Abstract
Sediment transport, one of the key processes of river systems, is altered or
stopped by dams, leaving lower river reaches barren of sand and gravel, both of which
are essential habitat for fish and macroinvertebrates. One way to compensate for losses in
sediment is to supplement gravel to river reaches below impoundments. Because gravel
addition has become a widespread practice, it is essential to evaluate the biotic response
to restoration projects in order to improve the efficacy of future applications. The purpose
of our study was to evaluate the response of the macroinvertebrate community to gravel
addition in a high-gradient, regulated river in western North Carolina. We collected benthic
macroinvertebrate samples from gravel-enhanced areas and unenhanced areas for 1
season before gravel addition, and for 4 seasons afterwards. Repeated measures multivariate
analysis of variance indicated that the responses of macroinvertebrates to gravel
addition were generally specific to individual taxa or particular functional feeding groups
and did not lead to consistent patterns in overall family richness, diversity, density, or
evenness. Non-metric multi-dimensional scaling showed that shifts in macroinvertebrate
community composition were temporary and dependent upon site conditions and season.
Correlations between macroinvertebrate response variables and substrate microhabitat
variables existed with or without the inclusion of data from enhanced areas, which suggests
that substrate-biotic relationships were present before gravel addition. A review
of the current literature suggests that the responses of benthic macroinvertebrates to
substrate restoration are inconsistent and dependent upon site conditions and the degree
habitat improvement of pre-restoration site conditions.