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ALGAL-NUTRIENT RELATIONS IN THE YELLOWSTONE RIVER, MONTANA.
D.A. Peterson1, S.D. Porter2, and S.M. Kinsey3.
U.S. Geological Survey, 1Cheyenne, WY 82001, 2Denver, CO 80225, and
3Billings, MT 59101
A water-quality investigation of the main stem of the Yellowstone River and major tributaries was conducted during August 2000, as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. The investigation of the main stem encompassed 830 river kilometers, 3 ecoregions, and stream settings ranging from montane to plains. Periphyton chlorophyll (chl a) and ash-free dry mass (AFDM) concentrations were largest in the middle section of the river, where Cladophora approached nuisance conditions. Rates of stream metabolism (productivity (Pmax) and respiration (Rmax)), as estimated from diel changes in dissolved oxygen concentrations, also were largest in the middle part of the river, and productivity was associated primarily with benthic algae. Ratios of chl a to AFDM, as well as Pmax/Rmax relations, indicate autotrophic conditions in the upper part of the Yellowstone River, whereas heterotrophic conditions prevailed in the lower part of the river. Nutrient and algal-species data indicate that nitrogen concentrations might be a limiting factor for algal growth. Seston chl a concentrations generally indicated oligo-mesotrophic conditions throughout the length of the river. Seston chl a concentrations and the proportion of centric diatoms generally increased in a downstream direction, consistent with changes in water quality and habitat conditions in the lower river.
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