LONG‐TERM IMPLICATIONS OF DAM REMOVAL FOR MACROINVERTEBRATE COMMUNITIES IN MICHIGAN AND WISCONSIN RIVERS, UNITED STATES

Abstract

ABSTRACTThe removal of the numerous ageing dams in the United States has become an important stream restoration technique. The extent to which the ecological damage done to streams by dams is reversed upon removal is unknown, especially on decadal time scales. The objectives of this study were to determine if macroinvertebrate assemblages within rivers recover following the removal of a dam and to estimate the time needed for recovery. A space‐for‐time substitution approach was used on eight rivers in various stages of recovery following a dam removal, ranging from <1 to 40 years post‐removal. Within each river, macroinvertebrates were sampled in a zone unaffected by the dam removal (reference zone) and two zones impacted by the dam removal (former impoundment and downstream zone). Insects were identified to the family level and placed into functional feeding groups. Various macroinvertebrate community metrics were compared between impacted and unimpacted zones to evaluate the extent of recovery, and plotted over time since removal to develop a temporal trajectory of recovery. Generally, the macroinvertebrate community recovered 3–7 years following removal both in terms of taxonomic similarity and richness, although densities could take decades to recover. Dam removals are a beneficial restoration technique, yet the recovery of important stream components can be variable and may take longer than previous research has suggested. Having realistic expectations of the ecological ramifications of dam removal efforts is paramount in ensuring the success and thus potential of future projects. Copyright © 2011 John Wiley & Sons, Ltd.