Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the gas exchange coefficient (k 2) and dissolved oxygen (O2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O2 (i.e., groundwater inflow, photosynthesis, and respiration in both the water column and benthic compartment) enabling direct hourly estimates of k 2 at the reach-scale (~ 150 m) without relying on the nighttime regression method. Obtained k 2 values ranged from 0.001 h-1 to 0.600 h-1. Average daytime k 2 were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m s-1). Time scale is thus an important consideration when resolving physical drivers of gas exchange. Mean estimates of k 600 from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O2 budget assessment (within < 10%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions.

中文翻译：

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从河段尺度的 O2 质量平衡量化的源头气体交换。

源头水流在碳循环中很重要，需要更好地参数化和量化碳相关气体的交换。因此，我们描述了埃文河（英国）两个低地源头的气体交换系数 (k 2) 和溶解氧 (O2) 气体传输速度 (k) 的可变性。传统的单站开放水域方法辅以对河流源和 O2 汇（即地下水流入、光合作用和水柱和底栖隔间的呼吸作用）的原位量化，从而能够直接每小时估算 k 2 在不依赖夜间回归方法的范围（~ 150 m）。获得的 k 2 值范围为 0.001 h-1 至 0.600 h-1。白天的平均 k 2 比夜间的值高两倍，这可能是由于水温和风的昼夜变化。在每小时尺度上，温度对 k 变化的贡献高达 46%，但聚类温度逐渐加强了统计关系。我们的分析表明，k 变化与主要的温度趋势一致，而不是与短期变化一致。类似地，当以与主要变化（1 m s-1）相对应的增量对风速进行聚类时，风与 k 的相关性增加。因此，在解决气体交换的物理驱动因素时，时间尺度是一个重要的考虑因素。当应用于本研究的设置时，从最近提出的用于升级的参数化的 k 600 的平均估计值被发现与我们的独立 O2 预算评估一致（在 < 10% 以内），进一步支持了升级努力的有效性，旨在量化大规模河流气体排放。