Decomposition of Fine Particulate Organic Matter

Abstract

Fine particulate organic matter (FPOM) ranges in size from 0.45 μm to 1 mm. It serves as an important food source for aquatic fauna, as a substrate for heterotrophic microorganisms, and as a carrier of nutrients, metals and other chemicals. In streams, FPOM is derived from leaf litter, algae and other organisms by physical, chemical, and biological processes. In addition, FPOM can be formed by the flocculation of dissolved organic matter (DOM). This chapter describes an approach to determine decomposition rates of FPOM in streams. An FPOM sample is collected in the field or generated in the laboratory by collecting the faeces of litter-consuming invertebrates. Known amounts of the collected FPOM are inserted in experimental tubes and deployed on the stream bed. Tubes are periodically retrieved and the FPOM mass loss is determined by drying and weighing. If contamination by mineral particles is suspected, FPOM samples can be ashed to determine the organic matter fraction. Decomposition rates of FPOM found to date range from 1.3 to 12.6 × 10−3 day−1, depending on particle size, chemical quality and associated microbial activity.