Collaborative Proposal: Landscape evolution and sediment-nutrient fluxes in a wetland-stream restoration experiment

Franklin And Marshall College, Lancaster PA

Investigators

Abstract

Prerequisite to designing sustainable stream and riparian restorations with high potential for improved ecosystem services is to increase multi-disciplinary knowledge of how these systems evolve and respond to environmental change and human impacts. The goal of the Big Spring Run (BSR) restoration experiment in southeastern Pennsylvania is to better understand the geological, biological, and environmental mechanisms responsible for development and stability of landscape patterns in shallow vegetated flow systems, and to test a new paradigm of stream-wetland restoration. This new approach is based on the hypothesis that removal of historic sediment that buried a pre-existing Holocene wet meadow for approximately three centuries can effectively restore a number of ecosystem functions. Goals of the restoration include enhancing hydrologic exchange between stream channels and shallow groundwater within the restoration area, increasing the residence time of groundwater emanating from springs onto an organic-rich floodplain, and improving water quality by reducing sediment and nutrient loads in surface water flowing out of the restored reach. The exchange of water and nutrients between surface and ground water fosters removal of sediment and nutrients in wetland ecosystems where surface water flow speeds are low and organic carbon availability is high. Comparison of pre- and post-restoration data enables us to determine whether or not these and other restoration goals are achieved, and to evaluate how an incipient wetland landscape evolves after restoration. With a team of 26 scientists and resource managers from 12 agencies and academic institutions, we recently completed the 3rd yr of pre-restoration monitoring at BSR. Post-restoration monitoring began after 1 km of valley bottom restoration was completed in August, 2011. Water quality monitoring includes continuous operation of three USGS stream gaging stations (with turbidity sensors and suspended sediment samplers), 18 USGS piezometers, and over 30 shallow groundwater wells installed by USEPA within the restoration watershed. In addition, we use numerical modeling to 1) investigate the evolution and stability of stream-floodplain systems over a range of environmental conditions, 2) identify ground water flow paths and zones of nutrient transformation, and 3) predict whether this new paradigm of stream restoration will be sustainable under present-day sediment inputs and hydrologic fluxes. Results of this work will have broad implications for restoring streams and improving water quality. Prior to this work, the dominant paradigm for stream restoration was based on the assumption that causes of stream impairment are largely the result of modern land use (e.g., excess storm water runoff from urbanizing areas) rather than a legacy of centuries of human impacts that included the burial of original wetland-stream landscapes beneath several meters or more of historic mud. Restoration at BSR involved removing historic sediment so as to accommodate storm flow within the entire valley bottom, and at a much lower velocity, flow depth, and shear stress than in the impaired state. We anticipate that such sediment removal and wetland rehabilitation will be a sustainable means of reestablishing ecosystem diversity and function, reducing storm water discharge to downstream reaches, and improving water quality in watersheds where similar impairments have been identified.