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

河流每年以温室气体二氧化碳（CO2）的形式向大气排放约2-3毫克的碳。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。人们对河网的甲烷（CH4）排放知之甚少。甲烷是一种强效的温室气体，在100年的时间框架内，其强度是二氧化碳的34倍。据估计，河流每年排放约27tg的CH4，相当于人为排放CH4的8%。然而，这些甲烷排放量在空间上和时间上都有很大的变化。河流作为陆地温室气体的管道，因此可以影响正在发生的气候变化。无论是人类活动还是气候变化造成的景观干扰，都会增加河流的碳排放，大大增加已经超负荷的大气碳库。这可能是对全球气候系统的一种反馈，因为气候变化对陆地碳循环的影响会增加河流碳排放。因此，我们迫切需要在全球具有代表性的生态系统中描述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其所排水的景观。但这些景观中的来源可能因生态系统而异。碳源可以包括最近通过光合作用固定在生物质中的大气二氧化碳，在北极、温带和热带泥炭地等有机土壤中积累了数千年的碳，甚至是由侵蚀和风化产生的古代地质碳。鉴于生态系统中潜在碳源的多样性，建立一个框架至关重要，以确定在河流网络中观察到的碳源是否与正常景观功能的预期相符，或者它是否代表了碳循环受到干扰的信号。也就是说，旧的、慢的碳循环是否变得越来越短、越来越快？同位素，尤其是放射性碳（14C），是识别受干扰碳循环的有力工具。通过一个由领先研究人员组成的网络，该项目将汇集新技术和研究地点，为深入调查全球河流碳排放奠定基础。该项目将利用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。这些将与使用英国研究人员开发的新技术的深入同位素调查相结合。将建立一个涵盖多种生态系统的现有研究地点和测量基础设施的网络。因此，该项目将提供一个跳板，通过全球代表性尺度的直接观测来限制河流碳排放的规模和来源。河流可以排走大片景观区域，因此它们的水化学成分代表了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，并确定它们是自然的还是受干扰的碳循环。该项目将建立一个现有这些信号观测数据的数据库。此外，我们将使用本项目中汇集的相互作用的互补技术来开展一个范围界定项目，以提供对受干扰景观子集的碳排放规模和来源的初步观察。CONFLUENCE还将包括为相关领域的研究人员举办一次国际会议的计划，以在该项目的生命周期之外扩大人员、技术和地点的网络。CONFLUENCE将被用作财团资助的一个启动平台，利用这一前所未有的基础设施，在空间和时间尺度上逐步改变淡水碳排放的观测能力，这是单个研究小组无法单独实现的。

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.