Substrate Roughness, Velocity Refuges, and Macroinvertebrate Abundance on Artificial Substrates in the Lower Mississippi River

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Journal of the North American Benthological Society


Articulated concrete mattress blocks (ACM) are now used almost exclusively for erosion control of banks along the lower Mississippi River (LMR) and provide habitat for macroinvertebrates and fishes which could not otherwise colonize the unstable substrate of the natural river channel. We studied the distribution and abundance of macroinvertebrates in the LMR on ACM blocks with smooth, rough, and grooved surfaces. Additionally, the effects of block surface modifications on substrate velocity profiles were determined at three flow velocities in a laboratory flume using a thermistor-based current meter. Total density of macroinvertebrates and the densities of individual taxa were significantly different on the three surface types after 3 mo of colonization; rough blocks had 1.4× greater densities than smooth blocks, and densities on grooved blocks were 2.3× higher than smooth and 1.6× higher than rough blocks. The caddisfly Hydropsyche orris and the amphipod Corophium lacustre were significantly denser on grooved than on the other block types. In a flume, velocities in groove bottoms were 7-24× lower than ambient water column velocities (0.12, 0.23, and 0.44 m/s) and increased significantly from 1 mm to 65 mm above the block surface at all flume velocities. For all surface types there was a negative relationship between height above the block surface and measured variance in velocities and a positive relationship between flume velocities and the measured variance in velocity readings which could be attributed to increased turbulence over the block surfaces. In the field, H. orris in grooves built retreats with the anterior opening containing the feeding nets extending up into the near-surface flows over the grooves. Low velocity eddies in the grooves provided a velocity refuge while still allowing the feeding structures to contact feeding flows over the block surface. Grooved blocks in the LMR supported, on average, more than twice the invertebrate density as smooth blocks, and are recommended for future deployment of mattress blocks.


ISSN: 2161-9549; e-ISSN: 2161-9565


Journal was later renamed Freshwater Science. It is the journal of the North American Benthological Society.


University of Chicago Press



Peer Reviewed