Erosion and sedimentation history of Emrick Lake, south-central Wisconsin, in response to Holocene environmental change

Lake sediments from Emrick Lake document Holocene environmental change near south-central Wisconsin's prairie-forest ecotone. The objective of the present dissertation is to evaluate the sedimentological responses to changes in climate, vegetation, and the onset of Euro-American settlement. A 9-m sediment core (basal age, 11,600 ± 320 14C-yr, uncalibrated), was extracted with a piston-corer and sub-sampled at 1-cm intervals. Magnetic analyses are used as proxies to estimate variations of erosion, climate, and lake productivity. Fossil pollen was analyzed at 10-cm intervals to reconstruct Holocene and Late-Glacial vegetation history and to assess local climate variations. Fossil pollen assemblages were compared to a modern calibration dataset to reconstruct climate and vegetation conditions. Loss-on-ignition measurements are used to estimate variations in organic carbon and carbonate content and as proxy indicators of local erosion and climate. Six AMS radiocarbon ages provided a robust age model and good temporal resolution for the interpretation of sedimentation rates. Results from this study show that hydro-geomorphic responses in this lake basin have been sensitive to Holocene climate changes. Late-Glacial sediments are highly magnetic, suggesting that erosion was occurring on the uplands surrounding the lake basin. Erosion decreased during the Late-Glacial/early-Holocene transition as an open, less vegetated landscape gave way to a Picea -dominated community. The middle-Holocene shows increased percentages of non-arboreal pollen and a decline of total pollen influx, suggesting climate became warmer and drier than before. Dominant middle-Holocene woodland taxon is Quercus. Middle-Holocene sediments are weakly magnetic and dominated by small magnetic grains suggesting minimal terrestrial inputs to the lake. The associated magnetic signal is of biogenic origin. Late-Holocene sediments reveal increased levels of erosion, especially at the time of Euro-American settlement. Climate has been cooler and more humid in the late-Holocene compared to the middle-Holocene and vegetation stabilized into a mixed forest dominated by Quercus and Pinus. Results of this study confirm that development of the warmest and driest Holocene climates occurred later than along the ecotone in south-central Minnesota and is similar to the environmental history previously documented for northeast Iowa and elsewhere along the ecotone in southern Wisconsin.