benthic macroinvertebrate communities reflects changes in the physical and chemical condition 

 within a reach over time. Biological monitoring is based on the fact that different species react to 

 pollution in different ways. Pollution-sensitive organisms, such as mayflies, freshwater mussels 

 and clams, are more susceptible than others to the effects of many physical or chemical changes 

 in a river. Pollution-tolerant organisms such as midge larvae and aquatic worms can cope with 

 adverse conditions more easily. Based on the chronic nature of sediment toxicity detected in 

 Reach 15 of the Upper Mississippi River, a program involving the monitoring of benthic 

 macroinvertebrates over time is recommended. A biomonitoring program would be relatively 

 inexpensive compared to a water or sediment chemistry monitoring program. Monitoring would 

 consist of collecting benthic macroinvertebrates from randomly selected sites in Reach 15 at 3- 

 month intervals. Identification and enumeration of the organisms could be done in the field 

 allowing for rapid collection of information. A change in the benthic community composition 

 from a diverse collection of pollution-sensitive and pollution-tolerant organisms to a relatively 

 homogenous collection of predominantly pollution-tolerant organisms would alert managers to a 

 problem potentially affecting a native mussel bed. Action could be taken immediately to identify 

 the source of pollution and possibly alleviate the problem. 



An innovative monitoring tool, The Mossel Monitor (Delta Consult. The Netherlands) has 

 been recently introduced (Kramer et al 1989) and consists of a tube containing zebra mussels 

 permanently attached to a platform with electrical sensors that detect the opening and closing of 

 the shells. Zebra mussels, as well as other mussels, open their shells for respiration and feeding 

 most of the time under normal environmental conditions. Similar monitoring devices have been 

 developed at North Texas State University (Waller et al. 1995) Under times of stress, such as 



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