DISTRIBUTION OF HEAVY METALS IN ESTUARINE SEDIMENT CORES FROM SALEM SOUND, MA

Salem Sound, located in Salem, MA is a well-mixed, mesotidal and tidally dominated estuary with average water depths of 9.15 m. The highly urbanized and industrialized estuary has a long history of contamination which has resulted in polluted sediments mainly associated with the most industrialized parts of the embayment. The main point sources of pollution are the South Essex Sewerage District Wastewater Facility, the Salem Harbor Power Plant, and historic point sources such as leather tanneries along the North River which enters Salem Sound. While non-point sources consist of stormwater runoff and atmospheric deposition. As a result of Salem Sound’s long pollution history over the last few hundred years, there is a well preserved record of heavy metal inputs within the sediments. Sediment cores were taken near the mouth of the North River (NR) and next to the Haste Outfall (HO) sewage discharge pipe. The HO core was dated using ¹³⁷Cs and the age constraints of the NR core were modeled after the HO dates by comparing similar patterns in the metal concentrations. The concentrations of various metals in each of the cores were measured using an x-ray fluorescence spectrometer. These metals include chromium, copper, nickel, zinc, and lead. The results from both cores indicate levels of chromium, nickel, zinc, and lead above the effects range medium (ERM) while levels of copper are above the effects range low (ERL). Chromium for example shows the greatest enrichment having a peak concentration of 4534 ppm which is 104 times as great as the ERM value. There is a dramatic increase in the concentrations of chromium, zinc, and lead at a depth of 24.5 cm (early 1840s) in the HO core and a significant increase at a depth of 26.5 cm (late 1820s) in the NR core. The observed increases in metal concentrations are associated at a time where the tanning industry was showing a great enhancement in technology. The peak concentrations of chromium, zinc, and lead in the HO core occur between 16.5 cm (mid 1890s) and 17.5 cm (late 1880s) while in the NR core they occur between 17.5 cm (late 1880s) and 18.5 cm (early 1880s) suggesting that they are coming from the same source. Copper and Nickel concentrations do not follow the same trend as the other metals in each of the cores which may be attributed to them originating from a different source.