حساسيت خاك ها با بافت متفاوت به فرسايش پاشماني تحت تأثير شدت باران و محتواي رطوبتي پيشين

The susceptibility of different texture soils to splash erosion under different rainfall intensity and antecedent water content

ﺳﺎﺑﻘﻪ و ﻫﺪف: ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺑﻪ ﻋﻨﻮان ﻧﺨﺴﺘﯿﻦ ﻓﺮآﯾﻨﺪ ﻓﺮﺳﺎﯾﺶ ﺧﺎك ﺷﻨﺎﺧﺘﻪ ﻣﯽ ﺷﻮد ﮐﻪ ﻧﺘﯿﺠﻪ ﻣﺘﻼﺷﯽ ﺷﺪن ﺳﻄﺢ ﺧﺎك ﺗﻮﺳﻂ ﻗﻄﺮات ﺑﺎران اﺳﺖ. ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﻓﺮآﯾﻨﺪي ﭘﯿﭽﯿﺪه ﺷﺎﻣﻞ ﺟﺪا ﺷﺪن ذرات ﺧﺎك ﺗﻮﺳﻂ ﻗﻄﺮات ﺑﺎران و ﺑﻪ دﻧﺒﺎل آن اﻧﺘﻘﺎل ﭘﺎﺷﻤﺎﻧﯽ ﺑﺨﺸﯽ از ذرات ﺟﺪا ﺷﺪه اﺳﺖ. ﮐﻤﯽ ﺳﺎزي ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ در ﺧﺎك ﻫﺎ ﺑﺎ ﺑﺎﻓﺖ ﻣﺨﺘﻠﻒ ﺑﺮاي ﺗﺮﮐﯿﺐ (Antecedent moisture content, AMC ﻫﺎي ﮔﻮﻧﺎﮔﻮﻧﯽ از ﺷﺪت ﺑﺎران و ﻣﺤﺘﻮاي رﻃﻮﺑﺖ ﭘﯿﺸﯿﻦ ) ﺑﻪ ﻣﻨﻈﻮر درك ﻓﺮآﯾﻨﺪﻫﺎي ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺿﺮوري اﺳﺖ. ﭘﮋوﻫﺶﻫﺎي ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ در ﺷﺮاﯾﻂ ﻣﺰرﻋﻪ اﻏﻠﺐ ﭘﺮﻫﺰﯾﻨﻪ و زﻣﺎن ﺑﺮ اﺳﺖ. ﺷﺒﯿﻪﺳﺎزي ﺑﺎران ﺑﻪ ﻃﻮر وﺳﯿﻊ ﺑﻪ ﻋﻨﻮان روﺷﯽ ﻣﺆﺛﺮ ﺑﺮاي ﺑﺮآورد ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ در ﻃﯿﻒ وﺳﯿﻌﯽ از ﻋﻮاﻣﻞ ﻣﺮﺗﺒﻂ ﺑﺎ ﻓﺮﺳﺎﯾﺶ ﺑﺎراﻧﯽ ﺑﻪ ﮐﺎر ﮔﺮﻓﺘﻪ ﺷﺪه اﺳﺖ. اﯾﻦ ﭘﮋوﻫﺶ ﺑﻪ ﻣﻨﻈﻮر ﺑﺮرﺳﯽ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ در ارﺗﺒﺎط ﺑﺎ ﺷﺪت ﺑﺎران و ﻣﺤﺘﻮاي رﻃﻮﺑﺖ ﭘﯿﺸﯿﻦ ﺧﺎك در ﺑﺎﻓﺖ ﻫﺎي ﻣﺨﺘﻠﻒ ﺧﺎك ﺑﺎ اﺳﺘﻔﺎده از ﺑﺎران ﺷﺒﯿﻪ ﺳﺎزي ﺷﺪه اﻧﺠﺎم ﮔﺮﻓﺖ. ﻣﻮاد و روش ﻫﺎ: ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ در ﺳﻪ ﺑﺎﻓﺖ ﺧﺎك (ﺷﻦ، ﺳﯿﻠﺖ و رس )و ﭼﻬﺎر ﺳﻄﺢَAMC از (حالت ﺧﺸﮏ ﺗﺎ اﺷﺒﺎع)ﺑﺎ اﺳﺘﻔﺎده از ﭼﻬﺎر ﺷﺪت ﺑﺎران ﺷﺒﯿﻪ ﺳﺎزي شده( اﻧﺪازه 40 و30 ،20 ،10 ميلي متر درساعت) اندازه ﮔﯿﺮي شد . براي اين منطور 48 واﺣﺪ آزﻣﺎﯾﺸﯽ در ﺳﻪ ﺗﮑﺮار ﻃﺮاﺣﯽ ﺷﺪ و ﺑﺎ اﺳﺘﻔﺎده از آزﻣﺎﯾﺶ ﻓﺎﮐﺘﻮرﯾﻞ در ﻗﺎﻟﺐ ﻃﺮح كاملا ﺗﺼﺎدﻓﯽ ﻣﻮرد ﺗﺤﻠﯿﻞ ﻗﺮار ﮔﺮﻓﺖ. واﺣﺪﻫﺎي آزﻣﺎﯾﺸﯽ ﻋﺒﺎرت از ﺟﻌﺒﻪ هاي 35 ﺳﺎﻧﺘﯽ متر × 25ﺳﺎﻧﺘﯽ ﻣﺘﺮ باعمق5 سانتي متر ﺑﻮد. ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺑﺎ ﺟﻤﻊآوري ذرات ﭘﺎﺷﻤﺎن ﯾﺎﻓﺘﻪ ﻃﯽ ﻫﺮ ﺑﺎران و ﺳﭙﺲ ﺧﺸﮏ ﮐﺮدن آن ﻫﺎ در دﻣﺎي 105 درجه سانتي گراد براي مدت 24 ساعت اندازه گيري شد. ﺧﺼﻮﺻﯿﺎت ﻓﯿﺰﯾﮑﯽ و ﺷﯿﻤﯿﺎﯾﯽ ﺧﺎك ﺑﺎ اﺳﺘﻔﺎده از روش ﻫﺎي راﯾﺞ آزﻣﺎﯾﺸﮕﺎﻫﯽ ﺗﻌﯿﯿﻦ ﺷﺪﻧﺪ. دادهﻫﺎي ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺑﺎ اﺳﺘﻔﺎده از آزﻣﻮن داﻧﮑﻦ ﺑﺮاي ﻣﻘﺎﯾﺴﻪ اﺛﺮات ﺑﺎﻓﺖ ﺧﺎك، ﺷﺪت ﺑﺎران و ﻣﺤﺘﻮاي رﻃﻮﺑﺖ ﭘﯿﺸﯿﻦ ﺑﺮ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺗﺠﺰﯾﻪ و ﺗﺤﻠﯿﻞ ﺷﺪ. داده ﻫﺎ ﺑﺎ اﺳﺘﻔﺎده از ﻧﺮم ﺗﺤﻠﯿﻞ و ﻧﻤﻮدارﻫﺎ ﺑﺎ اﺳﺘﻔﺎده از ﻧﺮم SAS 9.2 اﻓﺰار ﺑﻪSigmaPlot 12.0 اﻓﺰار دﺳﺖ آمد. يافته ها: تفاوت هاي معني دار فرسايش در بين بافت هاي خاك ( P>0/001) سطوح AMC ، (p<0/001) و شدت باران ( P<0/001) مشاهده شد.ﺑﯿﺶﺗﺮﯾﻦ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ در ﺑﺎﻓﺖ ﺳﯿﻠﺖ ﻣﺸﺎﻫﺪه شد( به ظور متوشط 257/2 گرم بر متر مربع ) كه اين موضوع مي تواند بع دليل قابليت جداشدن آسان ذرات سليت و انتقال پذيري آسان آن ها توسط ﻗﻄﺮات ﺑﺮﮔﺸﺖ ﯾﺎﻓﺘﻪ ﺑﺎران ﺑﺎﺷﺪ. ﺧﺎك ﺷﻨﯽ ﻣﻘﺎوﻣﺖ ﺗﺮﯾﻦ ﺑﺎﻓﺖ ﺧﺎك از ﻧﻈﺮ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺑﻮد. ﻣﻘﺪار ﭘﺎﺷﻤﺎن در اين خاك از 35/43 تا 155/70 گرم بر مترمربع تغييركرد . ﺗﻔﺎوتﻫﺎي ﻣﻌﻨﯽداري از ﻧﻈﺮ ﺑﺮهم كنش بافت خاك با شدت باران( P<0/001) بافات خاك با سطوح P<0/001) AMC ) و ﺷﺪت ﺑﺎران ﺑﺎ ﺳﻄﻮح P<0/001) AMC )مشاهده شد. ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺗﺤﺖ ﺗﺄﺛﯿﺮ ﻣﺜﺒﺖ ﺷﺪت ﺑﺎران ﻗﺮار ﮔﺮﻓﺖ. ﻧﺘﺎﯾﺠﯽ ﻣﺘﻔﺎوت از ﻧﻈﺮ ﺗﺄﺛﯿﺮ AMCﭘﺎﺷﻤﺎﻧﯽ ﺑﯿﻦ ﺧﺎك ﻣﻘﺪار ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ در ﺧﺎك ﺳﯿﻠﺘﯽ اﻓﺰاﯾﺶ ﯾﺎﻓﺖ در ﺣﺎﻟﯽ ﻫﺎ ﻣﺸﺎﻫﺪه ﺷﺪ. ﺑﺎ اﻓﺰاﯾﺶ ﮐﻪ ﻧﺸﺎن داد. ﺧﺎك ﺷﻨﯽ ﺗﻔﺎوﺗﯽ ﺑﺎرز از ﻧﻈﺮ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺑﺎ اﻓﺰاﯾﺶ AMCﺧﺎك رﺳﯽ روﻧﺪي ﮐﺎﻫﺸﯽ ﺑﺎ اﻓﺰاﯾﺶ ﻧﺸﺎن ﻧﺪاد. ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﻫﻤﭽﻨﯿﻦ ﺗﺤﺖ AMC ﺗﺄﺛﯿﺮ ﺑﺮﻫﻢ ﮐﻨﺶ ﺳﻪ ﻣﺘﻐﯿﺮ ﻣﻮرد ﺑﺮرﺳﯽ ﺑﺎﻓﺖ ﺧﺎك، ﺷﺪت ﺑﺎران ﻗﺮار ﮔﺮﻓﺖ. ﺑﯿﺶAMCو ﮔﺮم ﺑﺮ ﻣﺘﺮﻣﺮﺑﻊ در ﺧﺎك ﺳﯿﻠﺘﯽ داراي رﻃﻮﺑﺖ ﭘﯿﺸﯿﻦ 441/20 ﺗﺮﯾﻦ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﻣﯿﻠﯽ40 درﺻﺪ اﺷﺒﺎع و ﺗﺤﺖ ﺑﺎران ﺑﺎ ﺷﺪت 50 ﻣﺘﺮ ﺑﺮ ﺳﺎﻋﺖ ﻣﺸﺎﻫﺪه ﺷﺪ. ﮐﻢ ﮔﺮمﺗﺮﯾﻦ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ( 35/43 گرم بر متر مربع ) نيز مربوط به خاك شني داراي رظوبت 5درصد اشباع (ﻫﻮا ﺧﺸﮏ) و ﺗﺤﺖ ﺑﺎران ﺑﺎ ﺷدت 10ميلي متربر ساعت بود. ﻧﺘﯿﺠﻪ ﮔﯿﺮي: ﻧﺘﺎﯾﺞ اﯾﻦ ﭘﮋوﻫﺶ ﻧﺸﺎن داد ﮐﻪ ﺧﺎك ﺳﯿﻠﺘﯽ، ﺣﺴﺎس ﺗﺮﯾﻦ ﺑﺎﻓﺖ ﺧﺎك از ﻧﻈﺮ ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﻣﯽ ﺑﺎﺷﺪ. ﺑﻪ ﻋﻼوه ﺗﻐﯿﯿﺮات ﻣﻘﺪار ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﺑﺎﻓﺖ ﺳﯿﻠﺖ از ﺳﺎﯾﺮ ﺑﺎﻓﺖ ﻫﺎ ﺑﯿﺶ ﺗﺮ ﺑﻮد. ﻣﻘﺪار ﻓﺮﺳﺎﯾﺶ ﭘﺎﺷﻤﺎﻧﯽ ﻫﺮ ﺧﺎك را ﻣﯽ ﺗﻮان ﺑﺎ اﺳﺘﻔﺎده از دﯾﺎﮔﺮام ﺑﻪ دﺳﺖ آﻣﺪه ﺑﺮ ﻣﺒﻨﺎي ﺷﺪت ﺑﺎران و رﻃﻮﺑﺖ ﭘﯿﺸﯿﻦ ﭘﯿﺶ ﺑﯿﻨﯽ ﮐﺮد.

Background and Objectives: Splash erosion is recognized as the first stage in a soil erosion process and results from the soil surface bombing by rain drops. Splash erosion is a complex process including the detachment of soil particles by raindrops followed by splash transport of a part of the detached particles. Quantification of splash erosion in the soils with different textures for various combinations of rainfall intensities and antecedent moisture content (AMC) is essential to understand splash erosion processes. The investigation on the splash erosion in the field is often expensive and time-consuming. Rainfall simulation has been used extensively as a cost effective method for soil erosion prediction across a lot of related factors. This study was conducted to investigate splash erosion in relation to rainfall intensity and AMC in different soil textures using the simulated rainfalls. Materials and Methods: Splash erosion was measured in three soil textural classes (sand, silt and clay) and four AMC (from air-dried to saturation conditions) using the four simulated rainfalls (10, 20, 30 and 40 mm h-1 in intensity). Forty-eight experimental units were designed at three replicates and analyzed using the factorial experiment in the completely randomized design. The experimental units were splash boxes with 25 cm × 35 cm dimensions and 5-cm depth. Splash erosion was determined using the accumulation of splashed particles during each rainfall and accordingly drying in 105 °C for 24-h. The physicochemical soil properties were determined using the conventional methods in the laboratory. Splash erosion data were analyzed using the Duncan parametric test for comparison of the effects of soil texture, rainfall intensity and, AMC on the splash erosion. Data were analyzed using the SAS 9.4 software and the diagrams were delineated using the SigmaPlot software. Results: Significant differences were found in the splash erosion among the soil textures (P<0.001), AMC (P<0.001) and rainfall intensity (P<0.001). Silt showed the highest splash erosion (average value 257.2 g/m2) which was related to easy detachment of silt particles and readily transport by returned raindrops. Sand was the most resistant soil texture to splash erosion. Splash erosion in sand soil varied from 35.43 to 152.70 g per m2. There were significant differences interactions between soil texture and rainfall intensity (P<0.001), soil texture and AMC (P<0.001), rainfall intensity and AMC (P<0.001). Splash erosion was positively affected by the rainfall intensity. Silt showed the highest susceptibility the splash erosion with increasing rainfall intensity. Different results were observed for AMC among the soil textures in the splash erosion. With an increase in AMC, splash erosion in the silt significantly increased, while clay showed a negative trend with increasing AMC. Sand didn’t show an obvious difference in the splash erosion with increasing AMC. Splash erosion was significantly affected by the interactions of three variables (soil texture, rainfall intensity and AMC). The highest splash (441.20 g per m2) erosion was observed in Silt for AMC with 50% saturated point under the rainfall intensity of 40 mm h-1 Sand showed the lowest splash (35.43 g per m2) erosion for AMC with 5% saturated point under 10 mm h-1 rainfall intensity. Conclusion: Results of this study indicated that Silt is the most susceptible soil texture to splash erosion. Also, variations of splash erosion in silt texture were larger than other textures. Splash erosion of each soil could be reliably predicted based on the rainfall intensity and antecedent water content.