B43F-01
The prognosis for carbon storage in northern peatlands – evidence from peatlands in the UK
It is commonly recognised that one of the most important sources of DOC are organic-rich soils and particularly peat soils. Increasing concentrations of DOC from peat-covered catchments have been widely reported across the globe for a range of sub-Arctic settings. However, it is difficult to understand the consequence of these trends for carbon storage within peats – do such increases indicate that carbon storage in theses ecosystems is decreasing? This study brings together both field and modelling studies to understand the future of this vital carbon store: i) A complete carbon budget of a pristince peat catchment overa 13 year period shows that on average it is a net carbon store of 60 Mg C/km2/yr, but that in some years this net sink of carbon could be close to neutral. ii) Complete carbon budgets of managed peat catchments shows that can be net sources of carbon of upto 100 Mg C/km2/yr iii) Modelling of the pristine peat catchment in to the future given most probable climate scenarios shows the catchment progressing to being a net source of carbon by mid-century. This evidence suggests the UK peatlands are progressing from a net sink to a net source and indeed many of the marginal areas may already be net sources. However, the managed nature of these ecosystems does provide an opportunity to mitigate the effects of climate change.
B43F-02
Hydrologic Variability and its Influence on Peatland Dynamics
The present and future state of peatland carbon exchange depends on the climate sensitivity of peat accumulation and peat depletion processes. The climate sensitivity of these processes has been addressed by a range of studies that in general have focused on short time spans relative to peat processes. Long-term peat dynamic modeling studies suggest that peatlands can exist in bi-stable states; one having thin peat and deep water tables while the other has thick peat and shallow water tables. The climate sensitivity of peat accumulation and depletion inherent in bi-stable peatlands is not well understood or characterized. The bi-stability of peatland implies that gradual climate change and climate fluctuations may induce shifts between the two states. Such shifts may have long lasting impact on the peatland carbon exchange. The existence of peatland bi-stability in nature is indicated by the co-existence of fens and bogs across the northern hemisphere, and by the co-existence peatland hummocks and hollows. This presentation explores how precipitation variability affects peatland thickness, and peatland accumulation and depletion processes inherent in bi-stable peatlands. The results are based on a coupled peat accumulation/depletion hydrology model where precipitation/water availability is a stochastic forcing variable. While, the model is calibrated to represent the West Siberian Lowlands (WSL), our findings are applicable elsewhere as previous work shows that peatland bi-stability is possible across a wide range of climates. Model results for current climate conditions show that peatlands at steady state cycle through extended periods of peat accumulation and depletion. Therefore, observational studies limited to a few years are insufficient to detect fundamental changes in peatland carbon exchange due to climate change. For a drier and more variable future climate, results suggest that bi-stability (thin and thick peat states) will transition to a single steady state towards a new, more homogenous state with intermediate peat thickness. The transition may have profound and long lasting impact on the peatland carbon exchange, with some locations sequesting carbon while other areas losing carbon.
B43F-03
Seasonal Aspects of the Biogeochemistry of the Chena River near Fairbanks, Alaska
The Alaskan Interior is currently undergoing climate warming and this has caused permafrost degradation that will likely affect river biogeochemistry. The Chena River watershed is underlain by discontinuous permafrost and is thus a suitable location for monitoring how permafrost degradation may affect riverine biogeochemistry. We collected surface water from the Chena River near Fairbanks, Alaska biweekly from March 2005 to February 2006. Our goal was to measure biogeochemical parameters during varied flow regimes to determine how seasonal and meteorological conditions affected the watershed. We measured major element concentrations, oxygen and hydrogen stable isotopes, strontium isotopes and carbon and nitrogen organic and inorganic species. Oxygen isotope values suggest a steady replacement of the spring snow melt signature with that of old water and summer precipitation over the course of the summer. Major element concentrations (Na, K, Ca, Mg, Sr, Cl, SO42-, HCO3-) decrease in river waters as discharge increases suggesting a simple dilution of these ions in river waters. 87Sr/86Sr values become more radiogenic with increasing discharge during both spring melt and summer rain events further implying that during high flow the waters include a different mineral weathering signature than during base flow. Over 50% of the carbon we measured occurs as dissolved inorganic carbon while ~40% is dissolved organic carbon (DOC) and <10% is particulate organic carbon. A strong linear relationship between DOC and discharge indicates hydrological control of river DOC storage and export. Elevated DOC concentrations during spring runoff implies an accumulating soil leaching effect and/or a more efficient leaching of DOC from surface soils and overlying plant litter during spring melt. Our results suggest the biogeochemical signature of the watershed changes markedly during the year but flows can be categorized into six unique regimes. The complicated seasonal controls on river water biogeochemistry imply that monitoring campaigns in northern watersheds must apply long term sampling programs that bracket major precipitation and seasonal events before biogeochemical sources can be adequately measured or modeled.
B43F-04
Organic Matter Export from North Slope Rivers of Alaska: Variations in Stable C and N Isotope Ratios over the Annual Hydrograph and Implications for Tracking Land-Derived Organic Matter in Coastal Waters
Wide variations in dissolved and particulate organic matter concentrations have been identified in arctic rivers over the annual hydrograph, leading to revised estimates of organic matter export to coastal waters. The fate of this organic matter is of fundamental interest to researchers studying biogeochemical cycling in the Arctic, and also of broader interest as a component of the global carbon budget. Normalized carbon export (i.e. by watershed area) from arctic rivers is disproportionately large compared to rivers globally, and carbon export from arctic rivers may be particularly susceptible to change under warmer conditions. This presentation will focus on stable C and N isotope ratios of organic matter exported from the Kuparuk, Sagavanirktok, and Colville rivers during 2006 and 2007. Major increases in the stable isotope ratios of dissolved organic carbon (DOC) and particulate organic nitrogen (PON) were observed between ice break-up and late summer. At the same time, a major decrease in the stable isotope ratios of particulate organic carbon (POC) was observed. Monthly and annual discharge-weighted averages of the isotope values will be presented and the relevance of these values as end-members for organic matter tracking in coastal waters will be discussed.
B43F-05
The impact of changing glacial coverage on yields of freshwater and nutrients from coastal watersheds with in southeastern Alaska
Glaciers in southeastern Alaska are particularly sensitive to climate change because of their low elevation and proximity to the coast. Currently, glaciers in this region are experiencing high rates of ice loss resulting in rapid thinning and retreat. We are examining how changing glacial coverage is altering fluxes of freshwater and nutrients from coastal watersheds in southeastern Alaska. Our study includes three adjacent watersheds that range in area from 37 km2 to 230 km2 and span a range of watershed glacier coverage from 0% to 55%. Physical and hydrochemical parameters were sampled weekly to bi-monthly for the period May 2006-April 2007 in the three watersheds. Physical measurements included temperature, suspended sediment and conductivity; and hydrochemical parameters included total and inorganic nitrogen, dissolved organic carbon, sulfate, and orthophosphate. During the glacier melt season, glacial coverage within a watershed exerted a strong influence on physiochemical properties. Streamwater temperature and conductivity, as well as nutrient concentrations, were negatively correlated with glacier coverage, while suspended sediment loads were positively correlated with glacial coverage. Changing glacial coverage had a strong impact on watershed yields of carbon, nitrogen, and phosphorus. Watershed yields of dissolved organic carbon (DOC) ranged from 4246 to 7646 kg km-2 yr- 1 and were strongly negatively correlated with percent glacier coverage. Watershed yields of dissolved inorganic nitrogen ranged from 180 to 498 kg km-2 yr-1 and were highest in the watershed with intermediate glacier coverage that has a high proportion of transitional nitrogen fixing plant species. Watershed yields of orthophosphate ranged from 19 to 46 kg km-2 yr-1 and were strongly positively correlated with glacier coverage. Our findings suggest that the magnitude and timing of freshwater and nutrient fluxes from coastal watersheds to receiving marine ecosystems will be altered dramatically as glaciers in southeastern Alaska continue to decrease in volume. In addition, we hypothesize that changes in nutrient fluxes are mediated both by two basic factors: 1) changes in landcover associated with glacial recession and 2) changes in biological activity in riverine systems resulting from decreased inputs of glacial meltwater as glaciers continue to recede.
B43F-06
Increased Permafrost Thaw and Groundwater Contribution to Streamflow Affect DOM, DIC and DIN Export and Chemistry in the Yukon River Basin
Climate warming in arctic and subarctic watersheds is affecting hydrology and carbon and nitrogen biogeochemistry in multiple ways and at multiple scales. Permafrost thaw, thermokarst formation, wetland drying, melting of alpine glaciers and perennial snow fields, and vegetation change all have direct impacts on water and carbon budgets, especially at the local scale. We conducted a basin wide assessment of long-term change in the amount and timing of streamflow throughout the Yukon River basin of Northwest Canada and Alaska and related those hydrologic changes to recent within-basin measurements of carbon and nitrogen export and chemistry. Our analysis indicates that ongoing permafrost thaw and subsequent increased infiltration result in increased groundwater contribution to streamflow, which in turn is shifting the amount and chemistry of dissolved inorganic and organic carbon and nitrogen exported to the Bering Sea. Groundwater currently comprises about one fourth of Yukon River water and contributes 5-10 percent of the dissolved organic carbon and nitrogen (DOM) and 35-45 percent of the dissolved inorganic carbon (DIC) and nitrogen (DIN) loads. A general increasing trend in groundwater contribution to streamflow of 0.7-0.9 percent per yr, with no pervasive change in annual water discharge, will result in decreased DOM concentration and export and increased DIC and DIN concentration and export, consistent with recent measured changes in DOM and DIC export during the thaw season. Preliminary results also suggest that the increasing groundwater component has a greater hydrophilic fraction and bioavailability than surface-runoff derived riverine DOM. http://ak.water.usgs.gov/yukon/
B43F-07
DOC Transport to the Arctic Ocean: Improving Basin-Wide Annual Flux Estimates
River fluxes connecting land to ocean integrate processes and changes occurring on land and impact the chemistry, physics, and biology of the receiving marine systems. One of the more important constituents in river water is dissolved organic carbon, particularly in the Arctic where continued warming and permafrost thaw is expected to have substantial implications for DOC fluxes in coming decades. Accurate assessment of current DOC flux to the Arctic Ocean is essential for detecting widespread changes in the future, and several recent basin-wide flux estimates have been published. In spite of this, it is argued that considerable uncertainty remains, primarily because of inadequate assessment of DOC fluxes during the critical spring breakup period (which can be extremely difficult to adequately sample) and limited sampling of the relatively "small" rivers (less than 100 km3/y discharge) which account for about half of the riverine freshwater inputs to the Arctic Ocean. Here we report new annual DOC flux estimates for Siberia's Lena and Ob' rivers (with annual discharges of about 530 and 400 km3, respectively) which incorporate data from high frequency sampling from the May-June 2007 high flow period as well as new DOC flux estimates for the three largest rivers on Alaska's North Slope. We then consider how these new data impact total estimated annual DOC flux to the Arctic Ocean and discuss next steps for further constraining basin-wide DOC flux estimates.
B43F-08
Towards a Model of Dissolved and Colloidal Fe and Mn in the Yukon River Basin
Fe and Mn are key metals in natural waters because their redox cycling tends to involve the cycling of organic matter and because the oxides of these elements are important carriers of other trace elements. Process- oriented and site-specific studies have resulted in much progress in understanding the behavior of these two elements. However, we are not yet to the point where one can use the hydrological, landscape and chemical characteristics of a river system to make a reasonable prediction of the concentrations of Fe and Mn. Using results from an ongoing survey of trace elements in the Yukon River Basin, simple models have been developed to explain dissolved and colloidal Fe and Mn concentrations throughout this system. To a first order, Mn (which is mainly found in the dissolved phase) is largely controlled by the availability of reducing sources. Colloidal Fe is generally correlated with dissolved Mn, a result consistent with the more rapid precipitation kinetics of Fe than Mn. The behavior of dissolved Fe can be generally reproduced by a simple model balancing organic complexation versus FeOOH solubility control, both of which are pH-dependent. These models allow predictions of how changing landscapes (due, for example, to climate change) could affect the concentrations of Fe and Mn.