Survival of Walleye Eggs and Fry on Paper Fiber Sludge Deposits in Rainy River, Minnesota

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Abstract
Investigations of paper-fiber sludge deposits below paper mills were made to determine water characteristics over them with reference to survival of walleye (Stizostedion vitreum vitreum) eggs and fry and occurrence of bottom fish-food organisms. Sampling of water from the fiber-sludge water interface to the surface showed gradients in O as great as 0.1 ppm to near saturation, and in dissolved sulfides from 0.8 to 0.0 ppm. The most rapid gradient of these materials was in the bottom 20 mm. Levels of sulfides were most affected by current velocity and showed little relation to temperature or season. Walleye eggs placed in test trays on fiber mats had lower survival than those placed 12 in. above the mats and those placed on mineral substrates. Eggs and fry placed on mats died within 48 hr. Laboratory bioassays showed that sulfide levels of 0.3 ppm under controlled conditions approximating river conditions were acutely lethal to Gammarus pseudolimnaeus and walleye eggs and fry. Fiber released from paper mills forms sludge mats as far as 62 miles below outfalls and creates oxygen deficiencies and H2S concentrations near the sludge-water interface that are lethal to early life history stages of fish and some fish-food organisms.

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