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<br />~::_:' '1 <br /> <br />_1"-" <br /> <br />" <br /> <br />''oj,!: <br /> <br />.; ! <br /> <br />~ <br /> <br />HI: Changes in quantity and composition of organic matter drift are only related to the <br />ascending limb of an experimental flood event, all other components of the event having little <br />effect on organic drift. <br /> <br />, <br />~ <br /> <br />Methods <br />The five sampling sites for sampling benthos will also be used for sampling POM drift, <br />(I) near Glen Canyon Dam, (2) near (upstream of) confluence of Pari a River at Lees Ferry, (3) <br />near the USGS cable way at Little Colorado River (upstream of LCR), (4) near the USGS cable <br />way of the Grand Canyon gage, and (5) near the USGS cable way at Diamond Creek; and at <br />eddy locations studied for sediment transport. <br />Measurement of drift of coarse POM will be made with duplicate 0.5 m diameter nets <br />(500 um mesh) deployed from boats in the middle of the channel at each cable site and within <br />the eddies. Nets will be deployed at least 10 min to obtain samples. Timing of drift net sampling <br />will correspond to different stages of the experimental flood event Sampling will occur during <br />(I) pre-eventlow flow period. (2) ascending limb of the event, (3) high flow period. (4) <br />descending limb of the event, and (5) post-event low flow period. At each site samples will be <br />collected four times per day. <br />Characteristics of the experimental flood, taken as part of the sediment studies, will be <br />used for testing the hypotheses of this section. Water velocity will also be recorded at the net <br />mouth for volumetric calculations during each collection. <br />Samples will be sorted in the field immediately after each sampling period into the <br />following categories: Gammaros lacustris, other macroinvertebrates, detritus, Cladophora, and <br />other algae/macrophytes. Densities of G. lacustris, chironomids, simuliids and the remaining <br />combined macroinvertebrates will be recorded while sorting. Samples field-sorted in this way <br />later will be oven-dried to a constant weight and converted to g m3/s. <br />Drift of fine POM will be collected with zooplankton nets(154 um mesh) also deployed <br />in duplicate. These samples will be preserved with a known quantity of formalin and later <br />examined microscopically to enumerate biota, followed by determination of oven dry weight <br />The main purpose of these samples is to determine the downstream distribution of zooplankton <br />exported from Lake Powell. <br />Two grab samples of water associated with drift samples also will be collected and <br />appropriately preserved to allow later determination of bacterial densities (DAPI counts, Porer <br />and Fieg 1989). These data will provide information on densities and composition of bacteria <br />throughout the river corridor with the expectation that bacteria become more abundant with <br />distance downstream as autochthononus and terrestrial POM is entrained. All data will be <br />converted to mass flux per unit time of organic carbon and assessed with respect to the length of <br />the river corridor (e.g., position of sampling site relative to source of material drifting) and <br />passage of the flood using gradient analysis and other multivariate approaches (e.g., multiple <br />regression), <br /> <br />;1 <br /> <br />~~ <br /> <br />:;,! <br /> <br />~ <br /> <br />0{ <br /> <br />"I <br />" <br /> <br />" <br /> <br />,; <br /> <br />~-' <br /> <br />~ <br />~', <br /><, <br />~ <br />1 <br /> <br />Fishes in the G.'1Ind Canyon <br /> <br />21 <br />