عنوان مقاله [English]
Soil erosion by water is a worldwide environmental problem which degrades soil productivity and water quality, causes sedimentation and increases the probability of flood. Soil erosion is detachment and transmission of soil particles by erosive factors like water and wind.Different studies have indicated the positive effect of vegetation cover in regulation of hydrological processes of above ground and decrease of runoff and soil loss(Zheng, 2006Zhou et al., 2008 VÃ¡squez-MÃ©ndez et al., 2010Ouyang et al., 2010Zhang et al., 2010Nunes et al., 2011andWildhaber et al., 2011).To show the role of vegetation cover can be stated that decrease of vegetation cover due to overgrazing and deforestation cause detachment of soil aggregate stability which increase risk of runoff and soil loss.This study was carried out to assess the effects of different amounts of vegetation cover on controlling of runoff and soil loss in Nesho rangeland which placed on Mazandaran province, using rainfall simulator.
Forthis research,anarea about6 hectares, which includesdifferent vegetationcover percentages (minimum, moderateandmaximum) was selected. On the 110 sample points by a systematic sampling strategy on a regular grid spacing of 30 Ã 30 m, runoff and sediment yield samples were gathered using simulated rainfall experiment with 2 mm/min intensity and 11 minutes duration at 0.09 m2 plot and all the samples were transported to laboratory. Vegetation covers were measured in sample points using plot method.
Resultsof statistical analysis using one-way ANOVA and compare means (Duncan method) showed thatdifferent vegetationcover percentageshad significant effect onrunoffandsedimentcomponentsinthe study area.Time to runoff generationin Maximumvegetation coverwasmore than moderate and minimum vegetation cover significantly.As maximum vegetation cover with delaying of runoff generation enhances water infiltration into the soil and decrease soil loss. Mean of runoff yield in different vegetation covers had significant difference. Minimum and maximum vegetation cover percentages has highest and lowest runoff yield (liter/meter2) respectively. The reason maximum vegetation cover has lowest runoff yield is vegetation cover protects soil,by intercepting rainfall reducethe energy of rainfall drops, runoff yield and soil loss. Minimum and maximum vegetation cover percentages had highest and lowest runoff coefficientrespectively. Different vegetation cover percentages had significant difference from sediment yield. In minimum vegetation cover, sediment yield was increased 6.8 and 1.99 times to maximum and moderate vegetation cover and maximum vegetation cover had lowest sediment yield. Maximum vegetation cover by intercepting rainfall,decreasesurface flow and runoff yield reduces soil loss. Sediment concentration had negative relationship with vegetation cover percentages and as vegetation cover increases sediment yield rates is less. Minimum and maximum vegetation cover percentages had highest and lowest sediment yield rates respectively.
The results of simple linear Regression showed that vegetation cover had reducer effect on runoff yield, runoff coefficient, sediment yield and sediment concentration rates but had multiplier effect on time to runoff generation. Soil erosion and runoff can be predicted based on percentages of vegetation cover with coefficient of determination of 0.71 and 0.69 respectively.Results showed that different vegetation cover percentages had significant effect on runoff and sediment yield components and maximum vegetation cover had highest effect on reducing of runoff and sediment yield.Therefore, according to positive effects of vegetation cover,payspecial attention to rangeland vegetation cover to reduce runoff and soil loss is felt and it is proposed biological and soil conservation programs to reduce losses of soil erosionin areas with high erosion sensitivity in this region.