HR: 0800h
AN: GC31A-0109    [Abstracts]
TI: Paleolimnological Investigations Across a Physiographic Gradient Record Recent Aquatic Ecosystem and Watershed Scale Changes: Southwest Alaska National Parks and Preserves
AU: * Cohn, B R
EM: cohnmail@gmail.com
AF: University of Alaska, Fairbanks, 245 O'Neil Bldg, Fairbanks, AK 99775, United States
AU: * Cohn, B R
EM: cohnmail@gmail.com
AF: University of Alaska, Anchorage, 3211 Providence Dr., Anchorage, AK 99508, United States
AU: Finney, B P
EM: finney@peakpeak.com
AF: University of Alaska, Fairbanks, 245 O'Neil Bldg, Fairbanks, AK 99775, United States
AU: Heiser, P A
EM: ffpah@uaf.edu
AF: University of Alaska, Anchorage, 3211 Providence Dr., Anchorage, AK 99508, United States
AB: Climate change effects on lake ecosystems have been shown to be pronounced at high latitudes. Oligotrophic lakes, specifically in northern areas, are very sensitive to environmental conditions and more susceptible to even small environmental changes. The changing climate sets the framework for abiotic and biotic processes within the aquatic and terrestrial systems of Lake Clark and Katmai National Parks and Preserves in Southwest Alaska, which are often regarded as some of the most pristine ecosystems remaining on Earth. Extensive paleoecological analyses have revealed rapid recent changes in lake ecology that often surpass Holocene natural variability and that are generally attributed to climate warming since the end of the Little Ice Age. However, the possibility that climate is only one dimension of these ecological shifts remains generally untested, especially given that current warming may not yet exceed maximum, naturally mediated, postglacial warmth. In this project we explored the use of carbon and nitrogen isotopes (13C and 15N), Total Phosphorus, and the presence and abundance of siliceous microfossils (biogenic silica) as proxy indicators of trophic state and aquatic productivity in Southwest Alaska lakes. Stable isotope data from a suite of 210Pb-dated sediment cores were compared stratigraphically with established proxies for historical trophic state (biogenic silica, sediment C:N ratio and total phosphorus), however, disturbances driven by climate, glacial retreat, volcanism and other natural perturbations contribute to, and perhaps at times overprint, aquatic driven processes in lake sediment cores. However, paleolimnological analyses and the suite of biogeochemical proxies (total organic matter, biogenic silica, organic N and C contents, and stable isotopic ratios) reveal a complex set of progressive changes that are expressed in the study lakes. Biogenic silica abundance began to change as early as the mid-19th century, but major inflections in the biogeochemical proxies occurred significantly later, being most pronounced after 1950. Among these changes are increases in sediment organic matter, depletions in sediment 15N, and decoupling of 13C and 15N signatures due to increasing CO2atm as reflected in 13C (e.g., Suess effect). It seems likely that climate warming, subsequently coupled to landscape change (vegetation expansion) and disturbance (deglaciation and volcanism), are synergistically driving these ecosystems towards states for which no prior natural analogs exist. However, the time lag between increases in air temperature and the response within the lake systems due to watershed changes is difficult to predict and remains unanswered. Despite direct climate influences from temperature and precipitation, the delay before terrestrial vegetation and soil cover are in balance with climate conditions could be several hundred years. The results imply that warming will have rapid effects on the productivity of high latitude oligotrophic lakes, due in part to warmer temperatures and longer ice-free periods. However, a larger although delayed stimulation of lake productivity following increased watershed production, soil maturity, and weathering in a warmer climate will potentially result in more substantial increases of essential nutrients that stimulate production of lake biota.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1630 Impacts of global change (1225)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting