The probable reason is the disturbance of the natural concentration gradients in the soils, plants and the near-surface atmosphere. This phenomenon occurs at all microsite types; however, the highest overestimation occurs at hummocks and the lowest at flarks, probably due to the differing water table levels. We thus caution that nighttime chamber measurements have to be carefully checked with respect to prevailing turbulence conditions. Under low- turbulence conditions their results can be seriously biased. As the bias is difficult to correct, closed chambers might not be as suitable to replace eddy covariance night measurements under low-turbulence conditions as previously thought.
B13A-0416
Annual Carbon Gas Budget for a Subarctic Peatland, Northern Sweden
Temperatures in the Arctic regions are rising, melting permafrost and exposing previously stable soil organic carbon (OC) to decomposition. The result can be that northern latitude soils which have accumulated large amounts of OC potentially shift from atmospheric C sinks to C sources with positive feedback on climate warming. We estimate the annual net C gas balance (NCB) of the subarctic mire Stordalen, based on automatic chamber measurements of CO2 and total hydrocarbon (THC; CH4 and NMVOCs) exchange. We studied the dominant vegetation communities with different moisture and permafrost characteristics; a dry Palsa underlain by permafrost, an intermediate melt site with Sphagnum spp. and a wet site with Eriophorum spp. where the soil thaws completely. Whole year accumulated fluxes of CO2 were estimated to 30, -35 and -35 gC m-2 respectively for the Palsa, Sphagnum and Eriophorum sites (positive flux indicates an addition of C to the atmospheric pool). The corresponding annual THC emissions were 0.5, 6 and 32 gC m-2 for the same sites. Therefore, the NCB for each of the sites were 30, -29 and -3 gC m-2 respectively for the Palsa, Sphagnum and Eriophorum site. On average, the whole mire was a sink of CO2 (-2.58 gC m-2) and a source of THC (6.44 gC m-2) over a year. Consequently, the mire was a net source of C to the atmosphere (3.87 gC m-2). Snow season estimates of CO2 and THC emphasize the importance of winter measurements for complete annual C budgets. Decadal vegetation changes at Stordalen indicate that both the productivity and the THC emissions increased between 1970 and 2000. Considering the GWP100 of CH4, the net radiative forcing on climate increased 27% over the same time. Reduced C emissions in these environments are important for both the annual C balance and climate.
B13A-0417
Modeling C and N Dynamics in a Forested Wetland Watershed on Southeast Atlantic Coastal Plain, USA
Modeling dynamics of carbon (C) and nitrogen (N) in wetland watersheds requires spatial information of hydrology regulating the biogeochemical cycle in wetland ecosystems. To this end, we linked MIKE SHE, which is a distributed hydrologic model, to Forest-DNDC, which is a process-based biogeochemical model. To test the linkage, a 160 ha forested wetland watershed on the Atlantic Coastal Plain in South Carolina was divided into 665 cells with a 50x50 m grids; and water table, stream flow and soil respiration dynamics were observed in the watershed. The test results with model efficiencies (E = 0.65 – 0.70 for daily outflow, 0.49 – 0.94 for daily water table, and 0.57 – 0.61 for soil respiration) showed that the linkage is applicable for modeling C and N dynamics in the watershed. The simulation results also showed that this watershed is a significant C sink, with an average C sequestration rate of about 2.2 Mg C/ha/yr for the period of 2003-2007. However, the C sequestration in this watershed was substantially affected by the climate conditions. For example, the predicted annual C storages for 2004 and 2007 were over 45% lower than those for the other years because of drought; the precipitation in 2004 and 2007 was about 390 and 430 mm less, respectively, than the long-term average (1350mm). The results also showed that there was a significant relationship between annual soil heterotrophic CO2 emission and annual average water table depth (R2 ranging from 0.93 to 0.99 for each cell, P<0.01). High water table levels led to low soil CO2 but high methane emissions from the watershed. The predicted annual methane emission rates proportionally increased with precipitation. However, severe drought may cause a reduction in methane emission by over 80%, but an increase in CO2 emission by more than 50%. In addition, the average N2O emission from the watershed was 3.7 kg N/ha/yr in 2003-2007, and the annual emission was significantly decreased with increasing precipitation (R2 = 0.93, P<0.01). The predicted NEE fluxes showed substantial variations in space and time. The spatial variation was mainly due to the differences in vegetation and water table associated with topography across the watershed, and the temporal variation was primarily caused by climate. The spatial pattern of methane fluxes follows the topography.
B13A-0418
Carbon Dioxide and Methane Dynamics in Russian Tundra
This study focus on the contemporary carbon cycling and greenhouse gas budget of a lowland artic tundra ecosystem in northern Russia. The area is situated at 67°N in the European part of northeast Russia within the Pechora basin. The Russian tundra region is an area which has recently been subject to many speculations in relation to climatic change effects and greenhouse gas (GHG) exchange but still little scientific evidence is available from this region. At present, there are fundamental questions to answer about the CH4 concentration in the atmosphere and its oscillations and what role CH4 exchange may have under future climatic conditions, To do so, we need to better understand the ecosystem- atmosphere interactions and the annual carbon dynamics. Here we present eddy correlation measurements of CO2 and CH4 exchange during the period from early spring to late autumn, covering the full growing season, i.e., mid June to mid September. We present preliminary seasonal budgets of carbon, greenhouse gas exchange, and discuss possible implications of climatic change on this lowland tundra ecosystem. This study have been conducted as a part of the CARBO-North project (2006-2010), a project within the EU 6th framework programme, aiming at quantifying the carbon budget in Northern Russia across temporal and spatial scales.
B13A-0419
Decadal Change in Northern Wetlands Based on Analysis of ALOS/PALSAR and JERS SAR Data
Northern wetlands are believed to have hitherto served as carbon sinks, sequestering about one third of the total global pool of soil carbon. The warmer, drier conditions expected throughout the Arctic as a consequence of global warming may induce aerobic decomposition of northern wetland soils, which may cause them to become major sources rather than sinks of carbon dioxide. It is therefore critical to develop an ability to monitor long-term changes occurring in the condition of northern wetlands. Since L-Band synthetic aperture radar (SAR) is sensitive to vegetation structure, biomass, and moisture content, it is an appropriate choice for detecting changes in the characteristics of vegetated wetlands. We have used L-band SAR imagery from two different spaceborne sensors separated in time by approximately one decade, JERS and ALOS/PALSAR, to produce a thematic map of change in the type and extent of representative regions of wetlands in Alaska, such as tundra, scrub/shrub, and forested wetlands. JERS imagery characterizes the wetlands status for the 1997 time frame while dual-polarized ALOS/PALSAR imagery captures the wetlands status for the 2007 time frame. To produce each classified wetlands map, the SAR imagery is supplemented with the corresponding imagery collection dates, a digital elevation model (DEM), a slope model, an open water mask, proximity to water map, and geographic latitude. The classification algorithm applied to each set of imagery is based upon using a multitude of decision trees. The accuracy of the resulting thematic change map will be verified using ground reference data. The results could demonstrate the utility of multi-platform satellite SAR observations for characterizing the transitions across multiple years in extent and type of vegetated wetlands as a result of global climate change.
B13A-0420
Arctic Summer Surface Energy Balance at Two Coastal Drained Lake Basins, Barrow, Alaska
We examined the partitioning of the summer surface energy balance at two coastal drained lake basins using measurements from two eddy covariance towers in Barrow, Alaska. Drained lake basins are a common land feature covering approximately one fourth of the Arctic Coastal Plain but have been given limited attention. Overall, wetlands are extensive in the region in spite of an annual precipitation close to a desert and a negative summer P-ET. Included in the analysis was summer 2007, which experienced unusually high air temperatures and low precipitation compared to the long term mean. During the five analyzed summers, most of the energy available at the ground surface was partitioned into sensible heat flux despite saturated or nearly saturated near-surface soils. The maritime conditions resulted in a cool and close to saturated air mass with a few exceptions on individual days. With a ground surface often warmer than the air above and limited air vapor pressure deficits, the dissipation of the available heat at the ground surface was mainly partitioned into sensible heat flux resulting in midday Bowen Ratios (sensible divided by latent heat flux) above unity. Total daily latent heat flux presented in mm of water varied between 0.2 – 4.2 mm/day with a Jun-Aug mean of 1.5 mm. In 80% of the analyzed days, mean midday evapotranspiration occurred below the equilibrium rate resulting in a Priestley-Taylor alpha value below unity. The equilibrium evaporation rates of inland arctic wetlands have previously shown to occur at or above equilibrium rate. Further, the energy balance partitioning of a wetland located in a maritime or continental climate show differences such as in the Bowen Ratio. It is therefore necessary to analyze coastal and inland areas separately when examining the hydrological response of wetlands to climate changes.
B13A-0421
Carbon Fluxes Across Vegetated Drained Lakes of Different ages on the Arctic Coastal Plain, Alaska
Vegetated drained lakes are a major component of the Arctic Coastal Plain (the northern part of Alaska), accounting for 47% of the landscape in the northern portion of this region. Lake formation results from the combined action of thermal erosion at the edges of small ponds and permafrost melting that leads to coalescence of several adjacent ponds. The final stage of the thaw lake cycle involves drainage. After drainage, vegetation establishes on the drained lake basin and organic matter accumulates from the buildup of the plant detritus. Young lakes have maximum nutrient availability because of mineralization in the lake phase and because nutrients move with runoff from higher situated slope vegetation sites downward. During this time the high productivity of plants results in net CO2 uptake and accumulation in the above and below ground carbon pools. As nutrients mineralized during the drained lake phase, are progressively stored in plant material and organic matter, plant productivity declines. The resultant decrease in plant production through time causes a reduction in the rate of carbon accumulation with age since drainage. Greenhouse gas fluxes from lakes and vegetated drained lake basins have been largely understudied. There has been some research on CO2 flux over lakes, but the largest part of the research on the patterns and controls of CO2 flux in the tundra regions the has been done on areas outside of lakes or vegetated drained thaw lake basins. This may because these upland sites maybe drier and more accessible. As a consequence most of the knowledge of the greenhouse gases sink-source activity in the Arctic Coastal Tundra excludes the land features that represent the majority of the landscape. To assess with confidence current and future sink/source activity of the arctic tundra we characterized these vegetated drained lakes in terms of their net ecosystem exchange, and to investigate their differential responses to environmental parameters. In fact the different vegetations types in vegetated drained lakes of varying age since drainage could have different environmental controls (e.g. water availability, light intensity, etc.) and conclusions drawn for one site may well not hold for areas of another age, making generalization about the carbon cycle in the arctic challenging. To quantify differences in CO2 fluxes in vegetated drained lake age across the landscape, we measured CO2 fluxes at 14 sites that included drained lakes of three different age classes (young 0-50 years, medium 50-300 years and old 300-2000 years. In general young age lakes appeared to be the most productive ones. They showed the largest CO2 sink during the day and the highest CO2 emission at night. The medium age lakes were the driest ones, and as a consequence have the lowest ecosystem respiration, and showed medium net ecosystem uptake. The old basins showed sometimes similar or even higher productivity than the young age drained lakes. The old drained lakes have the most advanced degree of polygonization and the local mineralization occurring in the ponds leads to higher nutrients availability and to the presence of Arctophyla spp., the most productive and nutrient limited plant species. In general the age is a good predictor of the productivity of the basins, but other factors, like soil moisture and degrees of polygonization appeared to be very important as well
B13A-0422
Present and Future Surface Water
This poster presents a technical approach that is being developed to evaluate change in size and distribution of northern lakes and wetlands spatially and temporally under a climate warming scenario. The landscape shifts expected for the future restrain estimates of carbon dioxide and methane flux to the atmosphere and shape considerations of these local and regional measurements in the global budget. A high-resolution temperature model, TopoClimate, references USGS determined topographic features and the National Weather Service weather forecast model, Global Forecast System, to represent synoptically and topographically driven processes at present. For future simulations, TopoClimate references GCM model ECHAM5/MPI-OM under balanced energy sources in an integrated world emissions scenario, A1B, and topography. ECHAM5/MPI-OM best reproduces the present key features of both Alaska and the Arctic observed synoptic climates. A numerical model for estimating the permafrost thermal composition, TTOP, is used to improve the resolution of permafrost extent in the Yukon River Basin. TTOP will reference the TopoClimate temperature map, as well as maps of soil moisture and thermal properties, surface n-factors derived from landcover type, and snow cover. The propagation of surface temperature through soil is numerically modeled by TTOP, using soil properties and microclimatic effects. TTOP has been applied to the Seward Peninsula in estimating past, present, and future permafrost distributions. A physically based, potentiometric surface algorithm will extract steepness and relative elevation from topography. Precipitation inputs are National Climate Data Center meteorological data, distributed by MicroMet and SnowModel, and from ECHAM5/MPI-OM under the A1B scenario for future. Derived hydraulic head will be used to determine local groundwater discharge and recharge areas. Additionally, we plan to reference satellite image classification of wetlands. Hydraulic gradient, analyzed in concert with permafrost distribution provides insight into surface water presence. The approach includes continual change of surface water presence evaluated through time.
B13A-0423
A new model of long-term, coupled dynamics of carbon and water in northern peatlands
We present a new model that simulates coupled carbon and water dynamics of northern peatlands at an annual time step over time scales of decades to millennia. The Holocene Peatland Model (HPM) simulates peatland carbon and water dynamics as the net consequence of several interacting processes: (1) above- and below-ground vegetation NPP and litter production for bryophytes, woody and herbaceous plants; (2) aerobic and anaerobic litter/peat decomposition down the peat profile; (3) the dependence of peat physical and hydraulic properties on peat composition and degree of humification; and (4) peatland annual water balance, water table depth, and unsaturated zone water content. In this initial analysis, a simulation of long- term peat accumulation is compared against peat core data from a northern peatland in North America. The sensitivity of peatland carbon and water dynamics to climate variability are explored.
B13A-0424
Evaluation of the Holocene Peat Model with Data from Boreal and Subarctic Peatlands of the James Bay Lowlands, Quebec, Canada
The Holocene Peat Model (HPM) is a dynamic model simulating the transient evolution of a peatland since its early stages. HPM takes into account the feedbacks between vegetation, peat properties, water table depth, and climate. The aim of this study is to evaluate the HPM by means of empirical data. Three distinct sampling sites were chosen within a large region including boreal and subarctic peatlands in the James Bay lowlands, northern Quebec, Canada. One fen and one bog were selected in the subarctic region and another bog in the boreal region. These sites have different geographical, climatological and ecological features (e.g. pH, nutrient availability, hydrology and species composition). Five cores from those three sites were dated using 210Pb and 14C. Loss on ignition and plant macrofossils analysis were performed for each core. First, we compare the simulation results of the HPM for the study sites with the information earned in the field and laboratory. In order to capture the causes for discrepancies between simulated and observed data, we then constrained the model in two ways: 1) The water balance of HPM was forced with water table fluctuations reconstructions, obtained from a transfer function of Testate amoebae. 2) The bulk density of HPM was forced with the bulk density data obtained from the cores. In both cases, the results highlight the effectiveness of the water balance and the bulk density routines of the HPM and also draw attention to other potential causes of inaccuracy in the model.
B13A-0425
Carbon transport in a subarctic catchment: arctic tundra, birch forest to valley bottom permafrost peatlands
The release of soil carbon to atmospheric carbon influences the Earth's climate. Approximately one third of peatlands are in permafrost areas and these may becomes a large source of carbon to the atmosphere with climate change. The thawing of permafrost and the hydrological changes in these sensitive environments may lead to a positive feedback. Several studies have dealt with the carbon atmosphere – ecosystem exchanges but much less work has been done on the lateral movement of dissolved carbon (DOC) in subarctic catchments dominated by peatlands. In Abisko, Sweden, we are investigating the topographic controls on hydrology in individual peatlands and at the catchment scale to gain a better understanding of the system. In particular we have studied the relation of flow accumulation and the mass transport of DOC. We are using a nested catchment approach that includes flows from tundra, birch forest, valley bottom peatlands and permafrost peat plateaus. The DOC data covers two years. The elevation data used in the study is collected with a LIDAR system. A dense high resolution pulse pattern with an error that is less than 5 cm is the input for the DEM. A form based flow accumulation algorithm was used together with the ln(a/tan b) potential wetness index. We find that the carbon transport is related to topography but also to the presence of permafrost.
B13A-0426
The role of constructed wetlands in sequestering eroded carbon in an agricultural landscape.
The fate of carbon lost by erosion is not well understood in agricultural settings. Recent models suggest that wetlands and other small water bodies may serve as important long-term sinks of eroded carbon. An estimated 2.6 million small (less than 104 m2), artificial water bodies (e.g. water catchment reservoirs, farm ponds, and wetlands) are scattered across the United States. These areas are estimated to receive one third of all eroded materials. Consequently, carbon accumulation in small subaqueous environments may have a significant effect on carbon storage. The conversion of marginal farmland to constructed and restored wetlands is a growing land use in California's Central Valley. Many of these systems receive agricultural runoff as their main water supply, which is rich in suspended sediment and nutrients. This study examined the potential for carbon sequestration in an eight-year-old seasonally saturated constructed wetland that receives tailwater from over 4,000 acres of farmland. The temporal and spatial dynamics of carbon and sediment accumulation were evaluated by employing a spatially explicit sampling design to measure net sedimentation and net above-ground biomass in 2004 and 2005. Additionally, in 2006, sediment cores were collected to the antecedent (time zero) soil layer, which ranged between 2 and 50 cm below the surface. The spatial variability of carbon and sediment accumulation was modeled with geostatistics. Average sediment accumulation rate, nearly doubled from 2004 to 2005, with rates of 5.8 kg m-2 y-1 (range: 0-80 kg m-2 y-1) in 2004 and 11.9 kg m-2 y-1 (range: 0-93 kg m2 y-1) in 2005. Average carbon accumulation rate did not change between years, with rates of 0.290 kg m-2 y-1 in 2004 and 0.294 kg m-2 y-1 in 2005, indicating a change in carbon source between years. Average total carbon content of soils in the contributing watershed is 8 g kg-1, whereas average carbon content of inflowing sediment was 14 g kg-1, resulting in an enrichment ratio of 1.75. Average carbon content in the top 2.5 cm of the wetland surface was 24 g kg-1 and decreased to 10 g kg-1 in sediment directly overlaying the antecedent layer. These results indicate that inflowing sediment receives further enrichment of carbon from endogenous sources, however, due to fluctuating cycles of flooding and drying, the long-term storage of carbon (~10 g kg-1) is maintained at a level higher than the contributing watershed (8 g kg-1) but below that of inflowing sediment (14 g kg- 1). This study shows that wetlands can play a significant role in carbon storage through processes such as in-situ enrichment and protection of carbon deposited by erosion.
B13A-0427
Expanding Sloping bog Systems Under a Continental Climate in South-Central Alaska: Possible Causes and Carbon-Cycle Implications
Boreal peatlands play a key role in the global carbon (C) cycle, as they have accumulated up to about a third of the global soil carbon during the Holocene. Whilst numerous peat-based paleoecological records have been published on boreal Canadian and Siberian peatlands, there are few detailed C accumulation history studies on Alaskan peatlands. Here we report our field observations and preliminary data along several transects from a sloping (blanket) bog complex in the Susitna Valley of south-central Alaska and discuss possible causes for their occurrence in this continental setting and for their recent expansion. We observed, in the field and from satellite images, the presence of extensive peatland complexes in the Susitna River watershed, including both minerotrophic and ombrotrophic peatlands. Six peat cores were collected from a vast (> 1 km2) sloping bog complex (with pH from 3.92 to 4.46), located at ~ 450 m altitude and ~ 120 km NW of Talkeetna. These cores show a clayey, thick (15-30 cm thick) tephra layer at ~ 60 cm below the peatland surface that is attributable to the Hayes volcano eruptions at 4.4-3.6 cal ka. Preliminary macrofossil analyses along these cores indicate a transition from eutrophic conditions before the tephra, to mesotrophic/oligotrophic conditions after the tephra. We suggest that the tephra layer may have modified hydrology and chemistry of the site and facilitated the development of a nutrient-poor system. Active paludification (i.e., lateral expansion) was also observed at the margins of these peatland complexes, suggesting ideal hydroclimatic conditions for peat accumulation at the present. Given that the modern climatic envelope of peatland distribution indicates that ombrotrophic mires (e.g., raised and blanket bogs) usually occur under higher mean annual precipitation than what is measured in the study region, we suggest that the hydroclimatic regime of these peatlands is determined by a complex interaction among local substrate (fine-grained tephra deposits), topography (south-facing Alaska Range), and atmospheric moisture conditions (cloud cover, fog, and relative humidity). Actively melting glaciers in the watershed over the last centuries might have promoted the ongoing paludification by generating favorable local hydroclimatic conditions. This case highlights the need for identifying local and regional hydroclimatic drivers of C and water cycling in peatlands, with an emphasis on the potential importance of local substrate and topography in modifying regional moisture conditions and trophic status of peatlands. Our observations and data also have implications for understanding past peat accumulation and for projecting future dynamics of northern peatlands.
B13A-0428
Exploring the impacts of warming on arctic soils: increasing shrub dominance and changing below ground processes
Over the past several decades a 'greening' of the Arctic has been observed, characterized by increases in the abundance and growth rates of deciduous shrubs and their encroachment into sedge-dominated tussock tundra. If these changes result in an increase in biomass production and plant-influenced microbial decomposition processes, the system's carbon (C) storage capacity may increase. However, a warming-driven shift in community structure towards increasing shrub dominance may increase the system's potential for C storage only if microbial respiration remains constrained by nutrient availability, a limitation that may be exacerbated by increasing plant competition for nutrients. To test whether microbial respiration rates and microbial N limitation differ with shrub expansion, we collected soils from the Toolik LTER long-term tundra greenhouse warming experiment. In these plots, there has been a shift towards shrub dominance over 19 years of warming. Our results suggest that warming-driven shrub expansion tends to increase microbial respiration rates across the soil profile. All soils also showed a significant increase in respiration in response to N addition, although the response strength differed between greenhouse and control soils. This suggests that while warming increases C storage in live plants, it may lead to altered decomposition of existing soil organic matter through changes in N availability.
B13A-0429
Effects of plant species, organic matter quality, and microbial activity on peatland ecosystem function and resiliance to climate change
Uncertainties in peatland responses to climate change are due to our poor understanding of interactions between soil climate, plant community structure, organic matter quality, and microbial activity that operate on timeframes ranging from seconds to decades or longer. These uncertainties restrict our understanding of C cycling in peatlands under current and future climate regimes, and inhibit our ability to accurately predict and manage future C cycling patterns and magnitudes in peat accumulating systems. Therefore, our research addresses several fundamental questions regarding the interactive effects of warming and water manipulations on peatland carbon cycling and how they are modified by peat chemistry and vegetation changes. We are monitoring seven sites in Seney National Wildlife Refuge (SNWR), in the Upper Peninsula of Michigan, that represent a gradient of long-term water manipulations (~50 years of drainage), plus another peatland where we are conducting a short-term warming experiment to quantify how short-term warming influence peatland ecosystems, and if different types of experimental warming (warming lamps vs. open top chambers) produce different results. In SNWR we have installed two eddy flux towers, a series of micromet stations, collected soil for peat quality analysis, collected chamber based ecosystem carbon fluxes (GEP, ER and NEE) every 2 weeks, and are monitoring plant production, decomposition, water table levels, soil temperatures and climate data. We also established 18 plots at our other site and divided them into 3 treatments comprised of heating lamps, open top chambers, and control plots. Initial results indicate that carbon fluxes are influenced by temperature and hydrologic conditions. Increased temperatures generally increased GEP, ER and had mixed effects on NEE. Lowered water levels tended to increased GEP, ER and lowered NEE. There were also synergistic effects of temperature, water levels, plant community changes and peat quality on carbon cycling.
B13A-0430
Characterising Wetland Properties in Relation to the Abundance of an Invasive Species
Purple loosestrife (Lythrum salicaria) is a colorful but aggressive invasive species found at the Goodyear Swamp Sanctuary in Upstate New York. Flowering from June to September allows a large number of seeds to spread quickly throughout the growing season. This invasive species can alter can alter a wetland's functional properties by impacting the hydrology and soil properties. These modified properties are of concern to wetland scientists and wetland managers as the characterisation of wetland condition becomes more important. Control or eradication of purple loosestrife within the Goodyear Swamp has become regionally important and is carried out by a U.S. Department of Agriculture approved leaf-eating beetle Galerucella calmariensis. A study to investigate the environmental conditions in which purple loosestrife has propagated and changed the native flora of Goodyear Swamp was developed. The aim was to characterize the soil physiochemical properties and hydrological conditions under which the species occurs. These data are relevant to be able to highlight the wetland conditions under which purple loosestrife might invade and to be able to compare treated and untreated wetlands. We highlight key differences in wetland functional properties caused by the invasion of this species.
B13A-0431
Sphagnum's coup de grace: Carbon flow to acetate in northern peatlands
Isotopic estimates of the microbial pathway of methane formation in acidic northern peatlands conclude that methane is derived from the pathway of CO2 reduction, whereas, microbial incubation and genomic studies have identified an important role played by acetoclastic methanogens in similar acidic systems. We believe our first ever intramolecular acetate isotopic analyses from an acidic wetland in central Pennsylvania resolve the apparent conflicting pathway estimates by indicating that the isotopic and microbial incubation studies are consistent with each other and with a pathway of methane formation through acetate from an isotopically depleted autotrophic acetate source. Intramolecular acetate isotopic measurements allow us to estimate that as much as 1/3 of the acetate in acidic wetlands is derived from autotrophy. Given a simple case of glucose fermentation to acetate, carbon dioxide, and hydrogen, our acetate production pathway estimate requires that nearly all of the carbon products from fermentation must flow through the acetate pool. Our work confirms the prior hypothesis and prior observations that acetate is an important metabolic end product in northern acidic wetlands. Further, we hypothesize an alternative fate of acetate in peat porewaters that alludes to an ecological role of autotorophic acetogens and acetate oxidizers in creating the impermeable humified peat catotelm unique to sphagnum dominated systems. The diversion of carbon flow to from methane to acetate increases the organic acid production and we hypothesize that the net transport of dissolved fulvic acids into the catotelm allows coupled acetate oxidation and fulvic acid reduction. This process of acetate consumption would create a net addition of hydrophobic, amorphous, and therefore more impermeable organic carbon. We conclude that an ecological strategy of the sphagnum mosses may not simply be to decrease the pH of the environment to slow metabolism, but rather to force the microbial community in the catotelm toward the oxidation of acetate and the reduction of peat humus, thereby aiding production of the characteristic impermeable organic seal. The sensitivity of sphagnum ecosystems to external sources of alkalinity may prove to be an important control on the ancient flux of methane from peatlands and may be an important direction of continued research.
B13A-0432
Microorganisms Trapped Within Permafrost Ice In The Fox Permafrost Tunnel, Alaska
Several different types of massive ice are common in permafrost. Ice wedges are easily recognized by their shape and foliated structure. They grow syngenetically or epigenetically as a result of repeated cycles of frost cracking followed by the infiltration of snow, melt water, soil or other material into the open frost cracks. Material incorporated into ice wedges becomes frozen and preserved. Pool ice, another massive ice type, is formed by the freezing of water resting on top of frozen thermokarst sediment or melting wedges and is not foliated. The Fox Permafrost Tunnel in Fairbanks was excavated within the discontinuous permafrost zone of central Alaska and it contains permafrost, ice wedges, and pool ice preserved at roughly -3°C. We collected samples from five ice wedges and three pool ice structures in the Fox Permafrost Tunnel. If the microorganisms were incorporated into the ice during its formation, a community analysis of the microorganisms could elucidate the environment in which the ice was formed. Organic material from sediments in the tunnel was radiocarbon-dated between 14,000 and 30,000 years BP. However, it is still not clear when the ice wedges were formed or subsequently deformed because they are only partially exposed and their upper surfaces are above the tunnel walls. The objectives of our study were to determine the biogeochemical conditions during massive ice formation and to analyze the microbial community within the ices by incubation-based and DNA-based analyses. The geochemical profile and the PCR-DGGE band patterns of bacteria among five ice wedge and 3 portions of pool ice samples were markedly different. The DGGE band patterns of fungi were simple with a few bands of fungi or yeast. The dominant bands of ice wedge and pool ice samples were affiliated with the genus Geomyces and Doratomyces, respectively. Phylogenetic analysis using rRNA gene ITS regions indicated isolates of Geomyces spp. from different ice wedges were affiliated with different clusters. The enumeration of fungal colonies among the ice wedge and pool ice samples were also different. These results demonstrate that different massive ice structures had different microbial and geochemical environments or backgrounds when they were formed.
B13A-0433
A Novel Field Apparatus for Conducting Linked Geochemical-Microbiological Experiments in Shallow Sediments
Collecting in-situ experimental data for microbially mediated geochemical reactions is complex because it is difficult to assess the impact of the heterogeneity of natural systems. Specifically it is often difficult to constrain the degree of interaction between the pore water collected for geochemical analysis and a sampled microbial population. The newly developed apparatus, called a Native Organism Geochemical Experimentation Enclosure (NOGEE), provides the means to measure changes in well defined geochemical solutions that have been in direct contact with a known in-situ microbial population. The sampling apparatus is similar to a drive-point well. A short screened chamber (~60 ml) at the tip houses a polycarbonate sponge, which serves as a substrate for colonization by native microorganisms when it is open to the surrounding sediment. Following a colonization period dependent on season and temperature, the sponge chamber is closed to the surrounding environment by lowering an inner pipe and amended test solutions are introduced from the surface via tubing. An advantage to this method over laboratory microcosms is that the in-situ setting provides a natural, intrinsic control over environmental variables and minimizes disturbance to the system. To date, NOGEE's have been used to evaluate kinetic controls on sulfate reduction. Experimental results showed changing rates of sulfate reduction coincident with changes in microbial population and demonstrate the utility of using NOGEEs to quantify linkages between geochemistry and microbiology in complex natural environments.
B13A-0434
Reticulate Structures Reveal the Significance of Cell Motility in the Morphogenesis of Complex Microbial Structures in Pavilion Lake, British Columbia
Microbial communities are architects of incredibly complex and diverse morphological structures. Each morphology is a snapshot that reflects the complex interactions within the microbial community and between the community and its environment. Characterizing morphology as an emergent property of microbial communities is thus relevant to understanding the evolution of multicellularity and complexity in developmental systems, to the identification of biosignatures, and to furthering our understanding of modern and ancient microbial ecology. Recently discovered cyanobacterial mats in Pavilion Lake, British Columbia construct unusual complex architecture on the scale of decimeters that incorporates significant void space. Fundamental mesoscale morphological elements include terraces, arches, bridges, depressions, domes, and pillars. The mats themselves also exhibit several microscale morphologies, with reticulate structures being the dominant example. The reticulate structures exhibit a diverse spectrum of morphologies with endmembers characterized by either angular or curvilinear ridges. In laboratory studies, aggregation into reticulate structures occurs as a result of the random gliding and colliding among motile cyanobacterial filaments. Likewise, when Pavilion reticulate mats were sampled and brought to the surface, cyanobacteria invariably migrated out of the mat onto surrounding surfaces. Filaments were observed to move rapidly in clumps, preferentially following paths of previous filaments. The migrating filaments organized into new angular and ropey reticulate biofilms within hours of sampling, demonstrating that cell motility is responsible for the reticulate patterns. Because the morphogenesis of reticulate structures can be linked to motility behaviors of filamentous cyanobacteria, the Willow Point mats provide a unique natural laboratory in which to elucidate the connections between a specific microbial behavior and the construction of complex microbial community morphology. To this end, we identified and characterized fundamental building blocks of the mesoscale morphologies, including bridges, anchors, and curved edges. These morphological building blocks were compared with the suite of motility behaviors and patterns observed in reticulate morphogenesis. Results of this comparison suggest that cyanobacterial motility plays a significant and often dominant role in the morphogenesis of the entire suite of morphologies observed in the microbial mats of Pavilion Lake.
B13A-0435
Assessment of Surface Water Depth using Hyperspectral Reflectance: Case study from a Large-scale Hydrological Manipulation Experiment in the Arctic
As part of an NSF supported Biocomplexity project at Barrow, AK, this study focused on estimating surface water depth using hyperspectral reflectance data. Water tables have been manipulated (drained, flooded, control) in a vegetated Arctic thaw lake basin to investigate the effect of soil moisture on land-atmosphere carbon balance. Throughout the 2008 growing season, hyperspectral reflectance data were collected in the visible and near IR using a robotic tram system that operated along a 300m tramline situated in each treatment. Water table depths were also collected from water wells placed along transects. Our analysis shows a strong correlation between the 970nm reflectance band and the natural log of the water table depth (R2=0.72) for the flooded section, while this was not true for the drained (R2=0.36) or control (R2=0.38) sections, which had water tables at or below the ground surface. We discuss these results in light of using 970nm reflectance for the assessment of surface water depth.
B13A-0436
California's Future Carbon Flux
The diversity of the climate and vegetation systems in the state of California provides a unique opportunity to
study carton dioxide exchange between the terrestrial biosphere and the atmosphere. In order to accurately
calculate the carbon flux, this study couples the sophisticated analytical surface layer model ACASA
(Advance Canopy-Atmosphere-Soil Algorithm, developed in the University of California, Davis) with the
newest version of mesoscale model WRF (the Weather Research & Forecasting Model, developed by NCAR
and several other agencies). As a multilayer, steady state model, ACASA incorporates higher-order
representations of vertical temperature variations, CO2 concentration, radiation, wind speed, turbulent
statistics, and plant physiology. The WRF-ACASA coupling is designed to identify how multiple environmental
factors, in particularly climate variability, population density, and vegetation distribution, impact on future
carbon cycle prediction across a wide geographical range such as in California.
http://comet.ucdavis.edu/wiki/index.php/Main_Page
B13A-0437
Changes in Pedogenic Carbonate Accumulation Under Altered Atmospheric CO2 in a Mesic Calcareous Grassland
Numerous studies have examined the effect of elevated atmospheric CO2 on organic carbon (C) cycling, but less is known about the impacts of changing CO2 on inorganic C processes. Pedogenic carbonates are derived from C released during the decomposition of soil organic matter. Thus, increases in soil respiration resulting from the effects of increasing atmospheric CO2 on ecosystem productivity could impact the sequestration of C in inorganic C pools via pedogenic processes. We examined potential changes in pedogenic carbonate accumulation at different atmospheric CO2 concentrations in an intact ecosystem of mesic calcareous grassland. Plots were exposed to a CO2 gradient ranging from pre- Industrial (200 μL L-1 to mid-21st century concentrations (550 μL L-1) during the growing seasons from 1997 to 2000. Pre- and post-CO2-treated mineral soils were sampled at four depth increments from the soil surface to 53 cm depth in plots exposed to high, ambient, and low CO2 (550, 360, and 200 μL L-1, respectively). Pedogenic carbonate accumulations were quantified with an isotopic mixing model using δ13C values of bulk, pedogenic, and parent carbonate in soils. Isotopic values of the pedogenic carbonate end-member were estimated using the diffusion model of Cerling (1984), and the parent carbonate value was measured from a weakly developed modern floodplain soil at a nearby site (Nordt et al. 1998). For all post-CO2 treatment soils, the amount of pedogenic carbonates was greatest in 8-37 cm subsoil, and was positively correlated to soil organic matter C (SOM-C). Compared to pre-CO2 treatment soils, SOM-C concentrations did not change in surface soils (0-8 cm) exposed to low and ambient CO2, but increased 31% to 44% in subsurface soils (8-53 cm). Soils exposed to high CO2 increased in SOM-C in both surface and surface soils by 40% to 280% of pre- treatment soils, respectively. Further, the δ13C of bulk carbonate decreased as SOM-C increased across all soils, reflecting the isotopic signature of fossil CO2 used to augment atmospheric CO2 concentrations over four growing seasons. Our results indicate that increases in soil organic C pools are affecting the formation of pedogenic carbonates in this calcareous grassland, with potential short- and long-term effects of altered atmospheric CO2 on soil C sequestration.