Removal of Nitrogen, Phosphorus and Prodiamine from a Container Nursery by a Subsurface Flow Constructed Wetland

摘要

Plant nurseries apply large amounts of agricultural chemicals that may run off causing problems to surface water. Constructed wetlands have been used to treat agricultural chemical runoff. A 128 m2 gravel subsurface flow constructed wetland was designed and installed at Pirtle’s Nursery in Smithville, TN. The wetland was 46 cm deep and contained an estimated 16.5 m3 of water. Softstem bulrush (Scirpus validus), cattails (Typha latifolia L.) and juncus (Juncus spp.) were planted in the wetland. A standpipe controlled water level in the wetland, and a bypass pipe averted heavy flow. Total nitrogen (N), phosphorus (P) and the pesticide prodiamine were measured from the influent and effluent water during daily irrigation events. A valve controlled flow into the wetlands to produce computed nominal hydraulic retention times of 0.7, 1.2 and 1.9 d. A Stevens Chart Recorder measured the influent water level to develop a flow versus water stage correlation at specific valve settings. Mean N removal was 70 to 72% of total influent N. Mean P removal varied from -2 to 10% of total influent P. Mean prodiamine removal ranged from 49 to 65% of total influent prodiamine. The wetland required little maintenance other than occasional sediment removal after heavy rain and occasional sediment flushing of the inflow pipe to maintain flow.