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<br />,,~~ <br /> <br />Benthic Communities <br />Null Hypo'hesis- <br />HO: Benthic biomass and community structure is sufficiently stable that it will not be <br />significantly altered by any component of a experimental flood event <br /> <br />Alternative Hypothesis- <br />HI: Benthic biomass and community structure will be more altered in the upper reaches <br />below Glen Canyon Dam because different components of the experiment flood event, including <br />rate of the rising limb, duration, and rate of decline have greater influence in these reaches. <br /> <br />Methods <br />Sarnpling sites for benthos will be established: (1) near Glen Canyon Dam, (2) near <br />(upstream of) confluence of Pari a River at Lees Ferry , (3) near the USGS cable way at Little <br />Colorado River (upstream ofLCR), (4) near the USGS cable way of the Grand Canyon gage, and <br />(5) near Diamond Cree~ and in eddies being studied for sediment transport. <br />Within 10 days prior to and after the experimental flood, standing crops of attached algae <br />and invertebrates will be determined by dominant taxonomic group at each of the study sites. <br />Ponar-type dredges deployed with boat mounted winch will be used in eddy sediments and a <br />Hess sampler will be used in cobble substratum on bars and riffles. At each site, habitats created <br />by eddies will be sampled in duplicate at a minimum offive locations along transects (i.e. two <br />samples at each offive sampling points on each transect) through the pools previously <br />established by Blinn et al. (1993). Three pairs of Hess samples in cobble substratum will be <br />taken at specific points on bars associated with the eddy complex at each site also previously <br />established by Blinn et al. (1993). These samples need to be taken at or near the lower elevation <br />of the varia! zone created by fluctuating flows on channel margins. Hence, sampling crews must <br />be cogJ"i-n1nt of the spatial relations of minimum flows to insure sampling can occur at or below <br />the minimum elevation of the varia! zone, which is the only habitat that can contain a stable <br />benthic food web unaffected by desiccation. <br />Adult and pharate specimens will be collected with sweep nets, white and UV lights and <br />spot samples (e.g., collection of emerging adults along the shoreline). Water temperature, <br />dissolved oxygen, pH, specific conductance, substratum size, Secchi depth, river stage and time <br />will also be recorded at each sampling locations. Benthos will be sorted into the following 11 <br />biotic categories (Blinn et al. 1993): Cladophora, blue-green algal crust, chironomids, <br />Gammarus, gastropods, oligochaetes, simuliids, lumbricids, "other" invertebrates, detritus, and <br />miscellaneous algae and macrophytes. Numbers of organisms in each biotic category will be <br />determined along with oven-dry (60 C) mass. <br /> <br />Organic Matter <br />Null hypothesis- <br />HO 1: Quantity or composition of organic matter drift in the Colorado River below Glen <br />Canyon Dam will not be significantly altered by any component of an experimental flood event <br /> <br />Alternative Hypotheses: <br /> <br />20 <br />