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

在日本的坡地农田，暴雨时的土壤侵蚀造成了溪流浑浊的污染。本研究旨在弄清坡耕地与河流污染的实际关系，并从可持续农业的角度提出相应的保护措施。研究结果如下：[河流污染特征]在沉淀池正前方安装一台自记浊度仪，观测到浊度的波动。实测结果表明，入库水浊度对降雨短时分布较为敏感，浊度急剧上升，最高可达1,000 mg/L，短时间降雨后恢复到原来的清澈状态。另一方面，仅在10 mm/10min的大暴雨之后，水库的浊度就超过了1000 mg/L。淤积水库被认为是控制河流泥沙污染的限制性因素。[泥沙来源及影响水土流失的因素]我们用…分析了土壤侵蚀。多元回归分析表明，受田间条件(大小和坡度)、开沟方式、航道设置和生长阶段影响较大的因子较多。在安装了沉淀池的24个选定试验田中，跟踪了土壤流失量。10 mm/10min以上的强风暴后，土壤流失剧烈且多种多样。多元回归分析表明，沟道沟道纵断是造成土壤流失的主要原因。在严重的土壤流失区，沟渠纵断面下部平缓，上部陡峭。另一方面，轻度水土流失地下部沟渠较陡，草本植物生长，上部因泥沙沉积而较平缓。除草沟渠更新造成严重的侵蚀损失。[保护性耕作]更新后，土壤侵蚀通过沙袋设置的护沟装置与生长的原生草间隔进行沉积来控制土壤侵蚀。暴雨时下游径流滞留，上游山脊崩塌，造成严重水土流失，应引起高度重视。较少

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