1. The effects of a forest disturbance were investigated by comparing production of leaf-shredding aquaHc insects in three streams draining a mature hardwood forest and three streams draining an 11-year-oId, cable-logged clearcut. 2. Reference streams contained significantly greater mean annual standing crop of leaf material and significantly nnore slow-processing leaf material than disturbed streams. Disturbed streams had a significantly higher mean annual standing crop of fast-processing leaf material than the reference streams. 3. Leaf-shredding cranefly {Tipula abdominalis), caddisfly {Pycnopsyche gentilis), and stonefly {Tallaperla maria) larvae comprised over 95% of shredder biomass in all streams. Total shredder production was significantly greater (P<0.05) in disturbed versus reference streams, but individual production rates were not significantly different between stream types. 4. Pycnopsyche gentilis larvae were present at higher densities and achieved significantly greater annual biomass in disturbed versus references streams. Biomass of P. gentilis was significantly correlated with the standing crop of fast-processing, early successional leaf material in samples, whereas biomass of other shredders was correlated significantly with medium or slow-processing leaf spedes characteristic of later stages of forest succession.
Rates of leaf litter processing at eight sites were used in conjunction with other methods to evaluate the impact of highway construction on aquatic habitats. Monthly processing of white oak leaves from four different mesh size bags at unimpacted reference sites indicated that the three larger mesh sizes were useful for comparing sites, as they did not restrict invertebrate colonization and provided similar rates of processing within sites. Small mesh size (0.12 mm) prevented leaf shredding macroinvertebrates from colonizing bags, and caused significantly slower leaf processing in a riffle.Leaf processing was fastest in a reference rime above an area of highway construction but was significantly slower in the reference pool due to low current velocity and the absence of shredders. Leaf processing in a rifile below the highway was slower than the reference rime, and the number of shredders was reduced. Removal of streamside vegetation during highway construction caused increased stream temperatures and reduced the amount of natural leaf accumulations, thereby reducing shredder habitat. At other sites highway construction caused less of an impact than preexisting environmental influences. Leaf processing in an rime of a lower pH stream was significantly slower than in the reference rime. Shredders were absent from the low pH stream, and rates of leaf processing in the acid impacted rime and pool were similar to those of the reference pool. Comparisons of the low pH stream with the reference stream indicated that physical processes were less important than biological processes of leaf decay. Leaf processing in ponds was similar to that of stream pools. Processing was faster in a small versus large pond, and a high density of invertebrates was associated with leaf bags in the small pond after one year.
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