Ridge to Reef Management Implications for the Development of an Open-Source Dissolved Inorganic Nitrogen-Loading Model in American Samoa

• Published in: Environmental management (New York) 2020-09, Vol.66 (3), p.498-515
• Main Authors: Shuler, Christopher K., Comeros-Raynal, Mia
• Format: Article
• Language: English
• Subjects: Algal blooms; American Samoa; Anthropogenic factors; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Coastal ecosystems; Coastal management; Coastal resources; Coastal waters; Coastal zone; Coasts; Dilution; Discharge; Earth and Environmental Science; Ecology; Ecosystem; Ecosystem management; Ecosystem services; Ecosystems; Environment; Environmental Management; Environmental Monitoring; Eutrophication; Forestry Management; Groundwater; Groundwater discharge; Human influences; Humans; Hydrologic data; Islands; Marine resources management; Nature Conservation; Nitrogen; Nitrogen - analysis; Nutrient pollution; Nutrient sources; Nutrient transport; Pollution; Pollution dispersion; Quality standards; Strategic management; Stream discharge; Stream flow; Surface water; Waste Water Technology; Wastewater; Wastewater disposal; Water analysis; Water budget; Water Management; Water pollution; Water Pollution Control; Water quality; Water quality standards; Water resources; Water sampling
• ISSN: 0364-152X; 1432-1009
• DOI: 10.1007/s00267-020-01314-4

Excessive nutrient discharge to tropical island coastlines drives eutrophication and algal blooms with significant implications for reef ecosystem condition and provision of ecosystem services. Management actions to address nutrient pollution in coastal ecosystems include setting water-quality standards for surface waters 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 the 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, supporting findings from other tropical islands. On-site wastewater disposal systems were also found to be the primary anthropogenic sources 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. Understanding the sources and primary transport modes of inorganic nitrogen to nearshore reef ecosystems can help coastal resource managers target the most impactful human activities in the most vulnerable locations, thereby increasing the adaptive capacity of unique island ecosystems to environmental variation and disturbances.