Robison Andrew L, Wollheim Wilfred M, Turek Bonnie, Bova Cynthia, Snay Carter, Varner Ruth K
Department of Natural Resources and Environment University of New Hampshire Durham New Hampshire USA.
Stream Biofilm and Ecosystem Research Laboratory Ecole Polytechinque Fédérale de Lausanne Lausanne Switzerland.
Limnol Oceanogr. 2021 Dec;66(12):4063-4076. doi: 10.1002/lno.11943. Epub 2021 Sep 25.
Headwater streams are known sources of methane (CH) to the atmosphere, but their contribution to global scale budgets remains poorly constrained. While efforts have been made to better understand diffusive fluxes of CH in streams, much less attention has been paid to ebullitive fluxes. We examine the temporal and spatial heterogeneity of CH ebullition from four lowland headwater streams in the temperate northeastern United States over a 2-yr period. Ebullition was observed in all monitored streams with an overall mean rate of 1.00 ± 0.23 mmol CH m d, ranging from 0.01 to 1.79 to mmol CH m d across streams. At biweekly timescales, rates of ebullition tended to increase with temperature. We observed a high degree of spatial heterogeneity in CH ebullition within and across streams. Yet, catchment land use was not a simple predictor of this heterogeneity, and instead patches scale variability weakly explained by water depth and sediment organic matter content and quality. Overall, our results support the prevalence of CH ebullition from streams and high levels of variability characteristic of this process. Our findings also highlight the need for robust temporal and spatial sampling of ebullition in lotic ecosystems to account for this high level of heterogeneity, where multiple sampling locations and times are necessary to accurately represent the mean rate of flux in a stream. The heterogeneity observed likely indicates a complex set of drivers affect CH ebullition from streams which must be considered when upscaling site measurements to larger spatial scales.
源头溪流是大气中甲烷（CH）的已知来源，但其对全球尺度预算的贡献仍存在很大的不确定性。虽然已经努力更好地了解溪流中甲烷的扩散通量，但对冒泡通量的关注要少得多。我们在美国东北部温带地区的四条低地源头溪流中，对甲烷冒泡的时间和空间异质性进行了为期两年的研究。在所有监测的溪流中都观察到了冒泡现象，总体平均速率为1.00±0.23 mmol CH m² d，各溪流的速率范围为0.01至1.79 mmol CH m² d。在两周的时间尺度上，冒泡速率往往随温度升高而增加。我们观察到溪流内部和之间的甲烷冒泡存在高度的空间异质性。然而，集水区土地利用并非这种异质性的简单预测指标，相反，斑块尺度的变异性在一定程度上由水深和沉积物有机质含量及质量来解释。总体而言，我们的结果支持了溪流中甲烷冒泡的普遍性以及该过程的高度变异性。我们的研究结果还强调，在流水生态系统中对冒泡进行稳健的时间和空间采样很有必要，以考虑到这种高度的异质性，即需要多个采样地点和时间才能准确代表溪流中的平均通量速率。观察到的异质性可能表明，影响溪流中甲烷冒泡的驱动因素复杂，在将现场测量结果扩大到更大空间尺度时必须予以考虑。
