Hot spots of leaf breakdown within a headwater stream reach: comparingbreakdown rates among litter patch types with differentmacroinvertebrate assemblages

摘要

Detecting hot spots of litter decomposition will promote understanding of litter processing in a heterogeneous system. To identify hot spots of leaf breakdown within a headwater stream reach, the difference in leaf breakdown rate was examined among four types of litter patches, one that formed in riffles and three that formed in pools (middle, alcove, edge), in different seasons. Middle patches showed the highest breakdown rate in some seasons; the rate in middle patches was 1.5-4 times higher than in the other patches. Thus middle patches can be regarded as hot spots of leaf breakdown in the study reach. This result contrasted with other studies showing higher breakdown rate in riffles than in pools. Significant relationships between abundance of caddisfly shredders and breakdown rate were observed in seasons when the rate differed among patch types. Greater abundance of Lepidostoma seems to be responsible for middle patches being hot spots of leaf breakdown. It is expected that when the proportion of leaves retained in middle patches within a reach is higher, the breakdown rate of the entire reach will be increased. Clarifying how the proportion of leaves retained on middle patches within a reach varies temporally and spatially would improve our understanding of leaf breakdown in headwater streams.