Analysis of Coastal Sediment Plume Dynamics in Puerto Rico using MODIS/Terra 250-m Imagery

Abstract:

Anomalous events of suspended sediments can degrade water quality in nearshore ecosystems by reducing light penetration, inhibiting primary production, and delivering pollutants associated with the sediment particles. Coral reefs, for example, are subject to stress by anomalous sediment loads. The island of Puerto Rico has a diverse topography, with steep mountain slopes, episodic high-intensity rainfall events, and weathered soils that lead to episodes of high sediment volumes being delivered to the coastal zone by rivers. We developed a time series of turbidity observations based on Moderate Resolution Imaging Spectroradiometer (MODIS) imagery for use in the coastal areas of Puerto Rico. The product uses remote-sensing reflectance (Rrs) of Band 1 (645 nm) at a spatial resolution of 250 m. These estimates were compared to in-situ turbidity measurements collected in San Juan Bay. Sediment plumes from the major rivers of Puerto Rico were assessed quantitatively and compared with time-series of meteorological and other parameters, including precipitation, river discharge, and wind velocity. The spatial extent of plumes, the timing and duration of plume events, and their potential impact on coral reefs are examined. Results show that plume events are episodic and short-lived, but that they may affect coral reefs located several kilometers offshore.