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Algal-nutrient relations in the Yellowstone River during low-flow conditions
Stephen D. Porter and David A. Peterson
U.S. Geological Survey, Water Resources Division
Water quality and biological samples were collected during low flow conditions in August 2000 at 11 sites along the Yellowstone River, and near the mouths of two tributaries (Clarks Fork and Bighorn River), to assess algal-nutrient (eutrophication) relations with human and natural factors, and the influence of these factors on macroinvertebrate indicators of water quality. Maximum rates of river productivity and respiration were estimated from diel monitoring of dissolved oxygen concentrations. Results from the study, part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program in the Yellowstone basin, indicate that the quality of the Yellowstone River generally is good to excellent. However, the middle segments of the river appear to be experiencing signs of accelerated eutrophication: nuisance growths of filamentous algae and relatively high rates of productivity and respiration. The abundance and productivity of periphyton in the Yellowstone River increased downstream from tributary discharges, reflecting nutrient sources associated with irrigated agriculture and residential development in those basins. Concentrations of dissolved phosphorus were detected throughout the Yellowstone River, but were relatively smaller at sites where periphyton productivity was high. Dissolved nitrate concentrations generally were less than laboratory reporting limits, and periphyton communities contained nitrogen-fixing species, which may indicate that the availability of dissolved nitrogen controls algal production in the upper and middle segments of the Yellowstone River. Concentrations of total nitrogen, phosphorus, and carbon increased with water turbidity in downstream segments of the Yellowstone River, where algal productivity was low and appeared to be limited by the availability of light.
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