The patterns of spatial and temporal variability in CO₂ and CH₄ emission from reservoirs are still poorly studied, especially in tropical regions where hydropower is growing. We performed spatially resolved measurements of dissolved CO₂ and CH₄ surface water concentrations and their gas‐exchange coefficients (k) to compute diffusive carbon flux from four contrasting tropical reservoirs across Brazil during different hydrological seasons. We used an online equilibration system to measure dissolved CO₂ and CH₄ concentrations; we estimated k from floating chamber deployments in conjunction with discrete CO₂ and CH₄ water concentration measurements. Diffusive CO₂ emissions were higher during dry season than during rainy season, whereas there were no consistent seasonal patterns for diffusive CH₄ emissions. Our results reveal that the magnitude and the spatial within‐reservoir patterns of diffusive CO₂ and CH₄ flux varied strongly among hydrological seasons. River inflow areas were often characterized by high seasonality in diffusive flux. Areas close to the dam generally showed low seasonal variability in diffusive CH₄ flux but high variability in CO₂ flux. Overall, we found that reservoir areas exhibiting highest emission rates (“hotspots”) shifted substantially across hydrological seasons. Estimates of total diffusive carbon emission from the reservoir surfaces differed between hydrological seasons by a factor up to 7 in Chapéu D'Úvas, up to 13 in Curuá‐Una, up to 4 in Furnas, and up to 1.8 in Funil, indicating that spatially resolved measurements of CO₂ and CH₄ concentrations and k need to be performed at different hydrological seasons in order to constrain annual diffusive carbon emission.

中文翻译：

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热带水库的扩散性CO2和CH4排放热点随时间推移而变化

储层中的CO ₂和CH ₄排放的时空变化模式仍然缺乏研究，特别是在水力发电正在增长的热带地区。我们对溶解的CO ₂和CH ₄地表水浓度及其气体交换系数（k）进行了空间分辨测量，以计算不同水文季节巴西各地四个对比热带气库的扩散碳通量。我们使用了在线平衡系统来测量溶解的CO ₂和CH ₄浓度。我们根据浮动腔室部署与离散CO ₂一起估算了k和CH ₄水浓度测量。干旱季节的CO ₂扩散排放高于雨季，而CH _4的扩散没有一致的季节性模式。我们的结果表明，CO ₂和CH ₄扩散通量的大小和在储层内的空间格局在水文季节之间变化很大。河流入流地区通常以扩散通量的高季节性为特征。靠近大坝的区域通常在扩散CH ₄通量方面显示出较低的季节性变化，但在CO _2中具有较高的变化性。通量。总体而言，我们发现在整个水文季节中，表现出最高排放率（“热点”）的水库区域发生了显着变化。在水文季节之间，来自储层表面的总扩散碳排放量的估算差异最大，在ChapéuD'Úvas中高达7，在Curuá-Una中高达13，在Furnas中高达4，在Funil中高达1.8。为了限制年度扩散性碳排放，需要在不同的水文季节进行CO ₂和CH ₄浓度以及k的分解测量。