Relating fine sediment dynamics and best management practices (BMPs) to instream habitat conditions for priority fishes and mussels in the Copper Creek drainage
July 2016 - December 2018
- Virginia Department of Game and Inland Fisheries
The aquatic habitats in the Copper Creek drainage (CCD) are severely impacted by fine sediments, likely resulting from cattle access to streams and the reduction in riparian buffers. The CCD hosts 11 federally protected fishes and mussels. Silt loads and siltation from agriculture are the most significant threat to their persistence. Relating sediment dynamics to instream habitat conditions in the CCD is critical to identifying the habitat available for priority species and to prioritizing restoration actions. VDGIF has identified several BMPs, such as creating vegetated riparian buffers and excluding livestock from streams, as potentially contributing to recovery of imperiled species.
A spatially-explicit, calibrated watershed model of the CCD is needed to explain the effects that silt load, substrate embeddedness, and bank instability have on the distribution and abundance of priority fishes and mussels. In addition, measures of the effectiveness of BMPs in improving instream habitat conditions are needed to inform conservation actions.
1. Quantify expected magnitude of sediment load across the CCD using the SWAT watershed model.
2. Survey sediment dynamics and instream habitat conditions relevant to recovery of priority fishes and mussels in CCD subwatersheds.
3. Analyze relationships among watershed, reach, and instream habitat characteristics to map habitat quality in the CCD.
We conducted stratified-random field surveys of selected experimental units (e.g., subwatersheds, stream segments) to assess benthic habitat quality, focusing on measures that reflect effects of fine sediment on substrate composition, embeddedness, and streambed stability. Products developed per our objectives included:
1) a calibrated SWAT model of the CCD to be used in future conservation planning;
2) maps of sediment load threat and benthic habitat quality metrics critical to the recovery of priority fishes and mussels;
3) an investigation of the relationships between two BMP types and benthic habitat quality, and whether BMPs are associated with improvements in habitat quality (e.g., reducing sedimentation).
Our findings included four main takeaways:
1) Benthic habitat quality is low in numerous stream segments in CCD. Mainstem reaches suffer from excess fine sedimentation and streambed instability. Tributary reaches suffer most from excess fine sedimentation.
2) Sediment yield estimates suggest upland sediment supplies to stream channels in CCD are comparable to regional means.
3) Riparian zones were generally the most influential watershed component with respect to benthic habitat quality. The extent of riparian pasture was inversely related to benthic habitat quality.
4) Afforestation and cattle-exclusion BMPs were not positively related to benthic habitat quality. In the cases where BMP implementation was related most strongly to benthic habitat quality, the relations were negative (e.g. BMP deployment associated with more fine sediment).
Our findings suggest several tactics for improving benthic habitat to recover imperiled aquatic species in CCD:
(1) plan for and promote BMP investments that restore a more natural hydrologic regime and reduce sediment delivery to streams;
2) promote additional BMPs in conjunction with the widely applied fencing BMPs, so they collectively rectify agricultural impacts on benthic habitat quality;
3) target specific areas for conservation action based on the best available knowledge of instream and watershed conditions and BMP efficacy.