Drought and saltwater incursion synergistically reduce dissolved organic carbon export from coastal freshwater wetlands
Drought and saltwater incursion synergistically reduce dissolved organic carbon export from coastal freshwater wetlands
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DOI：
10.1007/s10533-016-0189-5
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发表时间：
2016-02-01
期刊：
影响因子：
4
通讯作者：
Bernhardt, Emily S.
中科院分区：
文献类型：
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作者：
Ardon, Marcelo;Helton, Ashley M.;Bernhardt, Emily S.
溶解有机碳（DOC）的水文输运既是生态系统的主要能量损失，也是生态系统之间的重要能量联系。沿海淡水湿地作为DOC的主要来源，河口，历史上的DOC转移的幅度和时间一直由水运动。美国东南部沿海平原广泛的农业发展通过运河在水文上连接了大部分景观，以促进排水。由此造成的地形起伏大规模丧失和平均海拔降低，与日益频繁和严重的干旱相互作用，促使海水通过高度连通的人工排水网络向陆地流动。由此产生的水文制度和盐度的变化，预计将减少DOC输出沿海淡水湿地，但他们的个人和组合的影响还没有得到很好的理解。在这里，我们表明，夏末干旱期间重复的盐水入侵大大降低了美国北卡罗来纳州沿海平原成熟和恢复的森林湿地地表水中DOC浓度（从接近40 mg/L降至接近18 mg/L）。这些DOC浓度的下降减少了70%的DOC出口到河口的年出口量，并抑制了76%的风暴通量。我们使用了一个长期的实验与完整的土柱测量干旱，盐度和硫酸盐负荷的独立和综合影响的DOC浓度的大的变化的潜在驱动程序。我们发现，土壤干燥和盐碱化各自降低DOC相似（干旱单独减少20%，盐碱化减少29%），它们的组合效应是累加的（盐碱化+干旱处理减少49%）。我们的研究结果表明，在海平面显著上升之前，干旱和相对较低水平的盐水入侵（< 6 ppt）已经显著改变了沿海森林湿地和下游河口之间溶解有机碳通量的时间和幅度。
The hydrologic transport of dissolved organic carbon (DOC) represents both a primary energetic loss from and a critical energetic link between ecosystems. Coastal freshwater wetlands serve as a primary source of DOC to estuaries; historically the magnitude and timing of DOC transfers has been driven by water movement. Extensive agricultural development throughout the coastal plain of the southeastern US has hydrologically connected much of the landscape via canals to facilitate drainage. The resulting large-scale loss of topographic relief and reduced mean elevation is interacting with increasingly frequent and severe droughts to facilitate the landward movement of seawater through the highly connected artificial drainage networks. The resulting changes in hydrologic regime and salinity are each expected to reduce DOC export from coastal freshwater wetlands, yet their individual and combined impacts are not well understood. Here we show that repeated saltwater incursion during late summer droughts substantially decreased DOC concentrations in surface water (from similar to 40 to similar to 18 mg/L) from a mature and a restored forested wetland in the coastal plain of North Carolina, USA. These declines in DOC concentration reduced annual export of DOC to the estuary by 70 % and dampened storm fluxes by 76 %. We used a long-term experiment with intact soil columns to measure the independent and combined effects of drought, salinity, and sulfate loading as potential drivers of the large changes in DOC concentration. We found that soil drying and salinization each reduced DOC similarly (20 % reduction by drought alone, 29 % by salinization) and their combined effect was additive (49 % reduction in salinization + drought treatments). Our results demonstrate that, well in advance of significant sea-level rise, drought and relatively low levels of saltwater incursion (< 6 ppt) are already significantly altering the timing and magnitude of dissolved organic carbon flux between coastal forested wetlands and downstream estuaries.