Oiti LiviiiK /ff.soHMc.i — hivcilfbratfi 



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tlic iipriver stations and contained racnilative 

 and some ciean-walcr taxa. indicating impiovcd 

 water quality. 



Although the total aquatic insect diversity in 

 the baskets at river mile 601 (968 km) in 1965 

 exceeded those at river mile 788 (1,268 km) by 

 about one-third, during the next 2 years the 

 diversity at Evansville increased over that at 

 Louisville by 30%-40%. This significant 

 increase was probably caused by environmental 

 changes (e.g.. increased eutrophication that pro- 

 vided more foods for these insects) that favored 

 Chironomidac nonbiling midges and 

 Hydropsychidae net-spinning caddisflies. 

 During the 3-year period, pollution-tolerant 

 species replaced some of the clean-water 

 ■■green" species. 



Aquatic in.sects are also useful indicators of 

 contamination of the sediments and waters that 

 may have gone unnoticed by routine physico- 

 chemical measurements. Uptake of toxic sub- 

 stances, such as heavy metals and organochlo- 

 rine compounds, causes various kinds of defor- 

 mities of the larval and pupal Chironomidae 

 (Hamilton and Saether 1971; Lenat 1993). 

 Depending on the severity of the pollution, these 

 deformed individuals do not reach maturity and 

 the populations are eventually reduced (van Urk 

 at al. 1992). During the 1963-67 Ohio River 

 monitoring program. Mason and Lewis 

 observed larval deformities in samples taken 

 from the sediments from the upper reaches of 

 the Ohio River near Pittsburgh, Pennsylvania, 

 the lower Monongahela River, and Kanawha 

 River (Mason, unpublished data). 



Management Implications 



There is a need to establish long-term moni- 

 toring and reporting on macroinvertebrate popu- 

 lations such as that carried out during 1963-67. A 

 monitoring program could evaluate the success 

 of pollution clean-up and identify biological 

 indicators to help balance water uses among 

 urban centers, transportation, industry, and fish- 

 ing and other recreation. Water chemistry and 

 physical measurements alone are not sufficient 

 to determine subtle shifts in aquatic populations. 



Locating point sources of contaminants or 

 thermal wastes so that they discharge directly to 

 trout streams and lakes usually results in loss of 

 stonetly populations, which, in turn, adversely 

 affects fisheries. The effects of aerial spraying 

 and other types of insecticide applications on 

 stonefly and other sensitive aquatic organisms 

 should be considered during site-preparation 

 planning. Natural resource managers often rec- 

 ommend set backs, or buffer strips of untilled 

 land adjacent to streams, as an effective way to 

 minimize harm from pollution runoff. 



■ 6,710 Mostly worms 



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Mississippi River Ephenieroptera 



The nymphs of burrowing maytlies 

 (Ephemeroptera) live in U-shaped tubes in the 

 silt bottoms of shallow, slow-moving waters 

 (Bemer and Pescador 1988). Although mass 

 emergences of adult burrowing mayflies in the 

 Upper Mississippi River have been considered a 

 nuisance (Fremling 1968), their abundance rep- 

 resents a wealth of fish food biomass; their 

 abundance also reflects environmental health. 



During 1957-69, three species of buirowing 

 mayflies (Hexagenia bilineata. H. limbata. and 

 Pentagenia viitigera) were monitored in the 

 3,218'-km (2,0()()-mi) reach of the Mississippi 

 River from Minneapolis, Minnesota, to New 

 Orieans, Louisiana (Fremling 1964, 1970). In 

 the 1930"s, 29 navigation dams were built in the 

 upper reaches of the Mississippi River, and bur- 

 rowing mayflies became abundant in the slow- 

 moving silted shallows. The insects were much 

 less abundant downstream from St. Louis. 

 Missouri, where no dams existed. The surveys 

 of Mississippi River mayflies continue today. 



During the years 1957-69 and 1976, about 

 1,300 collections of Hexagenia showed that 

 most of the navigation pools and impoundments 

 upstream from Minneapolis and St. Paul, 

 Minnesota, supported large populations of bur- 

 rowing maytlies. Both Hexagenia species were 



Fig. 1. (a) Total number of aquat- 

 ic insect and oilier macroinverte- 

 brate taxa and (b) average number 

 of individuals collected in basket 

 samplers in the Ohio River, 1965- 

 67 (Mason et al. 1971). 



