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

在日本的坡地农田中，暴雨造成的土壤侵蚀造成了河流淤泥污染。本研究旨在厘清坡地耕作与溪流污染的实际关系，并从永续农业的观点提出保育措施。获得的结果如下。【河流污染特征】在沉淀池前安装自记浊度计，在沉淀池内观察到浊度波动。测量表明，入流水的浊度对短时间降雨分布敏感，急剧上升至1，000 mg/l，并在短时间降雨后恢复到原始清澈状态。另一方面，仅在10毫米/10分钟的暴雨后，水库的浊度就超过1，000毫克/升。为控制河流泥沙污染，应限制沉淀型水库。[泥沙来源及影响土壤流失的因素]分析了土壤侵蚀的主要因素， ...更多信息 通过多元回归方法，分析了受田间条件（大小和坡度）、开沟方法、水道沟渠设置和萝卜生长阶段影响的行为者。在24个选定的试验田安装沉淀池跟踪土壤流失量。在10 mm/10 min以上的暴雨后，土壤流失剧烈，且变化较大。多元回归分析表明，土壤流失主要是由沿沟底沿着设置沟道引起的。【河道沟纵剖面】在严重水土流失田，沟渠纵剖面下部坡度平缓，无原生草，上部坡度陡。另一方面，轻度水土流失农田的下部沟渠相对陡峭，生长着原生草，上部沟渠因沉积而较为平缓。除草沟的更新造成了严重的侵蚀损失。【保护性耕作】更新后，通过设置沙袋的沟渠保护，进行间隔沉淀，并生长原生草，控制土壤侵蚀。暴雨时径流下渗滞流，上游山脊崩塌，造成严重的水土流失，应引起重视。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