Sediment organic matter at two stations in West Falmouth Harbor between 2007 and 2016

West Falmouth Harbor (West Falmouth, MA, USA) has been experiencing a dramatic increase in nitrogen loading from an upgradient municipal wastewater treatment facility since the early 2000’s. As part of a long-term study into the effects of this nitrogen enrichment, we have measured multiple biogeochemical processes at two locations within the harbor at either end of the eutrophication gradient - one in the well-flushed outer harbor (OH) and one in the inner basin closer to the dominant groundwater N source (Snug Harbor, SH). Samples of the top 4cm of the sediment profile were taken each year and analyzed for organic matter content via loss on ignition in the top 1cm and the sediment from 3-4cm deep. In a subset of years, intermediate depths were quantified, as well as samples below 4cm. Note, calculations for loss on ignition do not account for the weight of salt from porewater dried with the samples. A separate analysis found that salt accounts for between 3 and 19% of the dry weight of the sediment, depending on porosity. A calibration was done with percent carbon in 2009, showing a tight linear correlation between carbon content and organic matter across the entire site (%LOI = 2.71*%C + 0.2471).