Nitrate (NO₃^–) enrichment in rivers over the last four decades has potentially shifted how coastal ecosystems process nitrogen (N). Shifts in N dynamics may be particularly significant in coastal deltaic floodplains when sediments are inundated during river flood stage as this may change the fate of NO₃^– transported to the coastal ocean. We evaluated the relative importance of denitrification, dissimilative nitrate reduction to ammonium (DNRA), and anaerobic ammonium oxidation (anammox) in intact sediment cores of Wax Lake Delta (WLD) using continuous flow-through system. We manipulated this experimental system with two concentrations of riverine NO₃^– (lower concentration at 5 μM and ambient concentration at 100 μM) to test how nitrate-enriched waters may modify N cycling in coastal deltaic floodplains. Inundated sediments in a coastal deltaic floodplain removed bio-reactive N as a function of sediment organic matter (SOM) concentrations, indicating how N dynamics vary as a result of deltaic succession. Direct denitrification was the dominant N pathway in inundated sediments in WLD, which was several times greater than coupled nitrification-denitrification, DNRA, and anammox. Gross denitrification (direct denitrification + coupled nitrification-denitrification) rates generally increased with SOM concentrations and ranged from 4 to 12 μmol N m^–2 h^–1 under lower NO₃^– enrichment (5 μM) and 68 to 276 μmol N m^–2 h^–1 under higher NO₃^– enrichment (100 μM). Most of these changes in N fluxes with SOM and NO₃^– enrichment resulted from the increase in direct denitrification rates rather than coupled nitrification-denitrification rates. DNRA rates varied from 0 to 65 μmol N m^–2 h^–1, and the relative significance of DNRA increased as a percentage of total NO₃^– reduction (%DNRA) with increasing ratio of organic carbon to NO₃^– concentrations (OC/NO₃^–). Anammox rates increased among sites as SOM increased, but rates were lower from 0.0 to 38 μmol N m^–2 h^–1. The dominance of direct denitrification and increased anammox rates with SOM concentrations indicate that dynamic deltaic floodplains can permanently remove bio-reactive N in the proximal zone of river deposition of tidal freshwater wetlands.

硝酸盐（NO ₃ ^- ）富集的河流，在过去四个十年里已经潜在转移沿海生态系统如何处理氮（N）。当沉积在河流洪水水位都淹没，因为这可能会改变NO命运的N动态的变化可能是在沿海三角洲冲积平原特别显著₃ ^-运到沿海的海洋。我们评估了使用连续流水系统在完整蜡质三角洲（WLD）沉积岩心中反硝化，硝酸盐异化还原为铵（DNRA）和厌氧铵氧化（anammox）的相对重要性。我们用两个浓度的河水NO ₃操纵了这个实验系统^–（较低的浓度为5μM，环境浓度为100μM），以测试富含硝酸盐的水如何改变沿海三角洲泛滥平原的氮素循环。沿海三角洲泛滥平原中被淹没的沉积物去除的生物活性氮随沉积物有机质（SOM）浓度的变化而变化，表明氮的动态变化是三角洲演替的结果。直接反硝化是WLD中淹没沉积物中主要的N途径，比耦合的硝化-反硝化，DNRA和厌氧氨水高出几倍。总体反硝化（直接反硝化+耦合硝化-反硝化）速率通常随SOM浓度的增加而增加，在较低的NO _3-下范围从4到12μmolN m ^–2 h ^{–1 。}富集（5μM）和68至276微摩尔n×m个^-2 ħ ^-1下更高NO ₃ ^-富集（100μM）。大多数这些变化的N通量与SOM，NO ₃ ^-富集造成的直接反硝化速率，而不是加上硝化-反硝化速率的增加。DNRA率从0变化到65微摩尔n×m个^-2 ħ ^-1，和DNRA的相对重要性随着总NO的百分数₃ ^-随有机碳的比率为NO减少（％DNRA）₃ ^-浓度（OC / NO ₃ ^-）。随着SOM的增加，各部位的厌氧氨氧化速率增加，但速率从0.0降至38μmolN m ^–2 h ^–1。直接反硝化和厌氧氨氧化率随SOM浓度升高的优势表明，动态三角洲洪泛区可以永久去除潮汐淡水湿地河流沉积近端的生物活性氮。