Evaluation of Two Different Widths of Vegetative Filter Strips to Reduce Sediment and Nutrient Concentrations in Runoff from Agricultural Fields

Ramirez-Avila, J. J., Sotomayor, D. R., Martinez, G. A., Mas, E., & Ortega-Achury, S. L. (2010). Evaluation of Two Different Widths of Vegetative Filter Strips to Reduce Sediment and Nutrient Concentrations in Runoff from Agricultural Fields. 2010 Mississippi Water Resources Conference. Bay St. Louis, MS: Mississippi Water Resources Research Institute.

A vegetated filter strip (VFS) is intended to remove pollutants from runoff flowing through it as sheet flow. VFS can be effective in reducing sediments and associated pollutants such as hydrocarbons, metals and nutrients through sedimentation and filtration. Soluble pollutants may also be removed through uptake by vegetation. In a properly designed VFS, water flows evenly through the strip, slowing the runoff velocity and allowing contaminants to settle from the water. In addition, where VFS are established, fertilizers and herbicides no longer need to be applied right next to susceptible water sources. Vegetative filter strips also increase wildlife habitat. This study evaluated the relationship between VFS width and trapping efficiency for sediment, phosphorus and nitrogen and to produce a design aid for use where specific water quality targets must be met. Runoff collection devices were placed at 0, 10 and 20 m within a grassed VFS established at the outlet of two dairy farm fields in Puerto Rico, which received periodic application of inorganic and dairy sludge irrigated amendments. Collected runoff samples were analyzed for suspended solids (SS), dissolved phosphorus (DP), total phosphorus (TP) and total Kjeldahl nitrogen (TKN) concentrations. Nutrients concentrations high above environmental targets were observed in runoff events that occurred within 10 days after organic amendment irrigation. Runoff DP and TP concentrations were significantly reduced, while an important but not significant reduction in runoff TKN concentration was observed at the wider VFS. Results showed that SS concentrations in runoff were not significantly reduced because the entering concentrations were minimal. The 20-m VFS wide was effective to reduce runoff nutrient concentrations below target levels; however other best management practices (BMPs) such reducing application volumes but increasing frequency of application and by spreading and/or irrigating the amendments on dates when significant precipitation events are less expected, are needed to reduce the potential impact of nutrient losses on water quality of waterbodies.