Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2002
Publication Date: 1/1/2003
Citation: Vellidis, G., Lowrance, R.R., Gay, P., Hill, R., Hubbard, R.K. 2003. Nutrient transport in a restored riparian wetland. Environmental Quality. 32:711-726. Interpretive Summary: One of the most important functions of riparian (streamside) buffers is to keep nonpoint source (diffuse) pollution out of surface waters such as streams, rivers, and lakes. Although riparian buffers are being used to improve water quality through USDA cost-share programs such as the Conservation Reserve Program, there have been few studies of the effects of restored riparian buffers on water quality. This study is the first report of how a restored riparian wetland buffer affects water quality below intensively fertilized fields, including a liquid manure application area. To restore the riparian wetland, we converted an area of wet pasture to forest and permanent grasses in 1991. For the next 9 years, we monitored the amount of water and the concentrations of nutrients- nitrogen (N) and phosphorus (P) in water entering and leaving the riparian wetland. The stream flow concentrations of N and P leaving the riparian wetland buffer were one-half and one-quarter, respectively of the incoming concentrations in surface runoff from the adjacent fields. We estimated the water budget for the wetland and developed nutrient budgets (nutrient inputs minus nutrient outputs) to be able to estimate the percent of the entering nutrients that were retained or removed by the riparian wetland. The wetland retained or removed 59% of the N and 66% of the P that entered from the surrounding agricultural lands. The study showed that the potential nonpoint (diffuse) sources of N and P pollution that move from liquid manure application areas and heavily fertilized pastures can be reduced by a restored riparian wetland.
Technical Abstract: We determined the water quality impact of a restored 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-NRCS recommendations for three zone riparian buffers and averaged 38 m in width. The system included a grass strip immediately adjacent to the production areas and areas of planted pines and hardwoods down slope. Water quality data were collected for 9 years, 1991-1999. Maps of nitrate concentrations showed a nitrate plume moving through the restored wetland along preferential flow paths associated with old ditches that had filled with sediment. Surface runoff total N, total P, and phosphate-P concentration averaged 8.63 mg L-1, 1.48 mg L-1, and 1.37 mg L-1, respectively at the field edge. They were reduced to 4.18 mg L-1, 0.36 mg L-1, and 0.31 mg L-1, respectively, at the wetland outlet. An annual water balance and nutrient mass balance was used to develop nutrient retention/removal rates. For nitrogen species, the rates ranged from a high of approximately 78% for NO3-N to a low of 52% for NH4-N. Retention rates for PO4-P and TP were 65% and 66%, respectively. Mean annual concentrations of TN and TP leaving the restored riparian wetland were 1.98 mg L-1 and 0.24 mg L-1, respectively. These concentrations were less than concentrations thought to cause nutrient enrichment of downstream waters. The coupling of the restored riparian wetland with the manure application area and fertilized pasture produced good quality stream flow.