Macroinvertebrate Utilization of Leaf Detritus in a Riffle of the Illinois River, Arkansas

Small (5 g) leaf packs were placed in a shallow riffle area of the Illinois River in western Benton County, Arkansas, and sequentially retrieved after various exposure times during the winter and spring of 1980. Oak leaves (Quercus shumardii) were utilized more rapidly (9.2% remaining after 91 days), followed by oak/sycamore (Q. shumardii/Platanus occidentalis) leaf packs (31.8% remaining after 91 days). Sycamore {P. occidentalis) was the slowest processed type (32.2% remaining after 91 days). The initial colonization by shredders as characteristic of northern U S. streams did not occur in this study. Collector organisms were present in the leaf packs throughout the study. Predominant shredder organisms included stonefly nymphs (Plecoptera: Nemoura sp., Allocapnia sp., Taeniopteryx sp.) and caddisfly larvae (Trichoptera: Pycnopsyche sp., Limnephilidae). Predominant collector organisms included midge larvae and pupae (Diptera: Chironomidae) and mayfly nymphs (Ephemeroptera: Leptophlebia sp., Ephemerella sp., Stenonema sp.).