| Anthropogenic inputs of nitrogen have dramatically increased fluxes to coastal waters leading to eutrophication. Riparian zones are considered particularly effective at and typically host conditions favorable for denitrification. The in-situ push-pull method was used in riparian groundwater from May-November, 2013. A plume of groundwater amended with excess NO3- and Br- was injected to characterize nitrogen attenuation processes and electron donors. Median NO3- removal occurred in all experimental rounds (1.6-9.2 mg N/L*day), but less than half showed TDN removal (0.1-9.0 mg N/L*day). Shifts to net nitrogen production in November (3.0-10.6 mg N/L*day) could indicate seasonal nitrogen export. An inverse relationship was observed between available DOC and TDN removal contradicting results in similar studies. Alternative electron donors such as HS-, S0, Fe 2+, and Mn2+ could play a more important role in denitrification under ambient conditions than previously thought and should be considered in future field studies of nitrogen attenuation. |
