Extended Abstract



Introduction

Soil is one of the most important factors affecting human life and other living organisms. The soil formation is controlled by climate, organisms, topography, parent material and time. Alluvial fan is one of the most important depositional landforms of arid and semi-arid regions of Iran. Geomorphological landforms and processes of alluvial fan surfaces can strongly affect the physicochemical properties of soils of alluvial fans. Longitudinal positions (apex, toe), transversal positions (margin, inside), the surfaces (old and young), landforms (channels, interfluves, bars, and swales), of the alluvial fans can impact variations in soil characteristics on fan surfaces. The purpose of this research is to analyze the effects of geomorphological landforms and processes on the soil physicochemical parameters of two alluvial fans located in the northeast Damghan.





Methodology

To achieve the aim of this study, the borders of two studied alluvial fans were identified by the Google Earth images. Differentiating old from young surfaces of fans was done based on semes indexes including drainage pattern, surface morphology, weathering features and surface color/tone on satellite images. The lithological units and faults of the study area were derived from 1:100,000-scale geological maps. To study the soil physicochemical properties of the studied alluvial fan, a total of 40 soil samples (20 samples for each fan) were obtained from soil depths of 0–20 cm. On each fan, samples were gathered from longitudinal positions (apex, toe), transversal positions (margin, inside), surfaces (old and young), and landforms of the old surface (channel, interfluve), and the young surface (bar, and swale). Then, the sand%, silt%, clay%, PH, electrical conductivity (EC) and organic carbon (OC) were calculated. The soil texture was determined by the hydrometer method. The soil acidity (PH) was measured by a PH meter. The soil organic carbon (OC) was measured by Walkley-Black titration method. The electrical conductivity (EC) of soil samples was determined using an EC meter. The Pearson correlation coefficient was used to evaluate the relationship between soil properties. To compare the means of soil parameters in positions, surfaces, and landforms, the t-test were applied.





Results and Discussion

Results show that only the mean values of EC and PH have statistically significant differences in two alluvial fans. The mean value of organic carbon parameter has a significant difference in the old and young surfaces of fan 1. The means of clay%, silt% and sand% have statistically significant differences in the channels and interfluves of the old surfaces of both alluvial fans. This indicates that the existence of channels and interfluves in the old surfaces of the studied alluvial fans has played an important role in difference in the texture of their sediments. The means of sand% and silt% have significant differences in the bars and swales of the young surface of fan 2. This shows that the young surface landforms (bar and swale) have only caused a fundamental difference in the texture of the sediments of fan 2. The means of all soil parameters does not have a statistically significant difference on the margin and inside of fan 1. However, the means of EC and PH parameters have a statistically significant difference on the margin and inside of the fan 2. Evaluation of the correlation coefficient between soil parameters shows that organic matter has no significant relationship with other soil parameters in fan 1. In fan 2, there is a significant negative relationship between EC and sand%. There is also a significant positive relationship between sand% and PH in fan 2. Soil organic carbon in fan 2 is somewhat affected by the silt%, so that organic carbon increases with the increase of silt%. Also, the EC parameter has a significant negative relationship with PH parameter in fan 2.





Conclusion

Two studied alluvial fans in the northeast Damghan are located in south Alborz Mountain range. Under the effects of tectonic and climate, most parts of alluvial fans have been abandoned (old surfaces) whereas small parts (young surfaces) of the alluvial fans are subject to flooding and deposition. We analyzed the effects of fan’s surfaces, positions, and landforms on the soil physicochemical parameters. Results show that landforms of old surface (channel, interfluve), and young surface (bar, and swale) have strongly controlled the soil texture of studied alluvial fans. In general, it can be concluded the relative age of the fan surfaces, the soil texture, the channel deflection and continuous change in the location of deposition in the surface of fan, the vegetation cover of the fan surface, the morphology of the fan surface and its landforms, as well as the lithology and morphometry of upstream basins of fans are factors playing important roles in the divergence and difference of soil physicochemical parameters in the studied alluvial fans.