Department of Biological Sciences and Southeast Environmental Research Center, Florida International University, Miami, Florida, 33199, USA.
College of the Environment and Ecology, Xiamen University, Xiamen, 361102, China.
Ecol Appl. 2018 Dec;28(8):2092-2108. doi: 10.1002/eap.1798. Epub 2018 Oct 30.
Coastal wetlands are globally important sinks of organic carbon (C). However, to what extent wetland C cycling will be affected by accelerated sea-level rise (SLR) and saltwater intrusion is unknown, especially in coastal peat marshes where water flow is highly managed. Our objective was to determine how the ecosystem C balance in coastal peat marshes is influenced by elevated salinity. For two years, we made monthly in situ manipulations of elevated salinity in freshwater (FW) and brackish water (BW) sites within Everglades National Park, Florida, USA. Salinity pulses interacted with marsh-specific variability in seasonal hydroperiods whereby effects of elevated pulsed salinity on gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem productivity (NEP) were dependent on marsh inundation level. We found little effect of elevated salinity on C cycling when both marsh sites were inundated, but when water levels receded below the soil surface, the BW marsh shifted from a C sink to a C source. During these exposed periods, we observed an approximately threefold increase in CO efflux from the marsh as a result of elevated salinity. Initially, elevated salinity pulses did not affect Cladium jamaicense biomass, but aboveground biomass began to be significantly decreased in the saltwater amended plots after two years of exposure at the BW site. We found a 65% (FW) and 72% (BW) reduction in live root biomass in the soil after two years of exposure to elevated salinity pulses. Regardless of salinity treatment, the FW site was C neutral while the BW site was a strong C source (-334 to -454 g C·m ·yr ), particularly during dry-down events. A loss of live roots coupled with annual net CO losses as marshes transition from FW to BW likely contributes to the collapse of peat soils observed in the coastal Everglades. As SLR increases the rate of saltwater intrusion into coastal wetlands globally, understanding how water management influences C gains and losses from these systems is crucial. Under current Everglades' water management, drought lengthens marsh dry-down periods, which, coupled with saltwater intrusion, accelerates CO loss from the marsh.
滨海湿地是全球重要的有机碳 (C) 汇。然而，在多大程度上，湿地的碳循环将受到海平面加速上升 (SLR) 和盐水入侵的影响尚不清楚，特别是在水流量受到高度管理的沿海泥炭沼泽中。我们的目标是确定滨海泥炭沼泽生态系统的碳平衡是如何受到盐度升高的影响。在佛罗里达州的埃弗格莱兹国家公园，我们在淡水 (FW) 和微咸水 (BW) 地点进行了为期两年的每月现场盐度升高处理。盐度脉冲与季节性水文期的沼泽特定变异性相互作用，即升高的脉冲盐度对总生态系统生产力 (GEP)、生态系统呼吸 (ER) 和净生态系统生产力 (NEP) 的影响取决于沼泽淹没水平。当两个沼泽地都被淹没时，盐度升高对碳循环的影响很小，但当水位退回到土壤表面以下时，BW 沼泽地从碳汇转变为碳源。在这些暴露期间，我们观察到由于盐度升高，从沼泽中排放的 CO 通量增加了约三倍。最初，升高的盐度脉冲不会影响 Cladium jamaicense 生物量，但在 BW 地点暴露两年后，添加盐水的地块中地上生物量开始显著减少。我们发现，暴露在升高的盐度脉冲两年后，土壤中的活根生物量减少了 65%（FW）和 72%（BW）。无论盐度处理如何，FW 地点是碳中性的，而 BW 地点是一个强大的碳源 (-334 至-454 g C·m ·yr )，特别是在干旱期。活根的丧失加上由于沼泽从 FW 转变为 BW 而导致的每年净 CO 损失，可能导致在沿海大沼泽地观察到的泥炭土壤的崩溃。随着 SLR 增加全球滨海湿地的盐水入侵速度，了解水管理如何影响这些系统的碳增益和损失至关重要。根据当前的大沼泽地水管理，干旱延长了沼泽的干燥期，再加上盐水入侵，加速了沼泽地的 CO 损失。
