Rhizosphere to the atmosphere: contrasting methane pathways, fluxes, and geochemical drivers across the terrestrial–aquatic wetland boundary

Here we collected a data set to test whether the geochemical drivers of sedimentary methane were correlated with methane fluxes, from different vegetation/ wetland sites in a remediated subtropical Australian wetland. Our abstract is as follows:

Although wetlands represent the largest natural source of atmospheric CH4, large uncertainties remain regarding the global wetland CH4 flux. Wetland hydrological oscillations contribute to this uncertainty, dramatically altering wetland area, water table height, soil redox potentials and CH4 emissions. This study compares both terrestrial and aquatic CH4 fluxes in permanent and seasonal remediated freshwater wetlands in subtropical Australia over two field campaigns, representing differing hydrological and climatic conditions. We account for aquatic CH4 diffusion and ebullition rates, and plant-mediated CH4 fluxes from three distinct vegetation communities, thereby examining diel and intra-habitat variability. CH4 emission rates were related to underlying sediment geochemistry. For example, distinct negative relationships between CH4 fluxes and both Fe(III) and SO42- were observed. Where sediment Fe(III) and SO42- were depleted, distinct positive trends occurred between CH4 emissions and Fe(II) / acid volatile sulphur (AVS). Significantly higher CH4 emissions (p<0.01) of the seasonal wetland were measured during flooded conditions and always during daylight hours, which is consistent with soil redox potential and temperature being important co-drivers of CH4 flux. The highest CH4 fluxes were consistently emitted from the permanent wetland (1.5 to 10.5 mmol m-2 d-1), followed by the Phragmites australis community within the seasonal wetland (0.8 to 2.3 mmol m-2 d-1), whilst the lowest CH4 fluxes came from a region of forested Juncus sp. (-0.01 to 0.1 mmol m-2 d-1) which also corresponded with the highest sedimentary Fe(III) and SO42-. We suggest that wetland remediation strategies should consider geochemical profiles to help to mitigate excessive and unwanted methane emissions, especially during early system remediation periods.

本研究收集了一个数据集，旨在检验沉积甲烷的地球化学驱动力是否与来自不同植被/湿地区域的甲烷通量相关，这些区域位于修复后的澳大利亚亚热带湿地。我们的摘要如下：尽管湿地是大气甲烷（CH4）的最大自然来源，但全球湿地CH4通量的不确定性仍然较大。湿地水文振荡是这种不确定性的来源之一，它极大地改变了湿地面积、地下水位、土壤氧化还原势和甲烷排放。本研究对比了在两个不同水文和气候条件下的亚热带澳大利亚永久性和季节性修复淡水湿地中的陆地和水生CH4通量。我们考虑了水生CH4的扩散和沸腾速率，以及来自三个不同植被群落的植物介导的CH4通量，从而考察了昼夜和栖息地内的变异性。甲烷排放速率与底层沉积物地球化学相关。例如，观察到甲烷通量与Fe(III)和SO42-之间存在显著的负相关关系。在沉积物中Fe(III)和SO42-耗竭的地区，甲烷排放与Fe(II) / 酸性挥发性硫（AVS）之间出现了明显的正相关趋势。在洪水条件下，季节性湿地的甲烷排放（p<0.01）显著升高，并且始终在白天进行，这与土壤氧化还原势和温度是甲烷通量的重要共驱动因素相一致。甲烷通量最高的始终来自永久性湿地（1.5至10.5 mmol m-2 d-1），其次是季节性湿地中的Phragmites australis群落（0.8至2.3 mmol m-2 d-1），而最低的甲烷通量来自一片森林化的Juncus sp.区域（-0.01至0.1 mmol m-2 d-1），这也与沉积物中Fe(III)和SO42-的最高含量相对应。我们建议，湿地修复策略应考虑地球化学特征，以帮助减轻过度和不希望的甲烷排放，尤其是在系统早期修复阶段。