Influence of land-use development on suspended sediment and wetland vegetation in Kushiro Marsh

湿地对水文、水质和野生动物栖息地的影响是国际公认的。研究了河道化对日本北海道悬浮物流量和湿地植被的影响。河道化的影响不仅可以通过泥沙收支来证实，还可以通过河道化后的河流淤积或退化以及由此引起的植被变化来证实。悬沙收支表明，冲洗沙是主要成分，占进入湿地的悬沙总量的95%。这些悬浮沉积物主要是通过与暴雨相关的洪水进入湿地的。25%的冲洗液和75%的悬浮床质沉积在河道化河段，在河段末端产生约2米的淤积。由于曲流河流的渠化，河道长度缩短，使坡度变陡，增强了河流输送泥沙的动力。这种陡坡作用使细沙沉积带向下游移动了5km，使河床变厚。泥沙淤积降低了河道的承载能力，导致含沙水淹没湿地。湿地上积聚的细沙逐渐改变了湿地的土壤条件和湿地植被。黄柳（Salix spp.）和蒿（artemis princeps .）占据了水位波动大、总氮含量高、地下水氧化还原电位低的湿地。这些遗址是更多的证据，表明目前的情况与正常情况相差甚远。河道邻近地区的原始植被如莎草和桤木正在消失，取而代之的是柳树。

Wetlands' effects on hydrology, water quality, and wildlife habitat are internationally recognized. We examined the influences of channelization on discharge of suspended sediment and wetland vegetation in Hokkaido, northern Japan. The impact of river channelization was confirmed not only by the sediment gudgets but also by river aggradation or degradation lafter the channelization and by the resultant vegetational changes. The budgets of suspended sediment demonstrated that wash load was the predominant component accounting for 95% of the total suspended load delivered into the wetland. This suspended sediment was primarily transported into the wetland by floding associated with the heavy rainfall. 25% of the wash load and 75% of the suspended bed material load were deposited in the channelized reach, which produced aggradation of about 2 m at the end of the reach. A shorting of the length of the channel, due to channelization of a meandering river, steepened the slope and enhanced the stream power to transport sediment. This steepening shifted the depositional zones of fine sediment 5km downstream and aggraded the riverbed. The aggradation reduced the carrying capacity of the channel and caused sediment ladened water to flood over the wetlands. the fine sediment accumulated on the wetlands gradually altered the edaphic conditions and wetland bvegetation. Salix spp.and Artemisis princeps dominate the sites representing a high water-level fluctuation and high total nitrogen, and low redox potential of wetlands' ground water. These sites are more evidence indicating taht the present condition is far different from normal. Orifinal vegetation such as sedges and Alunus japonica sere disappearing from the adjacent areas of the river channel and were being replaced by willow trees.