The eddy-covariance (EC) technique is used to determine mass and energy fluxes between the Earth’s surface and the lower atmosphere at high temporal resolution. Despite the frequent and successful use of the EC technique at terrestrial sites, its application over water surfaces is rare. We present one season of EC measurements conducted on the Rappbode Reservoir, Germany’s largest drinking water reservoir. A floating observation platform in the centre of the reservoir is used for observations of fluxes that were unaffected by surrounding land surfaces and therefore representative of the actual water–atmosphere exchange. The temporal patterns of sensible heat flux are inverted compared to land sites, since the maxima and the minima occur at night and day respectively. The latent heat flux and the evaporation are unexpectedly low for a site where evaporation is not limited by the availability of water. The daily totals in summer and autumn are only 50% and 75% of the potential evaporation assessed by the FAO grass-reference evaporation, respectively. Measurement uncertainties and the effects of the energy balance closure are ruled out as potential factors, so that low values appear to be a general feature of large water surfaces. The observed carbon dioxide fluxes are characterized by distinctive diurnal variations in a typical range for lakes and reservoirs. However, the methane fluxes are low compared to other inland waters.

中文翻译：

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基于浮动平台观测的大面积水体上方涡流协方差通量的季节

涡流协方差 (EC) 技术用于以高时间分辨率确定地球表面和低层大气之间的质量和能量通量。尽管 EC 技术在陆地站点上得到了频繁和成功的使用，但其在水面上的应用却很少见。我们展示了在德国最大的饮用水水库拉普博德水库上进行的一季 EC 测量。水库中心的浮动观测平台用于观测不受周围地表影响的通量，因此代表了实际的水-大气交换。与陆地站点相比，感热通量的时间模式是颠倒的，因为最大值和最小值分别出现在夜间和白天。对于蒸发不受可用水量限制的场所，潜热通量和蒸发量出乎意料地低。夏季和秋季的每日总量分别仅为粮农组织草参考蒸发评估的潜在蒸发量的 50% 和 75%。测量不确定性和能量平衡闭合的影响被排除为潜在因素，因此低值似乎是大水面的一般特征。观察到的二氧化碳通量的特点是在湖泊和水库的典型范围内有明显的昼夜变化。然而，与其他内陆水域相比，甲烷通量较低。夏季和秋季的每日总量分别仅为粮农组织草参考蒸发评估的潜在蒸发量的 50% 和 75%。测量不确定性和能量平衡闭合的影响被排除为潜在因素，因此低值似乎是大水面的一般特征。观察到的二氧化碳通量的特点是在湖泊和水库的典型范围内有明显的昼夜变化。然而，与其他内陆水域相比，甲烷通量较低。夏季和秋季的每日总量分别仅为粮农组织草参考蒸发评估的潜在蒸发量的 50% 和 75%。测量不确定性和能量平衡闭合的影响被排除为潜在因素，因此低值似乎是大水面的一般特征。观察到的二氧化碳通量的特点是在湖泊和水库的典型范围内有明显的昼夜变化。然而，与其他内陆水域相比，甲烷通量较低。观察到的二氧化碳通量的特点是在湖泊和水库的典型范围内有明显的昼夜变化。然而，与其他内陆水域相比，甲烷通量较低。观察到的二氧化碳通量的特点是在湖泊和水库的典型范围内有明显的昼夜变化。然而，与其他内陆水域相比，甲烷通量较低。