DENITRIFICATION IN A RESTORED RIPARIAN FOREST WETLAND

Groundwater nitrate moving from upland areas toward streams can be rem oved by denitrification in mature riparian forests, but denitrificatio n in restored riparian forests has not been quantified. We determined denitrification rates in a restored riparian wetland below a liquid ma nure application site. A riparian forest buffer consisting of hardwood s along the stream and pines above the hardwoods was established accor ding to USDA specifications. Denitrification was measured monthly usin g the acetylene inhibition technique on intact soil cores for 2 mo bef ore manure application began and for 24 mo after manure application. G roundwater movement of NO3--N and total Kjeldahl N were estimated biwe ekly. Average annual denitrification rate was 68 kg N2O-N ha(-1)yr(-1) . Denitrification was significantly higher in a grassed area than in e ither of the forested areas. Denitrification did not differ significan tly between the hardwood and pine areas. Denitrification was greater t han a conservative estimate of groundwater input of total N. Denitrifi cation rates were higher in April and May 1992 and 1993, after manure application to the upland began, compared with April and May 1991, bef ore manure application began. These results indicate that a riparian w etland, which has not undergone hydrologic modifications, can have den itrification rates comparable to mature riparian forests. Higher denit rification rates in an adjacent grassed wetland and lack of difference s in denitrification in hardwood and pine zones indicates that the hig h denitrification rates were due to factors other than the reforestati on itself. Compared with groundwater inputs of N, denitrification was an important sink for N moving from the upland management system.