Actual Conditions of Stream Pollution caused by Slope Farming in Reclaimed Land

在日本的坡耕地中，暴雨造成的土壤侵蚀造成了河流泥质污染。本研究旨在厘清坡地耕作与河流污染之间的实际关系，并从可持续农业的角度提出保护措施。所得结果如下：【河流污染特征】在沉降库前端安装自记录浊度仪，在浊度仪内观察浊度波动。测量结果表明，入流水体浊度对短时降雨分布较为敏感，浊度急剧上升至1000 mg/l后，在短时降雨后恢复到原来的清澈状态。另一方面，仅在10 mm/10min的暴雨后，水库的浊度就超过了1000 mg/l。沉积水库被认为是控制河流泥质污染的限制。[泥沙来源及影响土壤流失的因素]我们用多元回归方法分析了受农田条件（面积和坡度）、犁沟方式、水道沟渠设置和萝卜生长阶段等因素影响的土壤侵蚀。选取24个试验田，设置沉降池，追踪土壤流失量。大于10 mm/10min的暴雨后土壤流失剧烈，且变化幅度较大。多元回归分析表明，土壤流失主要是由于沿沟端设置沟渠造成的。[水道沟渠剖面]在严重水土流失田中，沟渠纵向剖面下部坡度平缓，上部坡度陡。轻度土壤流失地下部沟槽较陡，有天然草生长，上部沟槽较平缓，有沉积作用。沟渠的更新除草造成了严重的侵蚀损失。[保护性耕作]土壤侵蚀是通过沟渠保护沙袋的设置来控制的，沙袋隔一段时间进行沉积，更新后生长出天然草。应注意下游因上游山脊断裂而造成的暴雨期径流停滞，造成严重的水土流失。少

In Japanese sloping farmlands, stream muddy pollution has been caused by soil erosion at heavy storms. This study was concerned to make the actual relations between slope farming and stream pollution clear and to propose the conservation practices from the viewpoint of sustainable agriculture. The results obtained were as follows.[Characteristics of stream pollution] Installing a self-recording turbidity-meter at just the front of sedimentation reservoir and in it, we observed turbididy fluctuations. Measurements showed that turbidities of inflow water were sensitive to short rainfall distributions and rised steeply up to 1,000 mg/l and recover to the original clear conditions after rainfall for a short time. On the other hand, turbidities in the reservoir were over 1,000 mg/l after only heavy storms of 10 mm/10min. Sedimentation reservoirs were considered to be restricted to control the stream muddy pollution.[Sediment source and factors affecting soil loss] we analysed soil erosion f … More actors affected by the field conditions (size and slope), furrowing practices, waterway ditch setups and raddish growing stages by the multiple regression method. The volume of soil loss was traced in 24 selected test fields installed a sedimentation tank. Soil loss was violent after heavy storms of over 10 mm/10min and varied. Multiple regression analysis showed clearly that soil loss was mainly caused by ditch setups along the end of furrows.[Waterway ditch profiles] In severe soil loss fields, the longitudinal profiles of ditches had gentle gradient at the lower parts without native grass and steep one at the upper parts. On the other hand, mild soil loss fields had relatively steep ditches at the lower parts with native grass growing and more gentle one at the upper parts by sedimentation. Renewal of the ditches removing grass caused severe erosion losses.[Conservation farming] Soil erosion was controlled by the ditches protection of sand bags setup conducting sedimentation at intervals with native grass growing up after the renewal. Attention should be paid at the lower parts stagnation of runoff at heavy storms which caused serious soil erosion by the upstream ridge break down. Less