PH19 Biomonitoring
Exhibit Hall
8:00 AM - Thursday
(PH227) Long term monitoring of constructed wetlands used to mitigate nutrients in container nursery offsite drainage.
Taylor, M1, White, S1, Klaine, S1, Whitwell, T2, 1 Clemson Institute of Environmental Toxicology Clemson University, Pendleton, SC, USA2 Department of Horticulture Clemson University, Clemson, SC, USA
ABSTRACT- Container-grown plants from commercial nurseries and greenhouses require large amounts of water and nutrients during their production cycle. Mitigation of offsite movement of nutrients in their runoff is a serious concern because of the potential for downstream eutrophication. Monthly monitoring at a commercial nursery of 3.77 ha of vegetated constructed wetlands, receiving 1.6 to 2.2 million liters of runoff per day, indicated strong seasonal differences in nitrogen removal efficiency associated with water temperature. Nitrogen removal between April and November each year averaged greater than 95% while removal efficiency from December to February averaged slightly below 50% when water temperatures dropped below 15 °C. Nitrite was not found in wetland discharge water. Nitrogen as nitrate in discharge water varied from 0.01 to 4.28 mg/L, well below drinking water quality standards. Orthophosphate phosphorus removal was highly variable with highest removal occurring during vegetative growth flushes, which occurred throughout the growing season. However, there was a net export of phosphorus from the wetlands during all winter months. Phosphorus, as phosphate, levels in wetland discharge ranged between 0.92 and 2.40 mg/L. While there is currently no set water quality standard for phosphorus, these levels are above the generally accepted level of 0.01 mg/L for preventing downstream eutrophication. The poor performance of constructed wetlands to remediate phosphorus in nursery runoff suggests that reducing phosphorus loading in runoff by lowering application rates or employing fired clays in potting media to hold phosphorus in the container until uptake by the growing plant are better alternatives for limiting phosphorus in nursery and greenhouse runoff.
Key words: constructed wetlands, nutrient remediation, phytoremediation, seasonal changes