RELATIVE IMPORTANCE OF MECHANISMS DETERMINING DECOMPOSITION IN A SOUTHEASTERN BLACKWATER STREAM

Chemical inhibitors were used to separate the effects and determine th e relative importance of microbial degradation, flow-related fragmenta tion, and shredder fragmentation on sweet gum (Liquidambar styraciflua ) decomposition rates in Upper Three Runs, in South Carolina. We corre lated several abiotic and biotic variables (current velocity accumulat ion of inorganic and fine particulate organic matter, water depth, bac terial density and shredder biomass) with the decomposition of individ ual sweet gum leaf packs. We also surveyed the biomass and density of shredders in natural leaf accumulations and in constructed leaf packs to help determine the importance of shredders in decomposition. Except for accumulated sediments (inorganic and fine particulate organic mat ter, FPOM), none of the independent variables, including base-flow cur rent velocity and shredder biomass, were significantly correlated with decomposition of individual sweet gum leaf packs. Sediment accumulati on was inversely related to decomposition rates. Experimental analyses suggested that microbial degradation dominated the decomposition proc esses. A constant flow regime characterized by low current velocities, plus a depauperate shredder abundance, accounted for the relatively m inor role of shredders and flow-related fragmentation.