title: Recovery of nitrogen pools and processes in degraded riparian zones in the southern appalachians.
abstract: Establishment of riparian buffers is an effective method for reducing nutrient input to streams. However, the underlying biogeochemical processes are not fully understood. The objective of this 4-yr study was to examine the effects of riparian zone restoration on soil N cycling mechanisms in a mountain pasture previously degraded by cattle. Soil inorganic N pools, fluxes, and transformation mechanisms were compared across the following experimental treatments: (i) a restored area with vegetation regrowth; (ii) a degraded riparian area with simulated effects of continued grazing by compaction, vegetation removal, and nutrient addition (+N); and (iii) a degraded riparian area with simulated compaction and vegetation removal only (-N). Soil solution NO(3)(-) concentrations and fluxes of inorganic N in overland flow were >90% lower in the restored treatment relative to the degraded (+N) treatment. Soil solution NO(3)(-) concentrations decreased more rapidly in the restored treatment relative to the degraded (-N) following cattle (Bos taurus) exclusion. Mineralization and nitrification rates in the restored treatment were similar to the degraded (-N) treatment and, on average, 75% lower than in the degraded (+N) treatment. Nitrogen trace gas fluxes indicated that restoration increased the relative importance of denitrification, relative to nitrification, as a pathway by which N is diverted from the receiving stream to the atmosphere. Changes in soil nutrient cycling mechanisms following restoration of the degraded riparian zone were primarily driven by cessation of N inputs. The recovery rate, however, was influenced by the rate of vegetation regrowth.
authors.affiliation: U.S. Environmental Protection Agency, National Risk Management Research Lab., Research Triangle Park, NC 27711, USA. walker.johnt@epa.gov
authors.forename: John T
authors.initials: JT
authors.lastname: Walker
authors.forename: James M
authors.initials: JM
authors.lastname: Vose
authors.forename: Jennifer
authors.initials: J
authors.lastname: Knoepp
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Geron
mesh_terms: D001061:Appalachian Region; D009584:Nitrogen / Q000032:analysis*; D012987:Soil / Q000032:analysis*; D014867:Water / Q000032:analysis*
chemical_list: D012987:Soil; D014867:Water; D009584:Nitrogen