SCALES OF INFLUENCE: MULTI-PROXY INDICTORS OF HIGH INTENSITY PRECIPITATION EVENTS IN NEW HAMPSHIRE LAKES

Limnic systems, especially lakes, accumulate deposits, which can be used to interpret climatic, geologic, biologic, and anthropogenic watershed scale histories. In New Hampshire, humans, and now climate change, have heavily impacted many of the watersheds since the Colonial Period. These impacts can be tracked through a wide variety of proxy indicators archived in the sediments. Watershed processes, operating across many different spatial scales, tend to smooth and lengthen the distribution of sedimentary deposits related to individual events. Even very large events, such as hurricanes, can be masked by mixing of “event sediments” with earlier deposits. For the New England region, model predictions of modern and near future climate change anticipate increased frequency and intensity of short-duration precipitation events. We wonder if high intensity, short duration events can stand out above low intensity, long duration events and, if so, which proxy or proxies best documents these events?

This project addresses these questions to better understand the magnitude of precipitation needed to create distinct and recognizable deposits in lakes. Between the fall of 2017 and 2018, we used a 60 cm-long Uwitee gravity-corer to collect nine sediment cores, including the sediment-water interface, from four New Hampshire lakes: two cores each from Norway Pond (Hancock) and Pleasant Lake (Deerfield), one from Newfound Lake (Bristol), and four cores from Spofford Lake (Chesterfield) in south-central New Hampshire. All the cores were subsampled at either 0.5 cm or 1 cm intervals. The subsamples were analyzed for several physical and chemical properties, including Pb210 age, carbon content, particle-size, frequency-dependent magnetic susceptibility and mineral geochemistry. These data help us identify sedimentary properties that correspond to episodes of regional flooding and consequent terrestrial erosion including two particularly high magnitude events for New Hampshire: Tropical Storm Irene, in 2011, and the Hurricane of 1938. The different sampling resolutions in side-by-side cores provide insight into the impact of sampling resolution on the detection of short duration, high-magnitude sedimentary responses to particular events.