ASSESSMENT OF LACUSTRINE PARTICULATE ORGANIC MATTER AND SURFACE SEDIMENTS: SLUICE POND, LYNN, MA

Paleolimnologic sedimentary archives are useful in the reconstruction of past environmental conditions; however proxy records contain a complex mix of allochthonous and autochthonous material, which can be geochemically altered during or after deposition. The study of modern particulate matter in lacustrine systems can help to constrain these paleolimnologic records. In this study, we evaluate the particulate matter entering and leaving a small, urban pond and compare these samples to the modern surface sediment record. Sluice Pond is an urbanized pond surrounded by residential and commercial properties and over the past decade multiple paleolimnologic studies have utilized the well-preserved sedimentary record to reconstruct climate and environmental conditions of the Holocene Epoch. We hypothesize that there is mixing of autochthonous phytoplankton matter with allochthonous watershed organic matter within the water column, and that stable isotopes and interparametric ratios of carbon and nitrogen will be sensitive to this mixing. Ongoing weekly monitoring has been conducted since September 2017 in which suspended particulate matter is collected from the natural inflow and outflow of the pond. Filtered samples were analyzed for δ13C, δ15N, and C/N ratios with an Elemental Analyzer and Stable Isotope Ratio Mass Spectrometer (EA/IRMS). Preliminary results of δ13C and C/N support the mixing hypothesis, and suggest that phytoplankton are the dominant source. The samples from the first five weeks relate to the sedimentary archives from lakebed sediments (McCarthy et al., 2017), which show a similar δ13C value for the averages of inflow and outflow. The preliminary data for the C/N ratio as compared to surface sediments (McCarthy et al., 2017) show lower values for particulate matter as compared to surface sediments. This study suggests that more sensitive proxy for organic matter mixing appears to be the C/N ratio, and that this ratio is also more susceptible to early diagenic alteration of the proxy value. Variation between the inflow and outflow data warrant further investigation into the mixing that occurs within the lake basin.