Phosphorus and the Chesapeake Bay: Lingering Issues and Emerging Concerns for Agriculture

Abstract

Hennig Brandt's discovery of phosphorus (P) occurred during the early European colonization of the Chesapeake Bay region. Today, P, an essential nutrient on land and water alike, is one of the principal threats to the health of the bay. Despite widespread implementation of best management practices across the Chesapeake Bay watershed following the implementation in 2010 of a total maximum daily load (TMDL) to improve the health of the bay, P load reductions across the bay's 166,000‐km2 watershed have been uneven, and dissolved P loads have increased in a number of the bay's tributaries. As the midpoint of the 15‐yr TMDL process has now passed, some of the more stubborn sources of P must now be tackled. For nonpoint agricultural sources, strategies that not only address particulate P but also mitigate dissolved P losses are essential. Lingering concerns include legacy P stored in soils and reservoir sediments, mitigation of P in artificial drainage and stormwater from hotspots and converted farmland, manure management and animal heavy use areas, and critical source areas of P in agricultural landscapes. While opportunities exist to curtail transport of all forms of P, greater attention is required toward adapting P management to new hydrologic regimes and transport pathways imposed by climate change. Core Ideas At the midpoint of the Chesapeake TMDL, dissolved P is increasing in some tributaries. Lingering concerns include legacy P, artificial drainage, animal heavy use areas. Extreme events represent an acute risk to water quality.

The Latitudes, Attitudes, and Platitudes of Watershed Phosphorus Management in North America

“…Monitoring across the bay watershed points to mixed success, with troubling increases in dissolved P reported in many agricultural tributaries (Moyer and Blomquist, 2017). Legacy P, critical source areas, artificial drainage, trade‐offs in conservation programs, farmland conversion, and manure management all contribute to a complex set of challenges, many of which are difficult to achieve under voluntary programs (Kleinman et al, 2019). …”

Phosphorus mirabilis: Illuminating the Past and Future of Phosphorus Stewardship

“…Kleinman et al (2019) explore some of these translational challenges that have resulted in “uneven improvements” in water quality in the Chesapeake Bay watershed. Despite the application and coordination of policies to reduce P loadings to the Chesapeake Bay since 2010, Kleinman et al (2019) show that soluble P is increasing in key tributaries where agriculture is a major source of P runoff, a phenomenon also observed in the Lake Erie watersheds (Jarvie et al, 2017). …”

“…With regard to climate change, both Bieroza et al (2019) and Kleinman et al (2019) document increased mobilization of legacy P sources with increased frequency of prolonged drought or activation of latent sources during extreme storm events. The implications of interactions between legacy P and climate change, as long‐term/historical factors affecting efficacy of agricultural P mitigation, are further explored by Smith et al (2019).…”

“…Despite two decades of intensive monitoring and implementation of an ethos of nutrient and land conservation management in the Chesapeake Bay watershed, Kleinman et al (2019) note increases in soluble P concentrations in some Chesapeake Bay watershed tributaries. They point to lingering concerns about legacy P in soils and reservoir sediments and the need to adapt P mitigation to address new and extreme events and hydrological regimes, brought on by climate change, which pose an acute risk to water quality (Kleinman et al, 2019). …”

“…This leads to a constantly shifting kaleidoscope of baselines and targets for P management ( Jarvie et al, 2013b). Bieroza et al (2019), Kleinman et al (2019), Osmond et al (2019), and Smith et al (2019) all highlight the need to address legacy P stores and mitigate the increased P losses that are expected with climate change. They also champion the need to consider potential trade-offs involving P management practices, such as between particulate and soluble forms of P ( Jarvie et al, 2017), as well as those practices that create "pollutant swapping" between P and nitrogen (N).…”