PM11 Treatment of Wastewater
Exhibit Hall
8:00 AM - Monday, 10 November 2003
(PM171) A Constructed Wetland System to Mitigate Nutrient Contaminants in Container Nursery Offsite Drainage.
Taylor, M1, Klaine, S1, Whitwell, T1, 1 Clemson University, Clemson, SC, USA
ABSTRACT- Container-grown plants at commercial nurseries require large amounts of water and nutrients during the production cycle. Nutrients are delivered through incorporation in potting media, by top-dressing, by injection into irrigation water, or some combination of these methods. Typically, surface water or groundwater is applied using overhead sprinklers or by drip irrigation to sloped production areas. Application rates are sufficient to ensure leaching of soluble salts resulting in substantial runoff. Thus, mitigation of offsite movement of nutrients in runoff is a serious concern. Wight Nurseries of Monrovia Growers, Cairo, Georgia, has installed 3.77 ha of planted wetlands to receive runoff from a 48.6 ha drainage basin and excess water diverted from retention ponds for adjacent watersheds. Water flows though trench drains between wetland cells and eventually into stilling ponds before exiting the property. Water flow ranges from 1.6 million to 2.2 million liters per day. Monitoring data indicates strong seasonal differences in nitrogen removal efficiencies. Nitrogen removal between late March and early November 2002 averaged 93.8% while removal from early December 2002 through early February 2003 averaged only 47.6%. Wetland efficiency was approx. 92% by early March 2003. No nitrite was found in discharge from the wetlands for any sampling period. Nitrate nitrogen in discharge water varied from 0.05 mg/L to 4.3 mg/L, well below drinking water quality standards, and was below 0.6 ppm between June and November 2002 except in September 2002 during construction activity. Orthophosphate phosphorus removal was highly variable with net removal from April 2002 through October 2002 and net export occurring during winter months. Phosphorus levels ranged between 0.9 and 1.9 ppm. While there is currently no legal water quality standard for phosphorus, these levels are above the generally accepted level of 0.01 ppm for preventing downstream eutrophication.
Key words: Mitigation, Runoff, Nutrient contaminants, Constructed wetlands