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

流域农田对整个生态系统的影响是多方面的。例如，农田对反生态因子具有一定的缓冲作用。另一方面，污染负荷的产生取决于耕作方式。为了实现农业的可持续发展，农田必须作为流域内的适宜系统进行协调。本研究以土壤流失为研究对象，探讨了雪寒地区农业流域的保护与管理。结果表明：(1)定量确定降雨对坡耕地保护的影响。而USLE的降雨径流因子R则满足了这一目的。但是，利用AMEDAS提供的降水数据不能正确计算R值。R， 0与土壤流失量密切相关。(2)取当地12月- 3月的1.0倍，可以得到解冻和积雪的子因子Rs的估计。降水，以厘米水为单位。该方法对北海道地区的Rs值估计过高。因此，用坡渗仪修正后的结果表明，北海道西南地区Rs为0.113。(3)为阻断侵蚀土壤进入河流，在坡耕地周围设置各种防护设施。但是完全拦截悬浮物质几乎是不可能的。在流域水文条件和土地利用条件下，研究了河流悬沙荷载的变化规律。积雪期悬沙负荷与气温-融雪量-河流流量密切相关。这种特征取决于仙人掌河，因为土壤条件，土地利用和气象也取决于每个流域。

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.