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GUNNISON RIVER Mean Percent Embeddedness 80% -60% C a E40% W _._ ?_ ._ -__._ ____. ___.... __. ......_..... Spring 1994 Fall 1994 Spring 1995 Fall 1995 PERIOD Figure 6. The mean and 95% confidence interval of the percent embeddedness values calculated for the river-wide substrate samples collected in 1994 and 1995 in the Colorado (above) and Gunnison (below) rivers. The mean interstitial void volume (Figure 7) represents the combination of substrate size, depth to embeddedness and percent surface area embedded. A mean value of 35,000 cm3/mz was found in the spring of 1994 and was significantly higher than in the fall 1994 (29,000 cm3/m2) and spring 1995 (32,000 cm3/m) . The fall 1994 and spring 1995 means were not significantly different. However, the void volumes in fall 1995 dramatically increased to 65,000 cm3/m2. This doubling of void volumes was significantly higher than all three previous sample dates. In the spring and fall of 1994, the Gunnison River had interstitial void volumes similar to the Colorado River, however, the increase in fall 1995 for the Colorado River was significantly greater than that experienced in the Gunnison River (Figure 7). COLORADO RIVER GUNNISON RIVER Mean Void Volume Mean Void Volume 7oooo 70000 0000 a x60000 .60000 E 0 o ____ ............... - ____. c40000 .............. §30000 .......... ............... 20000 20DOO Spring 1994 Fall 1994 Spring 1995 Fall 1995 Spring 19M Fall 1994 Spring 1995 . Fall 1995 PERIOD PFRInD Figure 7. The mean and 95% confidence interval of the void collected in 1994 and 1995 in the Colorado (left) and Gunnison (right) rivers. Water Quality-Light, which represents an important source of energy into the riverine ecosystem was measured in the various strata of the Colorado and Gunnison rivers in the spring of 1994 and 1995. The average light profiles (as a percent of surface intensity with depth) can be seen in Figure 8. 12