Nutrient transport in a restored riparian wetland.

We determined the water quality effect of a restored forested riparian wetland adjacent to a manure application area and a heavily fertilized pasture in the Georgia Coastal Plain. The buffer system was managed based on USDA recommendations and averaged 38 m in width. Water quality and hydrology data were collected from 1991-1999. A nitrate plume in shallow ground water with concentrations exceeding 10 mg NO3-N L(-1) moved into the restored forested riparian wetland. Along most of the plume front, concentrations were less than 4 mg NO3-N L(-1) within 25 m. Two preferential flow paths associated with past hydrologic modifications to the site allowed the nitrate plume to progress further into the restored forested riparian wetland. Surface runoff total N, dissolved reactive phosphorus (DRP), and total P concentrations averaged 8.63 mg N L(-1), 1.37 mg P L(-1), and 1.48 mg P L(-1), respectively, at the field edge and were reduced to 4.18 mg N L(-1), 0.31 mg P L(-1), and 0.36 mg P L(-1), respectively, at the restored forested riparian wetland outlet. Water and nutrient mass balance showed that retention and removal rates for nitrogen species ranged from a high of 78% for nitrate to a low of 52% for ammonium. Retention rates for both DRP and total P were 66%. Most of the N retention and removal was accounted for by denitrification. Mean annual concentrations of total N and total P leaving the restored forested riparian wetland were 1.98 mg N L(-1) and 0.24 mg P L(-1), respectively.