The Effects of Varying Current on Weight Loss from Willow Leaf Packs

ABSTRACT

Leaf packs of willow leaves (Salix amygdaloides) weighing 500 g each, were placed in four artificial stream channels with currents of 12, 19, 26, and 31 cm sec⁻¹ to determine the effects of velocity on weight loss of the packs in the absence of aquatic macroinvertebrates. In general, there was little difference in weight loss of the packs between channels. The exception to this was in the 26 and 31 cm sec⁻¹ channels, which had significantly lower leaf pack weights after six weeks than the two slower channels. These differences in leaf pack weight between the “slow” and “fast” channels appeared to be more a factor of greater accumulation of fine particulate organic matter (FPOM) in the packs in the slower velocity channels rather than increased breakdown of packs in the faster channels. The accumulated FPOM is thought to be primarily a result of microbial colonization of the packs. FPOM accumulation was greater in the two slower channels throughout the study, with the greatest amount (46.9 mg pack⁻¹) found in the slowest channel in week 6. This contrasted to only 12.2 mg pack⁻¹ accumulated fines in the fastest channel during the same time period. The results of this study suggest that current may affect the rate of breakdown of leaf packs more through control of microbial colonization or maintenance of microbial colonies, rather than physical abrasion.