Freshwater Mussel and Water Quality: a Review of the Effects of Hydrologic and Instream Habitat Alterations

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Proceedings of the First Freshwater Mollusk Conservation Society Symposium, 1999, pages 261-274 © 2000 Ohio Biological Survey

Freshwater mussels and water quality: A review of the effects of hydrologic and instream habitat alterations G. Thomas Watters1 Ohio Biological Survey and Aquatic Ecology Laboratory; 1315 Kinnear Road, The Ohio State University, Columbus, OH 43212 ABSTRACT: Hydraulic impacts represent a suite of habitat alterations that, although having different causes, often have similar methods of affecting the mussel fauna. For instance, logging and channelization are very different disturbances, but both generate sediments. These “hydraulic impacts” thus overlap each other to one degree or another. I have attempted to break them down into categories based on the type of disturbance, but what applies to 1 impact often may apply to others. By far, there is more published information on the effects of impoundments than on all other hydrologic impacts combined, and this review is dominated by that subject. Other subjects are not covered in any detail because they are too infrequent or ancillary to North American mussel conservation. For example, log runs in Finland are known to damage mussel populations (Valovirta 1990), but this is probably not a widespread problem. Keywords: freshwater mussels, water quality, impoundments, hydrology, habitat

Impoundments Perhaps mankind’s earliest attempt to manipulate freeflowing water was the dam. Dams could be used to divert water to mills and turbines, where its seemingly limitless power ground grain, cut lumber, and later generated electricity, generally freeing humanity to toil elsewhere. Dams could be used to divert water to irrigate ground that would not otherwise support crops. They could, in theory, alleviate flooding if the amount of water passing through the dam could be regulated. Dams could make a shallow river deep, allowing watercraft to operate. Impounded rivers could act as reservoirs for holding water to support the populace. Pristine natural areas could be turned into a recreational goldmine through impoundment. Real, perceived, or pork barrel, there were many reasons to dam rivers. It must be stressed that an artificial impoundment is not analogous to a naturally occurring pool within a river. Impoundments typically become deeper toward their downstream end, until they abut the dam. In contrast, natural pools are deepest toward their middle, then becoming shallow, forming runs and riffles. This results in a very different water flow pattern through the pool/impoundment, and subsequently downstream. These hydrologic differences result in faunal differences. For example, van der Schalie (1938) found 15 mussel species in Lake Cooper, a man-made 3

impoundment on the Mississippi River. In adjacent Lake Pepin, a naturally-formed pool, 30 species were encountered. The general impact of impoundments on existing aquatic habitats was reviewed by many authors. Yeager’s (1993, 1994) reviews are particularly thorough. Ellis (1942) gave an early review of the biotic and abiotic effects of impounding a river. He noted such deleterious consequences as silt accumulation, loss of shallow water habitat, stagnation, accumulation of pollutants, and nutrient-poor water. He concluded that “the initial period of high productivity may be very short in some reservoirs, and longer in others but the decline will inevitably come unless man makes some adjustments.” Baxter (1977) gave an excellent review drawing from examples worldwide. The author characterized impoundments as a distinct type of ecosystem, characterized by complicated flow patterns that may involve hypolimnion discharge, long periods of flooding, and heavy sediment loads. Downstream areas may be affected as well, particularly by flow regime. Baxter sagely noted that “since not all the hydraulic head of the world’s rivers has yet been utilized, it seems likely that more remain to be built.” Neel (1963) gave a...
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