Submitted to: Mississippi Water Resources Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2004
Publication Date: July 2, 2004
Citation: Cooper, C.M., Knight, S.S., Testa III, S. 2004. Constructed wetlands: An edge-of-field management practice for reduction of coliform. Mississippi Water Resources Research Conference Proceedings. p. 25-30. Interpretive Summary: Coliform bacteria are the most common cause of impairment of waterbodies in the U. S. and animal production areas are a predominant source even when animals are not come in direct contact with waterbodies. Scientists in the Water Quality and Ecological Processes Research Unit examined the potential of a small constructed wetland to treat worst-case coliform pollution from cattle. Lagoon-concentrated waste came from a dairy barn where coliform levels exceeded the Mississippi minimum criteria for surface waters over 70-fold. The constructed wetland treatment system totally eliminated discharge at 43% of observations and achieved greater than 89% elimination of coliform bacteria from the amount that did discharge. Further reductions were effected by discharge through a grassed buffer and vegetated ditch. Small, low cost constructed wetlands can provide highly effective reduction of coliform bacteria from animal production lands as well as improving soil retention, trapping other pollutants, and general ecological enhancement.
Technical Abstract: Coliform bacteria rank among the most commonly listed causes for stream impairment in Mississippi. Constructed wetlands have been shown to provide excellent treatment to reduce coliform bacteria in waters before entering receiving streams. Mississippi's 2002 303(d) list had 15 segments within the Coldwater River watershed that were included for pathogen contamination. For three years, we monitored a constructed wetland system located near Hernando, Mississippi, built for treatment of dairy farm wastes that flowed indirectly into the Coldwater River before entering Arkabutla Reservoir. These dairy wastes contained excessive concentrations of fecal coliform bacteria that threatened to cause harm to humans making use of the river and reservoir for recreation and fishing. The constructed wetland treatment pond size was only 6 m wide by 24 m long and was examined in triplicate. Our data showed that the constructed wetland totally eliminated discharge at 43% of observations (78 of 181 observation dates). When discharge occurred, the constructed wetland reduced the coliform bacterial counts by an average of 89%. The average fecal coliform count in water leaving the dairy farm and entering the constructed wetland system was 14,525 colony-forming units (CFU) per 100 ml water, well above (more than 70 times) the minimum numeric criteria adopted by the State of Mississippi for acceptable levels in surface waters (200 CFU per 100 ml). The average coliform count leaving the constructed wetland system was 1,585 CFU per 100 ml water, still above the minimum acceptable level for surface waters, but dramatically reduced from potential concentrations. Constructed wetland effluent flowed overland through a grassed buffer and then through an agricultural ditch further reducing fecal coliform bacterial levels prior to entering natural surface waters (Short Fork Creek and Coldwater River). Implementation of constructed wetlands at strategic locations on cattle grazing lands and other locations where elevated fecal coliform bacteria concentrations may occur in runoff would be extremely beneficial in lowering concentrations in surface waters throughout the state, reducing hazards to humans.