Beaulieu Jake J, Balz David A, Birchfield M Keith, Harrison John A, Nietch Christopher T, Platz Michelle C, Squier William C, Waldo Sarah, Walker John T, White Karen M, Young Jade L
1National Risk Management Research Laboratory, United States Environmental Protection Agency, Office of Research and Development, 26 W Martin Luther King Dr, Cincinnati, Ohio 45268 USA.
Pegasus Technical Services, Cincinnati, Ohio USA.
Ecosystems. 2018;21(4):657-674. doi: 10.1007/s10021-017-0176-2. Epub 2017 Sep 5.
Reservoirs are a globally significant source of methane (CH) to the atmosphere. However, emission rate estimates may be biased low due to inadequate monitoring during brief periods of elevated emission rates (that is, hot moments). Here we investigate CH bubbling (that is, ebullition) during periods of falling water levels in a eutrophic reservoir in the Midwestern USA. We hypothesized that periods of water-level decline trigger the release of CH-rich bubbles from the sediments and that these emissions constitute a substantial fraction of the annual CH flux. We explored this hypothesis by monitoring CH ebullition in a eutrophic reservoir over a 7-month period, which included an experimental water-level drawdown. We found that the ebullitive CH flux rate was among the highest ever reported for a reservoir (mean = 32.3 mg CH m h). The already high ebullitive flux rates increased by factors of 1.4-77 across the nine monitoring sites during the 24-h experimental water-level drawdown, but these emissions constituted only 3% of the CH flux during the 7-month monitoring period due to the naturally high ebullitive CH flux rates that persist throughout the warm weather season. Although drawdown emissions were found to be a minor component of annual CH emissions in this reservoir, our findings demonstrate a link between water-level change and CH ebullition, suggesting that CH emissions may be mitigated through water-level management in some reservoirs.
水库是全球大气甲烷（CH）的重要来源。然而，由于在排放率升高的短暂时期（即热点时刻）监测不足，排放率估计可能偏低。在此，我们研究了美国中西部一个富营养化水库水位下降期间的甲烷冒泡（即沸腾）情况。我们假设水位下降时期会触发沉积物中富含甲烷的气泡释放，并且这些排放构成了年度甲烷通量的很大一部分。我们通过在7个月的时间里监测一个富营养化水库中的甲烷沸腾情况来探究这一假设，其中包括一次实验性的水位下降。我们发现，沸腾的甲烷通量率是有史以来报道的水库中最高的之一（平均值 = 32.3毫克CH·平方米·小时）。在24小时的实验性水位下降期间，九个监测点的已很高的沸腾通量率增加了1.4至77倍，但由于整个温暖季节持续存在的自然高沸腾甲烷通量率，这些排放在7个月的监测期内仅占甲烷通量的3%。尽管在该水库中，水位下降排放被发现是年度甲烷排放的一个次要组成部分，但我们的研究结果表明了水位变化与甲烷沸腾之间的联系，这表明在一些水库中，甲烷排放可能通过水位管理来减轻。
