Red Maple ( Acer rubrum ) Leaf Decomposition in an Acid-Impacted Stream in Northcentral Pennsylvania

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Abstract
Decomposition rates of red maple (Acer rubrum) leaves in a variable pH environment were examined in Johnson Creek, a northcentral Pennsylvania acid-mine impacted stream. Two types of red maple leaf packs were placed at four locations along an increasing pH gradient ranging from 5.5 to 7.0. Fine-meshed nylon stocking packs were used to measure chemical and microbial decomposition rates and to exclude stream invertebrates; and, coarse-meshed nylon packs were used to allow for colonization of leaf shredding invertebrates. Differences in decomposition rates for both types of leaf packs were correlated less with increasing pH and more with condition of substrate, stream discharge, and invertebrate community structure. Leaf decomposition rates were significantly slower for the fine-meshed packs than for coarse-meshed packs at all sampling sites. This comparison suggests an important role for both stream discharge and shredder occurrence and density in determining faster decomposition rates in Johnson Creek. The study showed that rates of leaf decomposition vary along the course of recovery of an acid-impacted stream and that the primary agents of decomposition can change from one stream reach to the next.