Mass loss and qualitative change in stream-incubated fine particulate organic matter derived from leaves differing in rate of processing

Abstract

The initial quantitative breakdown of fine particulate organic matter (FPOM) was investigated by measuring the loss (over 73 days) of substrate mass of particles of known size ranges (53–125 µm, 125–250 µm, 250–500 µm, 500 µm-1 mm) and derived from known organic sources (Alnus rubra, Acer macrophyllum, Polystichum munitum). Qualitative examinations (organic content, C : N ratio) also were made. Particles ranging from 500 µm to 1 mm in diameter differed greatly from particles in other size ranges, and results of studies with these particles closely resembled results of coarse particulate (CPOM) leaf pack studies. Despite variation, alder particles generally exhibited the greatest mass loss, those of sword-fern, the least, and mass loss of bigleaf maple particles was intermediate. Organic contents of all particle substrates decreased over time. In general, the C : N ratios of alder particles increased, those of bigleaf maple decreased, and those of sword-fern exhibited little change. All particle substrates were incubated in the field in vials, which allowed for influx of natural detritus of unknown source and period of residence. Given the overall abundance and prevalence of the FPOM resource in lotic systems, standardization of a procedure such as that used in this investigation would be useful in extending understanding of stream system processes, including detrital processing and decomposition.