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

Filoso, S., et al., 2015. Environmental Science & Technology

Original research (primary data)
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Abstract

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.

Case studies

Basic information

  • Case ID: INT-045-2
  • Intervention type: Restoration
  • Intervention description:

    Constructed Stream−Wetland Complexes stream restoration focused on reducing sediment export from waterways to the estuary is part of an evolving strategy to meet total maximum daily load (TMDL) requirements to restore the Bay. Watershed managers and the stream restoration community in the Chesapeake Bay region have responded to the problem by implementing novel stream corridor restoration designs, including the conversion of eroded channels to stream−wetland complexes that enhance a channel’s capacity to trap and retain suspended materials being delivered from upstream sources while reducing erosion The reconfiguration design objectives were channel stabilization, wetland creation, stream-floodplain reconnection and creation of topographic conditions conducive to Atlantic white cedar propagation.

  • Landscape/sea scape ecosystem management: Yes
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Reduced water quality  No effect Quantitative assessment of changes in TSS loads within reconfigured stream reaches immediately upstream of the tidal boundary. quantify the magnitude of TSS retention in these modified stream corridors, (b) evaluate variability in loading patterns and retention rates, and identify factors that explain the variability, and (c) determine how loads entering and exiting the reconfigured valleys compare with loads from other streams in the region that have not been deliberately reconfigured into stream−wetland complexes. we assessed their effectiveness at trapping and retaining TSS transported from upstream by using a mass balance approach, where inputs upstream of the reconfigured stream reaches were compared with outputs downstream. To determine loads upstream and downstream, we installed sampling stations at the top and bottom of each restored stream reach to measure streamflow and TSS concentrations.
  • Approach implemented in the field: Yes
  • Specific location:

    Maryland’s Coastal Plain in nontidal lowland valley reaches containing second- and thirdorder streams draining the western shore of Chesapeake Bay within the lowland valley are two locations (for the two interventions) Intervention 2) Wilelinor Tributary (WIL)

  • Country: United States of America
  • Habitat/Biome type: Streams, rivers, riparian | Wetlands |
  • Issue specific term: Not applicable

Evidence

  • Notes on intervention effectivness: 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. Climate change that results in an increase in the frequency of large storms may ultimately determine their sustainability and effectiveness at reducing TSS loads to downstream waters. other measures such as the implementation of stormwater best management practices (BMPs) in the watershed should be part of the solution for reducing pollutant loads to Chesapeake Bay, either alone or in tandem with stream restoration projects since such practices will likely improve the effectiveness and long-term sustainability of stream restorations.
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures:
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures:
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: Yes
  • Experimental evalution done: In-situ/field
  • Non-experimental evalution done: Not applicable
  • Study is systematic:

Basic information

  • Case ID: INT-045-1
  • Intervention type: Restoration
  • Intervention description:

    Constructed Stream−Wetland Complexes stream restoration focused on reducing sediment export from waterways to the estuary is part of an evolving strategy to meet total maximum daily load (TMDL) requirements to restore the Bay. Watershed managers and the stream restoration community in the Chesapeake Bay region have responded to the problem by implementing novel stream corridor restoration designs, including the conversion of eroded channels to stream−wetland complexes that enhance a channel’s capacity to trap and retain suspended materials being delivered from upstream sources while reducing erosion The reconfiguration design objectives were channel stabilization, wetland creation, stream-floodplain reconnection and creation of topographic conditions conducive to Atlantic white cedar propagation.

  • Landscape/sea scape ecosystem management: Yes
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Reduced water quality  No effect Quantitative assessment of changes in TSS loads within reconfigured stream reaches immediately upstream of the tidal boundary. quantify the magnitude of TSS retention in these modified stream corridors, (b) evaluate variability in loading patterns and retention rates, and identify factors that explain the variability, and (c) determine how loads entering and exiting the reconfigured valleys compare with loads from other streams in the region that have not been deliberately reconfigured into stream−wetland complexes. we assessed their effectiveness at trapping and retaining TSS transported from upstream by using a mass balance approach, where inputs upstream of the reconfigured stream reaches were compared with outputs downstream. To determine loads upstream and downstream, we installed sampling stations at the top and bottom of each restored stream reach to measure streamflow and TSS concentrations.
  • Approach implemented in the field: Yes
  • Specific location:

    Maryland’s Coastal Plain in nontidal lowland valley reaches containing second- and thirdorder streams draining the western shore of Chesapeake Bay within the lowland valley are two locations (for the two interventions) Intervention 1) Howard’s Branch (HBR)

  • Country: United States of America
  • Habitat/Biome type: Streams, rivers, riparian | Wetlands |
  • Issue specific term: Not applicable

Evidence

  • Notes on intervention effectivness: 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. Climate change that results in an increase in the frequency of large storms may ultimately determine their sustainability and effectiveness at reducing TSS loads to downstream waters. other measures such as the implementation of stormwater best management practices (BMPs) in the watershed should be part of the solution for reducing pollutant loads to Chesapeake Bay, either alone or in tandem with stream restoration projects since such practices will likely improve the effectiveness and long-term sustainability of stream restorations.
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures:
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures:
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: Yes
  • Experimental evalution done: In-situ/field
  • Non-experimental evalution done: Not applicable
  • Study is systematic: