An Initial Assessment of NRCS Conservation Practices Effects on Stream Fishes

Sedimentation from agricultural activities is generally regarded as the largest threat affecting stream fish assemblages.  The US Department of Agriculture’s Natural Resource Conservation Service (NRCS) implements conservation practices on privately owned agricultural lands in an effort to reduce sedimentation and nutrient inputs in waterways.   Since most agricultural landholdings are privately owned, NRCS has the potential to remediate agricultural threats and affect fish habitats over large spatial extents.  Unfortunately, the effectiveness of NRCS conservation practices at conserving fish assemblages is largely unknown.  Our objective was to assess fish assemblage response to implementation of agricultural conservation practices designed to reduce stream sedimentation.  We used lithophilous spawning fishes as indicators of conservation practice effectiveness because they are negatively associated with threats that cause sedimentation (e.g., agriculture).  Conservation practices were considered effective if their implementation increased predicted lithophil guild abundance (#spp. within guild/# spp. in sample).  Multiple-regression modeling was used to predict the effects of natural factors (e.g., soil type and geology), human threats (e.g., agriculture and urbanization), and NRCS conservation practices (e.g., reduced tillage) on lithophil guild abundance for wadeable streams within portions of the Missouri River basin.  Lithophil guild abundance was negatively associated with agricultural and urbanization threats and positively associated with conservation practice density.  Our guild abundance predictions indicate that, in the Missouri River basin, currently implemented NRCS conservation practices have likely not been implemented in great enough density to effectively remediate agricultural threats.  Model predictions and simulations suggest that increasing the density of conservation practices above current levels would result in increased practice effectiveness.  The most effective conservation practices were those designed to reduce soil disturbances (e.g., conservation tillage) or prevent soil from entering stream channels (e.g., field borders).   NRCS conservation practices, when applied in great enough density, should have the potential to effectively remediate agricultural threats to aquatic systems.