New insights for reducing nutrient and sediment loads in agricultural watersheds prioritized for management activities
Agricultural activities and natural factors may offset nutrient and sediment reductions from management activities.
Issue
Reducing nonpoint source nutrient loads in agricultural watersheds relies on the voluntary use of management practices. The water-quality effects of management practices are, however, uncertain. Decades of active management have not substantially lowered the amount of nutrients reaching streams in many agricultural areas of the Chesapeake Bay watershed. Multiple factors, such as nutrient inputs from fertilizer and manure applications, and changing climatic conditions, can affect water-quality responses in agricultural watersheds. Insights are needed about the effects of these factors and management practices to inform watershed restoration efforts.
USGS Study
In 2010, the U.S. Geological Survey partnered with the U.S. Environmental Protection Agency and the U.S. Department of Agriculture to initiate water-quality monitoring in three agricultural Chesapeake Bay watersheds that were prioritized for management-practice implementation. These watersheds, namely, the Smith Creek watershed in the Shenandoah Valley of Virginia, the Upper Chester River watershed on Maryland’s Eastern Shore, and the Conewago Creek watershed in southeastern Pennsylvania, represent a gradient of physical settings and agricultural activities in the Chesapeake Bay watershed. Changes in the amount of nutrients and sediment in streams were assessed in each watershed from approximately 10-years of monitoring data. Analysis of management practices, landscape nutrient inputs, streamflow, and climate conditions, using data from this same period, helped evaluate the potential drivers of monitored water-quality changes.
Primary Findings
Despite a more than 50% increase in the number of agricultural management practices since 2010, most monitored nutrient and sediment loads did not decrease in the study watersheds over the same period (Fig 1).
- Some water-quality benefits may have been related to the use of management practices. These benefits, however, may have been offset by increasing nitrogen and phosphorus inputs, mostly driven by applications of fertilizer and manure, patterns that reflect increasing crop production and/or livestock and poultry populations.
- Since 1985, the amount of nutrients applied in each watershed has exceeded crop nutritional requirements (termed “surplus” nutrient inputs). Surplus inputs can result in the storage of nutrients in the environment and can increase the loss of nutrients from the landscape to streams.
- Changes in total nitrogen were closely related to changes in nitrate. Reducing total nitrogen loads may rely on the management of nitrate, which primarily reaches streams through groundwater.
- Changes in total phosphorus were likely affected by the delivery of suspended sediment to streams. Reducing total phosphorus loads may rely on the management of sediment loads.
- Although the three study watersheds were explicitly targeted for enhanced amounts of management-practice implementation, their water-quality trends were similar to trends monitored in nearby agricultural watersheds.
Management Implications
- Nutrient load reductions may not occur until manure and fertilizer inputs are lowered to align with local crop nutritional requirements; changes that would reduce surplus nutrient inputs and could prevent the accumulation of legacy nutrients stored in the environment.
- Management practices that control the delivery of nutrients and sediment to streams during periods of high flow may help reduce loads.
- Management of point-source discharges can improve nutrient loads in agricultural watersheds, even when point-source nutrient inputs are a small fraction of total nutrient inputs in the watershed.
- Water-quality trends may be affected by regionally consistent factors (such as agricultural activities or climate conditions), in addition to potential effects of management practices.
- Sustained water-quality monitoring and collaborative partnerships would increase the understanding of how agricultural nutrient and sediment loads respond to management practices.
- The challenge of associating monitored responses with management-practice effects could be reduced through long-term water-quality monitoring studies in small agricultural watersheds (zero-to third-order streams) with targeted management-practice implementation.
Publication Details
Webber, J.S., Chanat, J.G., Clune, J.W., Devereux, O., Hall, N., Sabo, R.D., & Zhang, Q. (2024). Evaluating water‐quality trends in agricultural watersheds prioritized for management‐practice implementation. JAWRA Journal of the American Water Resources Association. https://doi.org/10.1111/1752-1688.13197.
For more information, please contact the study leader
Jimmy Webber
Hydrologist
USGS, Virginia and West Virginia Water Science Center
Email: jwebber@usgs.gov
Agricultural activities and natural factors may offset nutrient and sediment reductions from management activities.
Issue
Reducing nonpoint source nutrient loads in agricultural watersheds relies on the voluntary use of management practices. The water-quality effects of management practices are, however, uncertain. Decades of active management have not substantially lowered the amount of nutrients reaching streams in many agricultural areas of the Chesapeake Bay watershed. Multiple factors, such as nutrient inputs from fertilizer and manure applications, and changing climatic conditions, can affect water-quality responses in agricultural watersheds. Insights are needed about the effects of these factors and management practices to inform watershed restoration efforts.
USGS Study
In 2010, the U.S. Geological Survey partnered with the U.S. Environmental Protection Agency and the U.S. Department of Agriculture to initiate water-quality monitoring in three agricultural Chesapeake Bay watersheds that were prioritized for management-practice implementation. These watersheds, namely, the Smith Creek watershed in the Shenandoah Valley of Virginia, the Upper Chester River watershed on Maryland’s Eastern Shore, and the Conewago Creek watershed in southeastern Pennsylvania, represent a gradient of physical settings and agricultural activities in the Chesapeake Bay watershed. Changes in the amount of nutrients and sediment in streams were assessed in each watershed from approximately 10-years of monitoring data. Analysis of management practices, landscape nutrient inputs, streamflow, and climate conditions, using data from this same period, helped evaluate the potential drivers of monitored water-quality changes.
Primary Findings
Despite a more than 50% increase in the number of agricultural management practices since 2010, most monitored nutrient and sediment loads did not decrease in the study watersheds over the same period (Fig 1).
- Some water-quality benefits may have been related to the use of management practices. These benefits, however, may have been offset by increasing nitrogen and phosphorus inputs, mostly driven by applications of fertilizer and manure, patterns that reflect increasing crop production and/or livestock and poultry populations.
- Since 1985, the amount of nutrients applied in each watershed has exceeded crop nutritional requirements (termed “surplus” nutrient inputs). Surplus inputs can result in the storage of nutrients in the environment and can increase the loss of nutrients from the landscape to streams.
- Changes in total nitrogen were closely related to changes in nitrate. Reducing total nitrogen loads may rely on the management of nitrate, which primarily reaches streams through groundwater.
- Changes in total phosphorus were likely affected by the delivery of suspended sediment to streams. Reducing total phosphorus loads may rely on the management of sediment loads.
- Although the three study watersheds were explicitly targeted for enhanced amounts of management-practice implementation, their water-quality trends were similar to trends monitored in nearby agricultural watersheds.
Management Implications
- Nutrient load reductions may not occur until manure and fertilizer inputs are lowered to align with local crop nutritional requirements; changes that would reduce surplus nutrient inputs and could prevent the accumulation of legacy nutrients stored in the environment.
- Management practices that control the delivery of nutrients and sediment to streams during periods of high flow may help reduce loads.
- Management of point-source discharges can improve nutrient loads in agricultural watersheds, even when point-source nutrient inputs are a small fraction of total nutrient inputs in the watershed.
- Water-quality trends may be affected by regionally consistent factors (such as agricultural activities or climate conditions), in addition to potential effects of management practices.
- Sustained water-quality monitoring and collaborative partnerships would increase the understanding of how agricultural nutrient and sediment loads respond to management practices.
- The challenge of associating monitored responses with management-practice effects could be reduced through long-term water-quality monitoring studies in small agricultural watersheds (zero-to third-order streams) with targeted management-practice implementation.
Publication Details
Webber, J.S., Chanat, J.G., Clune, J.W., Devereux, O., Hall, N., Sabo, R.D., & Zhang, Q. (2024). Evaluating water‐quality trends in agricultural watersheds prioritized for management‐practice implementation. JAWRA Journal of the American Water Resources Association. https://doi.org/10.1111/1752-1688.13197.
For more information, please contact the study leader
Jimmy Webber
Hydrologist
USGS, Virginia and West Virginia Water Science Center
Email: jwebber@usgs.gov