FROM PRE-SETTLEMENT TO THE 21ST CENTURY - LAKE SEDIMENT RECORDS OF LAND USE AND CLIMATE CHANGE IN NEW ENGLAND

Sediment records from lakes have been used for many purposes, but differentiating the proxy records for land use and climate remains a challenge, especially during extreme events. Here, Pb210-dated sediment records from four New England lakes are compared and assessed for regional trends in climate and land use change. Analytical results include standard measures of particle-size, geochemistry, magnetic susceptibility and organic content, yet discrepancies arise that point to high-magnitude events created by changes in lake-stratification. To examine these influences, sediment trap collections are combined with biweekly measurements of thermal structure and water chemistry in a year-round monitoring program started in 2013-14. Preliminary findings suggest that timing and intensity of stratification is highly correlated to seasonal conditions, especially the timing of ice-out and fall overturn. These factors have been oscillating between near-record extremes since the overwinter monitoring began, with a May ice-out during 2015 and a March ice-out in 2016. How do these extremes affect sediment characteristics? That work is ongoing. Preliminary findings point to influences on metal and nutrient chemistry.