Soil & Wter Res., 8, 213 (3): 124 132 Temporl Vritions of Runoff nd Sediment in Different Soil Cly Contents Using Simulted Conditions Mehdi BASHARI 1, Hmid Rez MORADI 1, Mir Msoud KHEIRKHAH 2 nd Mjid JAFARI-KHALEDI 3 1 Deprtment of Wtershed Siene nd Engineering, Fulty of Nturl Resoures, Trit Modres University, Noor, Irn; 2 Soil Conservtion nd Wtershed Mngement Reserh Institute, Tehrn, Irn; 3 Deprtment of Sttistis, Fulty of Mthemtil Sienes, Trit Modres University, Tehrn, Irn Astrt Bshri M., Mordi H.R., Kheirkhh M.M., Jfri-Khledi M. (213): Temporl vritions of runoff nd sediment in different soil ly ontents using simulted onditions. Soil & Wter Res., 8: 124 132. Soil ly ontent (SCC) plys n essentil role in the proesses of infiltrtion, sel nd rust formtion, runoff, nd soil erosion. The role plyed y SCC in wter erosion hs reeived muh ttention in reent yers. Hene, in order to investigte these effets on smll sle, simultion experiment ws onduted. Soil lking ly ontent ws omined with, 1, 2, 3, 4, nd 5% of ly soil, respetively. The experimentl setup onsisted of retngulr metl plots (1.5 1 m) omprising soil with seleted omintions of ly ontent, pled t 9% slope. Six tretments, three replites eh (totlly 18 plots), were exposed to simulted rinfll t n intensity of 7 mm/h for 3 min. The results were ompred y mens of sttistil tests. Generl trends in runoff volume were similr for different SCCs nd deresing nd inresing trends were hieved for sediment nd runoff, respetively. The results showed signifint differenes in the hydrologil nd erosionl responses of these soils sed on their ly ontents. The soils with intermedite ly ontent were more resistnt to erosion nd hd lower vlues of the runoff. Finlly, time hd signifint (P <.) effets on oth runoff nd sediment prodution during the rinfll. Keywords: ly; erosion plot; rinfll simultor Aelerted soil erosion from onstrution sites nd the resulting inrese in downstrem sediment lod onstitute signifint environmentl prolem (Kwmur & Dimond 1975). Vrious models re eing used to develop soil onservtion progrmmes nd identify optimum mngement prties. The so-lled Universl Eqution for lulting the long-term loss of soil due to erosion (USLE) hs widely een used for mny yers to determine soil erosion risks nd evlute the effetiveness of soil onservtion mesures (Bnsik et l. 21; Jneček et l. 212). This eqution enles plnners to predit the verge rte of soil erosion in speified soil type, rinfll pttern, nd topogrphy (Wishmeier & Smith 1978). Bsed on this model, soil erosion depends on mny ftors, mong others erosivity of the rin nd erodiility of the soil (Atwoo & Heersing 1997). Rinfll erosivity ssesses the pity of rin to erode unproteted soils (Atwoo & Heersing 1997). However, soil erosion depends not only on rinfll erosivity ut lso on the soil s resistne to erosion usully mesured s the soil erodiility ftor K. Wishmeier nd Smith (1978) gve empiril 124
Soil & Wter Res., 8, 213 (3): 124 132 nomogrph for estimting erodiility from si soil properties. This nomogrph is sed on the orgni mtter ontent, silt plus fine snd ontent, soil struture, nd permeility lss. Thus the soil texture is n importnt ftor influening the struture stility nd erodiility in soils. Soil erodiility expresses the resistne of soil prtiles to oth dethment nd trnsport y rindrop impt nd runoff (Renrd et l. 1997). These proesses re influened y soil properties, suh s prtile size distriution, struturl stility, orgni mtter, soil hemistry, nd wter trnsmission hrteristis (Ll 1994). Soil s erodiility is funtion of omplex intertions of sustntil numer of its physil nd hemil properties nd often vries within stndrd texture lss. The omplex proess of soil erosion omprises dethment nd trnsport of soil prtiles in onjuntion with rindrop impt nd surfe runoff. Thus, the mount of soil ville for removl y runoff depends on the strength of ggregtes to resist disruptive fore of rindrop impt (Riml & Ll 29). Different ftors hve een found to ount for the soil hydrologil nd eroding ehviours (Ruiz Sinog & Mrtinez Murillo 29). Over short within-storm periods, soils properties influene erosion minly through their hydrology, ggregte stility, nd tion dispersion (Kirky 21). Perhps the most signifint soil hrteristis is soil texture with ly eing the most importnt onding gent for ggregtion in soil texture. Cly ts s ementing mteril tht holds prtiles together in n ggregte. Inresing ly ontent is ssoited with inresed ggregte stility. Cly ontent physilly ffets ggregtion through swelling nd dispersion nd the potentil of swellingindued disintegrtion is redued t low ly levels (Feng-Ling et l. 21). Some ly soils re highly suseptile to erosion nd piping euse of dispersion or defloultion in pore wter (Zorluer et l. 21). In ly-rih soils, ggregtes eome more stle nd the struture of the sel more grnulr (Kuhn & Bryn 24). Both texture nd struture re unique properties of soils hving profound effet on their ehviour nd re losely relted to soil ly ontent (SCC). The effet of hnges in texturl omposition of soils ffets some other soil properties like ulk density nd wter pities (Rejmn et l. 1998). Additionlly, field nd lortory studies hve shown tht soil loss ws ffeted y hnges in the texture of soil (Commndeur 1992; Rejmn et l. 1998). The need to distinguish the different prtil proesses led to the development of rinfll simultions on smll plots. Rinfll simultions re widely used for the quntifition of runoff nd erosion proesses t different plot nd event mgnitude sles. It is evident tht suh types of simultions re designed to summrise severl proesses nd to oserve their sptil nd temporl development (Seeger 27). Field plot studies hve their own unertinties (Sdeghi et l. 213) nd some properties nd proesses vry onsiderly t the field plot sle (Srinivsn et l. 27). Generlly, smll field plots re ssumed to provide uniform onditions to investigte hydrologi proesses y eliminting the heterogeneities rising out of soil, surfe over, limti, nd topogrphil ftors (Srinivsn et l. 27). Numerous studies hve pointed out the role plyed y SCCs on erosion s well s on the hydrologil response of soils (suh s infiltrtion rte, surfe seling, nd runoff genertion) (Brue- Okine & Ll 1975; Mgwu & Bzzoffi 1998; Mordi & Sidin 21). The effet of SCC on soil erosion is omplex nd mivlent. SCCs might either redue (Sekine & Iizuk 2; Kuhn & Bryn 24; Feng-Ling et l. 21) or inrese (Zorluer et l. 21) erosion nd runoff rtes. It ws lso oserved tht soil loss vried ontrrily, in different soil ly ontents (Ben-Hur et l. 1985). In generl, literture reviews of erosion plot studies point to nonliner vritions in runoff nd erosionl proesses with inresing SCC. Hene, speil mention should e given to the SCC euse the mehnism of suh omplited phenomenon hs not een fully understood yet. In the present study, rinfll simultions hve een used for understnding the influene of different SCCs on runoff genertion nd erosion. To identify nd quntify ftors ffeting runoff nd erosion proesses, results of 18 plot sle rinfll simultions in different SCCs were nlyzed. Thus, the ojetives of the present study were to determine: (1) the temporl vritions of runoff nd soil erosion over the rinfll y the lortory experiments nd (2) the effets of SCCs on runoff genertion nd soil erosion under simulted rinflls. MATERIAL AND METHODS In the present study, soil-ly mixtures with different ompositions were used to form test smples eroded y simulted rinfll. For this im, 125
Soil & Wter Res., 8, 213 (3): 124 132 two soils were seleted sed on their textures (ly ontents) nd similr hemil properties. Then erosion plots ontining soil lking ly ontent, omined with, 1, 2, 3, 4, nd 5% of ly soil in three replitions (totlly 18 plots), respetively, were prepred using onrete mixer. Theoretilly it is elieved tht mixing two soil smples in regulr lsses should result in the soil lso exhiiting regulr hnges in its texture. However, due to the high volume of soil nd low ury of grnulometri methods, it is prtilly impossile to prepre soil smples of desired textures extly. In ddition, smll mounts of smples used for grnulometri methods nnot e good representtives of the whole mount of soil. However, hrteristis of omined soils indite proper mixture of the soils. Soil smples were tken from different mixtures for determintion of prtile size distriution, orgni mtter ontent, potentil hydrogen (PH), eletril ondutivity (EC), gypsum, nd the totl lium ronte ontent s min ftors ffeting erosion (Oygrden et l. 1997). Totl lium ronte ontent ws mesured y titrimetri method ording to Loeppert nd Surez (1996). Orgni mtter ws mesured following Rowell (2). Gypsum ws mesured ording to Artied et l. (26) nd prtile size ws nlyzed using hydrometri method ording to Gee nd Buder (1979). Informtion on soil properties is given in Tle 1. Artifiil rinfll ws produed from spry nozzle nd spinning disk-type FEL3 rinfll simultor with rindrop fll height of 2.65 m (Jywrden & Bhuiyn 1999) nd uniformity of 8%. Uniformity in rinfll pplition ws ssessed using the oeffiient desried y Mroufpoor et l. (21). The rinfll simultor sed on the design y Armfield (1998) (Figure 1) ws used to produe 3 min rinfll t n intensity of pproximtely 7 mm/h (Niolisen et l. 27). Erosion tests involved simulted rinfll on filled 1.5 m long 1. m wide plots. The experimentl plots were djusted to 9% slope grdient (Riml & Ll 29). These plots were onstruted from glvnized iron sheet with runoff funnel t the lower end (Figure 1). In eh plot,.2 m soil lyer ws pled over.75 m lyer of grvel filter (Riml & Ll 29). The ses of plots were onneted with pipe t one point to filitte infiltrtion. In the ourse of the plot filling the soil ws tmped lyer y lyer. The erosion plots were filled with sieved soil nd the soil surfe flttened using ord (Smets et l. 27). In the lortory, the soil smples were sturted with wter from the ottom upwrds. The wter ws then llowed to flow out y equilirting the free wter level of the smple to ottom level of the smple. All soil plots were kept on horizontl set to otin n even flow of perolting wter (Muukkonen et l. 29). After 24 h, the plots were pled under the rinfll simultor nd three replites were used for eh ly ontent nd temporl ssessments of the soil erosion nd runoff genertion were rried out over 3 min rinfll period within erosion plots with similr slope nd rinfll intensity onditions ut with differing SCCs. During simultion experiments, onstnt rinfll intensity ws pplied to generte 3 min of ontinuous runoff from plots tht were pproximtely t field pity t the time of rinfll initition (Srinivsn et l. 27). During the rinfll, plsti ontiners were used to ollet the runoff nd sediment t the outlet of eh plot. The simultion time ws sudivided into 12 time steps Tle 1. Some physil nd hemil properties of the studied soils Soil smples Mehnil omposition (%) Orgni mtter Gypsum snd silt ly (%) PH EC (mmol/m) CCO 3 (totl) (%) Cly soil 14 36 5.2 1.56 8.12 3.1 16.83 Mixture (%) 5 5.12 13.8 7.99 4.79 15.66 1 39 56 5.25 13.7 7.96 4.77 17.66 2 33 55 12.1 13.74 7.96 4.57 17.66 3 34 5 16.15 13.87 7.89 4.28 16.5 4 33 47 2.1 13.59 7.96 4.15 16.91 5 32 46 22.5 14.3 7.94 4.1 16.83 PH potentil hydrogen, EC eletril ondutivity 126
Soil & Wter Res., 8, 213 (3): 124 132 () () Figure 1. (): shemti view of rinfll simultor, 1 spry hed ssemly, 2 flow ontrol vlve, 3 eletril ontrol pnel, 4 entrifugl wter pump; (): erosionl set-up, 1 erosion plot, 2 runoff funnel, 3 plsti ontiner of 2.5 min eh. Runoff volumes were mesured t these time intervls to generte hydrogrph for eh 3 min runoff event. The time when wter strted to flow through the outlet ws reorded s runoff strt (Seeger 27) nd during rinflls, runoff smples for ssessment of soil loss were olleted t terminl funnels t intervls of 2.5 min. The olleted smples of surfe runoff were filtered through Whtmn Grde No. 42 Quntittive Filter Pper (Riml & Ll 29) nd soil loss ws determined y weighing the oven-dried (t 15 C) filtered smples (Seeger 27; Smets et l. 27). Runoff nd sediment onentrtion dt were nlyzed with PASW Sttistis 18. softwre (SPSS In., Hong Kong, Chin). Anlysis of vrine ws performed to identify the effets of SCCs on runoff nd sediment onentrtions nd the Fisher s lest signifint differene test ws used to determine sttistil signifine mong tretment mens. A proility level <.5 ws onsidered signifint. Finlly, to evlute the influene of SCC on the temporl vriility of runoff nd sediment, the effets of time intervls (repeted mesurements) were nlyzed using the Generl Liner Models (GLM) Proedure of SAS (Niolisen et l. 27; Riml & Ll 29). RESULTS AND DISCUSSION In order to investigte the temporl effets of SCC on sediment onentrtion during eh run, 2.5 min intervls mesured during eh experiment were plotted ginst orresponding sediment onentrtions verged over 3 replites. Figure 2 indites the effets of SCC on runoff volume nd sediment onentrtion vritions during eh experiment, respetively. It n e oserved tht, in ll tretments temporl trend of runoff hs inresed over the simultion period, ut sediment onentrtion deresed from the initil high vlue to onstnt one. Fisher s lest signifint differenes (LSD) etween oserved vlues of runoff nd sediment re listed in Tle 2. Also, s shown in Figure 3, Fisher s LSD test ws pplied to eh of the runoff (Figure 3) nd sediment (Figure 3) vlues in different SCCs to determine homogeneous susets. The mentioned outputs show tht in se of runoff, soils lking ly ontent nd 5% of ly soil mixture hve signifintly higher vlues in omprison with other tretments. For sediment onentrtion, 4 nd 5% of ly soil mixtures euse of their higher vlues in the initil time steps of rinfll nd then soil lking ly ontent euse of its higher onentrtion vlues over the rinfll, differ from other tretments. As it ws reported tht soil type ould influene runoff (Zhng et l. 27), the results of the rinfll simultion experiments showed signifint differenes in the hydrologil response of soils etween different SCCs. Expetedly, surfe runoff went signifintly up with inresing durtion of simulted rin. Besides, generl trends in runoff volume for different ly ontents were similr, euse during the rinfll simultion, there is redution in surfe storge, onsequently elerting sel formtion proesses nd generting high runoff. Similr trends in surfe runoff were reported y Slehi et l. (1993) nd Riml nd Ll (29). 127
Soil & Wter Res., 8, 213 (3): 124 132 Runoff volume (ml) 35 3 25 2 15 1 5 () () Mix (%) 1 2 3 4 5 Mix % Mix 1% Mix 2% Mix 3% Mix 4% Mix 5% () Mix (%) () Mix % Mix 1% 1 Mix 2% 2 Mix 3% 3 Mix 4 4% Mix 5 5% 1 2 3 4 5 6 7 8 9 1 11 12 1 2 3 4 5 6 7 8 9 1 11 12 Time (min) Time (min) Figure 2. Totl men surfe runoff () nd sediment () from six different soil ly ontents (SCCs) t different time intervls Sediment onentrtion (g/l) 3 25 2 15 1 5 Also, the results demonstrted signifint differenes in the erosionl response of soils ssoited with their ly ontents. In this regrd, Ben-Hur et l. (1985) found tht the effet of ly ontent on the suseptiility of soils to sel formtion nd soil loss vried with ly ontent. But Feng-Ling et l. (21) found tht erodiility generlly dereses with the rising ly ontent of the soil. Therefore, ly ontent in the soil might hve two opposing effets on runoff nd soil erosion. The soils with intermedite ly ontents (1, 2, nd 3% ly) were more resistnt to erosion. In this se, positive influene of ly on the ggregte stility grees with findings of MConnell (1989), Siegrist et l. (1998), nd Moreno de ls Hers (29). But soils lking ly (%) or ontining high (4 nd 5%) ly ontents showed similr responses to simulted rinfll in the ses of high produtions of runoff nd sediment. Wishmeier nd Smith (1978) delred tht usully soil type eomes less erodile with derese in silt frtion, regrdless of whether the orresponding inrese is in the snd frtion or the ly frtion. To expound these ontrditions in results, it should e noted tht the loss of struturl stility under the impt of rindrops results in smller nd more esily trnsportle soil prtiles. So, the ollpse of Tle 2. Results of the LSD multiple omprison tests of runoff nd sediment etween different soil ly ontents (SCCs) The soil mixture (%) 1 2 3 4 5 Runoff 1..*.2*.1*.4*.513 1 1..222.286.14.* 2 1..877.799.14* 3 1..682.9* 4 1..28* 5 1. Sediment 1..117.275.34*.298.657 1 1..633.573.1*.261 2 1..298.34*.517 3 1..2*.92 4 1..138 5 1. *Men differene is signifint t the.5 level 128
Soil & Wter Res., 8, 213 (3): 124 132 Runoff volume (ml) 3 25 2 15 1 5 () 14 () () 1 2 3 4 5 () d d d 1 2 3 4 5 Cly soil mixture (min) Cly soil mixture (min) Figure 3. Totl men runoff () nd sediment () for six different soil ly ontents (SCCs) nd their homogeneous susets Sediment onentrtion (g/l) 12 1 8 6 4 2 struturl ggregtes ssoited with surfe seling diretly influenes oth the dethility nd the trnsportility. Also, the surfe seling, y reduing infiltrtion nd inresing the mount of runoff wter, inreses the trnsportility of dethed prtiles (Vnelslnde et l. 1984). Overll, the suspended sediment onentrtion hs pek vlue t the eginning of simultion. Generl trends in sediment onentrtions were similr for 4 nd 5% of ly soil mixtures nd hd sudden derese in initil time intervls. This vriility my e explined y differenes in soil Runoff volume (ml) 5 3 () 25 2 15 1 () d d % d Mix. 4% d 3Mix. 3% d Mix. 2% 5 4 Mix (%) 2 1 Mix. 1% Mix. % 1 2 3 44 55 66 77 88 9 1 11 12 12 Sediment onentrtion (g/l) 25 2 15 1 5 () () 5 % 4 x. 5% 3Mix. 4% Mix (%) 2Mix. 3% 1 Mix. 2% Mix. % 1 2 3 4 5 6 7 8 9 1 11 12 No. of time intervl Figure 4. Totl men runoff () nd sediment () for six different soil ly ontents (SCCs) within eh time intervl nd their homogeneous susets 129
Soil & Wter Res., 8, 213 (3): 124 132 moisture ontents. At high soil moisture ontents ly prtiles rerrnge themselves, this leds to ge-hrdening nd inresing ohesion etween soil prtiles (Kuhn & Bryn 24), so smll inrese in the moisture ontent of the ggregtes inreses the ggregte stility (Boix-Fyos et l. 1998). But soils lking ly ontent (%) hd onstnt erosion rte. On the ontrry, Sekine nd Iizuk (2) found tht the erosion rte mkes sudden drop if the smple ontins only smll mount of ly nd y the ly ontent rtio etween 2 nd 8% the erosion rte is lmost onstnt. It is euse in the well-strutured soils only fine mteril is trnsported, wheres the onentrtion is more uniform over the different size lsses for soil without ny ggregte (Asdi et l. 26) similr to the soil smples used in the present study. Also, it ws diffiult to find generl trends for other SCCs. Temporl vritions nlysis hs een performed on runoff nd sediment dt using the GLM repeted mesures proedure. Signifint effets (F = 7.193 nd Sig. =.3) of durtion were oserved in the mount of the sediment onentrtion under simultion runs mong twelve time intervls. Thus, to determine whih levels differ relily from one nother, post-ho LSD test ws onduted (Figure 4). Among twelve time intervls in whih runoff were mesured, only in the lst ones no signifint differenes were found etween runoff dt in different tretments, lthough these differenes were redued grdully while the rinfll simultion proeeded. In this regrd Riml nd Ll (29) showed tht there ws signifint differene in surfe runoff mong tretments efore 35 min of simultion run. Also, the tests of within sujets effets revel signifint differenes etween time intervls in the runoff volumes (F = 399.528 nd Sig. =.). Study of temporl vritions of the sediment onentrtion during rinfll showed tht in the ninth nd eleventh time intervls, differenes etween vlues were not signifint unlike in the other tretments. However, in most of the time intervls, soil lking ly ontent ws the reson of these signifint differenes. A similr finding ws oserved y Ll (1981), who stted tht soil erodiility is time dependent funtion nd it is influened y deteriortion of the soil struture nd umultion of the less erodile orse frtion t the soil surfe. So, the struturl stility is n importnt ontrolling ftor (Vnelslnde et l. 1984). Finlly, it should e noted tht lthough in mny soil onservtion progrmmes soil erodiility is estimted from Wishmeier nd Smith (1978) nomogrph, the nomogrph estimted vlues differ onsiderly from those mesured diretly (Singh & Kher 21). In this regrd, Atwoo nd Heersing (1997) explined tht low soil erodiility ftors estimted from nomogrph n e ounted for y the reltively high ly ontent of ll the soils tested. Therefore pproprite modifitions to the nomogrph re needed nd in this respet soil ly ontent is one of the min ftors whih should e investigted. CONCLUSIONS In the present study, severl series of systemti experiments were onduted to investigte the erosionl hrteristis of ly mixtures in soil. Overll, the texturl hrteristis of soil were found to hve onsiderle influene on the potentil of soil loss nd runoff volume. The highest surfe runoff ws oserved in soil lking ly ompred to high ly ontent soil lso the studied soils with different ly ontent ffeted the volume of runoff signifintly. Generl trends in runoff volume were similr for different soil ly ontents ut it ws diffiult to find out generl trend for sediment onentrtion. Additionlly, time hd signifint effets on oth runoff nd sediment prodution lthough these differenes were redued grdully while the rinfll simultion proeeded. The present study showed tht the effets of SCCs on soil erosion re omplex nd mivlent, hene onsiderly more reserh is required in the future for fully understnding the erosion mehnism. Referenes Armfield (1998): Instrution Mnul of Rinfll Simultor FEL3. Armfield Ltd., Ringwood. Artied O., Herrero J., Drohn P.J. (26): Refinement of the differentil wter loss method for gypsum determintion in soils. Soil Siene Soiety of Ameri Journl, 7: 1932 1935. Asdi H., Ghdiri H., Rouhipour H., Rose C. (26): Intertion etween rin nd runoff proesses during rinstorm erosion events. In: 14 th Int. Soil Conservtion Orgniztion Conf. My 14 19, Mrrkeh. 13
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