- Animal Products: dairy
- Animal Production: manure management
- Soil Management: soil microbiology
- Sustainable Communities: sustainability measures
Agricultural vegetative filter strips were examined at two sites to assess the surface and subsurface effluent water quality following the application of farmstead runoff. Three filter strips were assessed and revealed significant reductions of nutrients, solids, oxygen demand, and other contaminant issues. Reduction in loading to surface water was highly effective with infiltration of all runoff for storm events within the 25-yr, 24-hr storm designation. Results for wastewater which had infiltrated had large variation and revealed soil type, influent characteristics, and other environmental factors have a large impact on performance and potential for groundwater contamination.
Farmstead runoff produced from animal waste, feed, and storage of other livestock operational necessities is a high contaminant source for surface and groundwater. In an effort to reduce the impact of farmstead animal operations, agricultural vegetative filter strips are widely used to control the outflow of pollutants through infiltration.
Engineered filter strips are designed to promote sheet flow to increase infiltration and contact time. The main mechanisms for pollutant removal include sediment trapping (where vegetation and sheet flow reduce flow velocities to capture sediment and sediment bound particles) and infiltration treatment processes. Sediment bound pollutants have greater removal rates than dissolved or soluble contaminants due to higher trapping efficiencies (Goel et al. 2004; Schmitt et al. 1999). However, infiltration is responsible for the majority of pollutant removal, in particular dissolved contaminants (Dosskey et al. 2007, Lee et al. 2003). Infiltration allows for pollutant soil assimilation, microbial degradation, and plant uptake. Removal rates by infiltration are determined by biological activity, adsorption, filtration, and oxidation, which are the primary mechanisms (Brown and Caldwell 2007). Biological activity removal rates are dependent upon environmental conditions including temperature, moisture, energy sources, and oxygen and nutrient availability (Donker et al. 1994).
Filter strip design dimensions of width, length, slope, soil type, and vegetation impact design and pollutant removal. Increases in the area available for infiltration and sediment trapping has been reported to increase pollutant removal. This can be achieved through increases in the width or length of the filter strip (Schmitt et al. 1999; Magette et al. 1989). A reduction in slope can also result in increased filter strip effectiveness (Hay et al. 2006). Sediment trapping and transport is strongly dependent upon the slope of the filter strip. An increase in the slope leads to a reduction in the trapping efficiency and an increase in pollutant transport (Jin and Romkins 2001, Dillaha et al. 1988). Soil hydraulic condictivities have been suggested from 0.27 – 0.5 in/hr in order to provide adequate infiltration and avoid ponding during wastewater application. Vegetation can uptake pollutants directly, but also impacts velocity and infiltration processes. In addition, vegetation develops dense mats of roots on the upper portions of soil profiles which can provide nutrient trapping and increases soil oxygen through respiration (Bhaskar 2003). Reported results have indicated that removal is contaminant specific with regards to differences in vegetation (Schmitt et al. 1999), and overall removal of all pollutants can be increased with the incorporation of multiple plant species to allow for numerous soil root sizes, and various stalk and leaf sizes to have the greatest overall impact on infiltration and sedimentation.
Although vegetated filter strips have been investigated over many years, reporting has indicated a large variance in efficiency of pollutant removal. Additionally, research has focused only on the removal of surface water contaminants through infiltration to limit surface discharge. With the focus on quantity concerns relating to overall infiltration, there has been a significant gap as to the fate of contaminants within the infiltration zone. Investigation as to the fate of these contaminants is critical to limiting exposure of groundwater to contaminants and maintaining a sustainable water cycle.
Project objectives:div style="margin-left:1em;">
Determine the pollutant removal of agricultural filter strips in typical environmental and farmstead conditions. Specific objectives include the following:
• Assess the surface and subsurface water quality at two field sites.
• Assess current practice standards in regards to operation and maintenance procedures.
• Determine if agricultural filter strips are an effective agricultural treatment/management option as designed, with a particular emphasis on metal leaching into groundwater.
• Determine treatment consistency throughout season and rainfall events.