Representative regional sampling of carbon dioxide and methane concentrations in hemiboreal headwater streams reveal underestimates in less systematic approaches
Representative regional sampling of carbon dioxide and methane concentrations in hemiboreal headwater streams reveal underestimates in less systematic approaches
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对半北方源头水流中二氧化碳和甲烷浓度的代表性区域采样揭示了系统性方法不足的低估结果
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发表时间：
2014
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通讯作者：
K. Bishop
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作者：
M. Wallin;S. Löfgren;M. Erlandsson;K. Bishop
北方源头河流已被确定为温室气体（GHG）逃逸的热点。这项研究是第一个系统地确定的浓度的CO2和CH4在半北河源流。使用侧重于温室气体的顶空取样方法，并结合从瑞典两个地区的200多个溪流中选出的具有统计代表性的数据，是确定CO2和CH4基流浓度的基础。所有的流都过饱和相对于大气中的CO2和大多数在CH4的82%的流中，其中CH4被检测到。在CO2和CH4的空间变异性高，但正相关的总有机碳，年平均温度，泥炭地在流域的比例。然而，在空间控制方面存在区域差异，这是预测模型需要考虑的问题。该数据集允许比较顶空法和基于碱度的CO2测定方法。超过50%的物流不含碱度，这使得基于碱度的CO2测定变得不可能。此外，有一半的碱度流的碱度足够低（<0.07 meq L−1），使CO2的测定非常不确定。具有低pH值和无碱度的流含有比含有碱度的流高45%的中值CO2浓度。因此，如果（1）水源代表性不足，（2）对水源进行采样，但根据其碱度计算CO2，则此类水源中CO2的大规模概括将被显著低估。
Boreal headwater streams have been identified as hot spots for evasion of greenhouse gases (GHGs). This study was the first to systematically determine the concentrations of CO2 and CH4 in hemiboreal headwater streams. The use of a headspace sampling method focusing on GHGs in combination with a statistically representative selection of more than 200 streams across two regions in Sweden was the basis for defining the base flow concentrations of CO2 and CH4. All streams were supersaturated relative to the atmosphere in CO2 and the majority in CH4 for the 82% of streams in which CH4 was detected. The spatial variability in both CO2 and CH4 was high but positively related to total organic carbon, mean annual temperature, and proportion of peatland in the catchment. There were, however, regional differences in the spatial controls, which are something that predictive models need to consider. The data set allowed for comparison between a headspace and an alkalinity‐based method for determining CO2. More than 50% of the streams contained no alkalinity which made the alkalinity‐based determination of CO2 impossible. In addition, half of the streams with alkalinity had alkalinities low enough (<0.07 meq L−1) to make the CO2 determination very uncertain. The streams with low pH and no alkalinity contained median CO2 concentrations that were 45% higher than the streams containing alkalinity. Therefore, large‐scale generalizations about CO2 in such headwaters will be significantly underestimated if (1) headwaters are underrepresented and (2) the headwaters are sampled but CO2 is calculated from their alkalinity.