Inputs, outputs, and retention of leaf litter from deciduous riparian forest were examined in a headwater section of Horonai Stream, a low-gradient, gravel-bed stream in southwestern Hokkaido, Japan. During the leaf-fall season (late September-early November), total inputs exceeded total outputs, and 56% of the former was stored in the stream section. In contrast, during the post-leaf-fall season (mid November-early March), total outputs amounted to 609% of total inputs, suggesting that leaf litter stored during the leaf-fall season was decreased by fluvial transport after all of the leaves had fallen from the riparian trees. Correspondingly, leaf litter retention was highest in late autumn (November), followed by early spring (March), and the lowest in early summer (June). Irrespective of season, pools were more retentive than riffles. Further more, leaf litter retention in riffles and pools increased with woody debris abundance in autumn and early summer, respectively. Pools and woody debris were suggested to be important retention structures in the low-gradient, gravel-bed stream.
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