Rovelli L, Attard K M, Heppell C M, Binley A, Trimmer M, Glud R N
Scottish Marine Institute Scottish Association for Marine Sciences Oban United Kingdom.
Nordcee, Department of Biology University of Southern Denmark Odense M Denmark.
Limnol Oceanogr Methods. 2018 Oct;16(10):696-709. doi: 10.1002/lom3.10281. Epub 2018 Sep 28.
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 ( ) and dissolved oxygen (O) gas transfer velocity () 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 O (i.e., groundwater inflow, photosynthesis, and respiration in both the water column and benthic compartment) enabling direct hourly estimates of at the reach-scale (~ 150 m) without relying on the nighttime regression method. Obtained values ranged from 0.001 h to 0.600 h. Average daytime 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 on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with increased when clustering wind speeds in increments correspondent with dominant variations (1 m s). Time scale is thus an important consideration when resolving physical drivers of gas exchange. Mean estimates of from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O budget assessment (within < 10%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions.
源头溪流在碳循环中起着重要作用，因此有必要更好地对与碳相关气体的交换进行参数化和量化。为此，我们对英国埃文河两条低地源头溪流的气体交换系数（）和溶解氧（O）的气体传输速度（）的变异性进行了表征。传统的单站开阔水域方法辅以对河流O的源和汇（即地下水流入、水柱和底栖生物区的光合作用和呼吸作用）进行原位量化，从而能够在不依赖夜间回归方法的情况下，直接按小时估算河段尺度（约150米）的。得到的值范围为0.001 h至0.600 h。白天的平均 值比夜间的值高两倍，这可能是由于水温和风的昼夜变化所致。在每小时尺度上，温度对 的变异性贡献高达46%，但将温度分组会逐步加强统计关系。我们的分析表明， 的变异性与主要温度趋势一致，而非与短期变化一致。同样，当按照与主要变化（1 m s）相对应的增量对风速进行分组时，风与 的相关性增强。因此，在解析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。将最近提出的用于尺度放大的参数化方法的平均估算值应用于本研究的设置时，发现与我们独立的O收支评估结果一致（误差在<10%以内），这进一步支持了旨在量化大规模河流气体排放的尺度放大工作的有效性。
