American Samoa EPA/ Pacific RISA / Water Resources Research Center
2017 – 2019
Chris Shuler, Aly El-Kadi, and Mia Comeros-Raynal
Excessive nutrient discharge to tropical island coastlines drives eutrophication and algal blooms with significant implications for reef ecosystems and provision of ecosystem services. Management actions to address nutrient pollution in coastal ecosystems include setting water quality standards for surface water discharging to the coast. However, these standards do not account for the effects of groundwater discharge, variability in flow, or dilution, all of which may influence assessment of true nutrient impacts on nearshore reef habitats. We developed a method to estimate dissolved inorganic nitrogen (DIN) loads to coastal zones by integrating commonly available datasets within a geospatial modeling framework for Tutuila, American Samoa. The DIN loading model integrated an open-source water budget model, water sampling results, and publicly available streamflow data to predict watershed-scale DIN loading to the island’s entire coastline. Submarine groundwater discharge (SGD) was found to deliver more terrigenous DIN to the coastal zone than surface water pathways, which supports findings from other tropical islands. Onsite wastewater disposal systems were also found to be the primary anthropogenic source of DIN to coastal waters. Our island-wide DIN loading model provides a simple and robust metric to define spatially-explicit sources and delivery mechanisms of nutrient pollution to nearshore reef habitats.
Shuler, C.K., and M. Comeros-Raynal. 2020. Ridge to reef management implications for the development of an open-source dissolved inorganic nitrogen-loading model in American Samoa. Environmental Management 1-18. https://doi.org/10.1007/s00267-020-01314-4
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