Management pathways for the successful reduction of nonpoint source nutrients in coastal ecosystems

Eutrophication remains a threat to coastal habitats and water quality worldwide. The U. S. Clean Water Act resulted in reductions of nutrient loading from point sources but management of nonpoint sources (NPS) of nutrients remains challenging despite efforts over at least three decades. The hydrological factors, best management practices (BMPs) and regulatory mechanisms that target nutrient NPS and improve coastal ecosystem function are poorly understood. We identified three case study sites in the U.S. with sufficient NPS management and monitoring history to quantify changes in estuarine habitat and water quality following BMP implementation and regulation targeting nutrient NPS. Utilizing publicly available data, we compared sites that are geographically distant and hydrologically distinct. We found that BMPs targeting NPS loads from surface waters into Roberts Bay (Florida) and Newport Bay (California) significantly reduced nutrient concentrations and harmful algal blooms within ∼20 years. Improvements occurred despite concurrent human population growth within both watersheds. Conversely, we found that the majority of BMPs implemented within the Peconic Estuary (New York) watershed targeted surface waters despite a dominance of nitrogen inputs (97%) from groundwater and atmospheric sources. Declines in habitat and water quality in Peconic Estuary may be due to a failure to control the dominant nutrient sources and the long residence time of nitrogen in groundwater. Compared to surface water, reducing groundwater and atmospheric nutrients face greater technical and financial challenges. Improvements to Peconic Estuary may occur with further reductions in surface water inputs and as nutrients leach out of the groundwater. Although the effectiveness of specific NPS BMPs has been examined at small spatial scales, our study is the first to quantify improvements at a watershed scale. We showed that successful NPS management pathways are those which targeted the dominant sources of nutrients to coastal ecosystems and applied multiple BMPs within watersheds.

Impact/Purpose

Over the last 40 years, there have been significant improvements in water quality and ecosystem condition in estuaries stressed by nutrient enrichment, which has been primarily attributed to reductions in point sources. In contrast, improvement of coastal condition through Non-point source (NPS) management has had limited evaluation. We evaluate three case study sites with sufficient NPS management and monitoring history to quantify changes in habitat and water quality following the implementation of regulation and Best Management Plans (BMPs) targeting nutrient NPS. We found that BMPs targeting NPS loads from surface waters into Roberts Bay (Florida) and Newport Bay (California) significantly reduced nutrient concentrations and harmful algal blooms within approximately two decades. Moreover, these improvements occurred despite significant concurrent increases in human populations, therefore, effective NPS management has the potential to offset elevated nutrient loading from increasing human population. Conversely, we found that the majority of BMPs implemented within the Peconic Estuary (New York) watershed targeted surface waters despite a dominance of nitrogen inputs (97%) from groundwater and atmospheric deposition. Therefore, we argue that continued declines in habitat and water quality in Peconic Estuary may be related to a failure to control the dominant nutrient sources from groundwater and atmospheric deposition. Pathways that targeted the dominant sources of nutrient loading to coastal ecosystems and applied multiple BMPs within watersheds were most successful.

Citation

Green, L., C. Magel, AND Cheryl A. Brown. Management pathways for the successful reduction of nonpoint source nutrients in coastal ecosystems. Elsevier B.V., Amsterdam, NETHERLANDS, 45:101851, (2021). [DOI: 10.1016/j.rsma.2021.101851]

DOI: Management pathways for the successful reduction of nonpoint source nutrients in coastal ecosystems