Marsh soil properties vary drastically across estuarine salinity gradients, which can affect soil strength and, consequently, marsh edge erodibility. Here, we quantify how marsh erosion differs between saline and brackish marshes of the Mississippi Delta. We analyzed long-term (1932–2015) maps of marsh loss and developed an algorithm to distinguish edge erosion from interior loss. We found that the edge erosion rate remains nearly constant at decadal timescales, whereas interior loss varies by more than 100%. On average, roughly half of marsh loss can be attributed to edge erosion, the other half to interior loss. Based on data from 42 cores, brackish marsh soils had a lower bulk density (0.17 vs. 0.27 g/cm³), a higher organic content (43% vs. 26%), a lower shear strength (2.0 vs. 2.5 kPa), and a lower shear strength in the root layer (13.8 vs. 20.7 kPa) than saline marsh soils. We then modified an existing marsh edge erosion model by including a salinity-dependent erodibility. By calibrating the erodibility with the observed retreat rates, we found that the brackish marsh is two to three times more erodible than the saline marshes. Overall, this model advances the ability to simulate estuarine systems as a whole, thus transcending the salinity boundaries often used in compartmentalized marsh models.

中文翻译：

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密西西比三角洲地区咸水沼泽的侵蚀速度是咸水沼泽的两倍

河口盐度梯度的沼泽土壤性质差异很大，这会影响土壤强度，从而影响沼泽边缘的可蚀性。在这里，我们量化了密西西比河三角洲的咸水沼泽和微咸沼泽之间的沼泽侵蚀差异。我们分析了沼泽损失的长期（1932-2015）地图，并开发了一种算法来区分边缘侵蚀和内部损失。我们发现边缘侵蚀率在十年时间尺度上几乎保持不变，而内部损失变化超过 100%。平均而言，大约一半的沼泽损失可归因于边缘侵蚀，另一半归因于内部流失。根据 42 个岩心的数据，微咸沼泽土壤的容重较低（0.17 与 0.27 g/cm ³)，与盐渍沼泽土壤相比，有机质含量更高（43% 对 26%）、剪切强度更低（2.0 对 2.5 kPa）以及根层的剪切强度（13.8 对 20.7 kPa）更低。然后，我们通过加入依赖于盐度的可蚀性来修改现有的沼泽边缘侵蚀模型。通过用观察到的退缩率校准可蚀性，我们发现咸水沼泽的易蚀性是咸水沼泽的两到三倍。总体而言，该模型提高了从整体上模拟河口系统的能力，从而超越了分区沼泽模型中常用的盐度边界。