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流中有机碳增加的机制。碳是水生食物网的重要组成部分，在水质中起着重要作用。这项研究是新颖的，因为不是从局部观察现象开始，建立基于过程的模型，将这些机制扩展到更大的范围，研究小组将挖掘大型天文台数据集，以获得更多的全球模式，然后调查较小规模的过程。该项目为多个研究生和本科生提供建模、实验室和实地方法的跨学科培训。此外，该团队将与一所服务于少数族裔的小学合作，为佛蒙特州的小学教师开发和管理一个专业发展研讨会。由于森林覆盖的水源集水区覆盖了很大的地理区域，它们对有机碳的溶解部分（DOC）产生了不成比例的影响，并在全球范围内受到密切监测。许多研究已经记录了北半球森林河流中DOC通量的显著增加，并对气候变化、土地利用或降水组成（即从酸化中恢复）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，预测未来DOC的通量几乎是不可能的。研究人员建议通过建模和实验相结合的方法来解决这一差距，以验证以下假设：1)水流DOC通量的增加是由区域观测到的酸化恢复（即pH值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释放是土壤成分和矿物学的函数。导致不同的反应（DOC是否增加），尽管潜在的区域强迫相似。使用新型数据驱动建模技术的大数据分析将使用USGS和关键带观测站数据集探测区域尺度数据（100公里）并确定一般模式（测试假设1）。这一步骤的结果将通过反应输运模型和实验（测试假设2-3），为在集水区（公里）到土壤团聚体尺度（微米）进行更详细的基于过程的调查提供信息。本研究解决了碳动力学中一个备受争议的话题（即增加DOC通量），并进一步致力于建立低温地球化学中尺度、学科和方法整合的框架。将统计和基于过程的建模与实验相结合，以跨越10个数量级的尺度，这对低温地球化学领域来说是新颖的，具有潜在的变革意义。本研究为三名研究生和多名本科生提供了跨学科的培训，扩大了研究的影响。此外，调查人员还将与教育学院和一所服务于少数族裔的幼儿园-五年级学校合作，为佛蒙特州的幼儿园-五年级教师开发和管理一个专业发展研讨会。本次研讨会的目标是i)为关键区域的K-5教育工作者提供专业发展，作为可持续学习的框架；ii)开始与参与的教育工作者一起开发适合K-5水平的教学模块。

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.