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Project 3— Aquatic Food Base (Bio 1.R1 and 4) <br />Start Date <br />2006 <br />End Date <br />2010 <br />Principal Investigators <br />T.A. Kennedy (GCMRC), R. Hall (University of Wyoming), E. Rosi - Marshall (Cary Institute of <br />Ecosystem Studies), and C. Baxter (Idaho State University) <br />Geographic Scope <br />Systemwide, from Glen Canyon Dam to Diamond Creek (RM 225) <br />Project Goals <br />The aquatic food base project will answer the following fall steady flow related questions: <br />1. Does flow regime affect rates of primary production or organic and invertebrate drift? <br />2. Does flow regime affect the residence time of water in backwater habitats? <br />Need for Project <br />After habitat, food is the resource that most often limits the distribution or abundance of animal <br />populations (Krebs, 1994). Algae and aquatic invertebrates are two of the most common food types <br />consumed by native and nonnative fish in the Colorado River (McKinney and Speas, 2001; Valdez and <br />Ryel, 1995). Preliminary data indicate rates of algae drift are positively related to discharge, at least in <br />Lees Ferry. Further, aquatic invertebrates in the Colorado River actually use filamentous algae as habitat <br />(Shannon and others, 1994), so rates of invertebrate drift may also be positively related to discharge. If <br />steady flows of low discharge decrease algae and invertebrate drift, then this could lead to an <br />accumulation of algae and invertebrates on the river bottom. However, algae and invertebrate biomass <br />data are extremely variable (Stevens and others, 1997), so it is unlikely that any observed changes <br />would be statistically significant or could be ascribed to the short duration fall steady flows. The food <br />base project has developed methods for quantifying algae production in the Colorado River using diel <br />changes in dissolved oxygen concentration. Further; we have refined the invertebrate drift collection and <br />sampling processing methods developed by McKinney and others (1999). Both of these process -based <br />metrics (algae production, grams 02'111-2. d- 1; invertebrate drift load, g AFDM•s -1) should be more <br />sensitive to the subtle changes that are likely with fall steady flows compared to static measures of algae <br />and invertebrate biomass (g AFDM•m 2). <br />The degree of nearshore warming appears to be related to the degree of isolation of those habitats from <br />the mainstem river. Water temperature data indicate residence time of water in nearshore environments <br />is greater when discharge is stable relative to fluctuating. However, the magnitude of this increase in <br />residence time is uncertain. Water residence time in backwaters may also influence the productivity of <br />25 <br />