Fine sediment and macroinvertebrate assemblages in Appalachian streams: a field experiment with biomonitoring applications

Forest management operations may result in above-ambient inputs of fine sediments to streams with consequences for stream biota. A field experiment was conducted at the Fernow Experimental Forest in West Virginia to examine the effects of fine sediment on macroinvertebrate assemblages. Fine sediment (<2 mm) was varied between 0 and 30% in 5% increments in otherwise natural substratum mixtures in 0.03-m(2) trays deployed at each of 3 sites along Elklick Run, a 4th-order stream, and allowed to colonize for 5 wk. Macroinvertebrate density (-, sign indicates response to fine sediment), biomass (-), EPT (Ephemeroptera, Plecoptera, and Trichoptera) taxa richness (-), the proportion of Ephemeroptera composed of Baetidae (+), and the proportion of chironomids composed of Chironominae (-) and of Orthocladiinae (+) were the most sensitive and reliable metrics. Sediment effects on metrics were generally subtle, even when statistically significant. Ordination and the relative abundance of individual taxa indicated that assemblage structure was altered by treatment, but the shift was generally less than the variation in structure among the 3 sites. Percent organic matter and interstitial velocity were quantified, but did not appear to explain observed responses to treatment. Comparison of assemblages colonizing treatment mixtures with assemblages colonizing natural substratum indicated that most aspects of the experiment were realistic. Macroinvertebrate assemblages were also sampled in 15 local streams, which varied in fine-sediment bed loads, to determine if predictions based on the field experiment were supported at a larger spatial scale. Survey results generally agreed qualitatively with experimental results suggesting that some metrics were robust at a regional scale for physically and geologically similar streams.