Watershed and Aquatic Ecosystem Evolution During the Late-Glacial and Early-Holocene Inferred From High-Resolution Diatom and Geochemical Records in the Yellowstone Region

High-resolution diatom records spanning the late-glacial and early-Holocene were developed from three lakes in the Yellowstone region to infer the lake history and to evaluate the relative importance of climatic versus non-climatic factors on the aquatic ecosystem evolution. Synchronous shifts in diatom community structure occurred in all lakes, which are located in regions of varied surficial geology and precipitation seasonality, in the intervals of 13.9-13.8, 13.2-13.1, 11.3-11.0 and 8.8-8.7 cal ka. The synchronous diatom community structure shifts suggest that large-scale climatic change is the primary driver of the aquatic ecosystem evolution in this region, whereas the influence of non-climatic factors is secondary. Four lake sediment cores collected from the Yellowstone region were examined with high-resolution geochemical analysis to investigate trends in watershed and lake evolution during the late-glacial and early-Holocene. During the early stage of lake development, clastic input was high, and lake productivity was low, and they decreased and increased, respectively, as vegetation gradually developed in the catchment. The decrease of clastic input was asynchronous among regional lakes, and occurred time transgressively from south to north. The long-term pattern of change in calcite precipitation was controlled primarily by lake-level change in small and shallow lakes and by lake productivity in large and deep lakes. The late-glacial and early-Holocene history of terrestrial and limnological development also was reconstructed from a high-resolution record of pollen, charcoal, diatom, geochemical, and lithologic data from Dailey Lake in southwestern Montana. Following deglaciation, the surrounding landscape was unstable and sparsely vegetated. As summer insolation increased, open parkland developed, and diatoms established in the lake at ~13.4 cal ka. Closed subalpine forest developed at ~12.2 cal ka and then was replaced by open forest at~10.2 cal ka. Warm dry summers prevailed after ~11.0 cal ka, as indicated by increasingly open forest and increased benthic diatoms, which differs from some nearly records that are located at higher elevation. Advisor: Sherilyn C. Frit