单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,第五章,环境生态学,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Erosion,New Words&Phrases,Erosion:,The group of natural processes,including weathering,dissolution,abrasion,(磨损）,corrosion,（腐蚀）,and transportation,by which material is,worn away,（磨损）,from the earths surface.,腐蚀，侵蚀：指使材料从地表磨损、消耗的一组自然过程，包括风化、溶解、磨蚀、浪蚀、腐蚀和搬运,.,fluvial erosion,河流侵蚀,geologic erosion,地质侵蚀,loess erosion,黄土侵蚀,rainfall erosion,降雨侵蚀,river erosion,河流侵蚀,sheet erosion,片状侵蚀,stream bank erosion,河岸侵蚀,wind erosion,风蚀,冲积层：河床、冲积平原或三角洲中的流水淤积所产生的沉积层,.,Alluviuml(j)uv,i,m:,Sediment deposited by flowing water,as in a riverbed,flood plain,or delta.,alluvial,：冲积,的，淤积的.,Erode:,To wear(something)away by or as if by abrasion;To cause to diminish,（减小）,deteriorate,（恶化）,or disappear as if by eating into or wearing away.,腐蚀；侵蚀：（象）被磨擦损耗掉,;侵蚀掉，腐蚀掉：象磨蚀、侵蚀那样使减少、减弱或消失.,Silt:,1）n,.（名词）,A sedimentary material consisting of very fine particles intermediate in size between,sand,and,clay,；,泥沙，淤泥：由大小介于,沙,和,泥,之间的非常细小的微粒 构成的沉淀性物质,2）v.intr.,（不及物动词）,To become filled with silt;,被淤塞：使塞满泥沙,3)v.tr.,（及物动词）,To fill,cover,or obstruct with silt.,使淤积：用沙充满、覆盖或阻碍,Siltation,：冲积,作用，淤积作用.,耕地：,已耕作的土地,耕种：开垦土地,Tillage:,Land that has been tilled,（耕种，耕耘）,;,Cultivation,（耕种）,of land.,黄土：一种风沉积而成的颗粒细小、含钙质的沙或泥土，呈浅黄色或黄褐色.,Loess:,A buff to gray windblown,（被风吹的）,deposit of fine-grained,calcareous,（钙化的）,silt or clay.,一、矿物质土,粒,石砾：,1mm,砂粒：1-0.05mm,粉粒：,粘粒：,0.002mm,土壤剖面结构,蒸散,TEXT,Erosion is an important natural process,rusulting in the redistribution of the products of geologic weathering,and is part of both soil formation and soil loss.The worlds landscapes have sculpted(雕刻）by erosion.When the results are spectacular enough,we enshrine（铭记）them in national parks as we did with the Grand Canyon（峡谷）.Where erosion has worn down mountains and spread soil over the plains,or deposited rich alluvial silt in river bottomes,we galdly farm it.Erosion is a disaster only when it occurs in the wrong place at the wrong time.,Erosion is an important natural process,rusulting in the redistribution of the products of geologic weathering,and is part of both soil formation and soil loss.,侵蚀是一个重要的自然过程，它导致了地质风化的产物的重新分配，是土壤形成和流失的部分原因。
The worlds landscapes have sculpted(雕刻）by erosion.,世界的地形和地貌就是由于侵蚀的作用而形成的When the results are spectacular enough,we enshrine（铭记）them in national parks as we did with the Grand Canyon.,有时候，侵蚀的效果如此壮观，以至于我们用国家公园把它铭记下来，如美国的大峡谷Where erosion has worn down mountains and spread soil over the plains,or deposited rich alluvial silt in river bottomes,we galdly farm it.,当侵蚀慢慢磨损了山脉，并使平原覆盖了土壤，或者在河流底部形成富饶的底泥，人们会非常高兴有了可耕地Erosion is a disaster only when it occurs in the wrong place at the wrong time.,只有当侵蚀在错误的时间和错误的地方发生时，它才会成为一种灾难。
In some places,erosion occurs so rapidly that anyone can see it happen.Deep gullies（冲沟）are created where water scours away（冲刷）the soil,leaving fence posts and trees sitting on tall pedestals（地基）as the land erodes away around them.In most places,however,erosion is subtler（微妙的）.It is a creeping disaster that occurs in small increments（增量）.,A thin layer of top soil is washed off fields year after year until eventually nothing is left but poor-quality sub-soil that requires more and more fertilizer and water to produce any crop at all.,In some places,erosion occurs so rapidly that anyone can see it happen.,在某些地区，侵蚀的速度是如此之快，任何一个人都可以看见它的发生。
Deep gullies are created where water scours away the soil,leaving fence posts and trees sitting on tall pedestals as the land erodes away around them.,当土壤受到水的冲刷，地表就形成了深深的沟壑，由于周围的土壤被冲走，只剩下树木和栅栏还树立在高高的地基上In most places,however,erosion is subtler.,然而，在大多数地区，侵蚀发生的更微弱些It is a creeping disaster that occurs in small increments.,它（侵蚀）只是以很小的增量缓慢地发展成一场灾难A thin layer of top soil is washed off fields year after year until eventually nothing is left but poor-quality sub-soil that requires more and more fertilizer and water to produce any crop at all.,表层土壤年复一年地被冲刷着，直到最后除了下层贫瘠的土壤什么也没有留下，为了产出庄稼需要越来越多的化肥和水。
The net effect,worldwide,of this general,wide spread top soil erosion is a reduction in crop production equivalent to removing about 1%of world cropland each year.,Many farmers are able to compensate for this loss by applying more fertilizer and by bringing new land into cultivation.Continuation of current erosion rates,however,could reduce agricultural production 25%in Central America and Africa and 20%in South America by the year 2000.,The total annual soil loss from croplands is thought to be 25 billion,metric tons,（公吨）,.About twice that much soil is lost from,rangelands,(牧场）,forests,and urban construction sites each year.,The net effect,worldwide,of this general,wide spread top soil erosion is a reduction in crop production equivalent to removing about 1%of world cropland each year.,在世界范围内，这种大规模的表层土壤被侵蚀的结果是，。