Determining organic matter sources to CH4 production and bubbling from Alaskan lakes using stable isotopes and radiocarbon ages
Methane production in Siberian thaw lakes is estimated to be 3.8 Tg CH4 yr -1. When entered into global models, this estimate increases northern wetland CH4 emissions (<6-40 Tg CH4 yr -1) by 10-63% (Walter et al 2006). Methane release of this magnitude from Siberian and other northern lakes, such as those in Alaska, may be linked to the rich carbon resources available to sediment-dwelling methanogens.
The goal of the Arctic LTER is to predict the future ecological characteristics of Arctic Alaska based upon our knowledge of the controls of ecosystem structure and function as exerted by physical setting and geologic factors, climatic factors, biotic factors, and the changes in fluxes of water and materials from land to water.
Arctic warming has been linked to changes in carbon cycling in this region. Cold temperatures and anoxic conditions in the Arctic inhibit microbial activity, lowering decomposition rates. As a result mineralization rates are low, resulting in nitrogen-limited-system, further reducing biological activity. Evidence has shown that eliminating this constraint on nutrient availability results in a vegetation shift and loss of soil carbon; however, the mechanisms behind soil carbon loss are not understood.
Despite substantial changes in climate, sea-ice and glacier extent, and vegetation in much of the Arctic, the area near Toolik Lake, Alaska has experienced no significant trends of increasing temperature, altered precipitation, or increasing active-layer thaw depth. There has been, however, a near doubling of alkalinity in Toolik Lake since 1975 and increases in alkalinity in many lakes of all depths and sizes in the surrounding area. Lake monitoring indicates that in-lake processes such as sulfate or nitrate reduction cannot account for these alkalinity increases.
The MIRADA project was launched in the fall of 2007 to establish a Microbial Biodiversity Survey and Inventory across all 13 of the major aquatic (marine and freshwater) Long Term Ecological Research (LTER) sites in the NSF US LTER Program. The long-term objective of our study is to document and describe baseline diversity and relative abundance data for both common and rare members of microbial communities and to relate this diversity to the underlying physical and chemical environment.
Much is known about the spatial and temporal distribution of macro-organisms and their activity rates. However, little is known about the spatial variability of microbial communities in lakes. In this study, we examined the spatial variability in both bacterial community composition and activity rates in Toolik Lake, Alaska. Community composition was characterized using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified rDNA, and activity rates were measured by uptake rates of 14C-leucine.
The north slope of the Brooks Range has been glaciated several times since the Late Tertiary, resulting in a landscape with glacial sediments of various ages (modern to ca. 2 million years old) in close proximity. We used space as a substitute for time to investigate how terrain age affects biological attributes of streams in the Toolik Lake region of Arctic Alaska. Similar studies have been limited to successional sequences of streams on terrains deglaciated for up to only 200 years. We extended this model to streams draining terrains that have been deglaciated for up to ca.
Microbes are of critical importance but are a poorly understood component of arctic stream ecosystems. They are responsible for recycling organic matter and regenerating nutrients that are essential to the food webs of aquatic ecosystems. We tested the hypothesis that differences in highly contrasting parent lithologies (non-carbonate and ultramafic), stream habitat (sediments and rocks), and stream biogeochemistry influence the structure of bacterial biofilm communities in arctic streams.
First-year effects of tundra fire on benthic macroinvertebrate communities in streams on the North Slope, Alaska
Post-fire nutrient enrichment is known to affect benthic macroinvertebrate assemblages and stream food webs in forested regions, but little is known about the impact of tundra fires. The 2007 Anaktuvuk River fire (North Slope, Alaska), the largest recorded tundra fire (≈1,000 km2), provided an opportunity to study the first-year effects of a tundra fire on stream communities. We predicted that a tundra fire would increase inorganic nutrient inputs to streams, thereby increasing primary production and in turn, increasing abundance and biomass of benthic macroinvertebrates.
Twenty year record of vegetation change from long-term plots in Alaskan tundra
William A. Gould1, Joel A. Mercado Diaz1,2, Jess K. Zimmerman2
1. USDA Forest Service, International Institute of Tropical Forestry, Río Piedras PR,
2. University of Puerto Rico, Río Piedras, PR