Sea Level Solutions Center, Institute of Environment, Florida International University, Miami, Florida, USA.
Department of Earth and Environment, Florida International University, Miami, Florida, USA.
Ecol Appl. 2022 Dec;32(8):e2702. doi: 10.1002/eap.2702. Epub 2022 Aug 12.
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 ( ) in the freshwater marsh under ambient conditions (NECB = 1119 ± 229 gC m year ; F = 317 ± 186 gC m year ). In contrast, the brackish water marsh exhibited substantial peat loss and aquatic C export with ambient (NECB = -366 ± 15 gC m year ; F = 311 ± 30 gC m year ) and elevated salinity (NECB = -594 ± 94 gC m year ; F = 729 ± 142 gC m year ) 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 year 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.
滨海湿地是全球重要的碳（C）储存库。然而，海平面上升（SLR）加速、海水入侵加剧以及淡水排放方式的改变，可能导致泥炭沼泽崩塌，将滨海泥炭地转变为开阔水域。本研究应用来自佛罗里达沿海大沼泽地以锯齿草（Cladium jamaicense）为主导的淡水和微咸水沼泽的多项实验结果，开发了一个系统水平的泥炭抬升模型（EvPEM）。我们应用该模型模拟了在淹没和干旱暴露条件下，由于盐分升高而导致的净生态系统碳平衡（NECB）和泥炭抬升。采用物质碳平衡方法，我们估算了在环境条件下（NECB = 1119 ± 229 gC m 年 ；F = 317 ± 186 gC m 年 ），淡水沼泽中净碳增益和相应的水相碳通量（ ）输出。相比之下，在延长暴露条件下，微咸水沼泽在环境（NECB = -366 ± 15 gC m 年 ；F = 311 ± 30 gC m 年 ）和升高的盐度（NECB = -594 ± 94 gC m 年 ；F = 729 ± 142 gC m 年 ）下表现出大量的泥炭损失和水相碳输出。此外，物质平衡表明，随着盐度的升高和季节性干旱，土壤碳和相应的抬升损失会大幅减少。应用 EvPEM，我们开发了盐度相关的关键沼泽净初级生产力（NPP）阈值，以模拟累积、稳定和崩塌的泥炭抬升。优化结果表明，在不断增加的淹没水平下，NPP 约为 150-1070 gC m 年 ，可支撑稳定的泥炭抬升（抬升变化~SLR），对应的盐度范围为 1-20 ppt。该碳预算和建模说明了海水入侵、淹没和季节性干旱的影响，减少了对沿海泥炭湿地在海平面上升和淡水恢复背景下命运的理解不确定性。该模型结果为水文恢复提供了管理目标，基于减少大沼泽地泥炭沼泽崩塌脆弱性所需的生态条件。该方法可推广至其他滨海泥炭地，以量化碳损失，并提高对生物控制对湿地碳储存变化影响的理解，从而为沿海管理提供参考。
