Changes in riparian hydrology and biogeochemistry following storm events at a restored agricultural stream

Quantifying changes in riparian biogeochemistry following rainfall events is critical for watershed management. Following storms, changes in riparian hydrology can lead to high rates of nutrient processing and export and greenhouse gas (GHG) release. We assessed shifts in hydrology and biogeochemistry 24 and 72 hours post-rainfall following storms of three different magnitudes in an agricultural riparian zone influenced by stream restoration in the Piedmont region of North Carolina, USA. Post-storm changes in water table height, soil moisture, groundwater flow, and lateral hydraulic gradient were related to biogeochemical processing. Though near-field nitrate (NO3-) concentrations were elevated (median: 13 mg nitrogen (N) L-1 across storms), substantial riparian NO3- removal occurred (89-96%). High N removal throughout the study occurred concurrently with release of dissolved solutes (e.g., soluble reactive phosphorus [SRP]) and fluxes of gases (carbon dioxide [CO2], nitrous oxide [N2O], and methane [CH4]), based on storm timing, magnitude, and intensity. A high intensity, short duration storm of low magnitude lead to release of CO2 across the riparian zone and low SRP removal. A storm of intermediate duration/magnitude towards the beginning of the summer lead to mobilization of near-field NO3- and release of N2O in the upper riparian zone and SRP in the lower riparian zone. Finally, a larger storm of longer duration lead to pronounced near-stream release of CH4. Therefore, it is important to expand research of biogeochemical response to different types of storm events in restored riparian zones to better balance water quality goals with potential greenhouse gas emissions.