Discharge-Export Relationships in Headwater Streams: The Influence of Invertebrate Manipulations and Drought

The role of physical (discharge) and biological (macroinvertebrate communities) factors in the control of coarse (>4 mm) and fine (≤4 mm > 0.5 μm) particulate organic matter (FPOM) transport was studied in three headwater streams of the southern Appalachian Mountains. The role of discharge was determined by relating two years of continuous measurements obtained over discrete (ca. 2-wk) time intervals. The role of macroinvertebrates was examined by treating one of the three streams, C 54, with an insecticide during Year 2 to reduce populations and alter community structure. Maximum discharge was the only discharge parameter which adequately predicted (linear regressions) FPOM export during a sampling interval (r 2 ≥ 0.70). These regressions were unique for each stream and were constant between years for the untreated streams, despite a record drought during the second year. Relationships between discharge and export of coarse particulate organic matter (CPOM) were not as strong nor as consistent ...