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Constructed wetlands clean up.

The same tail grasses that thrive in wetlands throughout the world could prevent pollution of water resources by dairy farms.

"Scientists studying wetlands are finding these areas perform a great ecological service. They're nature's way of protecting water quality by filtering out nutrients, organic chemicals, heavy metals, and sediment from inflowing waters," says Charlie Cooper, ARS ecologist at the USDA National Sedimentation Laboratory in Oxford, Mississippi.

Since 1990, Cooper, along with ecologist Scott Knight and biologist Sam Testa, has been evaluating three manmade wetlands built on the Allan Scott farm near Herando, Mississippi. Cooper says, "Constructed wetlands offer several benefits. They're energy efficient, relatively inexpensive to build, simple to operate, aesthetically pleasing, and they attract a variety of wildlife."

He adds, "Using wetlands to treat wastewater is not a new concept. Natural wetlands do an excellent job of processing contaminants, and cities have used them for years to treat municipal and some industrial wastewater."

On the 117-cow Scott dairy farm, a 135- by 170 by 8-foot-deep earthen settling

lagoon receives wastewater collected from cleaning milking equipment, barn washings, runoff from the loafing (pre-milking) area, and rainfall.

"The lagoon's purpose," Knight explains, "is to settle out most of the solid contaminants."

Just below the lagoon, three 20- by 80- by 3-foot-deep earthen wetland cells were built to further treat the runoff pumped from the lagoon to a holding tank, from which a constant flow moves to the three parallel cells.

Says Knight, "We planted giant bulrushes, Scripus validus, at 1-foot intervals in the cells. Their purpose was to provide substrate for microorganisms that process or remove contaminants such as nitrogen, phosphorus, ammonia, and total suspended solids."

The team has been monitoring 18 water-quality indicators bi-weekly since May 1991, when the treatment system began working. They include levels of chlorophyll, several forms of phosphorus and nitrogen, as well as oxygen.

Two months after evaluation began, they built a fourth cell to further treat outflow from cell 1 to see what effect the additional treatment would have.

"Adding this cell in series cuts in half the amounts of contaminants-- like dissolved solids and phosphorus-- that could be discharged from the system," Testa says.

The system is now entering its third year of operation. It has already proved very effective in removing two of the primary targets of the project--ammonia and coliform bacteria.

Each cell processes 51 cubic feet of wastewater a day, reducing the ammonia level by about 91 percent and coliform bacteria by 96 percent.

"That doesn't mean you can drink the water," Knight says, "but it is a major step toward reaching non-point contamination goals. These cells have no discharge more than half of the time, and a hay meadow below the cells retains run-off and nutrients when discharge does occur."

The constructed wetland project is part of the joint Demonstration Erosion Control Project in the Yazoo Basin involving ARS and the USDA Soil Conservation Service (SCS) in

Jackson, Mississippi, the Vicksburg District of the U.S. Army Corps of Engineers, and the U.S. Army Engineers Waterways Experiment Station of the Corps.

SCS, the cooperating partner, designed and constructed the lagoon and wetland cells, while ARS is evaluating the project's efficiency in cleaning up wastewater.

Cooper, Knight, and Testa expect to continue monitoring the system and to develop operational and maintenance procedures for anyone planning to install it.

Charlie Cooper, Scott Knight, and Sam Testa are in the USDA-ARS Water Quality/Ecology Research Unit, National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38655; phone (601) 232-2935, fax (601) 232-2915.
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Author:Becker, Hank
Publication:Agricultural Research
Date:Dec 1, 1993
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