جغرافیا و پایداری محیط (Mar 2016)
Studying and Comparing the Soil Characteristics of Gullies (Case Study: Chabar and Sistan Region)
Abstract
1- Introduction The severe environmental problems are emphasizing on the urgent need to evaluate the available natural resources in order to provide the requirements for rapid growth of human population. All the basic natural resources including the land, water, energy and biota have been inherently limited for the sake of human uses. As the human population continues to grow, the natural resources are being divided among the increasing number of people. Overuse of these resources has led to some changes in their quality and quantity worldwide. Soil erosion, a natural phenomenon occurred in the nature, is a main environmental problem, although expedition erosion in the places in which natural rate is increased due to human activity is considered as the most significant issue. Soil loss and water ensuing have become one of the most important reason of limiting local development. The studies have shown that human activities on the environment such as intensive farming practice, deforestation and overgrazing of livestock have in some ways triggered off flooding and soil erosion by both water and wind. Soil erosion in the form of shallow gullying, rill erosion, sheet erosion and river bank erosion is prevalent in the arid and semiarid regions. Gully erosion mostly occurs in the time when water flows in narrow channels during or after heavy rainfall. Gullies range in depth from 30 to 3,000 cm and contain just water during and immediately after precipitation events. The present research aims at studying and comparing soil characteristics of Gullies (Case study: chabar and Sistan region). 2- Materials and Methods The present study was carried out in Chabahar located in the south of Sistan and Baluchistan state, Iran. The study area lies on latitudes 25° 40′- 25° 46′ N and longitude 61° 14′ – 61° 15′E. The dry season lasts from May to December while rainy season from late December to May. The mean annual total rainfall is about 100mm receiving over the average about 20 raining days. The temperature is almost high. The vegetation cover is very poor which receives to 10-15 percentages. Another study area is located in the north of Sistan and Baluchistan state, Iran. The Sistan region is occupied mainly by dry land. The region is nearly flat and featureless arid plain with an average height of 475–500m ASL in its eastern parts. That is why this arid plain is called Sistan plain. It is bounded by latitudes 30o24’N and 30o36’N and; longitudes 61o02’E and 61o04’E close to the border of Afghanistan. The Sistan region, being a part of arid zone of Iran, experiences an arid climate with cold weather in the winter months and warm weather in the summer months. The temperature data indicated that July is the warmest month, when temperature rises above 50oC; whereas January is the coldest month of year with mercury dipping down to minus 12oC. The warm winds blow over the region of Sistan for about 120 days during the period from June to September, the dominant directions being the north and northwest. The preset research aims at studying and Comparing soil characteristics of gullies in the south and north of Sistan and Baluchistan state. In this study, the available Geologic maps, aerialphotographs, Jammab map and field observation were applied to find gully erosion region. The kind of dominant climate was recognized. Moreover, two gullies in each region were selected in which the gully morphometric and natural characteristic were measured. Soil samples were taken from, 25%, 50%, and 75% of gully length at each location which were analyzed for soil characteristic and pH, EC, SAR, CEC, ESP, SP and texture. The data were analyzed using SPSSsoftware. 3- Results and Discussion The data, gathered from field studies and the available maps, show that the headcuts of gullies number 1 and 2 Chabahar are slopping and cave-like while it is vertical plans from Sistan gully. Their cross sections are V and U shaped. According to the depth of the gullies, they are classified in the intermediate class (1-10m). Dominant causes of gully formation are degradation of vegetation cover, land use change, soil erodibility, heavy rain and irrigation mismanagement. The gullies damage the lands, rangelands, cultivate lands, roads and water channels. The findings show that there is no statistically significant difference among the soil properties of the regions. The profileofgully-headtypes in Chabahar and Sistan are cave-like and vertical, respectively. The analysis shows that the values of soil pH in Chabahar and Sistan area are 7.85 and 8.07, respectively. The amount of t for pH in the areas equals to 3.642. There is no statistically significantdifferenceamong the means in level 0.05 (p>0.05). The means of soil sample electrical conductivity (EC) are 2.75 and 2.84 (ds/m) in Chabahar and Sistan region. The t of this parameter is 1.187. There is no statistically significantdifferenceamong the means in level 0.05 (p>0.05). The means of soil sample sodium adsorption ratio (SAR) are 6.36 and 3.15 ( Meq/100g in Chabahar and Sistan, respectively. The amount of t equals 1.99. The means of soil sample cation-exchange capacity (CEC) are 13.22 and 17.82 meq/100g. The means of exchangeable sodium percentage (ESP) are 6.65 and 6.11 in Chabahar and Sistan region. The means of saturation percentage (SP) soil sample in the areas are 47.1 and 46.49, respectively. The amount of soil clay is 16.37 and 13.5 percentage in Chabahar and Sistan, respectively. The means of soil silt are 64.12 and 53.87 in the area. The averages of sand are 18.37% and 32.62% in Chabahar and Sistan regions. Range development of the gullies and their morphology are different in both regions. in other words, Sistan gully is poor with no development, for the flood which flows from Afghanistan is considered as the most important factors in gully erosion in Sistan region. Gully No 1 of chbahar is the same as Sistan gully, but, only developing from head. However, Gully No 2 of chbahar is type of uncontinue, young developing from all direction. Filed studies show that the sub-branch is more than the other gullies. 4- Conclusion The present studyshows that both physical and human factors including grazing over, destroyed vegetation cover, soil erodible, heavy floods from Afghanistan are important in the distribution of the gullies in Sistan region. There are several factors affecting on gully number 1 of Chabahar such as natural condition and basin physiographic, soil erodible, river flows, heavy flood, high intensity rain, land use, human activity and irrigation mismanagement. The causes of gully number 2 of Chabahar are including grazing over, destroyed vegetation cover, soil erodible, heavy floods, Agriculturalmismanagement of pasture and arable land, human activity, destruction of vegetationcover by nomadic peoples. Laboratoryanalyses show that gully number 2 of Chabahar has different morphologicalcharacteristics compared with other gullies. The main difference of this gully to other gullies is branches in head and other parts of this gully. The study shows that there are no differences in climate and human activity in study areas. So, it turns out that the soil characteristic and soil erodible make sub network in study gullies.
