Drought-induced saltwater incursion leads to increased wetland nitrogen export
Drought-induced saltwater incursion leads to increased wetland nitrogen export
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DOI：
10.1111/gcb.12287
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发表时间：
2013-10-01
影响因子：
11.6
通讯作者：
Bernhardt, Emily S.
中科院分区：
文献类型：
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作者：
Ardon, Marcelo;Morse, Jennifer L.;Bernhardt, Emily S.
沿海湿地具有截留和吸收大量活性氮的能力，这使得它们在减少人为增加的氮通量到沿海生态系统中发挥重要作用。沿海湿地保留和转化氮的能力正在减少土地开发造成的湿地损失。氮保留在沿海湿地进一步受到威胁的频率和空间范围的海水淹没在历史上的淡水生态系统，由于疏浚的综合影响，减少河流排放到沿海地区，由于人类用水，干旱频率增加，加速海平面上升。由于盐水入侵可能会影响N循环通过多种机制，盐渍化对沿海淡水湿地N的保留和转化的影响还没有得到很好的理解。在这里，我们表明，在夏末干旱的北卡罗来纳州沿海平原的海水入侵，改变了N的出口从有机无机形式，并导致每年的NH4+出口从440公顷的前农田进行湿地恢复的两倍。两个成熟湿地土壤溶液NH4+浓度也随盐渍化程度的增加而增加，但增加幅度小于原农田。长期盐水暴露实验与完整的土柱表明，大部分的活性氮释放的增加可以解释由盐阳离子与沉积物NH 4+交换。利用这些研究结果以及预测到2100年北卡罗来纳州沿海沿着1661 km（2）湿地的洪水，我们估计盐水入侵这些沿海地区可能释放高达18077 Mg N，或约为密西西比河年NH4+通量的一半。我们的研究结果表明，海水入侵到全球沿海淡水湿地可能会导致增加氮负荷敏感的沿海沃茨。
Coastal wetlands have the capacity to retain and denitrify large quantities of reactive nitrogen (N), making them important in attenuating increased anthropogenic N flux to coastal ecosystems. The ability of coastal wetlands to retain and transform N is being reduced by wetland losses resulting from land development. Nitrogen retention in coastal wetlands is further threatened by the increasing frequency and spatial extent of saltwater inundation in historically freshwater ecosystems, due to the combined effects of dredging, declining river discharge to coastal areas due to human water use, increased drought frequency, and accelerating sea-level rise. Because saltwater incursion may affect N cycling through multiple mechanisms, the impacts of salinization on coastal freshwater wetland N retention and transformation are not well understood. Here, we show that repeated annual saltwater incursion during late summer droughts in the coastal plain of North Carolina changed N export from organic to inorganic forms and led to a doubling of annual NH4+ export from a 440 hectare former agricultural field undergoing wetland restoration. Soil solution NH4+ concentrations in two mature wetlands also increased with salinization, but the magnitude of increase was smaller than that in the former agricultural field. Long-term saltwater exposure experiments with intact soil columns demonstrated that much of the increase in reactive N released could be explained by exchange of salt cations with sediment NH4+. Using these findings together with the predicted flooding of 1661km(2) of wetlands along the NC coast by 2100, we estimate that saltwater incursion into these coastal areas could release up to 18077Mg N, or approximately half the annual NH4+ flux of the Mississippi River. Our results suggest that saltwater incursion into coastal freshwater wetlands globally could lead to increased N loading to sensitive coastal waters.