Coastal wetlands are globally important stores of carbon (C). However, accelerated sea-level rise (SLR), increased saltwater intrusion, and modified freshwater discharge can contribute to the collapse of peat marshes, converting coastal peatlands into open water. Applying results from multiple experiments from sawgrass (Cladium jamaicense)-dominated freshwater and brackish water marshes in the Florida Coastal Everglades, we developed a system-level mechanistic peat elevation model (EvPEM). We applied the model to simulate net ecosystem C balance (NECB) and peat elevation in response to elevated salinity under inundation and drought exposure. Using a mass C balance approach, we estimated net gain in C and corresponding export of aquatic fluxes ($F_{\mathrm{AQ}}$) in the freshwater marsh under ambient conditions (NECB = 1119 ± 229 gC m⁻² year⁻¹; F_AQ = 317 ± 186 gC m⁻² year⁻¹). In contrast, the brackish water marsh exhibited substantial peat loss and aquatic C export with ambient (NECB = −366 ± 15 gC m⁻² year⁻¹; F_AQ = 311 ± 30 gC m⁻² year⁻¹) and elevated salinity (NECB = −594 ± 94 gC m⁻² year⁻¹; F_AQ = 729 ± 142 gC m⁻² year⁻¹) under extended exposed conditions. Further, mass balance suggests a considerable decline in soil C and corresponding elevation loss with elevated salinity and seasonal dry-down. Applying EvPEM, we developed critical marsh net primary productivity (NPP) thresholds as a function of salinity to simulate accumulating, steady-state, and collapsing peat elevations. The optimization showed that ~150–1070 gC m⁻² year⁻¹ NPP could support a stable peat elevation (elevation change ≈ SLR), with the corresponding salinity ranging from 1 to 20 ppt under increasing inundation levels. The C budgeting and modeling illustrate the impacts of saltwater intrusion, inundation, and seasonal dry-down and reduce uncertainties in understanding the fate of coastal peat wetlands with SLR and freshwater restoration. The modeling results provide management targets for hydrologic restoration based on the ecological conditions needed to reduce the vulnerability of the Everglades' peat marshes to collapse. The approach can be extended to other coastal peatlands to quantify C loss and improve understanding of the influence of the biological controls on wetland C storage changes for coastal management.

中文翻译：

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模拟暴露于海平面上升和盐水入侵的沿海湿地的净生态系统碳平衡和损失

沿海湿地是全球重要的碳储存库 (C)。然而，加速的海平面上升 (SLR)、增加的咸水入侵和改变的淡水排放可能导致泥炭沼泽的崩溃，将沿海泥炭地转变为开阔水域。应用佛罗里达沿海大沼泽地以锯齿草 ( Cladium jamaicense ) 为主的淡水和咸水沼泽的多项实验结果，我们开发了系统级机械泥炭高程模型 (EvPEM)。我们应用该模型来模拟净生态系统碳平衡 (NECB) 和泥炭海拔，以响应洪水和干旱暴露下盐度升高。使用质量 C 平衡方法，我们估计了 C 的净增益和相应的水生通量输出（$F_{\mathrm{水质}}$) 在环境条件下的淡水沼泽中（NECB = 1119 ± 229 gC m ⁻²  year ⁻¹；F _AQ  = 317 ± 186 gC m ⁻²  year ⁻¹）。相比之下，咸水沼泽表现出大量的泥炭损失和水生碳输出与环境（NECB = −366 ± 15 gC m ⁻²  year ⁻¹；F _AQ  = 311 ± 30 gC m ⁻²  year ⁻¹）和升高的盐度（ NECB = −594 ± 94 gC m ⁻² 年⁻¹；F _AQ  = 729 ± 142 gC m ⁻² 年⁻¹）在延长暴露条件下。此外，质量平衡表明土壤 C 显着下降，相应的海拔损失与盐度升高和季节性干旱有关。应用 EvPEM，我们开发了临界沼泽净初级生产力 (NPP) 阈值作为盐度的函数来模拟累积、稳态和塌陷的泥炭海拔。优化显示~150–1070 gC m ⁻²  year ⁻¹NPP 可以支持稳定的泥炭海拔（海拔变化≈SLR），相应的盐度在不断增加的淹没水平下从 1 到 20 ppt。C 预算和建模说明了盐水入侵、洪水和季节性干涸的影响，并减少了理解沿海泥炭湿地命运与 SLR 和淡水恢复的不确定性。建模结果根据降低大沼泽地泥炭沼泽崩塌脆弱性所需的生态条件，为水文恢复提供了管理目标。该方法可以扩展到其他沿海泥炭地，以量化碳损失并提高对生物控制对沿海管理的湿地碳储存变化的影响的理解。