Boodoo Kyle S, Trauth Nico, Schmidt Christian, Schelker Jakob, Battin Tom J
Department of Limnology and Bio-Oceanography, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria.
WasserCluster Lunz GmbH, Dr. Carl Kupelwieser Promenade 5, 3293, Lunz am See, Austria.
Sci Rep. 2017 Oct 31;7(1):14401. doi: 10.1038/s41598-017-14439-0.
Streams are significant sources of CO to the atmosphere. Estimates of CO evasion fluxes (f ) from streams typically relate to the free flowing water but exclude geomorphological structures within the stream corridor. We found that gravel bars (GBs) are important sources of CO to the atmosphere, with on average more than twice as high f as those from the streamwater, affecting f at the level of entire headwater networks. Vertical temperature gradients resulting from the interplay between advective heat transfer and mixing with groundwater within GBs explained the observed variation in f from the GBs reasonably well. We propose that increased temperatures and their gradients within GBs exposed to solar radiation stimulate heterotrophic metabolism therein and facilitate the venting of CO from external sources (e.g. downwelling streamwater, groundwater) within GBs. Our study shows that GB f increased f from stream corridors by [median, (95% confidence interval)] 16.69%, (15.85-18.49%); 30.44%, (30.40-34.68%) and 2.92%, (2.90-3.0%), for 3, 4 and 5 order streams, respectively. These findings shed new light on regional estimates of f from streams, and are relevant given that streamwater thermal regimes change owing to global warming and human alteration of stream corridors.
溪流是大气中一氧化碳的重要来源。对溪流一氧化碳逸散通量（f）的估算通常与自由流动的水体相关，但不包括溪流廊道内的地貌结构。我们发现，砾石滩（GBs）是大气中一氧化碳的重要来源，其f平均是溪水的两倍多，在整个源头水网层面影响f。由平流热传递与GBs内地下水混合之间的相互作用导致的垂直温度梯度，较好地解释了观察到的GBs中f的变化。我们提出，暴露于太阳辐射下的GBs内温度及其梯度的升高会刺激其中的异养代谢，并促进GBs内外部来源（如下流溪水、地下水）的一氧化碳排放。我们的研究表明，对于三级、四级和五级溪流，GB f分别使溪流廊道的f增加了[中位数，（95%置信区间）]16.69%，（15.85 - 18.49%）；30.44%，（30.40 - 34.68%）和2.92%，（2.90 - 3.0%）。这些发现为溪流f的区域估算提供了新的思路，鉴于全球变暖和人类对溪流廊道的改变导致溪流水热状况发生变化，这些发现具有重要意义。
