DIATOM INDICATORS OF ENVIRONMENTAL CHANGE IN SEDIMENTS OF NORTHERN NEW ENGLAND LAKES

Diatom sensitivity to very subtle changes in chemical and physical lake properties makes them good indicators for water quality of surface waters. Diatoms fossilize as silicate frustules that settle to the lake bottom and accumulate, in chronological sequence, in the sediments. This study uses these features of diatoms to examine similarities in the way northern New England lakes behave in response to climate and other environmental changes. We assess trends in diatom composition, carbon content, mineral chemistry and particle-size using ²¹⁰Pb-dated sediment cores from Newfound, Squam, Ossipee and Webster lakes, in central New Hampshire, and Horseshoe Pond and Kezar Lake, in western Maine. All these lakes exceed 20 m water depth and experience several months of seasonal ice cover in average winters. The sediment cores were collected between 2013-2019, as part of individual investigations on behalf of lake managers. While some of the physical data findings have been presented at prior GSA NE Section meetings, until now none of the records have included diatom analyses. For two lakes, Squam and Newfound, multi-year temperature profiles suggest increasing length and strength of warm-season stratification. We compare the impact of these climate-based trends on diatom composition to those from high-magnitude storm events, changes in land management, lake level and water quality.