have you ever noticed the colour of the water in a river or stream after a heavy rainfall阅读答案

《have you ever noticed the colour of the water in a river or stream after a heavy rainfall阅读答案》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。

1、Haveyouevernoticedthecolourofthewaterinariverorstreamafteraheavyrainfall阅读答案　　Haveyouevernoticedthecolourofthewaterinariverorstreamafteraheavyrainfall?Whatdoyouthinkcausedthischangeincolour?Itissoilthathasbeenwashedintotheriverfromtheriverbankorfromt}lenearbyfields．　

2、　ComponentsofSoft　　Soilismadeupofanumberoflayers（层），eachhavingitsowndistinctivecolourandtexture．Theupperlayerisknownasthelitter．Itactslikeablanket．limitingtemperaturechangesandreducingwaterloss．Thetopsoillayerismadeupofsmallparticlesofrockmixedwithrottenplantandanima

3、lmattercalledhumus（腐殖质），whichisblackandgivesthetopsoilitsdarkcolour．Thislayerisusuallyrichinnutrients，oxygen，andwater．Belowthetopsoilisthesubsoil，alayerthatcontainsmorestonesmixedwithonlysmallamountsoforganicmatter．Thislayerislighterincolourbecauseofthelackofhumus．Be

4、neaththesoilliesalayerofbedrock．　　Soilformsfromthebottomup．Overtimebedrockisattackedbyrain,wind，frost,andsnow．Itisgraduallybrokendownintosmallerparticlesinaprocesscalledweathering．Plantsbegintogrow，androttenmaterialsenrichthetopsoil．MostofthesoilinEasternCanada．forex

5、ample．Wasformedfromweatheredrockthatwasexposedwhentheicedisappearedl2．000yearsag0．　　WaterBeneaththeSoil　　Surfacewatercollectsandflowsabovethegroundinlakes．ponds．andrivers．Onceinthesoilorrock，itiscalledgroundwater．Gravitypullsgroundwaterthroughthesoilinaprocesscalledp

6、ercolation（渗透）．Eventuallythewaterreachesalayercalledthewatertable．Underthisisbedrockthroughwhichwatercannotpercolate．　　Aswaterpercolatesdownward，itdissolvesorganicmatterandmineralsfromthesoilandcarriesthemtodeeperlayers．Thiscausesaseriousproblembecauseplantsrequireth

7、esenutrientsforgrowth.　　SoilpH　　Soilcanbeacidic．neutral．orbasic．ThepHofthesoilisdeterminedbythenatureoftherock　　fromwhichitwasformed．andbythenatureoft}leplantsthatgrowandrotinit．　　TheacidityofrainandsnowcanlowerthepHofthegroundwaterthatentersthesoil．Byburningfossilfu

8、elssuchascoal，oilandgasoline，humanshavebeencontributingtohigherlevelsofacidityinmanysoils．Whenfossilfuelsareburned．gasesarereleased