Department of Oceanography and Coastal Sciences, College of the Coast and Enviroment, Louisiana State University, Baton Rouge, LA 70808, USA.
Department of Oceanography and Coastal Sciences, College of the Coast and Enviroment, Louisiana State University, Baton Rouge, LA 70808, USA.
Sci Total Environ. 2022 May 1;819:152942. doi: 10.1016/j.scitotenv.2022.152942. Epub 2022 Jan 7.
Nitrate (NO) and ammonium (NH) are reactive nitrogen (N forms that can exacerbate eutrophication in coastal regions. NO can be lost to the atmosphere as N gas driven by direct denitrification, coupled nitrification-denitrification and annamox or retained within the ecosystems through conversion of NO to NH via dissimilatory nitrate reduction to ammonium (DNRA). Denitrification and DNRA are competitive pathways and hence it is critical to evaluate their functional biogeochemical role. However, there is limited information about the environmental factors driving DNRA in oligohaline habitats, especially within deltaic regions where steep salinity gradients define wetland spatiotemporal distribution. Here we use the Isotope Pairing Technique to evaluate the effect of temperature (10, 20, 30 °C) and in situ soil/sediment organic matter (OM%) on total denitrification (Dtotal = direct + coupled nitrification) and DNRA rates in oligohaline forested/marsh wetlands soils and benthic sediment habitats at two sites representing prograding (Wax Lake Delta, WLD) and eroding (Barataria- Lake Cataouatche, BLC) deltaic stages in the Mississippi River Delta Plain (MRDP). Both sites receive MR water with high NO (>40 μM) concentrations during the year via river diversions. Denitrification rates were significantly higher (range: 18.0 ± 0.4-113.0 ± 10.6 μmol m h) than DNRA rates (range: 0.7 ± 0.2-9.2 ± 0.3 μmol m h). Therefore, DNRA represented on average < 10% of the total NO reduction (DNRA + Dtotal). Unlike denitrification, DNRA showed no consistent response to temperature. These results indicate that DNRA in wetland soils and benthic sediment is not a major nitrogen transformation in oligohaline regions across the MRDP regardless of wide range of OM% content in these eroding and prograding delta lobes.
硝酸盐（NO）和氨（NH）是活性氮（N）的两种形式，它们会加剧沿海地区的富营养化。NO 可以通过直接反硝化作用、耦合硝化-反硝化作用和厌氧氨氧化作用转化为 N 气体而损失到大气中，或者通过异化硝酸盐还原为铵（DNRA）将 NO 转化为 NH 而保留在生态系统中。反硝化作用和 DNRA 是竞争途径，因此评估它们的功能生物地球化学作用至关重要。然而，关于寡盐环境中 DNRA 的环境因素的信息有限，特别是在三角洲地区，那里的陡盐度梯度定义了湿地的时空分布。在这里，我们使用同位素配对技术来评估温度（10、20、30°C）和原位土壤/沉积物有机质（OM%）对寡盐森林/沼泽湿地土壤和底栖沉积物栖息地中总反硝化作用（Dtotal=直接+耦合硝化）和 DNRA 速率的影响，这两个地点代表了密西西比河三角洲平原（MRDP）中进积（Wax Lake Delta，WLD）和侵蚀（Barataria-Lake Cataouatche，BLC）三角洲阶段。这两个地点都通过河流改道接收来自密西西比河的高硝酸盐（>40μM）浓度的 MR 水。反硝化作用速率明显高于 DNRA 速率（范围：18.0±0.4-113.0±10.6μmol m h）（范围：0.7±0.2-9.2±0.3μmol m h）。因此，DNRA 平均仅占总 NO 还原（DNRA+Dtotal）的<10%。与反硝化作用不同，DNRA 对温度没有一致的反应。这些结果表明，无论这些侵蚀和进积三角洲叶瓣中的 OM%含量范围如何，DNRA 在 MRDP 寡盐地区的湿地土壤和底栖沉积物中都不是主要的氮转化。
