LIMNOGEOLOGIC RECORD OF ANTHROPOGENIC ALTERATIONS PRESERVED IN SLUICE POND, LYNN MASSACHUSETT

Anthropogenic activities can have profound limnologic responses, many of which become recorded by physical and chemical proxies preserved in sediment records. An environmental history of Sluice Pond (Lynn, MA) has been reconstructed through analysis of a well-dated composite sediment core, with the goal of quantifying anthropogenic influence on the system. An age model was constructed from radioisotopes (²¹⁰Pb, ¹³⁷Cs, ¹⁴C), the Ambrosia pollen horizon, the mid-1970s Pb peak, and modern surface. Physical stratigraphy was defined using a variety of techniques which include magnetic susceptibility (MS), high-resolution CT scans, composite imagery, bulk density, and detailed core descriptions. Geochemical proxies include inorganic XRF data as well as organic stable isotopes (δ¹³C, δ¹⁵N, δ³⁴S) and elemental values and ratios (OC/N, OC/S). The sediment record from the bottom of the composite record to the Ambrosia horizon exhibits low variability of proxies and organic-rich very dark brown mud transitioning to dark brown muds. Above the Ambrosia horizon, sediment transitions from dark brown muds to lighter brown organic-rich muds, and shifts are observed in physical and geochemical proxies: sedimentation rates and mass accumulation of carbon increase, concentrations of Zr and Rb increase, MS increases, δ¹³C and δ¹⁵N become more depleted, and OC/N and bulk density increase. The noted proxy shifts are indicative of increased fluxes of allochthonous material from the watershed, likely due to anthropogenic agricultural land use changes. Black laminated organic-rich muds are preserved above the light brown massive mud, indicating substantial changes in environmental conditions from the late 19^th Century to present. Laminated sediments, coupled with decreasing δ³⁴S and Mn/Fe ratio, increased organic carbon preservation, and reduced MS values suggest water column stratification and deep water anoxia until present day. Furthermore, Pb concentrations exhibit a classic industrial record of increased concentrations terminating with the mid-1970s Clean Air Act. Upper proxy data are consistent with anthropogenic influence during the industrial revolution and population growth in the city of Lynn.