2018 Volume 31 Issue 3 Pages 178-189
To clarify the hydro-biogeochemical processes of a riparian wetland upstream from a stone masonry check dam built in a stream channel about 100 years ago, observations were conducted in a forested catchment with granite bedrock. On the upstream side of the observation plot, sandy soil was deposited in all layers. By contrast, on the downstream side close to the check dam, muddy soil was deposited on the surface layer; sandy soil was deposited in the lower layer. The two sedimentation patterns produced different hydrological pathways: one through the underground layer consisting of permeable sandy soil and one with flow over the low-permeable muddy soil layer as surface flow. Reductive conditions resulting in the removal of NO3− by denitrification were maintained within the wetland. Moreover, depending on the amount of annual rainfall and the different hydrologic pathways, the strength of the reductive environment fluctuated spatiotemporally. Fluctuations in the chemistry of stream water passing through the wetland were also observed in accordance with the outflow route. Small riparian wetlands formed by check dams exist in many rivers. To evaluate the effects of such riparian wetlands on hydrobiogeochemical phenomena, it is necessary to consider the sedimentation patterns, distribution, scale, and fluctuation of the wetlands within the catchments in a global and continuous manner, and to make detailed observations.
