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Increasing nitrate (NO 3 − ) loading in rivers due to agricultural fertilization alters benthic nitrogen (N) cycling and shifts coastal wetlands from being a net source to net sink of reactive N. Heterotrophic N 2 fixation that converts N 2 to reactive N is often assumed negligible in eutrophic ecosystems and excluded in coastal N budget evaluations. We investigated N 2 fixation and denitrification in response to increasing NO 3 − loading (0, 10, and 100 μM) and sediment organic matter (OM sediment ) concentrations in the emerging Wax Lake Delta. Continuous flow-through incubations with 30 N 2 addition was applied to measure N 2 fixation. The variation of N 2 fixation rates from 0 to 437 μmol N m −2 h −1 among different NO 3 − and OM sediment concentrations were comparable to the estimated denitrification rates of 141-377 μmol N m −2 h −1 . Increasing overlying NO 3 − concentrations reduced N 2 fixation rates and facilitated denitrification rates at each OM sediment concentration. However, 100 μM of overlying NO 3 − did not thoroughly inhibit N 2 fixation rates in sites with intermediate and higher

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