Color in the Upper Wisconsin River : Sources and Effects on Primary Poduction
University of Wisconsin-Stevens Point, College of Natural Resources
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The Wisconsin River, which drains 21% of the state of Wisconsin, has been extensively used for power production and industrial and municipal wastewater disposal. Man's past uses of the river caused serious water quality problems. However, water quality in the Wisconsin River has substantially improved since the implementation of the wastewater treatment requirements of the 1972 amendments to the Federal Water Pollution Control Act (PL 92-500). The sixteen pulp and paper mills on the Upper Wisconsin River may in the future be required to further treat their wastes to remove true color and increased amounts of suspended solids. At present, the color of the Wisconsin River is significantly influenced by wastewater discharges from the pulp and paper industry, especially during periods of low flow. During seven water quality surveys, their cumulative contribution to true color ranged from 2.2% at Hat Rapids Dam in May, 1979, to 62.9% at Mosinee Flowage in August, 1979. Similar results were observed for apparent color. The effect of color and associated effects of light penetration on the growth of the indigenous algal populations of a large Wisconsin River reservoir, Lake Du Bay, were investigated. A special experimental apparatus was constructed for field studies. Plastic bags six feet long were attached to a wooden raft and filled with river water diluted with well water to simulate color changes which might be caused by reduction of industrial discharges. Light and dark bottles filled with water from a common source were then inoculated with a radioactive sodium bicarbonate solution and incubated in the bags. Light penetration in the bags was measured for the total visible spectrum and the blue, green, and red spectral ranges. Carbon assimilation rates were found to increase as water color decreased, except for occasional instances of surface inhibition. The overall average increase in carbon assimilation rates in bags, with a true color decrease of 27.6% and an apparent color decrease of 22.2%, was 28.2%. Increases in carbon assimilation rates varied with depth, from 8.9% at .2 meters, to 54.5% at 1.2 meters. Multiple regression analysis indicated that red light penetration was the most significant predictor of carbon assimilation rate changes. The contribution of industry to the true and apparent color of the Wisconsin River therefore appears to lower algal productivity in reservoirs. However, one such reservoir, Lake Du Bay, is presently considered eutrophic as a result of nutrient inputs from industries, municipalities, and tributaries. Reduction of nutrient pollution, especially from nonpoint sources, will be necessary to prevent increases in nuisance algal blooms if industrial color discharges are reduced in the future. Such relationships must be seriously considered in water quality planning and implementation of the provisions of PL 92-500.