NI: CONFLUENCE - Disentangling the role of rivers as greenhouse gas conduits

河流每年向大气中排放约2-3pg的碳作为温室气体二氧化碳(CO2)。这相当于每年人为二氧化碳排放量的20%，是全球碳循环的重要组成部分。人们对河流网络排放的甲烷(CH4)知之甚少。CH4是一种强有力的温室气体，在100年的时间框架内，甲烷的强度是二氧化碳的34倍。据估计，河流每年排放约27Tg的甲烷，相当于人为甲烷排放量的8%。然而，这些甲烷排放在空间和时间上都有很大的变化。河流作为陆地温室气体的管道，因此可以影响正在进行的气候变化。通过人类活动或气候变化造成的景观干扰可能会增加河流的碳排放，大大增加本已超载的大气碳库。这可能是对全球气候系统的反馈，因为气候变化对陆地碳循环的影响可能会增加河流的碳排放。因此，我们迫切需要确定具有全球代表性的生态系统中河流碳排放的大小和来源，以了解和预测当前和未来的气候变化。河流的碳排放主要来自河流排放的景观。但这些景观中的来源可能会因生态系统的不同而不同。碳源可以包括最近通过光合作用固定到生物质中的大气二氧化碳，几千年来在有机土壤中积累的碳，如北极、温带和热带泥炭地，甚至来自侵蚀和风化的古代地质碳。由于生态系统的潜在碳源如此多样，因此必须建立一个框架，以确定在河流网络中观察到的碳源是否与正常景观功能预期的碳源相符，或者它是否代表着被干扰的碳循环的信号。也就是说，较老和较慢的碳循环是否变得更短、更快？同位素，特别是放射性碳(14C)，是识别受干扰的碳循环的有力工具。通过一个领先的研究人员网络，该项目将汇集新的技术和研究地点，作为深入调查全球河流碳排放的基础。该项目将使用由国际项目合作伙伴开发的低成本传感器来测量河流碳排放量的大小。这些将与使用英国调查人员开发的新技术进行的深入同位素调查相结合。将建立一个由现有研究场地和测量基础设施组成的网络，覆盖各种生态系统。因此，该项目将提供一个跳板，通过在全球具有代表性的尺度上的直接观测来限制河流碳排放的规模和来源。河流可以排干大片景观区域，因此它们的水化学代表着景观碳损失的综合信号。这个项目将提供技术来梳理这些信号，并确定它们代表的是自然的还是受干扰的碳循环。该项目将为这些信号的现有观测建立一个数据库。此外，我们将使用这个项目中相互作用的、互补的技术来实施一个范围确定项目，以提供对受干扰地貌的子集的碳排放的大小和来源的初步观察。结果还将包括计划召开相关领域的研究人员的国际会议，以在该项目的生命周期之后扩大人员、技术和地点的网络。汇流将被用作联盟资金的发射台，利用这一史无前例的基础设施，在空间和时间尺度上实现淡水碳排放观测能力的阶梯式变化，这是单独的研究小组无法实现的。

Rivers emit ~2-3 Pg of carbon as the greenhouse gas carbon dioxide (CO2) to the atmosphere, each year. This is equivalent to 20% of annual anthropogenic CO2 emissions and an important component of the global carbon cycle. Methane (CH4) emissions from river networks are very poorly understood. CH4 is a potent greenhouse gas, 34 times stronger than CO2 over a 100-year timeframe. Rivers are estimated to emit ~27 Tg of CH4 each year, equivalent to 8% of anthropogenic CH4 emissions. However, these CH4 emissions vary greatly both spatially and over time. Rivers, acting as conduits for terrestrial greenhouse gases, can thus influence ongoing climate change. Landscape disturbance, either through human activity or climate change, can enhance river carbon emissions adding substantially to an already overloaded atmospheric carbon pool. This may represent a feedback to the global climate system as river carbon emissions can be enhanced by the impact of climate change on the terrestrial carbon cycle. Characterising the magnitude and source of river carbon emissions across globally representative ecosystems is therefore urgently needed for us to understand and predict current and future climate change.Carbon emissions from rivers are primarily derived from the landscapes they drain. But sources within these landscapes can vary depending on the ecosystem. Carbon sources can include recent atmospheric CO2 fixed into biomass via photosynthesis, carbon that has accumulated in organic soils over millennia such as in Arctic, temperate and tropical peatlands, and even ancient geological carbon derived from erosion and weathering. With such a diverse range of potential carbon sources across ecosystems, it is vital to establish a framework from which to determine whether the source of carbon observed in river networks matches what would be expected from normal landscape function, or if it represents signals of a disturbed carbon cycle. I.e. are older and slower carbon cycles becoming shorter and faster?Isotopes, especially radiocarbon (14C), are a powerful tool for identifying disturbed carbon cycles. Through a network of leading researchers, this project will bring together novel techniques and study sites to serve as a foundation for in-depth investigations into river carbon emissions around the globe. The project will utilise low-cost sensors for measuring the magnitude of river carbon emissions developed by the international Project Partners. These will be combined with in-depth isotopic investigations using novel techniques developed by the UK investigators. A network of existing study site and measurement infrastructure will be established covering a diverse range of ecosystems. The project will therefore provide a springboard from which to constrain the magnitude and source of river carbon emissions through direct observations at globally representative scales.Rivers can drain large landscape areas and as such their water chemistry represents an integrated signal of landscape carbon loss. This project will provide the techniques to tease apart these signals and determine if they represent natural or disturbed carbon cycling. The project will build a database of existing observations of these signals. In addition, we will use the interacting, complimentary techniques brought together in this project to carry out a scoping project to provide preliminary observations of the magnitude and source of carbon emissions from a subset of disturbed landscapes.CONFLUENCE will also include planning for an international meeting of researchers in relevant fields to grow the network of people, techniques and sites beyond the lifetime of this project. CONFLUENCE will be used as a launchpad for consortium funding to use this unprecedented infrastructure to make a step-change in observational capability of freshwater carbon emissions at spatial and temporal scales that individual research groups alone cannot achieve.