Barriers and Bridges in Abating Coastal Eutrophication

Abstract

Over the past 30 years concerted campaigns have been undertaken to reverse nutrient-driven eutrophication in coastal waters in Europe, North America, Asia, and Australia. Typically, eutrophication abatement has proven a more recalcitrant challenge than anticipated, with ecosystem improvements only recently beginning to emerge or falling short of goals. Reduction in nutrient loads has come mainly from advanced treatment of wastewaters and has lagged targets set for diffuse agricultural sources. Synthesis of the major campaigns-varying in terms of physical settings, ecosystem characteristics, nutrient sources, socio-economic drivers, and governance-identified barriers inhibiting eutrophication abatement and potential bridges to overcome them. Actionable science can be advanced by: application of the well-established and emerging knowledge and experience around the globe, client-responsive strategic research, and timely and conclusive adjudication of scientific controversies. More accountable governance requires: enduring engagement of high-level officials of the responsible governments; effective communication of the causes, risks and benefits to the public and stakeholders; quantitative and accountable allocation of responsibility for nutrient load reductions; and binding requirements, as opposed to simply voluntary actions. Effective reduction in nutrient loads requires: reduction strategies for both nitrogen and phosphorus; inclusion of actions that reduce atmospheric emissions of nitrogen in addition to direct inputs to waterways; efficacious regulations; public subsidies based on performance; limitations on biofuel production that increases nutrient loads; and enhancing the sinks and losses for legacy nutrients retained in soils and groundwater. Outcomes must be measured and strategies appropriately adjusted through: sustained monitoring of essential indicators and processes, the use of multiple models, truly adaptive management, and cautious interventions within the coastal ecosystem. The changing climate must be taken into account by reassessing achievable future conditions and seeking alternatives for mitigating and adapting to climate change that also reduce nutrient loads.

Nutrient Status of San Francisco Bay and Its Management Implications

“…Loading goals are usually developed using models that range from simple to complex. The management target for Chesapeake Bay is a 43% reduction of both N and P loading from 1985 levels (Boesch 2019), and these targets were set using simulations with a coupled airshed-watershed-estuarine model (Linker et al 2013). Nutrient management of San Francisco Bay will require a similar model to project water-quality and ecological responses to different levels of N and P load reduction.…”

“…These projections are best viewed as a starting place because responses to nutrient load reduction often deviate, sometimes substantially, from the model projections used to set loading targets. Realized responses to nutrient reduction have "variously been effective, ineffective, recalcitrant and sometimes surprising" (Boesch 2019). Ineffective, recalcitrant and surprising responses to action plans imply that strategies of nutrient management require adaptability (e.g., changing targets), patience (over decades), and ongoing monitoring to capture and understand surprises as they unfold.…”

“…Nutrient enrichment alters coastal ecosystems through a suite of changes that begin with increased algal production and biomass, leading to increased ecosystem metabolism, turbidity, and occurrences of harmful algal blooms, and decreases of oxygen, vascular plants, biological diversity, and ecosystem goods and services upon which we depend (Ferreira et al 2011). Manifestations of this eutrophication syndrome have been expressed along many of the world's coastlines, from the Baltic, Black, and Seto Inland Seas to Tokyo, Chesapeake, and Moreton Bays, and coastal waters of the Gulf of Mexico, North Sea, and South China Sea (Boesch 2019).…”

A Global Perspective on Phosphorus Management Decision Support in Agriculture: Lessons Learned and Future Directions

“…One example of a multistate DSS driven by the Clean Water Act is the Chesapeake Bay Model (CBM), which serves as the overarching DSS guiding P mitigation in the Chesapeake Bay watershed of the mid‐Atlantic United States. The CBM integrates a suite of models (watershed model, estuary model, scenario builder, airshed model, and land change model) and “big data” to assess the implication of mitigation activities proposed by jurisdictions within the watershed on P, N, and sediment reductions (Boesch, 2019; Chesapeake Bay Program, 2019). Both point and nonpoint sources of P are considered by the CBM, providing a framework for nutrient trading credits that several Chesapeake Bay states have implemented (Chesapeake Bay Program, 2018).…”

“…2). As seen in the legal frameworks available to EU member nations (Boesch, 2019) or Norway, linking DSS adoption to a legally binding mechanism (e.g., EU cross compliance measure) can result in improved DS and DST adoption and water quality goals versus where such mechanisms do not exist. However, as in the case of New Zealand, legally binding mechanisms are not always needed if scientific, political, and cultural factors align to improve water quality.…”