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

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.