Sean Smith

Stream restoration strategies for reducing river nitrogen loads

Despite decades of work on implementing best management practices to reduce the movement of excess nitrogen (N) to aquatic ecosystems, the amount of N in streams and rivers remains high in many watersheds. Stream restoration has become increasingly popular, yet efforts to quantify N-removal benefits are only just beginning. Natural resource managers are asking scientists to provide advice for reducing the downstream flux of N. Here, we propose a framework for prioritizing restoration sites that involves identifying where potential N loads are large due to sizeable sources and efficient delivery to streams, and when the majority of N is exported. Small streams (1st–3rd order) with considerable loads delivered during low to moderate flows offer the greatest opportunities for N removal. We suggest approaches that increase in-stream carbon availability, contact between the water and benthos, and connections between streams and adjacent terrestrial environments. Because of uncertainties concerning the magnitud...

Restoring watersheds project by project: trends in Chesapeake Bay tributary restoration

Restoration of aquatic ecosystems is a high priority regionally and globally, yet only recently have such efforts adopted holistic approaches that include the restoration of streams and rivers flowing to coastal areas. As the largest estuary in the US, the Chesapeake Bay has been the focus of one of the most high-profile restoration programs ever undertaken in North America. While the primary emphasis has been on tidal waters, freshwater tributary clean-up strategies have recently been developed. We have compiled the first comprehensive database of over 4700 existing river and stream restoration projects in the Chesapeake Bay Watershed (CBW) to examine where dollars are being spent, what issues motivate restoration, and what approaches are used. By conservative estimates, in excess of

Closing the Gap Between Watershed Modeling, Sediment Budgeting, and Stream Restoration

400 million has been invested in restoration projects since 1990. The majority of projects were implemented to restore forest vegetation in riparian areas and improve water quality. Although the CBW has an extremely high density of restoration activities relative to other regions of the US, only 5.4% of the project records indicated that related monitoring of project performance has occurred. To provide cost-effective management solutions, we recommend that a centralized tracking system be developed that includes restoration projects associated with both tidal and non-tidal waterways, along with a substantial increase in investment in the comprehensive monitoring of individual projects following implementation.

The Efficacy of Constructed Stream-Wetland Complexes at Reducing the Flux of Suspended Solids to Chesapeake Bay.

Stream Restorat Approaches, Anal Geophysical Mon Copyright 2011 b 10.1029/2011GM The connection between stream restoration and sediment budgeting runs both ways: stream restoration is proposed as a means to reduce sediment yields, but an accurate understanding of sediment supply is necessary to design an effective project. Recent advances in monitoring technology, geochemical techniques, high-resolution topography data, and numerical modeling provide new opportunities to estimate sediment erosion, transport, and deposition rates; upscale them in a geomorphically relevant fashion; and synthesize sediment dynamics at watershed scales. For practical application at large scale, watershed models used to predict yield often do not resolve lower-order channels, leaving an essential “blind spot” regarding sediment processes. We illustrate the challenges and emerging approaches for estimating sediment budgets using examples from two very different physiographic settings: the Mid-Atlantic Piedmont and the agricultural plains of southern Minnesota. We highlight common challenges and themes in defining an effective watershed sediment model. In both cases, reliable estimates of sediment yield depend essentially on the accurate identification of sediment sources and sinks and, hence, require careful delineation of landscape units and identification of dominant sediment sources and sinks. The primary elements needed to bridge the gap between sediment budgeting, watershed modeling, and stream restoration are (1) specificity regarding location, mechanism, and rates of erosion, (2) accurate accounting of sediment storage, (3) appropriate methods for upscaling local observations, (4) efficient means for incorporating multiple lines of evidence to constrain budget estimates, and (5) stream restoration methods that incorporate sediment supply in assessment and design procedures.

Reservations About Dam Findings

Studies documenting the capacity of restored streams to reduce pollutant loads indicate that they are relatively ineffective when principal watershed stressors remain intact. Novel restorations are being designed to increase the hydraulic connectivity between stream channels and floodplains to enhance pollutant removal, and their popularity has increased the need for measurements of potential load reductions. Herein we summarize input-output budgets of total suspended solids (TSS) in two Coastal Plain lowland valleys modified to create stream-wetland complexes located above the head-of-tide on the western shore of Chesapeake Bay. Loads entering (input) and exiting (output) the reconfigured valleys over three years were 103 ± 26 and 85 ± 21 tons, respectively, and 41 ± 10 and 46 ± 9 tons, respectively. In both cases, changes in loads within the reconfigured valleys were insignificant relative to cumulative errors. High variability of TSS retention among stormflow events suggests that the capacity of these systems to trap and retain solids and their sustainability depend on the magnitude of TSS loads originating upstream, design characteristics, and the frequency and magnitude of large storms. Constructed stream-wetland complexes receiving relatively high TSS loads may experience progressive physical and chemical changes that limit their sustainability.

Hydraulic performance of a morphology-based stream channel design

In the Research Article “Natural streams and the legacy of water-powered mills” (18 January, p. [299][1]), R. C. Walter and D. J. Merritts observe that milldam density is regionally more important than previously recognized ([1][2]–[7][3]). We have several reservations: (i) Local observations