6C – Construction and Maintenance of Vegetated Treatment Systems
Promote the strategic use of engineered vegetated treatment systems, which include constructed wetlands, vegetated filter strips, buffers, and swales
Constructed wetlands increase the residence time (duration that water "ponds" on the ground surface) of surface waters so that interactions between sediments and vegetation is increased. Increasing the soil-plant-water interaction time also increases the ability of pollutants (nutrients, some metals, and some organic molecules) to be attenuated, transformed, absorbed, and volatilized by various processes. A degraded wetland has less ability to remove NPS pollutants and to attenuate stormwater peak flows (Bedford and Preston, 1988; Richardson and Davis, 1987; Richardson, 1988). In addition, a degraded wetland can deliver increased amounts of sediment, nutrients, and other pollutants to the adjoining water body, thereby acting as a source of NPS pollution instead of a treatment (Brinson, 1988; Richardson, 1988). Additionally, constructed wetlands are not usually designated for wildlife and aquatic habitat beneficial uses and can cause harm to wildlife. Kesterson National Wildlife Refuge is a case and point. This managed and constructed wetland was designed to treat agricultural runoff and provide habitat for aquatic birds. In 1983 it was discovered that breeding populations of stilts, grebes, shufflers, coots, and other aquatic birds were experiencing reduced fertility and severe birth defects. The surface waters at Kesterson National Wildlife Refuge had accumulated lead, boron, chromium, molybdenum, and other pollutants, specifically selenium which exposure was linked to teratogenic effects in exposed aquatic birds. USEPA (2001) recommends deterring wildlife from using vegetated treatment systems.
The practices listed below should be used where engineered systems of wetlands or vegetated treatment systems can treat NPS pollution. Vegetated treatment systems can be placed in upland regions and protect wetlands and aquatic resources from NPS pollution. For the purposes of this management measure, vegetated treatment systems are vegetated filter strips and constructed wetlands.
- Install vegetated filter strips to remove sediment and other pollutants from runoff and wastewater.
- Construct vegetated filter strips in areas adjacent to water bodies that may be subject to suspended solids and/or nutrient runoff. Key elements to be considered in the design of such areas include the type and quantity of pollutant, slope, native/non-native species, length, detention time, monitoring performance, and maintenance.
- Construct properly engineered systems of wetlands for NPS pollution control. Several factors to consider in the design and construction of an artificial wetland include hydrology, soils, vegetation, influent water quality, geometry, pretreatment, and maintenance.
- Manage constructed wetland systems to avoid negative impacts on surrounding ecosystems or ground water.
- If measured concentrations of biological oxygen demand (BOD) or dissolved oxygen (DO) are low, use techniques to aerate the water column.
- Conservative Buffer Initiative is an effort to encourage farmers, ranchers, and other landowners to use conservation buffers more extensively for a variety of conservation purposes.
- Reuse of Agricultural Wastewater: Agricultural wastewater can be reclaimed and beneficially used on the farms close to the location where the wastewater is generated. Runoff from the low end of furrows can be utilized for irrigation of fields at lower elevations without treatment and without pumping.
- USDA NRCS, Buffers: Common Sense Conservation provides information on buffers, their use, and technology specifications. It describes success stories and provides links for more information.
- USDA, Constructed Wetlands Bibliography, compiled by the Natural Resources Conservation Service and the Water Quality Information Center at the National Agricultural Library, consists of more than 600 citations.
- USEPA, Guiding Principles for Constructed Treatment Wetlands: Providing for Water Quality and Wildlife Habitat this guidebook presents guiding principles for siting, design, construction, operation, maintenance, and monitoring of constructed treatment wetlands.
- USEPA, Handbook of Constructed Wetlands is a guide to creating wetlands for agricultural wastewater, domestic wastewater, coal mine drainage, and storm water in the Mid-Atlantic Region.
USEPA. 2001. Chapter 6: Management Measure for Vegetated Treatment Systems. In National Management Measures to Protect and Restore Wetlands and Riparian Areas for the Abatement of Nonpoint Source Pollution (Draft). EPA 841-B-01-001. U.S. Environmental Protection Agency, Washington, DC.