Distribution of the Phytoclast Group

Abstract

Coarse phytoclast material (> 1 mm) is usually only dominant in high, first and second order, headwater streams (Minshall et al., 1985, p. 1051). Although the input of organic matter to head waters is largely in the form of such coarse (CPOM) material, biological processing and the high retention characteristics of such streams result in the export to lower order streams being predominantly of fine material (FPOM, < 1 mm). In consequence, the ratio of transported coarse to fine material tends to decrease rapidly downstream (Naiman, 1982, p. 1078), although in specific cases habitat type is often more important than stream order (Minshall et al., 1983, p. 9). Steady state downstream decreases in mean particle size have also been recorded within the suspended FPOM fraction of higher order streams (Wallace et al., 1982, p. 829). As smaller particles show higher microbial respiration rates (Naiman and Sedell, 1979b, p. 412) phytoclast particles tend to become more refractory as particle size decreases, eventually resulting in increases in both lignin content and C/N ratios (Cummins and Klug, 1979, p. 149; Ward, 1984; Bowen, 1984, p. 444).