Vorobyev Sergey N, Kolesnichenko Yuri, Karlsson Jan, Pokrovsky Oleg S
BIO-GEO-CLIM Laboratory, Tomsk State University, Tomsk, Russia.
Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, Linnaeus väg 6, 901 87 Umeå, Sweden.
Sci Total Environ. 2024 Dec 1;954:176294. doi: 10.1016/j.scitotenv.2024.176294. Epub 2024 Sep 14.
Carbon emission from Arctic rivers constitutes a positive feedback between the climate warming and C cycle. However, in case of rivers with extensive floodplains, the impacts of temporary water bodies and secondary channels on CO exchange with atmosphere, compared to the main stem and tributaries, remain strongly understudied. In order to quantify the relative role of various water bodies of the Arctic river basin in the C cycle, the hydrochemical variables and greenhouse gases GHG concentrations and fluxes were measured within the floodplain of the largest Arctic River, Ob, in its low reaches located in the permafrost zone. These included the main stem, secondary channels, tributaries and floodplain lakes sampled over a 900 km north-south transect (25,736 km of the main stem and adjacent floodplain area; 7893 km water surface) during peak of spring flood (May 2023). In addition to main stem and tributaries, providing less than a half of overall C flux, floodplain lakes and secondary channels acted as important factor of C emission from the floodplain water surfaces. Multi-parametric statistical treatment of the data suggested two main processes of C emission from the Ob River floodplain waters: terrestrial organic matter-rich flooded wetlands (fens) provided elevated pCO, whereas the sites of possible groundwater discharge in the secondary channels decreased the CO fluxes due to more alkaline environments, rich in labile metals and anionic elements. Based on available high-resolution Landsat-8 images, which matched the period of field work, it was found that the total water coverage of the floodplain during spring 2023 was 30 % of overall territory, compared to 18 % during the baseflow. Based on chamber-measured CO fluxes (1.56 ± 0.47 g C-CO m d), overall CO emissions during 2 months of the spring flood from the entire Lower Ob River floodplain water surfaces including the main stem amounted to 0.73 ± 0.25 Tg C. Diffuse CH flux represented <1 % of total C flux. The main stem of the Ob River accounted for 34 % and 18 % of CO and CH emissions, respectively, whereas the floodplain lakes provided 59 % and 50 % of CO and CH emission, respectively. Considering that the low reaches of the Ob River represent >70 % of total river basin floodplain, and that during some years, the entire floodplain can be covered by water, emissions from the river - if assessed solely from summer (July-August) measurements - can be at least 3 times underestimated. It is therefore important to account for extended water surface during high water levels on Arctic rivers when assessing global riverine C emissions.
北极河流的碳排放构成了气候变暖和碳循环之间的正反馈。然而，对于拥有广阔河漫滩的河流而言，与干流和支流相比，临时水体和二级河道对与大气进行二氧化碳交换的影响仍未得到充分研究。为了量化北极河流域不同水体在碳循环中的相对作用，在北极最大河流鄂毕河位于多年冻土区的下游河漫滩内，对水化学变量以及温室气体（GHG）浓度和通量进行了测量。这些水体包括在2023年5月春季洪水高峰期，沿南北向900公里断面（干流及相邻河漫滩面积25,736平方公里；水面7893公里）采样的干流、二级河道、支流和河漫滩湖泊。除了干流和支流（其提供的碳通量不到总量的一半），河漫滩湖泊和二级河道是河漫滩水面碳排放的重要因素。对数据进行的多参数统计处理表明，鄂毕河河漫滩水体的碳排放主要有两个过程：富含陆地有机物质的被洪水淹没的湿地（沼泽）导致较高的pCO₂，而二级河道中可能存在地下水排放的区域，由于环境碱性更强、富含活性金属和阴离子元素，二氧化碳通量降低。根据与实地调查期匹配的高分辨率陆地卫星8号图像，发现2023年春季河漫滩的总水域覆盖率为整个区域的30%，而基流期为18%。根据气室测量的二氧化碳通量（1.56±0.47克碳-CO₂/平方米·天），包括干流在内的整个鄂毕河下游河漫滩水面在春季洪水的两个月期间的总二氧化碳排放量为0.73±0.25太克碳。甲烷的扩散通量占总碳通量的比例不到1%。鄂毕河干流的二氧化碳和甲烷排放量分别占34%和18%，而河漫滩湖泊的二氧化碳和甲烷排放量分别占59%和50%。考虑到鄂毕河下游占整个流域河漫滩的70%以上，并且在某些年份，整个河漫滩可能被水覆盖，如果仅根据夏季（7 - 8月）的测量来评估河流的排放量，可能至少低估3倍。因此，在评估全球河流碳排放量时，考虑北极河流高水位期间扩展的水面面积非常重要。
