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

众所周知，溪流收集、处理和释放盆地的大部分水。鲜为人知的是，溪流也收集、处理和释放了大量盆地的碳。河流以各种形式收集碳，其中一些碳被流床中的微生物加工成二氧化碳(CO2)，其中大部分二氧化碳在下游流动期间被排放到大气中。这些过程在小型源头溪流中尤为重要。由于源头流域大量消耗陆地表面，这些水-碳耦合过程可能对全球产生重大影响。该项目将通过深入研究一条排放俄勒冈州西部一个96公顷流域的源头溪流中的溪流碳循环，来测量、模拟和理解这种耦合的水-碳循环。通过使用HJ Andrews实验森林的分水岭1，这项研究将利用详细的数据收集和大量现有测量的历史。该项目团队将与奥杜邦协会合作，在该领域教授1000名学童河流水文学和生态学。该项目有两个主要目标。第一个是开发一个集成的模拟框架来模拟河流中的碳循环，该框架可以广泛地移植到地球系统模型中的河流的地下和表层过程的模拟中。二是验证和提出了河流-地下水水文、碳生物地球化学以及河流中二氧化碳的产生和排放的综合理论。这些目标将通过为源头河流开发一个综合的碳模型来实现，该模型模拟水文过程(例如，输送、潮汐交换)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”的好氧呼吸速率)。建模将与直接测量土壤呼吸的二氧化碳的地下水输送、控制碳循环的生物和物理过程、测量从溪流到树冠下呼吸的溶解氧、水文学和CO2外流的测量相结合，在溪流上方的通量塔测量。原位高孔性中胚层将被用来操纵和监测沿流动路径的反应传输，以参数化生物地球化学速率表达式，以用于集成模型中。最后，该项目将把河流尺度的过程提升到流域尺度，以解释河流网络的碳通量。

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.