COMPARISON OF LEAF PROCESSING RATES UNDER DIFFERENT TEMPERATURE REGIMES IN 3 HEADWATER STREAMS

1. We studied the effects of different temperature regimes on leaf lit ter processing in three forested Appalachian headwater streams of diff erent pH (mean pH = 4.2, 6.5, 7.5). 2. We compared leaf breakdown rate s, microbial biomass and macroinvertebrate shredder density and biomas s between two 12-week processing periods (October-January and November -February) in each stream. Leaf processing rates were calculated both as k (day(-1)) and k(d) (degree day(-1)). 3. There were no significant differences in processing rates (k day(-1)) between the two study per iods for any leaf species in any stream. The average difference in tem perature between the two study periods was 175 degree days. Shredder d ensity was significantly higher during the earlier study period on 40% of the sample dates, but shredder biomass was not significantly diffe rent between the two study periods. ATP concentration was significantl y higher during the early study period for 60% of the sample dates. 4. More significant differences in these variables (shredder density and biomass, ATP concentration) were seen among the three study streams t han between the two study periods. This indicates that in this study o ther factors, particularly stream pH, contributed more to processing r ate variation than did differences in thermal regime.