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Preliminary data on primary and secondary productivity and detrital abundance in run and riffle <br />habitats indicated that in both run and riffle habitats, highest periphyton biomass (primary <br />productivity) was observed in Reaches 4 and 6, while invertebrate biomass (secondary productivity) <br />was highest in Reach 8 and steadily decreased with downstream distance. Benthic detritus <br />concentrations were significantly lower in Reaches 1 through 3 than in upper reaches (i.e., Reaches <br />4 through 8). Other detailed habitat data currently being used by Bliesner and Lamarra (1996) to <br />evaluate differences in depth, velocity, and embeddedness among various habitat types have not yet <br />been analyzed based on the geomorphic reach designations. Completion of these analyses should <br />provide additional information on habitat characteristics associated with the geomorphic reaches. <br />Results of a study on cobble substrate characterization, where substrate characteristics of suspected <br />Colorado squawfish spawning locations in the San Juan River, near RM 131 -132, were compared <br />with substrate characteristics of known and suspected spawning areas in the Yampa and Colorado <br />rivers, indicated that substrate characteristics were similar in all three systems, except that cobble <br />size at the Colorado River sites was slightly larger. These results suggest that the site at RM 131 -132 <br />in the San Juan River is suitable for Colorado squawfish spawning. Comparison of substrate <br />characteristics of the sites between RM 131 -132 to other locations within the San Juan River System, <br />both upstream and downstream, indicated that substrate characteristics of other cobble areas in the <br />San Juan River study area, particularly upstream of RM 132, also appeared to be suitable for <br />spawning, primarily due to similarities in the size of cobble and depth of open interstitial space. <br />These sites were all located in geomorphic Reach 6 between RM 163 and 174. In Reach 3 between <br />RM 76 and 89, suitability of cobble areas for spawning appeared to be reduced based on less open <br />interstitial space at the sites sampled. <br />Summary <br />Studies by Bliesner and Lamarra (1995, 1996) have provided substantial data on habitat <br />characteristics in distinct geomorphic reaches of the San Juan River. Their information has provided <br />thorough descriptions of macrohabitat composition, substrate characteristics, availability of low <br />velocity habitat, and water temperature. This objective has essentially been completed. <br />5.2.2. Determine Changes in Channel Morphology from Historical Conditions <br />with Changes in Flow Regime. <br />Contributing Investigations <br />Changes in channel morphology from historical conditions were investigated by Bliesner and <br />Lamarra (1994) by comparing cross - sectional survey data from the San Juan River floodplain, <br />collected by the New Mexico Interstate Stream Commission (NMISC) in 1962, with survey data <br />collected from eight cross - sections that were resurveyed in the summer of 1993, all located below <br />' Hogback Diversion (see Figure 1). Evaluations of changes in channel morphology associated with <br />recent changes in flow regime are being assessed based on changes in river channel geometry over <br />time and in association with specific flow conditions (Bliesner and Lamarra 1996). Comparative <br />studies of aerial photography from the mid 1930s, early 1950s and 1960s, and 1986 -88 are in <br />progress and will be completed late in 1998. <br />San Juan River Recovery Implementation Program December 1997 <br />Summary Report 12 PR -602 -1 <br />