MULTI-PROXY ANALYSIS OF ORGANIC MATTER SEDIMENTATION IN THREE MAINE LAKES

The dynamics of organic matter (OM) deposition in lakes are influenced by environmental, climatic and anthropogenic factors and a more thorough understanding of modern sedimentation can assist in the interpretation of sediment cores. The goal of this study is to quantify seasonal OM deposition in three Maine lakes. In July 2009, funnel-type sediment traps were deployed in the deep holes of Conroy Lake (CL), Lobster Lake (LL), and Tea Pond (TP), at depths of 33.5m, 32.3m, and 32.9m, respectively. Sediment traps were recovered in July 2010 and samples were frozen using dry ice in the field to preserve the OM collected. Each trap was sub-sampled at a resolution of 0.5cm in the lab and subsequently dried at low temperature. After weighing, dry subsamples were logged for volume magnetic susceptibility. Acidified subsamples were analyzed for stable carbon isotopic ratios (δ13C), stable nitrogen isotopic ratios (δ15N), and C/N ratios using a continuous flow elemental analysis/isotope ratio mass spectrometer.

The annual mass accumulation rate (MAR) of sediment from each lake was determined: CL: 7.63mg/cm2 yr, TP: 5.23mg/cm2yr and LL: 23.0mg/cm2yr of sediment accumulation. Organic Carbon (OC) MAR’s were calculated as 1.17 mg/cm2yr at CL and 1.02mg/cm2yr at TP. Analyses of δ13C vs. C/N data at CL and TP suggest a mix of aquatic and C3 land plant organic matter sources. δ15N for CL has a mean value of 6.26 which is much higher than TP (4.05‰) and LL (4.48‰). The heavier values found at CL suggest higher anthropogenic effects due to human and/or animal waste from the watershed.

Seasonal variability is also noted within each record. For instance, all three lakes show seasonal variability in organic matter characteristics, likely attributed to seasonal changes in productivity. In addition, LL exhibits a shift between winter and spring in δ15N and %N values suggesting that the flooding of the western branch of the Penobscot River during the spring season loaded nutrients into the system causing an increased productivity rate.