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detritus (organic debris; e.g. broken down leaves, animal feces, etc.) which collect • around rocks. Collectors-filterers filter food particles suspended in the water column. Grazers scrape the surface of submerged objects such as rocks and logs, feeding on periphyton. Predators feed on other invertebrates. The relative abundance of each of these functional groups at each station in Trout Creek is presented in Table 2.7-15. The most obvious trend is the increased importance of collectors-filterers downstream of Station I and collectors-gatherers at Station 4. Shredders and predators decreased in importance from Station I to Station 4. Grazers made up a sizeable portion of the community at all stations except Station 4. Apparently Trout Creek changes character through the study area from a shaded headwater stream more dependent on input of leaf litter as a food base (hence more shredders) to a more open lowland stream relying more on algae production and The import of fine particulate organic detritus from upstream as a food base (hence more collectors). The relative abundance of These functional groups of invertebrates aT the stations on Oak Creek is presented in Table 2.7-16. There were obvious changes in the functional groups between stations with increased importance of grazers and collectors-filterers of Station 2. This was due more to the decreased importance of • collectors-gatherers at Station 2 than actual increased abundance of other groups. In general This decrease in collectors-gatherers gave Station 2 a more balanced functional community. The seasonal influence on invertebrate numbers and biomass typically found in most streams was apparent in different degrees in Trout Creek (Exhibits 2.7-16, 2.7- 17). Season had little apparent effect on either density or biomass at Station I. The seasonal pattern at the other three stations was very similar. Low numbers and biomass in A ugusT reflected the emergence of The majority of The aquatic insects as well as the results of spring runoff. The subsequent increase in fall resulted from the hatching of eggs laid during the summer and growth of these larvae (primarily caddisflies and midges). The differences between stations was highly significant (pc 0.01) in October with a signficanT linear trend (p< 0.01). Interestingly, Station I was statistically different from The other three stations (p < 0.05) and Stations I and 2 were different from 3 and 4. Obviously, the increase in fall is relatively greater at these lower stations. The decline in winter reflected mortality during ice cover, especially among the caddisflies and beetles. Winter biomass at Stations 3 and 4 did not show as large a decrease due to the growth of the surviving insects. Despite • lower standing crop in January, the stations were still significantly different (pc 0.05) 2.7-52