Tidal salt marsh is a key defense against, yet is especially vulnerable to, the effects of accelerated sea level rise. To determine whether salt marshes in southern New England will be stable given increasing inundation over the coming decades, we examined current loss patterns, inundation-productivity feedbacks, and sustaining processes. A multi-decadal analysis of salt marsh aerial extent using historic imagery and maps revealed that salt marsh vegetation loss is both widespread, and accelerating, with vegetation loss rates over the past four decades summing to 17.3%. Seaward retreat of the marsh edge, widening and headward expansion of tidal channel networks, loss of marsh islands, and the development and enlargement of interior depressions found on the marsh platform contributed to vegetation loss. Inundation due to sea level rise is strongly suggested as a primary driver: vegetation loss rates were significantly negatively correlated with marsh elevation (r2=0.96; p=0.0038), with marshes situated below mean high water (MHW) experiencing greater declines than marshes sitting well above MHW. Growth experiments with Spartina alterniflora, the Atlantic salt marsh ecosystem dominant, across a range of elevations and inundation regimes further established that greater inundation decreases belowground biomass production of Spartina alterniflora and thus negatively impacts organic matter accumulation. These results suggest that southern New England salt marshes are already experiencing deterioration and fragmentation in response to sea level rise, and may not be stable as tidal flooding increases in the future.
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机译：潮汐盐沼是抵御海平面上升影响的关键防御措施，但尤其容易受到其影响。为了确定新英格兰南部的盐沼在未来几十年中由于洪水泛滥而是否会保持稳定，我们研究了当前的流失模式，淹没生产力反馈和维持过程。利用历史图像和地图对盐沼空中范围进行了数十年的分析，结果表明，盐沼植被的丧失既广泛且在加速，过去四年的植被丧失率总计为17.3％。沼泽边缘向海的退缩，潮汐河道网络的扩大和向前扩展，沼泽岛的丧失以及在沼泽平台上发现的内部洼地的发展和扩大都是造成植被丧失的原因。强烈建议将海平面上升引起的淹没作为主要驱动因素：植被丧失率与沼泽海拔高度呈显着负相关（r 2 = 0.96； p = 0.0038），而沼泽位于平均高水位以下（ MHW）的下降幅度要大于远高于MHW的沼泽。以大西洋盐沼生态系统优势植物互花米草在各种海拔和淹没方式下的生长实验进一步证实，更大的淹没会降低互花米草地下生物量的产生，从而对有机物积累产生负面影响。这些结果表明，随着海平面上升，新英格兰南部的盐沼已经开始恶化和破碎，并且随着未来潮汐洪水的增加可能不稳定。
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