Title: Impact of legacy phosphorus sources on diffuse phosphorus pollution from agriculture: lessons from the Chesapeake Bay watershed Authors
Submitted to: Proceedings 2nd International Water Association Conference on Odor and Volatile Organic Compounds
Publication Type: Abstract Only
Publication Acceptance Date: May 14, 2010
Publication Date: September 12, 2010
Citation: Buda, A.R., Kleinman, P.J.A., Bryant, R.B., Allen, A.L. 2010. Impact of legacy phosphorus sources on diffuse pollution from agriculture: lessons from the Chesapeake Bay watershed. Proceedings of the 14th International Water Association Conference on Diffuse Pollution Specialist Group: Diffuse Pollution and Eutrophication. p. 63. Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Legacy phosphorus (P), the accumulation of P in soils and sediments due to past agricultural management activities, represents an emerging challenge to ongoing efforts to mitigate diffuse P pollution from agriculture. Nutrient management programs, already tasked with minimizing the effects of today’s P applications, must now also address the influence of legacy P, which threatens to mask or delay water quality improvements expected from P conservation activities and nutrient management programs that are currently in place. In this presentation, we draw upon case studies from the Chesapeake Bay watershed to describe major factors controlling the delivery of legacy P sources to surface and ground waters including terrestrial soils, hydrology, and riverine sediments. Terrestrial soils are often considered to be important sinks for applied P; however, over-application of P from manures and fertilizers can convert some soils to P sources. On the Delmarva Peninsula, continuous application of poultry litter to soils has increased Mehlich-3 soil P concentrations to levels that are nearly one order of magnitude greater than what is required for crop growth, and recent evidence suggests that reducing these high soil P levels by ceasing P applications may take decades or more. Therefore, appropriate management strategies are needed that minimize the potential impacts of legacy P on water quality. In developing these strategies for the Chesapeake Bay watershed, key differences in physiography and hydrologic processes that govern P transport will need to be considered. In areas of low relief like the Delmarva Peninsula (Coastal Plain), the majority of P is delivered to streams and ditches via subsurface flow pathways, whereas in steeper headwater regions (Ridge and Valley), variable source area hydrology can result in substantial P losses in surface runoff from discrete portions of the landscape. Legacy P management approaches will also need to account for the role that riverine sediments play in P storage and retention. For instance, practices such as routine ditch dredging may reduce the P sorption capacity of riverine sediments, which could potentially exacerbate downstream P transport in streams, ditches, and rivers. Ultimately, a clear understanding of legacy P and the processes that influence its delivery from soils to waters will be critical as watershed managers and action agencies attempt to evaluate the effectiveness of P conservation measures and communicate reasonable expectations for water quality improvements in the Chesapeake Bay watershed.