Table 8. — Number of insects and other organisms per square foot 

 (0.092 m. ^) collected in a riffle area in Sunny Brook before 

 chemical treatment and 1 week and 6 weeks after treatment, 

 Uke Michigan, 1963 



SUMMARY OF EFFECTS 1 WEEK AFTER 

 TREATMENT 



Sixteen families of insects and four other 

 groups of aquatic invertebrates were rep- 

 resented by five or more individuals per 

 square foot (0.092m. 2) in samples from sand 

 and detritus areas. In these samples, 77 

 percent of the groups decreased in number 1 

 week after treatment of the stream, 17 percent 

 increased, and 6 percent showed little or no 

 change {table 9). Elmidae and Heleidae declined 

 in all streams. The decline of various groups 

 was more general in Sturgeon River and 

 Gongeau Creek; however, these streams were 

 subjected to greater concentrations of TFM 

 than was Iron River (table 2). 



Twenty-one families of insects andsixother 

 groups of aquatic invertebrates were repre- 

 sented by five or n->ore individuals per square 

 foot (0.092nn.2) in san-iples from riffles in 

 treated and untreated streams. In the six 

 treated streams, 64 percent of the groups 

 decreased in number 1 week after treatment, 

 19 percent increased, and 17 percent showed 

 little or no change (table 10). In the two control 

 streanis, 33 percent of the groups decreased. 

 50 percent increased, and 17 percent showed 

 no significant change. For the orders of 

 aquatic insects that were well represented, 

 Trichoptera, Coleoptera, Ephemeroptera, and 

 Diptera declined in the treated streams. Most 

 other groups of invertebrates also declined in 

 treated streams but showed no change in 

 abundance in the two control streams. 



Table 9. — Change in the abundance of organisms-"- in 

 sand and detritus areas of various streams 1 week 

 after treatment. Lakes Superior and Michigan, 

 1962-63 



[Increase or decrease is greater than 20 percent 

 qhange; increase (+), decrease ( -) , little or no 

 change (0)] 



Organism 



Insects: 

 Plecoptera 



Nemouridae 



Chloroperlidae. . 

 Ephemeroptera 



Ephemeridae 



Caenidae 



Baetiscidae 



Heptageniidae . . . 



Baetidae 



Odonata 



Gomphidae 



Trichoptera 



Rhyacophilidae. . 



Phryganeidae . . . . 

 Coleoptera 



Elmidae 



Dytiscidae 



Diptera 



Tipulidae 



Chironomidae. . . . 



Heleidae 



Empididae 



Other invertebrates: 



Annelida 



Crustacea 



Cladocera 



Amphipoda 



Hydracarina. 



Increase. . 

 No change. 

 Decrease. . 



Iron 

 River 



Sturgeon 

 Fiiver 



Gongeau 

 Creek 



-"-Based on groups that contained five or more 

 individuals per square foot (0.092 m.^). 



SUMMARY OF EFFECTS 6 WEEKS AND 

 1 YEAR AFTER TREATMENT 



Recovery was rapid in four of the five 

 streams in which the abundance of organisms 

 was reduced 1 week after treatment: samples 

 collected 6 weeks after treatment indicated 

 that the pretreatment numbers of organisms 

 had been exceeded in three streams, partially 

 restored in one, and further reduced in one 

 (table 11). The one further decline (in Sunny 

 Brook) was probably not entirely due to the 

 effects of TFM. 



Rapid reestablishment of decimated popula- 

 tions of invertebrate fauna has been demon- 

 strated also by Moffett (1936). Most of the 

 factors that contribute to rapid reestablish- 

 ment as reported by Frey (1961) existed in the 

 present study: (1) most of the aquatic forms 

 were not eliminated from the treated areas 

 and they, themselves, could help in recoloni- 

 zation; (2) untreated streams near the treated 



