Constructing a Long-Term Record of Hydrologic Variability in the Seneca Lake, NY Watershed

Understanding the occurrence of floods and their relationship with climate change is critical for the northeastern United States because not only has the annual precipitation increased over the last century, the frequency and magnitude of heavy precipitation events has also risen. Like precipitation records, historical stream-gage data can be used to improve estimations of flood frequency in watersheds. However, the duration of instrumental meteorological- and stream-monitoring records is often limited, especially in rural areas such as the New York Finger Lakes. Lake sediment provides an opportunity to extend flood records because high stream-discharge events move sediment from the watershed into the lake that accumulates on the lake bottom. The main objectives of this study were: 1) to establish a relationship between modern precipitation, stream flow, and the chemical composition of the sediment currently washed into Seneca Lake during storms and 2) use that relationship to infer changes in stream discharge in the past using shifts in the composition of the sediment that accumulated in Seneca Lake over the ~12,000 years. Extending the record of paleoflood events prior to instrumental record allows us to evaluate how the Finger Lakes were impacted by storms during warm (8-4 ka) versus cold (11-9 ka and 4 to 0 ka) climates. Seneca Lake, NY offers an ideal site to reconstruct past flood histories due to its deep and narrow confined basin, simple bathymetry, steep relief, and inflow dominated by tributaries. One short sediment box core (spanning the last century) and seven sediment piston cores (spanning the last 12,000 years) were collected from Seneca Lake and were analyzed using a magnetic susceptibility meter and m-XRF core-scanner. Comparison of modern climate and stream data with sediment influx into the lake revealed titanium could be used as a proxy for terrigenous influx, zirconium-rubidium for coarse-grained sediment inwash and rubidium-potassium and iron-potassium ratios as indicators of fine-grained sediment influx. More coarse-grained sediment was washed in at ~14-11 ka, ~6 ka, ~3.8-3.5 ka, ~2 ka, and 0 ka and higher fine-grained influxes from ~8 to ~4 ka. Coarse-grained sediment influx was likely delivered to the lake after convective storms impacted the watershed. More fine-grained sediment may have been transported to the lake during periods of greater snowmelt rather than convective storms. By contributing to paleoflood research in the northeastern region of the United States, we can better understand the patterns of flooding in the region under different climate states.