Human impact on fluvial environment during the reclamation period in Tokachi Plain, Hokkaido, JAPAN.

北海道是明治维新时期，北海道的主要生产要素由爱奴狩猎采集型社会向瓦津农耕型社会急剧转变的地区。因此，该地区是考察人类影响对自然环境影响的极其重要的地区。可以认为，下游的洪泛平原和湖泊沼泽的沉积记录了过去流域内发生的环境变化，如大规模砍伐森林和开垦。通过对高知县河漫滩和湖泊沉积的详细分析和对流域土壤剖面的观察，证实了Sou…大部分流域的沉积粗化和沉积速度的加快是人类活动的结果更多的塞恩·托卡奇平原。通过137Cs和Tephra的年代学研究，证实了托贝里河流域的快速沙积是对战后农田突然扩张的响应。我们还发现了明治早期频繁发生森林火灾的证据。通过粒度沉积物示踪技术和矿物学研究，确定粗颗粒物质的主要来源是一条支流(Toberi Horonai River)。此外，河流的这种活跃的泥沙供应诱导了芦苇根茎从上游向湿地输送，形成了新的种群。取自泻湖(鱼斗塘)的湖泊沉积岩芯进行分析。结果表明，泥沙粗化始于1920年左右，到1960年S沉积速度进一步加快。通过对鱼斗河流域土壤剖面的观察，认为开垦牧场是造成土壤侵蚀的主要原因。较少

Hokkaido is a region where the main factor of production changed drastically from hunting and gathering society of Ainu to farming society of Wajin on the boundary of Meiji Restoration. Therefore, the region is an extremely important region for examining the influence of human impact to natural environment. It can be thought that the deposit of the flood plain and lakes and marshes in the downstream recorded past environmental changes occurred in the drainage area, such as large-scale deforestation and reclamation. The aim of this research is to clarify the situation of the artificial environmental destruction and its influence to the fluvial environment during the development period in Tokachi Plain.By means of detailed analysis of the floodplain and lake deposits and observation of soil profiles in the drainage basins, it was confirmed that the coarsening of the deposits and increasing of depositional speed occurred in response to the human activity in the most of river basins of sou … More thern Tokachi Plain. By the chronological investigation using 137Cs and tephra, it was confirmed that rapid sand deposition occurred in response to the postwar abrupt farmland expansion in the Toberi river basin. And we also found the evidence of frequent forest fires during early Meiji era. The main source of the coarse materials was identified as a tributary (Toberi Horonai River) by grain-size sediment-tracer technique and mineralological investigation. Furthermore, such active sediment supply from the river induced the transportation of reed rhizomes from the upper course to the wetland to form new population. The lake sediment core was taken from the lagoon (Yudou-Pond) and analyzed. As a result, it was clarified that the coarsening of the deposit began in around 1920, and depositional speed had accelerated further in 1960's. By the observation of soil profiles in the Yudou river basin, it was suggested that the reclamation of pastures is the most important cause of the soil erosions. Less