DETERMINATION OF SEDIMENT PROVENANCE AND CONTAMINANT SOURCES IN THE RIO LOCO WATERSHED OF PUERTO RICO

Terrestrially-sourced sediment pollution has been repeatedly shown to have adverse impacts on nearshore coral reefs. However, remedial actions are dependent on tracing this sediment to individual sources within the watershed. Over recent decades, the nearshore coral reefs adjacent to the Guánica watershed in southwest Puerto Rico have been negatively impacted by anthropogenically-derived sediment pollution. This study used sediment fingerprinting, a multi-parameter analytical technique, to identify the sources and relative contribution of sediment to the Guánica watershed. Incorporation of the corresponding analytical data into the USGS Sediment Source Assessment Tool showed the majority of sediment (≥75%), from 1897 to the present, was derived from lower watershed sources, including riverbank, pasture, agricultural land, and urban areas. A potential temporal link between elemental concentrations and anthropogenic modifications within the watershed was observed in sediment cores. Lastly, concentrations of select trace metals (Pb, Zn, Cr, and Ni) were found in excess of their threshold effect concentrations for aquatic life, both in urban source samples and throughout sediment cores. These results suggest watershed managers should consider erosion control efforts, such as bank stabilization and the restoration of the Guánica lagoon, to prevent sediment from reaching nearshore reefs.