Doctoral Dissertation Research: Connectivity and Discontinuity in River Systems

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The interchange of water, sediment, nutrients, pollutants and other matter is a fundamental process of river systems that affects channel form, ecologic integrity, and human activities. Contemporary river restoration and rehabilitation theory calls for process-based approaches that aim to protect and reinstate this connectivity at watershed scales. There are fundamental unanswered questions about this connectivity, however, which hinder efforts to understand and safeguard the physical and biological systems of rivers. In particular, it is unclear how disturbance and the recovery from disturbance, such as dam removal, affect connectivity and channel form; over what time and spatial scales does this recovery occur; and what characterizes the natural rates and dimensions of continuity and discontinuity. Recent developments in the use of isotopes as both tracers and chronometers can be applied to quantify the spatial and temporal aspects of connectivity and how it affects channel form, sediment residence time and nutrient flux. In addition, large-scale river restoration projects, such as dam removals, enable watershed-scale experiments to test predictions on connectivity. This doctoral dissertation research project will analyze the connectivity of riparian processes in pristine and disturbed river systems and investigate the effects of restoration on sediment transport, channel form and nutrient flux. The doctoral student will conduct a series of field experiments in New England, using innovative applications of lead-210, beryllium-7, and carbon-14 isotopes to determine residence time of instream sediment and add a temporal dimension to a widely used metric of instream sediment storage, V*. These same isotopes will be used in another manner in the riparian zone to establish the flux of sediment and nutrients between floodplains and channels. Building on recent advancements on effects of dam emplacement on channel morphology, this project will test predictions on channel adjustments due to dam removal, which reestablishes continuity of sediment.This project will advance both basic understanding of riverine systems and practical knowledge to guide river restoration efforts. Reestablishing the multiple dimensions of connectivity is a paramount goal in river restoration. This group of field experiments will examine what controls the spatial and temporal scales of sediment continuity, how connectivity is affected by dam emplacement and removal, and how variation in connectivity affects river channel form and nutrient exchange. These questions collectively typify the foremost challenges facing fluvial geomorphology and the science of river restoration -- the delineation and prediction of the multiple, interacting temporal and spatial scales of river response to disturbance. The field work will be conducted in New England, which is currently experiencing more than ten dam removals per year. In addition to advancing basic knowledge of river restoration and river response to disturbance, the results of this research will be leveraged by key stakeholders and agencies to advance their ongoing studies, and it will help managers and scientists guide restoration efforts regionally and nationally. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.