Document Type


Journal/Book Title/Conference

Report to the Glen Canyon National Recreation Area


Utah State University

Publication Date



nutrient limitation, chemical gradient, zooplankton

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Last Page



From 18-21 April 1996, students in a Utah State University class (Aquatic Ecology Laboratory; FW 560) measured limnological and fisheries characteristics in two side canyons (Halls Creek Bay and Moki Canyon) and the main channel of Lake Powell. Inclement weather precluded sampling of two other side canyons. Most of the sub-projects, directed by indiVIdual students, addressed the following two hypotheses: (1) productivity gradients existed from the inflows of the side canyons toward the main channel and; (2) productivity was higher in the side canyons than in the main channel of the lake. In most cases, parameters were measured at 3-5 stations in each side canyon. Near the inflows, Secchi depths were near 1.0 m in both side canyons, but increased rapidly and were greater than 10m in the main channel. Similarly, vertical light extinction coefficients ranged from 0.9 (Halls) and 1.6 (Moki) near the inflows, to 0.29 in the main channel. The estimated depth of the photic zone (1 % light) increased from 3 to 16 m along the gradients. Suspended inorganic sediments (SS) contributed significantly to the extinction of light: near the inflows SS ranged from 152 to 216 mg/L, whereas in the main canyon levels were near 70 mglL. Conductivity measurements indicated that side canyons were relatively well mixed: higher conductivities indicative of non-mixed conditions occurred only at depths> 40 m. Oxygen levels were above 75% of saturation at all depths in the side canyons. The lowest oxygen levels (66%) were found in the deep monomolimnion of the main channel. Measurements of total phosphorus suggested that levels were near 20 J.1g/L in the main channel, and increased to near 70 J.1g/L near the inflow of Moki Canyon. Phosphorus measurements in Halls Creek Bay were unsuccessful.