Are leaf breakdown rates a useful measure of stream integrity along an agricultural landuse gradient?

Abstract

Biological indicators often are used to assess and manage water quality in anthropogenically altered stream systems. Leaf breakdown has the potential to be a good indicator of stream integrity because it integrates a variety of biological, chemical, and physical conditions. Red maple (Acer rubrum L.) leaf breakdown rates were measured along a gradient of agricultural land use in southern Appalachian streams to assess the use of leaf breakdown rates as a measure of stream integrity. Landuse categories included forested, light agriculture, moderate agriculture, and heavy agriculture. Leaf breakdown rates were related to landuse category but did not differ significantly among landuse categories. Nutrient concentration, temperature, and sedimentation increased, and dissolved O2 decreased along the landuse gradient from forest to heavy agriculture. Macroinvertebrate richness, macroinvertebrate density, and shredder density were the only significant predictors of leaf breakdown rates. We conclude that leaf breakdown rates may not be a useful indicator of stream integrity because of the confounding effects that agricultural land use has on breakdown rates.