Progress in reducing nutrient and sediment loads to Chesapeake Bay: Three decades of monitoring data and implications for restoring complex ecosystems

Abstract

For over three decades, Chesapeake Bay (USA) has been the focal point of a coordinated restoration strategy implemented through a partnership of governmental and nongovernmental entities, which has been a classical model for coastal restoration worldwide. This synthesis aims to provide resource managers and estuarine scientists with a clearer perspective of the magnitude of changes in water quality within the Bay watershed, including nitrogen (N), phosphorus (P), and sediment for the River Input Monitoring (RIM) watershed and the unmonitored below‐RIM watershed. The flow‐normalized N load from the RIM watershed has declined in the period of 1985–2017, but P and sediment loads have lacked progress. Reductions of riverine N are largely driven by reductions of point sources and atmospheric deposition. Future reductions will require significant progress in managing agricultural nonpoint sources. The below‐RIM watershed, which comprises a disproportionately high fraction of inputs to the Bay, has shown long‐term declines in major sources, including point sources (N and P), atmospheric deposition (N), manure (N and P) and fertilizer (P), based on a combination of monitoring and modeling assessments. To date, the Bay cleanup efforts have achieved some progress toward reducing nutrients from the watershed, which have resulted in improving water quality in the estuary. However, further reductions are critical to achieve the Chesapeake Bay Total Maximum Daily Load goals, and emerging challenges due to Conowingo Reservoir, legacy nutrients, climate change, and population growth should be considered. Continued monitoring, modeling, and assessment are critically important for informing the restoration of this complex ecosystem.This article is categorized under: Science of Water > Water Quality Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness

Effects of point and nonpoint source controls on total phosphorus load trends across the Chesapeake Bay watershed, USA

“…Point source reductions were reported to have contributed to water-quality improvement, which can be attributed to implementations of enhanced wastewater treatment technology [22,26,[35][36][37]. By contrast, nonpoint sources were reported to have made limited progress [26,27,36,37]. Focusing on recent trends of TP, this work provides encouraging evidence that efforts to reduce point sources (figure S10(a)) and agricultural nonpoint sources (i.e.…”

“…Declining TP trends (cluster 2) have a larger chance to occur in watersheds with large declines in point source loads (PointSource_MK) and agricultural fertilizer inputs (Fertilizer_MK) (figure 3). Point source reductions were reported to have contributed to water-quality improvement, which can be attributed to implementations of enhanced wastewater treatment technology [22,26,[35][36][37]. By contrast, nonpoint sources were reported to have made limited progress [26,27,36,37].…”

“…A majority of the segments (56%) have increasing TP trends (cluster 1) and most of them (78%) have high likelihoods. In addition, cluster 1 segments are generally closer to the Bay than cluster 2 segments, which may hinder the restoration progress because changes in areas closer to and directly connected to the tidal waters should have a stronger impact on the estuary than upland areas due to limited opportunities for retention and mitigation [37,49,50]. Optimizing the management and use of P in farm operations in the Coastal Plain, as well as controlling erosion, will be key for reversing the upward trends of TP.…”

Assessment of the Chesapeake Bay watershed socio-ecological system through the Circles of Coastal Sustainability framework

“…Finally, the "Biochemical and physical flows" category score is based on reducing nitrogen, phosphorus, and suspended sediments (Ator et al, 2020;Frankel et al, 2022;Zhang et al, 2023). The reduction has decreased hypoxia by 50-90 days (Frankel et al, 2022).…”

Evaluating water‐quality trends in agricultural watersheds prioritized for management‐practice implementation

“…Decreased point‐source nutrient loads and atmospheric nitrogen loads have likely contributed to water‐quality improvements (Burns et al., 2021; Clune et al., 2021; Eshleman et al., 2013; Lyerly et al., 2014; Shenk & Linker, 2013), but these combined sources contribute a smaller fraction of nutrients to the Bay than agricultural lands (Ator et al., 2019). While nutrient loads have decreased in some agricultural watersheds (Mason et al., 2023), the net amount of nutrients from agricultural lands throughout the Chesapeake Bay watershed has not substantially decreased in recent decades (Ator et al., 2020; Boesch, 2019; Brakebill et al., 2010; Shenk & Linker, 2013; Stephenson et al., 2022; Zhang et al., 2023). Some commonly used agricultural MPs in the Chesapeake Bay watershed include nutrient management plans, tillage management, cover crops, animal waste management, pasture management, and buffers (Chesapeake Assessment Scenario Tool, 2023a; Sekellick et al., 2019).…”