Recovery of Channel Morphology and Benthic Macroinvertebrate Assemblages after Livestock Exclusion

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Virginia Tech

Measurements in paired stream reaches with and without livestock access in southwestern Virginia suggest that livestock exclusion practices installed on short, isolated stream reaches result in improved geomorphic and riparian vegetation condition, but do not significantly improve the benthic macroinvertebrate assemblage. Detailed longitudinal and cross-sectional surveys, pebble counts, and rapid geomorphic assessments were conducted on contiguous, paired stream reaches (5 pairs) with and without active livestock access across a range of time since livestock exclusion was implemented. In addition, bank characteristics were quantified by measuring groundcover biomass, shrub crown volume, tree density and diameter, soil bulk density, and particle-size analysis. Benthic macroinvertebrates were collected with a D-frame dip net and quantified using the Virginia Stream Condition Index (SCI), and other benthic macroinvertebrate metrics. We determined that: 1) small lengths of livestock exclusion can significantly increase channel depth and decrease the width to depth ratio, and increase groundcover vegetation growth, but do not significantly alter benthic macroinvertebrate assemblages; and, 2) qualitative geomorphic assessment results showed trends over time since exclusion (0 to greater than 50 years), but not in any of the other parameters evaluated. These observations suggest that a more targeted and holistic approach that addresses watershed-wide impacts must be implemented to restore aquatic habitat. (Key Words: CREP, stream channel morphology, livestock exclusion, agriculture, benthic macroinvertebrates, riparian buffers.)

livestock exclusion, stream channel morphology, CREP, agriculture, benthic macroinvertebrates, riparian buffers