Comparison of organic matter decomposition rates between benthic and hyporheic zones in a headwater stream

Li Yanda, Kasahara Tamao, Chiwa Masaaki

doi:10.15017/4776827

Allochthonous organic matter that supports aquatic organisms is retained in the benthic and hyporheic zones in headwater mountain streams. In this study, we examined relative importance of the hyporheic zone as the zone of decomposition over 5 seasons (winter, spring, rainy season, summer and fall) and contribution of macroinvertebrate to organic matter decomposition. Cotton-strip assay and tensile strength loss were used to measure organic matter decomposition rates, and relative contribution of macroinvertebrate was estimated using the differences in tensile strength loss of cotton strips in 0.1 mm and 5 mm mesh-opening bags. Both benthic and hyporheic zone showed seasonality, where lowest decomposition rate observed in winter and highest in summer. The relationship between organic matter decomposition rate and water temperature suggested that water temperature was a primary factor resulting in seasonal variation. The decomposition rates in the hyporheic zone were similar to the benthic zone in fall and winter, but from spring to summer, the rates were significantly lower. Thus, as the zone of decomposition, the relative importance of the hyporheic zone differ depending on seasons. Contribution of macroinvertebrate to decomposition was significant in all seasons but winter in benthic zone and was significant only in summer and fall in the hyporheic zone. Thus, macroinvertebrate plays important role even in the hyporheic zone in some seasons.

Comparison of organic matter decomposition rates between benthic and hyporheic zones in a headwater stream

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