Research Sites

Fairview Constructed Wetland System - Additional Information

Pollution from agricultural run-off and irrigation return flows is a problem in surface and ground water throughout the arid and semi-arid regions of the western United States. Most farming operations use chemicals to obtain maximum crop production. Not all of these chemicals are utilized by the crops. Irrigation wastewater and natural runoff can carry these unused chemicals to rivers, lakes, or reservoirs (IDHW-DEQ, 1995; Poulson, 1996). These pollutants can lead to undesirable aquatic plant growth which in turn reduces oxygen availability, increases water temperature, and decreases human enjoyment of the river (Kadlec, 1996). To maintain water quality, farmers must practice better stewardship of their soil and water resources by reducing concentrations of chemicals in wastewater and runoff.

The photo above is of the sediment pond, the first component of our constructed wetland system. Note the light brown plume of sediment in the upper left corner, material that was carried from a furrow irrigated field.

Good management practices such as conservation tillage help reduce non-point-source pollution; however, they do not eliminate it. Research suggests that a Constructed Wetlands System is the only cost effective way to treat agricultural wastewater before it is returned to surface or groundwater (e.g. Hoag, 1994; IDHW-DEQ, 1995; Wengrzynek and Terrell, 1990). A Constructed Wetland System (CWS) is a method of treating wastewater using wetland plants and microbes. A CWS is both a physical system for removing sediments and a biological treatment system that utilizes wetland plants and microbes to assimilate and breakdown excess nutrients and remove them from irrigation waste water (DuPoldt et al., 1993). For a large watershed, a CWS requires a relatively small area of land and has relatively low construction costs. Other benefits of a CWS include long life, easy management, increased aesthetics, increased wildlife habitat, and the value of nutrients that are harvested from the wetland.

Wetland systems have been built in the eastern United States and in California, but few systems designed to treat agricultural wastewater have been built in the arid and semiarid West. One problem is that irrigation water is only available from April through October and the plants must survive the winters on the small amount of precipitation that occurs naturally. Another problem is that the temperature extremes frequently found in the West are not conducive to the survival of species used in wetlands in other areas. Installed systems in the West have functioned effectively mainly because of the use of adapted plants and different management techniques (Hoag, 1994).

The watershed for this CWS is about 55 ha (137 acres) of Poulsonís farm, located on the west side of American Falls Reservoir. This area is managed for spring and winter wheat, alfalfa, potatoes, grass seed, and pasture. The Fairview CWS has five ponds, each with different characteristics for the treatment of water polluted with agricultural chemicals. This design was based in large part on work by Wengrzynek and Terrell (1990) indicating that a five-element system works well for the treatment of non-point-source pollution.

Cell Type

Function

Water Depth

Vegetation

Sediment Pond
(1 pond)

collect organic matter, larger sediment particles, provide water storage and regulate flows through CWS

variable, depending on inflow and outflow to other cells only along banks to prevent erosion
Primary Filter
(8 cells)

remove fine sediments and dissolved N

inflow from sediment pond
outflow to any cell listed below

< 10 cm

Carex nebrascensis

Juncus balticus

Eleocharis palustrisSchoenoplectus maritimus

Shallow Wetland
(4 cells)

remove nitrates, ammonia, bacteria

inflow from sediment pond, primary filter, or other shallow wetland cells

10 - 50 cm Typha latifoliaSchoenoplectus acutus
Deep Water Pond
(1 pond)

remove dissolved nutrients,
    fine sediments

inflow from any cell listed above
outflow to final filter

100 - 300 cm Sago pondweed
(floating)
Final Filter
(1 cell)

remove dissolved nutrients

inflow from any cell
outflow is directly to American Falls Reservoir

variable

Carex nebrascensis

Juncus balticus

Eleocharis palustrisSchoenoplectus maritimus, Typha latifolia,   Schoenoplectus acutus

A photo of the Primary Filter (PF) cells is below. Water flows from left to right. Cells are separated by black plastic dividers. Four PF cells were planted with a single species (Carex nebrascensis); one of those is in the foreground. Four PF cells were planted with strips of four species. Dark green patches of Juncus balticus are visible in the 2nd and 3rd cells from the bottom of the photo.

The CWS was designed so the water entering the wetland can be routed to bypass any of these elements. This will allow the CWS to model many simpler wetlands, making it possible to directly compare the effectiveness of different pond types, different combinations of pond types, and different plant communities at removing agricultural chemicals from agricultural runoff and return flows. The information generated in this study will be used to improve CWS designs so that farmers will have a more economically feasible method of solving some of their own pollution problems.

There are wetland systems which have been or are in the process of being built in the West using this multi component concept: the Nature Conservancy CWS, near Hagerman, Idaho; the Cedar Draw Water Quality Research and Demonstration Project, Twin Falls, Idaho; and the H-Drain Constructed Wetland System at Burley, Idaho. These all treat water from large areas, such as canal return flows. None of these allow replicated trials of different water flow patterns and different vegetation. None is suitable to be used for small flows from a small, on-farm watershed.

To identify the specific requirements for reducing non-point source pollution at the Fairview wetland site, samples were collected from head water and tail waters of several fields, from irrigation canals that provide water to the site, and from the Snake River above the American Falls Reservoir. Results of this sampling indicated that total suspended solids, nitrogen, and phosphorus are likely candidates for improvement in a CWS.

 

Literature Cited

Dupoldt, C.A., R.W. Franzen, C.R. Terrell, and R.J. Wengrzynek. 1993. "Nutrient and Sediment Control System." Chester, PA: Environmental Quality Technical Note No. N4, USDA-SCS, NNTC. 19 pp.

Hoag, J. Chris, and Jichael E. Sellers. 1994. Constructed wetland system for water quality improvement of irrigation wastewater. Riparian/Wetland Project Information Series No. 8. December, 1994. 3 pp.

Kadlec, Robert H. 1996. Treatment wetlands. Boca Raton : Lewis Publishers.

Wengrzynek, R. and C. Terrell. 1990. Using constructed wetlands to control agricultural nonpoint source pollution. International Conference on the Use of Constructed Wetlands in Water Pollution Control. Cambridge, United Kingdom. 13 pp.