Conservation and Management of Agricultural Watersheds in the Snowy-cold Region

流域农用地对整个生态系统的影响是不同的。例如，农田对反生态因子有适当的缓冲作用。另一方面，污染负荷是根据耕作方式发生的。为了实现农业的可持续发展，必须使流域内的农田与适宜的系统相协调。本研究从水土流失的角度，对雪寒地区农业流域的保护与管理进行了研究。研究结果如下：(1)坡耕地保护必须定量确定降雨的影响。USLE的降雨径流因子R就是为这一目的服务的。但AMEDAS提供的雨量资料不能准确计算R值。而R，o与土壤流失量密切相关。(2)融化和积雪的子因子Rs的估计值是当地12-3月的1.0倍。降雨量，以厘米水为单位。在北海道，这种方法的RS值被高估了。在北海道西南部地区，利用斜率蒸渗仪测得的修正值为Rs=0.113。(3)为了拦截侵蚀土壤进入河流，在坡耕地周围设置了各种防护设施。但完全拦截悬浮物几乎是不可能的。本研究结合流域内的水文条件和土地利用情况，对河流悬移质输沙特性进行了研究。积雪期间的悬移质输沙量与温度-融雪量-河流流量密切相关。而这一特征取决于仙人掌河流，因为土壤、土地利用和气象条件也取决于每个流域。

Agricultural farmland in watershed influences variously for all of the ecosystem. For example, farmland have a properly of buffer to the anti-ecological factors. On the other hand, pollutional loads occur according to the farming practices. For the sustainable agriculture, farmland have to harmonize as suitable system in the watershed. In this research, conservation and management of agricultural watersheds in the snowy-cold region investigated through soil loss. And the results may be summarized as follows :(1)Influences of the rainfall must be determine quantitatively for conservation of the sloping farmland. And rainfall-runoff factor R of USLE serves this purpose. But R value can't be calculated correctly by the rainfall data as offered from AMEDAS. And R, o is closely, correlated to the soil loss amount.(2)An estimate of subfactor Rs for thaw and snowmell may be obtained taking 1.0 times the local Dec. -Mar. precipitation, measured as cm of water. Rs values by this method is overestimated in Hokkaido. So modified values investigate by the slope-lysimeter that Rs is 0.113 in south-west district in Hokkaido.(3) For interception the eroded soil enter rivers, various prevention facilities set around the sloping farmland. But complete interception of suspended matter be almost impossible. In this research, behaviors of suspended sediment load in the river are investigated with hydrological conditions and land use in the watershed. Suspended sediment load in snowmell period indicated the closely correlation with temperature-snowmelt amount-river discharge. And this characteristics depends on cacti rivers, because the conditions of soil, land use and meteorology depend on each watersheds too.