河畔湿地表流水の硝酸態窒素と溶存有機炭素の濃度変化に対する表層土壌水の寄与

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Riparian wetlands, which form the transition zone between hillslopes and streams, are important landscape units controlling water chemistry in catchments. Concerning the forest-related nonpoint source pollution in Japan, however, there have been few studies in which the roles of riparian wetlands in catchment water chemistry were clarified. We examined the changes in riparian stream nitrate (NO3-N) and dissolved organic carbon (DOC) concentrations in seven riparian wetlands during nonstorm periods in a forested headwater catchment. In addition, we discussed the contribution of surface soil waters to the changes in NO3-N and DOC concentrations. The stream NO3-N concentrations at the outlets of riparian wetlands were lower than those at the inlets; in contrast the stream DOC concentrations at the outlets were higher than those at the inlets. Among the riparian streams, the maximum changes in concentration per unit flow distance on a riparian wetland were 8- and 12-fold as high as the minimum changes in NO3-N and DOC concentrations, respectively. We conclude that for NO3-N, the differences in concentration change between riparian streams can result from the spatial variability of water permeability of surface soil; for DOC, the differences can be due to the spatial variability of both water permeability and soil water DOC concentration.
2007-04-10