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D.Y. Panayotou, K.P. Chmiel, E.B. Villa, S.P. Lawler, J.E. Reuter, and C.R. Goldman Tahoe Research Group, University of California, Davis Department of Entomology, University of California, Davis The purpose of this research is to quantify the effects of anthropogenic habitat degradation and restoration on stream insects in the Tahoe basin. The data will add new information on biological diversity, species composition and food web structure of aquatic insects in Tahoe basin streams. Funding for this project is provided by the California Tahoe Conservancy as part of their efforts to evaluate stream restoration projects. Data was collected to test three hypotheses: 1) Fauna does not change significantly over scale of study so that unimpacted upstream sites can be used as within stream controls; 2) Restored streams have similar aquatic communities to reference sites; and 3) Degraded streams have lower biodiversity and species richness indices than reference or restored sites. Five streams were chosen in three categories: 1) reference (Burton, Eagle, General, Glen Alpine and Meeks) 2) impacted and not restored (Blackwood, Snow, Trout, Upper Truckee and Ward) and 3) impacted and restored (Angora, Burke, Cold, Griff and Lonely Gulch). We sampled five riffles at each of two sites per stream, within and above a current or future restoration. Streams were sampled during the early autumn and late summer of 1999 and 2000, respectively. Four categories of environmental variables were measured: geographical, physical, chemical and biological. We compared all sites by relating the physical and chemical water quality data to the aquatic insects in the streams. All three categories of sites were compared with one another to judge the impacts of habitat degradation and the effectiveness of stream restoration projects. Streams were dominated by four major orders: Ephemeroptera, Plecoptera, Trichoptera, and Diptera (see Figure) with Chironomids dominating the Diptera order. The other categories included small numbers of: Coleoptera, (mostly Elmidae beetles), Hemiptera, Megaloptera, Hymenoptera, Odonata and Collembola. Absolute insect abundance (# per m2) was used to calculate analysis of variance for the upstream vs. downstream sites for the reference streams. None of the main orders showed statistical significance for the 1999 data. Also, absolute insect abundance was used to determine possible statistical differences between the different categories of streams. There was no statistical significance for any of the ANOVAs at the ordinal level. Insects identified to order do not provide enough information to determine significant differences among the treatments; further work to the family and or genus level is necessary for this analysis. Future work is in progress to classify aquatic insects into lower taxonomic levels and functional feeding groups. Total insect abundance ranged from a low of 214 insects per m2 to a high of 25,802 insects per m2. In addition, the environmental data will be analyzed and used to explain some of the variation in aquatic insect abundance; a multivariate approach will be used in the data analysis to determine which environmental variables have the strongest impacts on the Tahoe basin aquatic insect communities. Multi-metric indices will be examined to see if they are appropriate for the Lake Tahoe watershed; these indices condense and summarize information that can be used to compare sites of a large watershed area.
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