INFLUENCE OF SEASON, SIZE, AND COLLECTION SITE ON SURFACE-AREA OF FINE PARTICULATE MATTER IN STREAMS

Benthic detritus was collected from an unnamed stream in Holly Springs Experimental Forest, Mississippi, and from King's Creek, Kansas. Detritus was wet-sieved into five size classes from 1 mm down to 0.075 mm. Water and particles passing through the 0.075-mm sieve were vacuum-filtered through 0.45-mum membrane filters (Millipore); particles retained on these filters represent the sixth size class. Scanning electron microscopy revealed fine particulate organic matter (FPOM), fine particulate inorganic matter (FPIM), and fine particulate matter (FPM), i.e., aggregates of organic and inorganic particles. Many of these particles fell within the expected size ranges; however, we also detected numerous particles too small to have been retained by the sieves. Laboratory techniques were developed to separate the FPOM from the FPIM. Using nitrogen-adsorption techniques, surface-area measurements were made on the separated fractions as well as on samples that had been only wet-sieved. Comparisons of mean mass-specific surface areas (m2/g) revealed significantly lower values when inorganic material was left in the sample (FPM) or when the sample contained only inorganic material (FPIM). King's Creek samples had much greater mean surface area per unit mass than did Holly Springs samples. When location and particle size class were considered together, location explained most (85%) of the variation in surface area. When season and size class were analyzed together, most of the variation (61%) was explained by size class. Organic content, size class, season of collection, and collection site are all important influences on FPM surface area and should be considered in studies of surface-related phenomena.