Evaluating water quality benefits of manureshed management in the Susquehanna River Basin

Evaluating water quality benefits of manureshed management in the Susquehanna River Basin

Author: Marali Kalra & Cibin Raj

Livestock manure is a valuable source of agricultural nutrients. However, manure source areas are often geographically disconnected from agricultural fields in need of fertilizer. The concept of the manureshed, which connects manure sources with agricultural fields in need of nutrients, is a helpful tool for managing manure distribution. A manureshed (analogous to a watershed) is the land area that receives manure from a specific source, when manure is applied at a rate that meets crop nitrogen or phosphorus needs. The manureshed approach allows for better nutrient budgeting on a regional scale, but its effects on stream water quality are not well understood. Excessive or untimely manure application can increase nitrogen and phosphorus concentrations in runoff from agricultural fields, which leads to downstream eutrophication. This type of nutrient pollution is of particular concern in estuaries such as the Chesapeake Bay watershed, which receives water from highly agricultural regions in the surrounding states. Our study uses the Soil and Water Assessment Tool (SWAT) to examine the water quality impacts of manureshed management in the Susquehanna River Basin, a major tributary of the Chesapeake Bay.

We devised a scenario-based modeling study to evaluate various manureshed management scenarios in the Susquehanna River Basin. We formulated six scenarios (including a baseline), involving variations in crop nitrogen and phosphorus demand, to compare the impacts of different manureshed management strategies. Simulation results showed improved manure nutrient use efficiency and significant water quality benefits with manureshed-based manure management, especially when manure application was based on crop phosphorus demand. A nutrient-balanced manureshed scenario, where manure was transported from source to sink areas, also reduced the agricultural nutrient contribution from the Susquehanna River Basin to the Chesapeake Bay. Impacts on local streams in livestock-intensive areas were even more pronounced. We conclude that manureshed management, in combination with existing nutrient management plans, can aid in protecting streams around concentrated animal feeding operations.

Original article: https://acsess.onlinelibrary.wiley.com/doi/10.1002/jeq2.20429