Constructed Wetland Research
There is growing interest in off-site methods for treating agricultural runoff. This is evidenced by a recent report from the USEPA’s Science Advisory Board’s Integrated Nitrogen Committee. One of the committee’s recommendations to reduce excess flows to reactive nitrogen (Nr) to surface waters is through improved landscape management using wetland management, improved tile-drainage systems, and riparian buffers on cropland.
In a large part of the U.S., profitable farming is possible because of artificial drainage and the application of inorganic or organic nitrogen and phosphorus fertilizer. The combination of these two practices has resulted in increased crop yields but has also contributed to nutrient loss from farmland producing negative human and environmental effects. Subsurface drainage is also frequently cited as contributing to increased streamflow and flooding.
One possible method to affect streamflow patterns and nutrients in the environment is by the establishment of wetlands. Wetlands have the ability to remove nutrients through various chemical and biological reactions. One disadvantage of wetland restoration is that the wetlands often disrupt the continuity of farming practices because of their location.
The objective of this project is to better understand and measure the effectiveness of three types of constructed basins designed to affect agricultural water quantity and quality through temporary water storage and nutrient and sediment removal from combined surface runoff and subsurface drainage systems.
The entire complex of constructed basins provides multiple ecosystem services. Regulation functions and related services include: water supply regulation, soil retention, nutrient cycling, and pollination. The site has so far created water storage and apparent soil and nutrient retention/cycling. Various forbs and grasses at the site also provide natural pollination. Habitat functions and related services include: living space for plants and animals and breeding and nursery areas. During spring and summer, various frogs, toads, shorebirds, and waterfowl have been observed using the site. There have been several nesting pairs of waterfowl at the site. Production functions and related services include: grasses and wild flowers. While raw materials are produced, there are no plans at this time to harvest and use these raw materials. The capacity exists to harvest upland native grasses for biomass/bioenergy. In addition, there are markets for seed harvested from native grasses and wildflowers that could potentially be used for restoration activities and plant enthusiasts. Information functions and related services include: aesthetic, recreational, scientific, and educational information. The complex of constructed basins also has intrinsic value as a research and demonstration site.
Types of Systems
Surface flow system: This system consists of a three-tiered basin having a soil bottom and a water surface 1.0 (0.3 m) to 2.0 (0.6 m) ft. deep. Vegetation consists of various rushes and water tolerant grasses and forbs. Water flow is primarily horizontal and aboveground. Water treatment is primarily through bacteria that live in the soil as well as by plant uptake.
Horizontal flow system: This system consists of a basin having an impermeable bottom and filled with substrate composed of layers of coarse and fine grade rock capped with soil. The substrate supports vegetation roots. Vegetation consists of various rushes and water tolerant grasses and forbs. Water flow is primarily horizontal and is maintained by a sloping bottom. The system also contains an adjustable outlet structure that allows the water level to be raised or lowered at the outlet of the bed. An adjustable outlet provides greater flexibility and flow control. Treatment is primarily through bacteria and beneficial fungi that live in the substrate as biofilm attached to the substrate and plant roots.
Vertical flow system: This system is similar to the horizontal-flow system except that this system is designed to treat water by passing it vertically through soil planted with various rushes and water tolerant grasses and forbs. This system consists of a level basin under which is installed shallow, narrow spaced corrugated plastic drain pipe. Water is allowed to temporarily pond in the basin and then must infiltrate through the soil to the drain pipe. This system also contains of an adjustable outlet structure. Treatment is primarily through bacteria that live in the soil as well as by plant uptake.
Each basin occupies an area equal to approximately one-half acre. Sediment, along with nitrogen and phosphorus are the main focus of water quality monitoring from agricultural runoff. The basin cells receive surface runoff water from a contributing area of 71 acres of land annually planted to corn and soybean. The subsurface drainage system area contributing to the systems consists of 114 acres.