Trophic response patterns in select benthic invertebrates over a 3 year period following removal of a low head dam

Shifts in community structure, physical habitat or diadromous fish movements are among the most commonly studied responses to dam removal.  However the trophic dynamics of secondary consumers like benthic invertebrates will also be important to structural and functional rehabilitation of a restored river.  If dam removal leads to changes in the material exported to downstream, then the characteristics of representative functional feeding groups we examined (mayflies, caddis flies, crayfish, snails, Odonates, and Megaloptera) should reflect it. To test this, response patterns of select benthic taxa of the East Branch of the Eightmile River, Connecticut over 3 years - pre-removal (2005), 1 (2006) and 3 years post (2008) were examined. Comparisons used the C/N stable isotope signature (SI), C/N ratios and dry weights of 5-10 individuals per taxa. Findings show a mixed response among taxa and year with functional feeding group being an important consideration. One important conclusion about expected trophic response in this and other situations is that dam removal should be thought of as a type ecological disruption of trophic  structure and interactions.  The implication is that both a food webs structure and associated ecological functions may be unsettled for a longer post-removal lag than many commonly monitored attributes of community structure.