This is the fifth report from a project to assess land-based sources of pollution (LBSP) and their effects, and to characterize the biological community within the St. Thomas East End Reserves (STEER) in St. Thomas, USVI. Here we summarize the results of nearly two years of monthly monitoring for nutrients, sedimentation, and total suspended solids (TSS) at six sites in the STEER.
Concentrations of nutrients in the western part of the STEER and in nearshore areas were significantly higher than in the rest of the STEER. Specifically, ammonium (NH4+), nitrite (NO2-), and dissolved inorganic nitrogen (DIN) were higher in Mangrove Lagoon and Benner Bay than the other sites (i.e., Cowpet Bay, Rotto Cay, Saint James Island, and Little St. James Island). There did not appear to be a correlation between rainfall and nutrients. Using a set of nutrient concentrations, above which may be associated with the overgrowth of algae on reefs, approximately 60% of the samples collected in the STEER were above the threshold for orthophosphate (HPO4=), while 55% of samples were above the DIN threshold, indicating the reefs in the STEER may be at risk to blooms of macroalgae and phytoplankton, as a result of these elevated concentrations.
Benner Bay had the highest sedimentation rate of any site in the STEER, including Mangrove Lagoon. There was also an east to west and a north to south gradient in sedimentation, indicative of higher sedimentation rates in the western, more populated areas surrounding the STEER, and in the more nearshore sites. Rainfall was not correlated with sedimentation. Although none of the sites had a mean or average sedimentation rate above a proposed threshold that could indicate impacts to coral reefs, the mean sedimentation rate in Benner Bay was just below the proposed threshold.
TSS also tended to be higher in the western and nearshore areas of the STEER. There appeared to be no correlation between rainfall and TSS in the STEER. Finally, none of the sites had a mean TSS value that exceeded a threshold above which has been shown to impact coral reefs, although the mean Benner Bay TSS during the study was close to the threshold.
Citation: Pait, A. S., Hartwell, S. I., Mason, A. L., Apeti, D. A., Jeffrey, C. F. G., Pittman, S. J., Hoffman, A. M., Galdo Jr., F. R. April 2015. An assessment of nutrients, sedimentation, and Total Suspended Solids (TSS) in the St. Thomas East End Reserves (STEER). NOAA Technical Memorandum NOS/NCCOS 184. Silver Spring, MD. 74 pp.
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