Greenhouse gas emissions from rivers and streams along a steep gradient of biogeochemical constituents and land use

内陆水域在区域到全球碳循环中发挥着至关重要的作用。在这方面最新也是最不为人所知的方面之一是从内陆水域排放到大气中的二氧化碳(CO2)和甲烷(CH4)的量。最近的估计表明，从陆地生物群进入淡水生态系统的碳中，只有不到一半最终到达海洋。陆地碳的剩余量被处理并最终从内陆水域排放到大气中，是碳循环和温室气体(GHG)预算中一个重要但往往被忽视的组成部分。虽然最近的研究工作主要集中在湖泊和水库作为温室气源，但在小溪和水源系统的排放以及甲烷对排放气体总温室气体潜力的贡献方面存在重大研究空白。拟议项目的目标有两个：我们的主要目标是对控制完整流域河流网络中二氧化碳和甲烷排放强度和通量路径的关键过程进行定量评估。这项以过程为基础的评估将从核心研究区域内的广泛测量中获得，该区域是奎奇河271平方公里分水岭的河流网络。这一地区由发源于生物圈保护区PFälzerwald的溪流组成，在不到100公里的距离内流经土地利用方面形成鲜明对比的地貌。测量包括流水中的温室气体分压、气体交换速度、气泡和植物中介的气体通量、流代谢和表面积。将使用地理信息系统将河段尺度的测量扩大到整个研究区。作为这项提议的第二个目标，我们将分析这种扩大尺度的准确性，以及区域尺度温室气体通量估计的准确性及其对基础数据质量和数量的依赖。这些发现将被应用于估计扩大研究区域的温室气体排放量，在那里将只进行低水平采样。我们预计，土地利用和河流结构质量将是控制当地通量的关键过程和区域规模排放量的主要决定因素之一。我们的测量计划和拟议的分析允许对人类活动对碳处理和相应的溪流温室气体排放的影响进行定量评估。因此，该项目可作为评估人类活动改变的河流网络温室气体排放的参考研究。

Inland waters play a vital role in regional to global carbon cycling. Among the latest and least understood aspects in this context is the amount of carbon emitted from inland waters into the atmosphere as carbon dioxide (CO2) and as methane (CH4). Recent estimates suggest that less than half of the carbon that enters freshwater ecosystems from the terrestrial biome ultimately reaches the ocean. The remaining amount of terrestrial carbon, which is processed and eventually emitted into the atmosphere from inland waters, is a significant, though often neglected component of carbon cycling and greenhouse gas (GHG) budgets. While recent research effort focused mainly on lakes and reservoirs as GHG sources, major research gaps exist in respect to emissions from small streams and headwater systems, as well as in respect to the contribution of CH4 to the total GHG potential of emitted gases. The objectives of the proposed project are twofold: Our major goal is a quantitative assessment of the key processes controlling the intensity and flux paths of CO2 and CH4 emission from the fluvial network of a complete watershed. This process-based assessment will be obtained from extensive measurements within the core study area, the fluvial network of the 271 km2 watershed of the River Queich. This area consists of streams originating within the biosphere reserve Pfälzerwald and flowing through a contrasting landscape in terms of land use within less than 100 km distance. The measurements include GHG partial pressures in stream water, gas exchange velocity, bubble- and plant-mediated gas fluxes, stream metabolism, and surface area. A geographic information system will be used for up-scaling of the reach-scale measurements to the entire study area. As a second objective of this proposal, we will analyze the accuracy of this up-scaling, and there with the accuracy of regional-scale estimates of GHG fluxes and its dependence on quality and quantity of underlying data. These finding will be applied to estimate GHG emissions from an extended study area, where only low-level sampling will be performed. We expect land use and stream structural quality to be among major determinants for the key processes controlling local fluxes and for the magnitude of regional-scale emissions rates. Our measurement program and proposed analyses allows for a quantitative assessment of the impacts of anthropogenic activities on carbon processing and corresponding GHG emission from streams. Thus, this project may serve as a reference study for assessing GHG emissions from anthropogenically altered fluvial networks.