Paper No. 310-13
Presentation Time: 12:15 PM
CULTURAL EUTROPHICATION OF SLUICE POND, LYNN MASSACHUSETTS, RECONSTRUCTED FROM STABLE ISOTOPES PRESERVED IN DATED SEDIMENT CORES
Anthropogenic influence on sediment deposition and productivity within Sluice Pond, Lynn Massachusetts, was interpreted from a dated composite sediment record. An age model was created using radioisotopes (210Pb, 137Cs, 14C) and the well-constrained Ambrosia pollen horizon indicative of European contact in the region. Physical stratigraphy was interpreted with core descriptions, bulk density, magnetic susceptibility, and high-resolution CT scans. Stable isotope and elemental values/ratios of carbon, nitrogen and sulfur (δ13C, δ15N, δ34S) were used to reconstruct nutrient loading, productivity and water column stratification. Sediments below the Ambrosia horizon are massive black organic-rich muds, and proxies exhibit little variability. Deposition within and above the Ambrosia horizon suggests evidence of anthropogenic influence: sedimentation rates increase, mass accumulation of organic carbon increases, δ13C and δ15N become less depleted, OC/N and bulk density increase, and sediments transition to very dark brown organic-rich muds. These proxy shifts are consistent with the arrival of European settlers and the associated changes in land use for agricultural purposes. Overlying these shifts, until the late 19th century, isotopic values (δ13C, δ34S, δ15N) stay relatively stable with less variability; observations consistent with an achieved equilibrium in regard to organic processes and deposition. From the late 19th century to present sediments are laminated, sedimentation rates accelerate, and bulk density and magnetic susceptibility both increase. Concurrent with δ34S decreasing to negative values, laminations suggest permanent anoxia within the lower water column. Increased mass accumulation rates of organic carbon accompanied by an increasing trend in δ13C and decreased OC/N, suggest increased productivity. Increased productivity is likely associated with increased nutrient fluxes, as indicated by a large increase in δ15N values, leading to increased organic matter, decay and depleted bottom water dissolved oxygen. The sediment record from Sluice Pond, Lynn, MA, indicates complex history of cultural eutrophication from the 17th century to modern times that help to refine our understanding of lake response to anthropogenic influences.