Pasture BMP effectiveness using an HRU-based subarea approach in SWAT

Area of Science:

• Environmental Science
• Agricultural Science
• Water Quality Management

Background:

• Conservation programs aim to reduce pasture runoff and nutrient loads.
• Assessing the effectiveness of best management practices (BMPs) is crucial for targeted implementation.
• Livestock pastures are significant contributors to non-point source pollution.

Purpose of the Study:

• To develop and demonstrate a method for evaluating the water-quality impacts of pasture BMPs.
• To assess the effectiveness of off-stream watering sites and stream fencing on livestock pastures.
• To quantify the reduction in pollutant loads achieved by these BMPs.

Main Methods:

• Utilized the Soil and Water Assessment Tool (SWAT) model for a watershed in eastern Kansas.
• Calibrated the model for streamflow, nutrients, and sediment runoff.
• Simulated five scenarios with varying combinations of off-stream watering and stream fencing on synthetic and whole pastures.

Main Results:

• Pollutant loads increased with higher stocking rates.
• Off-stream watering and stream fencing reduced cattle's time in streams and lowered nutrient loads.
• Organic phosphorus and nitrogen loads decreased by over 59%; nitrate loads by 19%.
• Total suspended solids (TSS) and sediment-attached phosphorus loads showed minimal change.

Conclusions:

• Off-stream watering and stream fencing are effective BMPs for reducing nutrient runoff from livestock pastures.
• The developed methodology provides an adaptable framework for assessing pasture BMP effectiveness.
• The study highlights the need to incorporate stream bank contributions for a comprehensive assessment.