Collaborative Research: How do hydrology and biogeochemistry control carbon flux from headwater streams to the atmosphere?

众所周知，溪流收集、处理和释放了盆地的大部分水。鲜为人知的是，河流也收集、处理和释放了盆地的大部分碳。碳以各种形式被河流收集，其中一些碳被河床中的微生物加工成二氧化碳（CO2），而大部分二氧化碳在下游流动时被排放到大气中。这些过程在小的源头溪流中尤为重要。由于水源盆地消耗了大量的陆地表面，这些耦合的水-碳过程可能具有全球意义。该项目将通过深入研究俄勒冈州西部96公顷流域的一条源头河流的碳循环，来测量、模拟和理解这种耦合的水-碳循环。通过使用HJ安德鲁斯实验森林的分水岭，这项研究将利用详细数据收集的历史和大量现有的测量数据。该项目团队将与奥杜邦协会合作，在实地教授1000名学童河流水文和生态学。这个项目有两个主要目标。首先是开发一个集成的建模框架来模拟河流中的碳循环，该框架可以广泛地转移到地球系统模型中模拟河流的地下和地表过程。第二步是测试并提出溪流和地下水水文学、碳生物地球化学以及溪流中二氧化碳产生和流出的综合理论。这些目标将通过开发一个模拟水文过程（例如，运输、潜流交换）和生物地球化学过程（例如，颗粒和溶解有机碳之间的转化，这些碳“池”的有氧呼吸速率）的源流综合碳模型来实现。建模将与地下水输送土壤呼吸二氧化碳的直接测量相结合，控制碳循环的生物和物理过程，溶解氧的测量，水文学，以及在溪流上方通量塔测量的从溪流到冠层呼吸的二氧化碳外排。原位隐沉中观系统将用于控制和监测沿流动路径的反应性输运，以参数化生物地球化学速率表达式，用于综合模型。最后，该项目将河段尺度过程提升到流域尺度，以解释河网的碳通量。

It is known that streams collect, process, and release much of a basin's water. It is less known that streams also collect, process, and release much of a basin's carbon. Carbon is collected by streams in various forms, some of that carbon is processed by microbes in the streambed into carbon dioxide (CO2), and much of that CO2 is vented to the atmosphere during downstream flow. These processes are particularly important in small, headwater streams. Since headwater basins drain significant land surface, these coupled water-carbon processes may be globally significant. This project will measure, model, and understand this coupled water-carbon cycle via intensive study of the stream carbon cycle within one headwater stream draining a 96-hectare basin in western Oregon. By using the Watershed 1 of the HJ Andrews Experimental Forest, this study will leverage a history of detailed data collection and a large number of existing measurements. The project team will partner with the Audubon Society to teach 1000 school children stream hydrology and ecology in the field.This project has two main goals. The first is to develop an integrated modeling framework to simulate carbon cycling in streams that is widely transferable to model subsurface and surface processes of streams in earth system models. The second is to test and present an integrated theory of stream and groundwater hydrology, carbon biogeochemistry, and CO2 production and efflux in a stream. These goals will be accomplished by developing an integrated carbon model for headwater streams that simulates hydrologic processes (e.g., transport, hyporheic exchange) and biogeochemical processes (e.g., transformation between particulate and dissolved organic carbon, aerobic respiration rates of these carbon "pools"). Modeling will be coupled with direct measurements of groundwater delivery of soil-respired CO2, biological and physical processes controlling carbon cycling, measurements of dissolved oxygen, hydrology, and CO2 efflux from the stream to subcanopy respiration measured at a flux tower above the stream. In situ hyporheic mesocosms will be used to manipulate and monitor reactive transport along flow paths to parameterize biogeochemical rate expressions for use in the integrated model. Finally, the project will upscale the reach-scale processes to watershed scale to explain carbon fluxes from river networks.