Nitrate removal in a riparian wetland of the Appalachian Valley and Ridge physiographic province

Riparian zones within the Appalachian Valley and Ridge physiographic province are often characterized by localized variability in soil moisture and organic carbon content, as well as variability in the distribution of soils formed from alluvial and colluvial processes. These sources of variability may significantly influence denitrification rates. This investigation studied the attenuation of nitrate (NO₃/^--N) as wastewater effluent flowed through the shallow ground water of a forested headwater riparian zone within the Appalachian Valley and Ridge physiographic province. Ground water flow and NO₃/^--N measurements indicated that NO₃/^--N discharged to the riparian zone preferentially flowed through the A and B horizons of depressional wetlands located in relic meander scars, with NO₃/^--N decreasing from >12 to <0.5 mg L^-1. Denitrification enzyme activity (DEA) attributable to riparian zone location, soil horizon, and NO₃/^--N amendments was also determined. Mean DEA in saturated soils attained values as high as 210 μg N kg^-1 h^-1, and was significantly higher than in unsaturated soils, regardless of horizon (p < 0.001). Denitrification enzyme activity in the shallow A horizon of wetland soils was significantly higher (p < 0.001) than in deeper soils. Significant stimulation of DEA (p = 0.027) by NO₃/^--N amendments occurred only in the meander scar soils receiving low NO₃/^--N (<3.6 mg L^-1) concentrations. Significant denitrificafion of high NO₃/^--N ground water can occur in riparian wetland soils, but DEA is dependent upon localized differences in the degree of soil saturation and organic carbon content.