The magnitude of diffusive carbon dioxide (CO2) and methane (CH4) emission from man-made reservoirs is uncertain because the spatial variability generally is not well-represented. Here, we examine the spatial variability and its drivers for partial pressure, gas-exchange velocity (k), and diffusive flux of CO2 and CH4 in three tropical reservoirs using spatially resolved measurements of both gas concentrations and k. We observed high spatial variability in CO2 and CH4 concentrations and flux within all three reservoirs, with river inflow areas generally displaying elevated CH4 concentrations. Conversely, areas close to the dam are generally characterized by low concentrations and are therefore not likely to be representative for the whole system. A large share (44-83%) of the within-reservoir variability of gas concentration was explained by dissolved oxygen, pH, chlorophyll, water depth, and within-reservoir location. High spatial variability in k was observed, and kCH4 was persistently higher (on average, 2.5 times more) than kCO2. Not accounting for the within-reservoir variability in concentrations and k may lead to up to 80% underestimation of whole-system diffusive emission of CO2 and CH4. Our findings provide valuable information on how to develop field-sampling strategies to reliably capture the spatial heterogeneity of diffusive carbon fluxes from reservoirs.

中文翻译：

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CO2和CH4浓度的空间分辨测量以及气体交换速度对储层碳排放估算有很大影响。

人造油藏的扩散性二氧化碳（CO2）和甲烷（CH4）排放量的大小不确定，因为通常无法很好地反映出空间变异性。在这里，我们使用气体浓度和k的空间分辨测量结果，研究了三个热带气藏中分压，气体交换速度（k）以及CO2和CH4扩散通量的空间变异性及其驱动因素。我们观察到所有三个水库内的CO2和CH4浓度及通量具有很高的空间变异性，河流入流区通常显示CH4浓度升高。相反，靠近大坝的区域通常以低浓度为特征，因此不可能代表整个系统。储层内部气体浓度的很大一部分（44-83％）由溶解氧，pH，叶绿素，水深和储层内部位置解释。观察到k的高空间变异性，并且kCH4持续高于kCO2（平均高出2.5倍）。不考虑储层内浓度的变化和k可能导致对整个系统的CO2和CH4扩散排放低估多达80％。我们的发现为如何开发现场采样策略以可靠地捕获来自储层的扩散碳通量的空间异质性提供了有价值的信息。不考虑储层内浓度的变化和k可能导致对整个系统的CO2和CH4扩散排放低估多达80％。我们的发现为如何开发现场采样策略以可靠地捕获来自储层的扩散碳通量的空间异质性提供了有价值的信息。不考虑储层内浓度的变化和k可能导致对整个系统的CO2和CH4扩散排放低估多达80％。我们的发现为如何开发现场采样策略以可靠地捕获来自储层的扩散碳通量的空间异质性提供了有价值的信息。