Aquatic community structure and stream habitat in a karst agricultural landscape

Background:Watersheds dominated by agriculture often have significant,negative impacts on local stream habitats and fauna.Our study examined stream biota and habitats within an entire stream in a karst agricultural landscape to determine if several decades of watershed conservation and management had reversed the severe degradation caused by poor land use and catastrophic soil erosion during the 1920s and 1930s.Results:Fish communities and stream habitats were degraded at over half of the 22 stream sites examined,and benthic macroinvertebrate communities were mostly poor throughout the entire stream.Poor fish communities were associated with missing or narrow riparian buffers,high percent fine sediments,high embeddedness of coarse sub-strates,and homogeneous run habitat.Invertebrate communities were dominated by filter-feeding taxa and those adapted to life on or within fine sediments.Stream sites with wide buffers and influenced by groundwater springs had higher fish community integrity and good to excellent instream habitat.Conclusions:Our results suggest that wide riparian buffers and karstic springs may have allowed recovery of some stream reaches,but more extensive buffers and additional soil conservation practices in upland areas likely are necessary to protect most stream segments and their biota from on-going agricultural activities.New state stream buffer laws instituted after this study resulted in establishment of vegetated buffers at all study sites,which may lead to improved stream habitat and biotic communities in future years.Benthic invertebrate community improvement also may require translocation of sensitive taxa from nearby watersheds due to limited dispersal abilities of many species currently absent from the study stream.Increased frequency and intensity of storm events and flooding may hinder future recovery of stream habitats and biota.