Tuesday, June 5, 2007
556

Macroinvertebrate Assemblages Associated With Las Vegas Wash In Nevada, USA: Response To Erosion Control Structures

S. Mark Nelson, Bureau of Reclamation, Denver Federal Center, Building 56, Rm 2010, 86-68220, P.O. Box 25007, Denver, CO 80225

Effects of stream erosion control structures on aquatic macroinvertebrates were studied in the urban Las Vegas Wash (Wash) drainage in Nevada from 2000-2006.  The Wash is potentially impacted by wastewater treatment plant inputs and hydrology /temperature alterations.  Variables important in structuring macroinvertebrate communities, as suggested by direct ordination, included hydrology and channel characteristics (velocity and width), along with conductivity and nutrients.  Wash tributaries had the highest taxa richness.  Invertebrate assemblages differed between sites, with several midge taxa important at tributary sites while Fallceon mayflies were common at erosion control structures.  Stepwise regression indicated mainstem taxa richness was negatively associated with flow magnitude in the preceding month and that macroinvertebrate abundance increased at sites with erosion control structures.  The furthest upstream site had richness and abundance values similar to control structure sites but differed significantly from sites that either lacked structures or where structures were damaged by large flows.  Several taxa were unique to the upstream site that was unaffected by altered temperatures and high baseflows.  Control structures increased richness by 66% but did not reach the level of the upstream site.  Data suggests that macroinvertebrate richness was limited at some Wash sites by habitat simplification, hydrological alterations, and thermal pollution.

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