A paleolimnological analysis of lake sediments in northern and central Vermont

Vermont has physically changed much during the 250 years since the beginning of European settlement. Agriculture, deforestation, shoreline development, water flow alteration, and other human activities have all changed the physical and ecological landscape of the state. Archives of these interactions are recorded in lake sediments and can be elucidated using proxies including carbon content, nitrogen content, and the ratio of C to N (via organic matter characterization); aluminum content, phosphorus content, sulfur content, and lead content (via X-ray fluorescence (XRF)). Direct measurements of current lake condition such as Chlorophyll-a concentration, total phosphorus, and Secchi depth were also used.Six lakes (Bald Hill Pond, Lake Carmi, Harvey’s Lake, Lake Morey, Spring Lake, and Ticklenaked Pond) were selected for this study which were previously cored, and sediments analyzed two decades ago, allowing for the unique opportunity to examine the evolution of lake conditions over time. Spatial trends in lake sediments are common in the literature but temporal comparisons are not. This study aims to extend the paleolimnological record in these lakes to the present day to determine and assess chemical and physical changes that have occurred during the intervening 20 years. XRF was used to establish temporal markers in the sediment column using lead concentration and reference markers in sediment layers deposited following aluminum sulfate treatments on Ticklenaked Pond (2014) and Lake Morey (1986) via patterns in aluminum, phosphorus, and sulfur. We found that lead concentrations in sediment cores can be used to infer temporal markers, though conclusions must be informed by known records of human interactions within the specific watershed. Aluminum and phosphorus concentrations were found to clearly define layers of sediment deposited during and shortly after the 2014 Alum treatment of Ticklenaked Pond. However, the 1986 treatment of Lake Morey did not produce a clearly recognizable geochemical signature in the sedimentary record. Generally, trends described by previous studies in the cores collected in the late 1990s were also present in the newly collected cores, with anthropogenic alterations evident throughout all cores. None of the modern Spring Lake, Ticklenaked Pond, nor Bald Hill Pond cores continue the previous pattern of decreasing C/N values (by proxy deteriorating trophic conditions), with the Alum treatment likely stabilizing Ticklenaked Pond. Lake conditions are stable in Harvey’s Lake. Continually decreasing C/N values, indicating a trend toward increasingly eutrophic conditions in Lake Carmi and Lake Morey, has persisted, however anthroturbation from the whole-lake aeration system has likely affected the top of the Carmi core. Comparisons of water quality measurements (sourced from the VT Integrated Watershed Information System) to patterns in sediment proxies were positively correlated. However, more analysis needs to be performed to explore this relationship due to the relatively short time frame of water quality measurements