Temporal trends in methane emissions from a small eutrophic reservoir: the key role of a spring burst.
Temporal trends in methane emissions from a small eutrophic reservoir: the key role of a spring burst.
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DOI：
10.5194/bg-18-5291-2021
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发表时间：
2021-09-30
期刊：
影响因子：
--
通讯作者：
Walker JT
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文献类型：
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作者：
Waldo S;Beaulieu JJ;Barnett W;Balz DA;Vanni MJ;Williamson T;Walker JT
坝后蓄水的沃茨（即，水库）是温室气体（GHG），尤其是甲烷（CH 4）的重要来源，但由于空间和时间变异性大、表征热点和热点时刻排放的监测方法有限，以及研究数量有限，排放估计没有受到很好的限制。调查排放的日、季节和年际模式。在这项研究中，我们调查的时间模式和生物物理驱动程序的甲烷排放阿克顿湖，一个小型富营养化水库，使用的方法相结合：涡度协方差监测，连续暖季沸腾测量，空间排放调查，测量的关键驱动程序的甲烷生产和排放。我们使用了人工神经网络来填补涡度协方差时间序列的空白，并探讨生物物理驱动因素在年际时间尺度上的相对重要性。我们结合空间和时间的监测信息，估计全年整个水库的排放量。阿克顿湖在2017年和2018年的累计面积排放率分别为45.6 ± 8.3和51.4 ± 4.3 g CH 4 m−2，或在2017年和2018年整个2.4 km 2湖泊面积的109 ± 14和123 ± 10 Mg CH 4。不同年份之间的主要差异是2018年春季持续不到2周的排放量升高期，这一时期贡献了水库浅水区年排放量的17%。春季爆发恰逢浮游植物大量繁殖，这可能是由2018年与2017年相比有利的降水和温度条件驱动的。结合空间上广泛的测量与时间上连续的监测，使我们能够量化的空间和时间的变化方面的甲烷排放。我们发现，甲烷排放量和沉积物温度之间的关系取决于水库内的位置，我们观察到一个明确的时空偏移的最大甲烷排放量作为水库深度的函数。这些研究结果表明，在这个相对较小的（2.4平方公里）水库的甲烷地球化学强的空间格局。在解决更好地了解水库温室气体排放量的需要时，对一个水体的密集测量与对许多水体的短期和/或空间有限的测量之间存在着权衡。从多年的，连续的，空间广泛的研究，如这一个的见解，可以用来通知研究设计和排放量放大从空间或时间有限的结果，特别是营养状态和水库内的变异性的重要性，在假设放大甲烷排放量。
Waters impounded behind dams (i.e., reservoirs) are important sources of greenhouses gases (GHGs), especially methane (CH4), but emission estimates are not well constrained due to high spatial and temporal variability, limitations in monitoring methods to characterize hot spot and hot moment emissions, and the limited number of studies that investigate diurnal, seasonal, and interannual patterns in emissions. In this study, we investigate the temporal patterns and biophysical drivers of CH4 emissions from Acton Lake, a small eutrophic reservoir, using a combination of methods: eddy covariance monitoring, continuous warm-season ebullition measurements, spatial emission surveys, and measurements of key drivers of CH4 production and emission. We used an artificial neural network to gap fill the eddy covariance time series and to explore the relative importance of biophysical drivers on the interannual timescale. We combined spatial and temporal monitoring information to estimate annual whole-reservoir emissions. Acton Lake had cumulative areal emission rates of 45.6 ± 8.3 and 51.4 ± 4.3 g CH4 m−2 in 2017 and 2018, respectively, or 109 ± 14 and 123 ± 10 Mg CH4 in 2017 and 2018 across the whole 2.4 km2 area of the lake. The main difference between years was a period of elevated emissions lasting less than 2 weeks in the spring of 2018, which contributed 17 % of the annual emissions in the shallow region of the reservoir. The spring burst coincided with a phytoplankton bloom, which was likely driven by favorable precipitation and temperature conditions in 2018 compared to 2017. Combining spatially extensive measurements with temporally continuous monitoring enabled us to quantify aspects of the spatial and temporal variability in CH4 emission. We found that the relationships between CH4 emissions and sediment temperature depended on location within the reservoir, and we observed a clear spatiotemporal offset in maximum CH4 emissions as a function of reservoir depth. These findings suggest a strong spatial pattern in CH4 biogeochemistry within this relatively small (2.4 km2) reservoir. In addressing the need for a better understanding of GHG emissions from reservoirs, there is a trade-off in intensive measurements of one water body vs. short-term and/or spatially limited measurements in many water bodies. The insights from multi-year, continuous, spatially extensive studies like this one can be used to inform both the study design and emission upscaling from spatially or temporally limited results, specifically the importance of trophic status and intra-reservoir variability in assumptions about upscaling CH4 emissions.