Rivers are the dynamic link between terrestrial and aquatic ecosystems. The biogeochemical processes that produce, consume, and transform organic carbon in rivers are critical to understanding regional carbon budgets, the controls on river water quality, and ultimately the export of terrestrial organic carbon to coastal regions. Our basic understanding of river carbon cycling is based largely on data from pristine rivers; yet today virtually all rivers are managed to optimize water supply, flood control and hydropower. On the Colorado River a system of dams and reservoirs has dramatically altered hydrodynamics and geomorphology, water residence time, particle load, light conditions, and sediment-water interactions. Comparatively little is known about the effects of these reservoirs on carbon biogeochemistry. This project will assess the distribution, composition and reactivity of terrestrial and riverine carbon along a sequence of well-characterized reservoirs in a single watershed.

This CAREER project integrates hypothesis-driven biogeochemical research questions, state-of-the-art analytical approaches, and innovative teaching strategies to address three fundamental research elements:

1. Developing a regional carbon budget for the Colorado River System using a combination of field measurements and laboratory manipulation experiments.

2. Examining the composition, reactivity, and fate of dissolved and particulate organic carbon in the Colorado River System.

3. Enhancing learning outcomes for geoscience students through field-based teaching.

Longitudinal water sampling, carbon characterization, and biogeochemical process studies, culminating in a carbon budget for each reservoir, will assess the trophic state of the river system and reveal new insights into the interactions among the biological and physico-chemical mechanisms that transform terrestrial and riverine carbon. The research and teaching will be integrated through inquiry-based student field-projects that address discrete questions complementary to the broader scientific objective; the students results will be integrated into classroom activities, enhancing science education for hundreds of other students. This project will provide undergraduate geoscientists the skills to address complex environmental problems by exposing them to field-based research at an early stage in their academic career. The Colorado river system provides a unique opportunity to study a large managed river, and the results of this work will provide insight for the biogeochemical mechanisms that support carbon cycling in contemporary river systems.