A Preliminary Verification of the Influences of Hydrologic Regime Change and Nutrients Influx on Vegetation Recruitment on Riparian Bars

In this study, two hypotheses were examined to preliminarily verify for the vegetation recruitment and establishment on riparian bars in unregulated rivers; hydrologic regime change and nutrients influx into streams. In order to preliminarily verify the first hypothesis, precipitation patterns were analyzed during a period from March through to May when reeds, the most common riparian vegetation in Korea, germinate and start to grow in riparian areas. The results show that during the last 35 years, the total precipitation during the three-month period decreased by about 15 %, while the total annual one increased by about 15% in Korea. In order to verify the second hypothesis, a preliminary experiment was conducted with a set of two-vegetative flumes for one year. In this experiment, a stream flow with reeds on the riparian sand bars was simulated with a flume with reeds planted on the sand bed and water with a concentration of 3.5 mg of N flowing in the flume for four hours. For comparison, clean water was circulated in the same way in another flume for simulating a stream flow without N. The experimental results show that the growth rate of reeds in N-mixed flow exceeds that in clean water flow by about 30%. The above two results could explain the phenomenon of change in unregulated rivers from white river to green river in Korea, although they were obtained through limited extents of analysis and experiment.