No abstract

The role of plant roots in stabilizing slopes is obvious, but the amount of the effect is varied in different species. The purpose of this study was to evaluate the effect of alder (Alnus subcordata) roots on hillslope stability. The profile trenching method was used to obtain root characteristics and a standard Instron testing machine was used for determining the tensile strength of roots. Direct shear test with undisturbed samples was used for determining the soil strength parameters. Using the results of biotechnical characteristics and the Wu model, the reinforcement effect was calculated. Using the reinforcement values and soil strength parameters and Slip4Ex program, factor of safety with and without vegetation was calculated. The obtained results indicated that the root density and number of roots decreased with increasing depth and the average root area ratio was 0.071% ± 0.01. Tensile strength decreased with increasing diameter of roots following the power function with an average of 16.29 ± 3.10 MPa. The minimum and maximum of reinforcement were 0.55 KPa and 110.76 KPa, respectively. The results of this paper augment the knowledge about biotechnical characteristics of root systems of Alder species and indicate that this species increases the factor of safety about 16.79%.

Heavy metal (HM) contamination in road dust is a potential environmental and human health threat. The sources, concentrations, spatial distribution, and ecological risk of As, Cd, Cu, Cr, Ni, Pb, and Zn in road dust in Rafsanjan City, Iran, were investigated. Pollution was assessed using the enrichment factor (EF). The potentially harmful effects of HMs were evaluated by calculating the potential ecological risk factor of individual metals (E ) and of multiple metals (RI) using the Hakanson method. Correlation and principal component analyses (PCA) were applied to identify HM pollution sources. The concentrations of HMs in road dust were higher (ca. 5-10 folds) than their natural background values. The EF and E increased according to the following order Cu > Pb > As > Zn > Cd > Cr > Ni and Cu > Cd > Pb > As > Ni > Zn > Cr, respectively. Thus, Cu is regarded as the pollutant of highest concern. Based on potential ecological risk index (RI) spatial distribution, all parts of Rafsanjan are characterized by significantly high potential ecological risk. HM concentration heat maps, PCA, and correlation analysis suggest that Cu, Pb, As, Cd, and Zn may have originated from the same source and follow the same spatial distribution pattern. These metals originated mainly from anthropogenic sources like copper mining and smelting plants, industrial and chemical activities, inordinate application of chemical fertilizers and pesticides in farmlands, and heavy traffic. Ni and Cr are likely to origniate from the industrial activities and traffic load in Rafsanjan City.

The excessive input of trace elements into urban soil has become one of the most important concerns in industrial and crowded cities all over the world. The contamination of urban soils can affect the health of people living in urban areas, and the surrounding ecosystems. Current study was conducted to assess the effects of human activities as well as different land-use on accumulation of trace elements in urban topsoil and also identify the potential risks to human health in Rafsanjan (Iran). A total of 100 topsoil samples were taken from different localities of Rafsanjan City and analyzed for Zn, Pb, Cu and Cr using the atomic absorption spectrophotometric method. Pollution index (PI) was calculated for each trace element to identify the rate of trace element accumulation with respect to the background values. Land-use map and geochemical maps were also created for evaluating of spatial distribution of pollution index and trace elements concentration in the studied area. Overlapping the concentrations map and land-use map revealed that the highest values of pollution index and trace elements concentration were located in central part of the city and highways with a great vehicle traffic load and also in the vicinity of industrial factories that increased potential health hazards to the local community. On the other hand, lowest values of trace elements were located in green-lands with strict vehicle traffic laws. These results indicated that different land-use and human activities have affected quality of urban topsoil of Rafsanjan resulting in great apprehensions regarding public health in crowded parts of the city.