Washington State University School of the Environment Vancouver, Washington 98686 United States.
U.S. Geological Survey Southwest Biological Science Center , Flagstaff, Arizona 86001 United States.
Environ Sci Technol. 2017 Feb 7;51(3):1267-1277. doi: 10.1021/acs.est.6b03185. Epub 2017 Jan 9.
Water-level fluctuations due to reservoir management could substantially affect the timing and magnitude of reservoir methane (CH) fluxes to the atmosphere. However, effects of such fluctuations on CH emissions have received limited attention. Here we examine CH emission dynamics in six Pacific Northwest U.S. reservoirs of varying trophic status, morphometry, and management regimes. In these systems, we show that water-level drawdowns can, at least temporarily, greatly increase per-area reservoir CH fluxes to the atmosphere, and can account for more than 90% of annual reservoir CH flux in a period of just a few weeks. Reservoirs with higher epilimnetic [chlorophyll a] experienced larger increases in CH emission in response to drawdown (R = 0.84, p < 0.01), suggesting that eutrophication magnifies the effect of drawdown on CH emission. We show that drawdowns as small as 0.5 m can stimulate ebullition events. Given that drawdown events of this magnitude are quite common in reservoirs, our results suggest that this process must be considered in sampling strategies designed to characterize total CH fluxes from reservoirs. The extent to which (and the mechanisms by which) drawdowns short-circuit connections between methanogenesis and methanotrophy, thereby increasing net CH fluxes to the atmosphere, should be a focus of future work.
由于水库管理导致的水位波动会极大地影响水库甲烷（CH）向大气释放的时间和规模。然而，这种波动对 CH 排放的影响受到的关注有限。本研究中，我们研究了美国太平洋西北地区六个具有不同营养状态、形态和管理模式的水库中的 CH 排放动态。在这些系统中，我们表明，水位下降至少在短期内会极大地增加单位面积水库向大气的 CH 通量，并且在几周的时间内可以占到年度水库 CH 通量的 90%以上。富营养化程度较高的上覆水层 [叶绿素 a] 的 CH 排放量对下降的响应更大（R = 0.84，p < 0.01），这表明富营养化放大了下降对 CH 排放的影响。我们表明，水位下降仅 0.5 米就可以刺激鼓泡事件。鉴于这种幅度的下降事件在水库中非常常见，我们的研究结果表明，在设计用于表征水库总 CH 通量的采样策略时，必须考虑这一过程。未来的工作应该重点研究下降事件如何以及通过何种机制（short-circuit connections）使产甲烷作用和甲烷氧化作用之间的连接短路，从而增加向大气的净 CH 通量。
