An Assessment of Nutrients, Sedimentation, and Total Suspended Solids (TSS) in the St. Thomas East End Reserves (STEER)
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
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
Appearing as solitary forms in the fossil record more than 400 million years ago, corals are extremely ancient animals that evolved into modern reef-building forms over the last 25 million years. Continue Reading →
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