Benthic organic matter dynamics in an intermittent stream in South-East Spain

This study investigates (1) the standing stocks of benthic particulate organic matter (BPOM) and its fractions; (2) their temporal and spatial variability; (3) the environmental variables that explain their dynamics; and (4) the relationship between the standing stocks of the different fractions and total BPOM on the one hand and functional feeding group densities on the other. The study was conducted at four sties (two pools and two runs) located along a perennial middle section (354 m length) of Chicamo stream, a 4th-order saline and intermittent tributary of the Segura river basin in southeast Spain. Three benthic organic matter samples were collected monthly by corers in a stratified pattern in each site during 1994. Coarse (CPOM, >1 mm), fine (FPOM, 56 μm-1 mm) and ultrafine (UPOM, 0.7-56μm) size fractions were determined. Benthic POM at all sites was dominated by FPOM, followed by UPOM and CPOM fractions. There were no significant differences in the overall amount of BPOM or its fractions between dates. In contrast, spatial variation was considerable between sites, in accordance with the high spatial heterogeneity of the stream. Habitat-specific variables (type and size of habitat, substrate, current, depth and type of primary producers) determined the production, retention and storage of the different BPOM fractions in the streambed. Shredders were absent from the stream due to the scarcity of their food (CPOM). No significant correlations were found between the densities of the detritivorous feeding groups and their presumed food resources. This lack of correlation may reflect an over-abundance of detritus in the stream.