Here, we estimate denitrification in shallow groundwater to help determine if current streamside management zones (SMZs) can mitigate nitrate input from short-rotation pine management in the Upper Atlantic Coastal Plain. Water samples were collected monthly for a year and analyzed for nutrient (NO3-, NH4+, TN, DOC) and dissolved gas (N2, Ar, N2O) concentrations from the Fourmile Watershed at the Savannah River Site. Excess-N2 produced by denitrification was measured using MIMS and N2:Ar ratios. Nitrate concentrations decreased between the edge of the SMZ and the intermittent stream valley. N2O was the dominant end product in the pine plantation. Median denitrification reaction progress ranged from 0.47 to 0.94. Environmental conditions, such as low pH, fluctuating water table, high concentrations of NO3-, and low levels of DOC, inhibited complete denitrification in the shallow groundwater. Denitrification in the SMZ mitigates the additional nitrogen inputs from short-rotation woody crop (SRWC) management.