An Estimate of Basin-Wide Denitrification Based on Floodplain Inundation in the Atchafalaya River Basin, Louisiana

Maximizing the reduction of nitrate to dinitrogen gas (denitrification) has been advocated as a means to decrease nitrate pollution that causes eutrophication and hypoxia in estuaries worldwide. Managing this flux in bottomland forest wetlands of the Mississippi River could potentially reduce the world's second largest hypoxic zone. We used published denitrification rates, geospatial data on habitat area and inundation frequency, water level records (1963-2011), and average monthly temperatures to estimate annual denitrification in the Atchafalaya River Basin, the principal distributary of the Mississippi River. Denitrification rates ranged from 5394kgNyear(-1) (3.07kgNkm(-2)year(-1)) in 1988 to 17420kgNyear(-1) (9.92kgNkm(-2)year(-1)) in 1981, and rates were consistently higher in fall compared with those in spring. Total NO3- denitrified in the basin was negligible compared with total NO3- entering the Gulf of Mexico. If all N denitrified in the basin instead entered the Gulf, the hypoxic zone was predicted to increase only 5.07km(2) (0.06%). This negligible effect of the basin on N dynamics in the Gulf agrees with other mass balance and isotopic studies in the region. Copyright (c) 2014 John Wiley & Sons, Ltd.