Collaborative Research: Combining complex systems tools, process-based modelling and experiments to bridge scales in low temperature geochemistry

研究人员将结合新的建模方法和实验来了解溪水中有机碳增加的机制。碳是水生食物链中的重要组成部分，在水质中起着重要作用。这项研究是新颖的，因为研究小组不是从局部观察到的现象开始，然后建立基于过程的模型，将这些机制扩大到更大的规模，而是将从大型观测站数据集中挖掘更多的全球模式，然后调查较小规模的过程。该项目为多名研究生和本科生提供建模、实验室和现场方法方面的跨学科培训。此外，该团队将与一所服务于少数族裔的K-5小学合作，为佛蒙特州的K-5教师开发和管理一个专业发展研讨会。由于森林水源集水区覆盖了大片地理区域，它们对有机碳的溶解部分(DOC)有不成比例的影响，并在全球范围内受到密切监测。大量研究证明，北半球森林溪流的DOC通量显著增加，并对气候、土地利用或降水组成的变化(即酸化恢复)等潜在原因进行了辩论。由于缺乏对潜在驱动DOC释放的具体机制的关注，因此几乎不可能预测未来的DOC通量。研究人员建议通过模拟和实验相结合的方法来解决这一差距，以检验以下假设：1)溪水DOC通量的增加是由区域观察到的酸化恢复(即pH的增加和干湿沉积离子强度的降低)驱动的，2)DOC是从在这些变化条件下变得不稳定的土壤团聚体中释放的，3)团聚体稳定性和DOC的释放是土壤组成和矿物学的函数，导致不同的响应(是否存在DOC增加)，尽管可能是相似的区域作用力。使用新颖的数据驱动的建模技术的大数据分析将使用美国地质调查局和临界区观测站的数据集，以探测区域规模的数据(100公里)并确定一般模式(测试假设1)。这一步骤的结果将为选择地点提供信息，以便使用反应迁移模型和实验(测试假设2-3)在集水区(Km)到土壤集合体尺度(微米)进行更详细的基于过程的调查。这项研究解决了碳动力学中一个备受争议的主题(即增加DOC通量)，并进一步致力于建立一个框架，以整合低温地球化学中的尺度、学科和方法。将统计和基于过程的建模与实验相结合，以弥补10个数量级的差异，这对低温地球化学领域是新颖的，具有潜在的变革意义。这项研究的影响通过为三名研究生和多名本科生提供的跨学科培训而扩大。此外，调查人员将与教育学院和一所为少数族裔服务的K-5学校合作，为佛蒙特州的K-5教师开发和管理一个专业发展研讨会。该讲习班的目标是：i)为关键区域的K-5教育工作者提供专业发展，以此作为可持续发展学习的框架；ii)开始与参与的K-5教育工作者一起为适当的K-5水平制定教学模块。

Investigators will combine new modelling approaches and experiments to understand the mechanisms by which organic carbon in stream waters increases. Carbon is an important constituent in the aquatic food web and plays an important role in water quality. This research is novel because, instead of beginning with locally-observed phenomena and build process-based models that scale those mechanisms up to a larger scale, the investigator team will mine large observatory datasets for more global patterns followed by the investigation of smaller scale processes. The project provides interdisciplinary training in modeling, lab and field approaches for multiple graduate and undergraduate students. Furthermore, the team will collaborate with a minority-serving, K-5 elementary school to develop and administer a professional development workshop for Vermont's K-5 teachers.Because forested headwater catchments cover large geographical areas, they have disproportionate effects on the dissolved fraction of organic carbon (DOC) and are closely monitored across the globe. Significant increases in DOC fluxes from forested streams across the northern hemisphere have been documented by numerous studies and potential causes such as changes in climate, land use or precipitation composition (i.e. recovery from acidification) are debated. The lack of focus on the specific mechanisms potentially driving the DOC release makes the prediction of future DOC fluxes nearly impossible. The investigators propose to address this gap with a combination of modelling and experiments to test the hypotheses that 1) an increase in stream water DOC flux is driven by the regionally observed recovery from acidification (i.e. the increase in pH and decrease in ionic strength of wet and dry deposition), 2) DOC is released from soil aggregates that become unstable under these changing conditions, and 3) aggregate stability and DOC release is a function of soil composition and mineralogy, leading to the varied responses (presence or absence of DOC increase) despite potentially similar regional forcings. Big Data analysis using novel data-driven modelling techniques will use USGS and Critical Zone Observatory datasets to probe regional-scale data (100 km) and identify general patterns (test hypotheses 1). Results from this step will inform selection of sites for more detailed process-based investigation at the catchment (km) to soil aggregate scale (micrometer) using Reactive Transport Modelling and experiments (test hypotheses 2-3). This research addresses a highly debated topic in C dynamics (i.e. increase DOC fluxes) and furthermore works toward a framework for the integration of scales, disciplines and approaches in low temperature geochemistry. The combination of statistical and process-based modelling with experiments to bridge scales varying 10 orders of magnitude is novel and potentially transformative for the field of low temperature geochemistry. The impact of this research is broadened by the interdisciplinary training provided for three graduate students and multiple undergraduate students. Furthermore, the investigators will collaborate with the College of Education and a minority-serving, K-5 school to develop and administer a professional development workshop for Vermont's K-5 teachers. Goals for this workshop are to i) provide professional development for K-5 educators on the Critical Zone as a framework for sustainability learning and ii) to begin to develop teaching modules with participating educators for the appropriate K-5 level.