Denitrifying Bioreactors: Opportunities and Challenges for Managing Offsite Nitrogen Losses

摘要

watersheds that deliver elevated levels of agricultural nitrogen (N), denitrifying bioreactors — often simple trenches or denitrification walls filled with a solid carbon (C) substrate — hold great promise for treating non-point discharges of nitrate-rich water. These systems have been developed largely in the temperate zone for high-input, high-production croplands and nitrified waste streams. A wide range of nitrate removal rates (0.014-22 g N-m"3-d"1) have been reported infield-based bioreactorstudies generally reflecting differences in C substrates, hydrologic setting, temperature, seasonal/site variation in N loading and hydraulic residence time. The use of stable N isotopes has been critical for determining that denitrification is the process most responsible for observed declines in nitrate loads. Further, investigations with N isotopes provide insights into factors that can inform placement and design to minimize the extent of nitrous oxide (N_2O) and methane (CH4) emissions from this type of management practice.