Individuality and Distribution Pattern of Riparian Wetlands Controlling Longitudinal Change in Dissolved Organic Carbon Concentration in a Forested Stream

Here, we discuss the effects of individuality and the distribution pattern of riparian wetlands on longitudinal changes in dissolved organic carbon (DOC) concentration in a headwater stream using model simulations. The model, which was composed of the catchment area, the flow distance of tributary channels, the DOC concentration of spring water and the DOC supply capacity of tributaries, well reproduced a longitudinal change in stream DOC concentration during a nonstorm period. This model calculation showed that the roles of riparian wetlands as DOC sources varied greatly among riparian wetlands, even though such wetlands were predominant sources of stream DOC. When we simulated for the longitudinal changes using three representative values (average, minimum and maximum) of the DOC supply capacity, the simulation results could not explain the features of the longitudinal changes, implying that the individuality of riparian wetlands strongly affects longitudinal changes. In addition, when we simulated the features under the different distribution patterns of riparian wetlands, i.e., wide, one-point and dispersed (two-point) distributions, there was a major difference between each simulation result, suggesting that the distribution pattern of riparian wetlands control longitudinal changes. Owing to the individuality and the distribution pattern of riparian wetlands, features of longitudinal changes in stream DOC concentration can vary largely even in the same region.