Tang Angela Che Ing, Bohrer Gil, Malhotra Avni, Missik Justine, Machado-Silva Fausto, Forbrich Inke
Department of Environmental Sciences, University of Toledo, Toledo, Ohio, USA.
Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, Ohio, USA.
Glob Chang Biol. 2025 Feb;31(2):e70053. doi: 10.1111/gcb.70053.
Coastal freshwater wetlands are critical ecosystems for both local and global carbon cycles, sequestering substantial carbon while also emitting methane (CH) due to anoxic conditions. Estuarine freshwater wetlands face unique challenges from fluctuating water levels, which influence water quality, vegetation, and carbon cycling. However, the response of CH fluxes and their drivers to altered hydrology and vegetation remains unclear, hindering mechanistic modeling. To address these knowledge gaps, we studied an estuarine freshwater wetland in the Great Lakes region, where rising water levels led to a vegetation shift from emergent Typha dominance in 2015-2016 to floating-leaved species in 2020-2022. Using eddy covariance flux measurements during the peak growing season (June-September) of both periods, we observed a 60% decrease in CH emissions, from 81 ± 4 g C m in 2015-2016 to 31 ± 3 g C m in 2020-2022. This decline was driven by two main factors: (1) higher water levels, which suppressed ebullitive fluxes via increased hydrostatic pressure and extended CH residence time, enhancing oxidation potential in the water column; and (2) reduced CH conductance through plants. Net carbon dioxide (CO) uptake decreased by 90%, from -267 ± 26 g C m in 2015-2016 to -27 ± 49 g C m in 2020-2022. Additionally, diel CH flux patterns shifted, with a distinct morning peak observed in 2015-2016 but absent in 2020-2022, suggesting changes in plant-mediated transport and a potential decoupling from photosynthesis. The dominant factors influencing CH fluxes shifted from water temperature and gross primary productivity in 2015-2016 to atmospheric pressure in 2020-2022, suggesting an increased role of ebullition as a primary transport pathway. Our results demonstrate that changes in water levels and vegetation can substantially alter CH and CO fluxes in coastal freshwater wetlands, underscoring the critical role of hydrological shifts in driving carbon dynamics in these ecosystems.
沿海淡水湿地对于本地和全球碳循环而言都是至关重要的生态系统，它在封存大量碳的同时，由于缺氧条件也会排放甲烷（CH）。河口淡水湿地面临着因水位波动带来的独特挑战，水位波动会影响水质、植被和碳循环。然而，CH通量及其驱动因素对水文和植被变化的响应仍不明确，这阻碍了机理模型的建立。为了填补这些知识空白，我们研究了大湖地区的一个河口淡水湿地，那里水位上升导致植被从2015 - 2016年的挺水香蒲优势种转变为2020 - 2022年的浮叶物种。利用两个时期生长旺季（6月至9月）的涡度协方差通量测量数据，我们观察到CH排放量下降了60%，从2015 - 2016年的81±4 g C m下降到2020 - 2022年的31±3 g C m。这种下降由两个主要因素驱动：（1）水位升高，通过增加静水压力抑制了冒泡通量，并延长了CH的停留时间，增强了水柱中的氧化潜力；（2）植物对CH的传导性降低。净二氧化碳（CO）吸收量下降了90%，从2015 - 2016年的 - 267±26 g C m下降到2020 - 2022年的 - 27±49 g C m。此外，CH通量的日变化模式发生了改变，2015 - 2016年观察到明显的早晨峰值，而2020 - 2022年则没有，这表明植物介导的传输发生了变化，并且可能与光合作用解耦。影响CH通量的主导因素从2015 - 2016年的水温及总初级生产力转变为2020 - 2022年的大气压力，这表明冒泡作为主要传输途径的作用增强。我们的结果表明，水位和植被的变化会显著改变沿海淡水湿地的CH和CO通量，突出了水文变化在驱动这些生态系统碳动态中的关键作用。
