Sorbonne Université, Centre National de la Recherche Scientifique, Institut Pierre Simon Laplace, UMR, 7619 METIS, Paris, France.
Université de Liège, Unité d'Océanographie Chimique, Liège, Belgium.
Sci Rep. 2018 Sep 18;8(1):13961. doi: 10.1038/s41598-018-32332-2.
Carbon evasion from rivers is an important component of the global carbon cycle. The intensification of anthropogenic pressures on hydrosystems requires studies of human-impacted rivers to identify and quantify the main drivers of carbon evasion. In 2016 and 2017, four field campaigns were conducted in the Seine River network characterized by an intensively cropped and highly populated basin. We measured partial pressures of carbon dioxide (pCO) in streams or rivers draining land under different uses at different seasons. We also computed pCO from an existing data set (pH, water temperature and total alkalinity) going back until 1970. Here we report factors controlling pCO that operate at different time and space scales. In our study, the Seine River was shown to be supersaturated in CO with respect to the atmospheric equilibrium, as well as a source of CO. Our results suggest an increase in pCO from winter to summer in small streams draining forests (from 1670 to 2480 ppm), croplands (from 1010 to 1550 ppm), and at the outlet of the basin (from 2490 to 3630 ppm). The main driver of pCO was shown to be dissolved organic carbon (DOC) concentrations (R = 0.56, n = 119, p < 0.05) that are modulated by hydro-climatic conditions and groundwater discharges. DOC sources were linked to land use and soil, mainly leaching into small upstream streams, but also to organic pollution, mainly found downstream in larger rivers. Our long-term analysis of the main stream suggests that pCO closely mirrors the pattern of urban water pollution over time. These results suggest that factors controlling pCO operate differently upstream and downstream depending on the physical characteristics of the river basin and on the intensity and location of the main anthropogenic pressures. The influence of these controlling factors may also differ over time, according to the seasons, and mirror long term changes in these anthropogenic pressures.
河流碳逃逸是全球碳循环的一个重要组成部分。水系统受到的人为压力不断加剧，这就要求对受人类活动影响的河流进行研究，以确定并量化导致碳逃逸的主要驱动因素。2016 年和 2017 年，在塞纳河流域进行了四次实地考察，该流域的特点是耕地面积大、人口密度高。我们在不同季节测量了不同土地利用类型下的溪流或河流中的二氧化碳分压（pCO2）。我们还根据现有的数据集（pH 值、水温、总碱度）计算了 1970 年之前的 pCO2。本文报告了在不同时间和空间尺度下控制 pCO2 的因素。研究表明，相对于大气平衡，塞纳河及其支流处于过饱和状态，是 CO2 的源。我们的结果表明，从小溪流到夏季，森林（从 1670 到 2480 ppm）、农田（从 1010 到 1550 ppm）和流域出口（从 2490 到 3630 ppm）的 pCO2 会增加。结果表明，pCO2 的主要驱动因素是溶解有机碳（DOC）浓度（R=0.56，n=119，p<0.05），DOC 浓度受水热条件和地下水排放的影响。DOC 的来源与土地利用和土壤有关，主要是从小溪流上游淋溶，但也与有机污染有关，主要出现在较大河流的下游。对主要河流的长期分析表明，pCO2 随时间变化与城市水污染的模式密切相关。这些结果表明，取决于流域的物理特征以及主要人为压力的强度和位置，控制 pCO2 的因素在上游和下游的作用方式不同。这些控制因素的影响也可能随时间变化而不同，与季节有关，并反映出这些人为压力的长期变化。
