فصلنامه پژوهش های فرسایش محیطی
سال نهم شماره 4 (پیاپی 36، زمستان 1398)

Various factors influence the karstification process in the dissolution of carbonate rocks. Karst is common influence result of internal morphodynamics (geological structure and lithology) and external morphodynamics (climate, altitude, vegetation, and time). They affect the karstification of the demise of carbonate rocks. Karst is the result of numerous methods that occur in calcareous zones and climatic, geological, and hydrological conditions, and its effects can be seen in multiple forms, such as pits and caves above and below ground. One of the climate indices that determines the environmental conditions is the amount of moisture and its changes. The presence of water is a significant climate factor in karst development. They reflected in the formation of the environment in several Forming systems: in the high elevations and latitudes as glacier systems, in the piedmont as ice sheet systems, in the marginal zone as ice tab and mudflat systems, in the lower zones as runoff and in the smaller pit as waterfall system (Seif et al., 2015). The solubility of carbonate rocks is sensitive to temperature changes (Ghobadi, 2009: 142); Limestone dissolution is more rapid at low temperatures and in colder climates, and the amount of karst erosion in cold and humid regions is much higher than in hot and humid regions (Zanganeh Asadi et al., 2002). With the impact of elevation on temperature and precipitation, erosion processes and consequently the face of the Earth and geomorphological phenomenon change (Alipour et al., 2017). The purpose of this paper is to investigate the physiographic differences of calcareous Zagros sub-basins concerning altitude variation and the interpretation of disagreements concerning temperature and precipitation elements.

In this paper, considering the karst features and the effect of dissolution on the basin in terms of physiographic properties (shape parameters), slope, roughness (topographic parameters) in the Arc Map, the basins of the rivers that were located in the calcareous zones were determined. The settings of such as environment, basin area, and rivers length, minimum and maximum height were calculated. The shape and topographic parameters of the basins were estimated, by using the existing relationships, and then the final rank of the basin's main waterway was obtained based on the Australian method. The collected data were entered into Excel software. Finally, linear regression equations between altitude as the independent variable and other parameters as the dependent variables were estimated to investigate their variation concerning the altitude factor. They were also studied in elevation classes, different climatic zones, and distance to the fault.

Investigation of the estimated linear regression relation between height as an independent variable and other parameters as a dependent variable at different ranks indicates that with increasing elevation, area, roughness coefficient, length, elongation ratio, and basin shape factor become less and form element lower. Increasing the area of sub-basins at ranks similar to elevation implies that surface erosion overcomes linear erosion. When corrosion is direct, the intermediates are usually less extensive, and the basins are consequently getting smaller. However, the sub-basin area increases due to elevation in single lithology, and as in similar waterways. Due to the karst-fission effect on basin dimensions and their influence on climatic elements, the sub-basin area has grown and increased the area of the sub-basin has made the erosion from the line (water) to surface (dissolution) more inclined. In 297 sub-basins with rank 2 and 3 northwest Zagros, there was no significant relationship between altitudes with other parameters except ruggedness. That is, their coefficient of explanation was less than 0.4, and it could not be analyzed solely by the height factor. Examination of these parameters indicates that their changes, sometimes with increasing altitude, are minor and occasionally unanticipated and sometimes have no specific direction. As the river rises, the area of the sub-basins also increases. We identified in the southeastern part of the folded Zagros, 48 basins. In each rank basin, there is a direct correlation between height and other parameters. It means that all of them are affected by altitude. They increase with the coefficient of all of them, except the form factor, it has grown. In low Zagros, 68 catchments in calcareous zones, with ranks two to four, it was considered that the regression relationships between altitude and parameters except the form factor had a direct correlation with the difference that this unit had higher correlation coefficient than the other Zagros units.

The physiographic coefficients of the basins in the calcareous zones, the change in temperature and precipitation due to elevation changed. The transformations of karstification can analyze the change in temperature and precipitation — these changes reflected in different parts of Zagros (except for the folded northwest Zagros). The increasing of the coefficient of explanation in low altitude Zagro indicates that due to the physiographic characteristics of the basins, the role of climate change (temperature and precipitation) in this part of Zagros can be better traced. The examining factor such as basin physiography due to the increase of altitude shows that the elongation and length of the sub-basins increase with increasing. And it is reflected almost like the basin drag coefficient. Erosion at the basin surface may have a homogeneous or heterogeneous distribution. If the coefficient of roughness is high, it indicates that the distribution of decay has become seamless. In calcareous regions, as the altitude increases, the ratio of hardness increases too because the distribution of erosion becomes heterogeneous. Investigation of the physiographic characteristics of the watersheds concerning altitude shows that the elongation and length of the basins increase with increasing Zagros with an explanation coefficient of 0.5. The results show that increasing the coefficient of elongation and length of the basin in calcareous zones lead to more dissolution, and the form factor, with a ratio of explanation of 0.53 for the whole Zagros indicate the geometric shape of the basin to square and rectangle. It almost reflects results similar to the basin drag coefficient. In calcareous areas, as the altitude increases, the coefficient of roughness increases by an average of 0.6% due to heterogeneous surface erosion.
Morphometric study of Zagros calcareous sub-basins about climatic factors indicates that several factors affect these properties, only some of which are related to dissolution conditions; Crashes, landslides, topography, faults, seams and crevices, and any other factors can affect these properties that may be addressed in separate studies.

Changing the forests and pasture landuses to agricultural lands is one of the major global concerns about environmental degradation and climate change. As a result of the rangeland and forest changes into agricultural land and also tillage operations, about 430 million hectares, representing 30% of the world's total plowed land, are annually eroded and leaving the optimal production cycle at different countries. Non-scientific and unknowingly land use changes have negative effects on desirable physical and chemical properties of soil. However, these lands have low production potential on one hand and high erodibility potential on the other hand. In the past four centuries, about 30 percent of the world's forests and natural grasslands have changed to pastures of livestock and agricultural land. Such activities reduce the input of fresh plant residues into soil and result in significant changes in physical and chemical properties of the soil (Haghighi et al., 2010). Landuse changing leads to loss of soil organic carbon, reducing nutrient availability and maintenance, changing soil biological community, degradation of soil structure, decreasing soil permeability and hydraulic conductivity and increasing soil bulk density (Golchin & Asghari, 2008). In addition, land use change and deforestation have increasingly increased CO2 that resulted in global warming and climate change in recent years.

The study area is located in the forest lands of Andebil village, 5 km northeast of Khalkhal city. Khalkhal city is a suburb of Ardabil province and is about 110 kilometers far from Ardabil city. The study area covers an area of ​​about 270 hectares and includes three types of forest, pasture and agricultural land uses. The geological structure of the area is uniformly composed of sandy limestone from the Upper Mesozoic period.  30 samples were randomly taken from each landuse (90 sampling sites in total) and surface sampling from the depth 0-30 cm was performed. The geographical location of each sample was also recorded by GPS. Undisturbed (clod) and disturbed (with shovel) samples were prepared. The experimental design was completely randomized with forest, pasture and agricultural treatments and 30 replications (in total 90 samples). Analysis of variance and Duncan's post hoc test were performed using SPSS 16.0 software after normality test of data.

The effect of landuse on all the studied characteristics was significant (p <0.01). The percentage of sand in the three forest, pasture and agricultural landuses was significantly different. The highest average of sand was obtained in forest and the lowest amount was in agricultural use. A similar trend is observed for the significant decrease in silt mean in agricultural compared to the other two landuses. The mean of clay also shows the effect of landuse changes with a significant increase compared to other two landuses. forest and pasture samples mainly belong to the two texture classes of loamy sand and sandy loam, while agricultural samples include sandy loam, sandy clay loam and clay loam classes which are finer than the others. Bulk density was significantly increased in agricultural (1.59 g / cm3) compared to forest and pasture and there was no significant difference between forest and pasture landuse. The effect of landuse change on soil organic carbon content was significant. Comparison of the mean of this parameter in three landuses shows that the highest average of soil organic carbon was obtained in forestuse (6.32%) and the lowest (1.49%) in agricultural landuse. The amount of total soil nitrogen was significantly different at between different landuses. The highest amount of calcium carbonate (11.31%) was for agricultural use and the least (7.36%) was for forestuse. Soil EC in forest was significantly higher than pastures and agricultural landuse. The highest soil reaction (7.38) was related to agricultural use and the lowest (5.88) to forest use. The reason for the increase in soil pH in agricultural use should be the application of fertilizers and pesticides.

Discussion & Conclusions

The result of this study showed that the landuse change affected the soil properties significantly. Changing the landuse of forest significantly resulted in increasing of silt, clay, bulk density, soil reaction and equivalent calcium carbonate) and a decreasing in the amount  of sand, organic carbon, total nitrogen and electrical conductivity of the soil. Along with properties changing, soil qualities (which are a combination of two or more properties) are also affected by landuse changing. In most cases, landuse change has the same effects at different locations that are baring the soil surface, reducing soil permeability and ultimately speeding up surface water movement. The result of all this will be an increase in erosion in lands that once served as forest conservationists. Therefore attention to this issue can prevent the great risk of erosion threat.

Water erosion has been a problem worldwide, which causes the phenomenon of land degradation in semi-humid areas of dry land. The risk of soil erosion in arid and semiarid areas, especially in mountain ranges is of significant cases in land use planning. Soil erosion in these areas is one of the important consequences of climate change, or in general, the obvious impacts of environmental and ecological changes. The erosion implications include soil loss, sediment deposition in reservoirs, and vegetation loss, and vegetation cover. Among the different cases of water erosion, gully erosion is one of the most important factors affecting soil destruction, land aspect change, and degradation of water resources and land setbacks. Due to the importance and role of gully erosion inland waste and land depletion, especially in the study area due to the existence of fertile agricultural land with high potential production and proximity of these lands to urban areas in Darrehshahr county, the aim of this study is identifying effective soil factors in the development of gully geometry characteristics and their prediction. Identifying effective factors in the development of this process can be an approach for helping managers and authorities to control and prevent the development of gully erosion.

There are many gully areas in the province of Ilam, where the study of Darrehshahr has been investigated. It is located in the Darrehshahr county and the eastern city of Ilam in the geographic range between 47° 30¢ 8² to 47° 46¢ 03² longitude and 33° 12¢ 14² to 33° 23¢ 03² latitude. Geological formation is composed of the sediments of the lake, which is caused by the landslide. It is a cold semi-arid climate that is based on synoptic stations at an average temperature of 21 C° and the average precipitation in the region is 497 mm. The basic data and statistics required are topographic maps of scale 1: 25,000 military organizations and the country's mapping organization, on a scale 1: 100,000 geological maps of the country, map of soil and land resources on a scale of 1: 25,000 of the institute for water conservation and soil. The measurement of gully geometric properties, including depth, length, high and low level, cross-sectional area, lateral slope, was done by surveying in the field using the Total survey camera at three cross-sections (head cut, median and outlet) of the gully. Then the region was divided into 12 work units, and in each case, three replicates were selected, and finally, 36 gullies were selected in the study area. The geometrical features of the gully using aerial photographs, digital maps and field operations, and physical-chemical properties of soil were determined using laboratory methods. To determine the impact of these factors on each of the geometric characteristics of the gully and the relationship between the dependent and independent variables was obtained using multivariate regression.

After grouping the gullies, the relationship of soil properties with geometry properties, including depth, length, Up and down width, was investigated based on the methods of correlation analysis and multiple regression models. The results showed that EC (3.43), SAR (7.55) and Na+ (3.95) have the highest impact factor and the most important role in the development of the gully. Whereas the amount of organic matter and total of Ca++Mg++, will be the role of adherence to the soil and prevent gully development. Also, based on the cross-section development model, the amount SAR (3.41), Na+ (2.87), and the Gypsum (2074) has the highest impact factor in the increasing cross-section of the gully.  But the amount of total of Ca++ and Mg++ (-0.36) and OM (-0.097), playing the most important role in the control and prevention of the gully development. The validation of the geometric characteristics of the gullies using statistical indexes (MRE and RMSE) was calculated. Due to very low RMSE values for both models, we can say that the proposed models are highly valid and can be used for regions with similar conditions of the study area.

Due to the importance and role of gully erosion in soil loss, especially in the case study area, this study aimed to identify effective soil factors in the development of protective gully characteristics. Therefore, according to the findings of this study, it was found that: Based on the conceptual model of extension of gully length, the amount of EC, SAR, and Na+ have the highest impact and the most important role in the development of the gully. Conversely amount of organic matter and total of Ca++Mg++, will be the role of adherence to the soil and prevent gully development. Based on the cross-section development model, the amount SAR and the Na+ have the highest impact in the increasing cross-section of the gully.  But the amount of gypsum and total of Ca++ and Mg++ playing the most important role in the control and prevention of the gully development.
Soil texture, especially silty texture, plays a more effective role in gulling and sedimentation of gullies.

Sarakhs is strategically and geopolitically important in Khorasan Razavi province and the country. Existence of Khangiran Refinery, Sarakhs Special Economic Zone, Silk Highway, Sarakhs Great Transit Customs, etc ... It has led to the development and prosperity of the city that has added to the city's population in recent years. On the other hand, the three of the wind erosion crisis, and progress of the wind erosion zones in the region due to drought and the persistence of dust storms, are the most important threats to the strategic locations of the region. It is important for planners and managers to be aware of changes in wind erosion zones over a period of time and their relationship to climate. One of the most cost-effective ways to determine sandy zones variations is to use satellite images and related indicators. Among the many vegetation indices, NDVI is one of the global vegetation indices. On the other hand, global warming has had a significant impact on vegetation growth in recent years and has had a significant impact on vegetation dynamics. The purpose of this study was to compare the capability of detecting satellite and climate indices in the changes occurring in Sarakhs plain. That drought has detrimental effects on environmental and human resources, In this research, we are trying to identify the trend of expansion of sandy areas that is a serious threat to the resources available in Sarakhs city, using drought, dust storm and satellite indicators

In this research required data including implemented projects, general statistics and information of the area, layers and topographic maps, meteorological data, satellite images, field sampling and ... were collected and were analyzed with statistical software, satellite image processing and geographic information systems software. The statistical term for studying changes in climate and satellite indices is 15 years, from 2000 to 2015, based on this time base, meteorological data were selected for qualitative, homogeneous and reconstructed Landsat satellite images. The climate indices calculated in this study were SPI and DSI index. That daily data of dust, horizon and daily precipitation data of synoptic stations, rain and evaporometer stations were used to calculate these indices and the satellite indexes include the NDVI and SDI, which use the Landsat ETM + satellite imagery. The results of the calculation of these indices were compared and analyzed.

 Investigation between the values of climate and satellite indices showed, according to climate indices, the years 2000, 2005, 2007 and 2010 are considered as dry years, with NDVI and vegetation levels also decreasing. In 2015, the vegetation level is at its highest level and this means that the amount of vegetation has increased as the rainfall changes and the climate changes to normal or wetter compared to other years. The results of the indices were also compared with the changes of the sandy area for the four periods of 2000, 2005, 2010 and 2015. Results show that the 2005 drought occurred after four years of climate-normal conditions in the region therefore, the area of sandy zones was less than other years of statistical period. Comparison of the surface of the sandy zones in the four studied periods shows in 2015, despite the SPI index showing normal natural climate conditions and the DSI index showing the lowest number of days of dust in the region during the statistical period, the area of sandy areas has increased dramatically due to years of continuous drought. 

 The study of drought index shows that during the study period 2007 and 2015 are the driest and most productive years, respectively. This is also confirmed by the results of the dust index That highest and lowest number of dust storms occurred in the Sarakhs plain in 2007 with 98 days of storms and 2015 with 16 days of storms, respectively. A comparison of land use changes in the Sarakhs plain shows that the highest agricultural land development is 7% in 2010 compared to the previous period and while in 2015 the area has fallen by 12 percent due to droughts. On the other hand, rangeland degradation in 2010 reduces land use by 15% in 2010 Caused by the droughts of 2007-2010. Reduced rangeland and bare land could be another reason, including dryland cultivation in the area. Calculation of the NDVI index for the period 2005-2010 also showed that the amount of vegetation decreased significantly (From 125/69 to 111/53 km2) While in 2015 as an almost normal year, the vegetation rate increased according to the NDVI index. (Approx. 60 Km2) which indicates the effect of drought on the vegetation of the region. In this study, the ability of detecting two climate indices and one satellite index, to study changes in wind erosion zones in Sarakhs plain was studied. The results show that the NDVI index is in good agreement with the SPI and DSI climate indices. As a result, the level of sandy zones varies according to the drought situation, the intensity of dust storms, and the level of vegetation cover in the years studied.

Land use changes are identified as main driver for global changes with considerable effects on the ecosystems, climate and earth planet. At local to global scales, land resources have effective role on the humanity subsistence and ecosystem performance and its health. Changing in land use, degradation of vegetation and habitats are main causes for biodiversity destruction. Such changes are created by natural factors and anthropogenic activities (deforestation, agricultural unsuitable activities, overgrazing, etc.) resulting in land degradation. Rainfall and temperature are the two most important climatic variables which they use to climatic zonation and classification, and these variables are effective factors on the human, natural, economic and agricultural activities. Regarding to great area of the coastal region in Iran, in order to assessing land degradation and desertification, monitoring effective cover, land use and climatic variables is vital, and therefore understanding relationship between land use changes and driver factors are essential.

In this research, we studied trend of land use changes in the coastal regions of southern Iran involving three provinces (Hormozgan, Sistan and Baluchestan and Busher) during period 1998-2019 using Landsat images (OLI and TM sensors). Likelihood maximum method applied to classifying satellite images and then SAVI, as a vegetation cover index, used to show vegetation dynamic and exploring land degradation and desertification trend. In order to map temperature and precipitation, we applied inverse distance weighting (IDW). For predicting land use changes, SAVI, temperature and precipitation, we used CA-Markov automat cell.

Studying land use change trend in the coastal regions of the southern Iran during 1998-2019 indicates Salt land and man-made classes were increased 8.6 and 1.2%, and among all classes these two classes show the most changes, whereas a decreasing trend observed in the vegetation cover (with – 3.5%) and sand dunes (with -6%) classes, and also, a decreasing trend observed in water bodies. Based on the results, an increasing trend (with 0.8%) observed in the class 0-0.2% for SAVI, whereas we found a decreasing trend in the 0.2-0.4% class. According to results, a decreasing trend -0.7 and -8.6% were observed in the < 25.5 C and > 28.5 C classes, whereas 27-28.5% class shows an increasing trend with 9.7%. Studying precipitation changes showed that < 150 mm and 250-300 mm classes show an increasing and decreasing trend, respectively. Based on the predictions for 2039, three classes including salt land, man-made region and vegetation cover land uses show an increasing trend with 0.4%, 1.5% and 0.99% respectively. We observed a decreasing trend with -6.8% in the sand dune land use whereas water bodies have constant trend. Based on the forecasting results for SAVI, we observed an increasing trend 1.8% for 0.2-0.4% class and observed a decreasing trend (-1.7%) in the 0.4-0.6% class. Results showed that 25.5-27 C and 27-28.5 C classes experience an increasing trend (17%) and a decreasing trend (-18%) in 2039, respectively. According to precipitation predictions for 2039, we observed an increasing trend in the < 150 mm and 150-200mm classes, whereas we found a decreasing trend in the 250-300mm and 200-250mm classes, respectively.

Land use changing has an important role in instability ecosystem and its services, and it is an effective factor in direction of land degradation. According to results provided for effective climatic variables (with an increasing trend in temperature and a decreasing trend in the precipitation) changes vegetation cover and result in low SAVI. We can conclude that climatic variables and SAVI are related factors which play important roles in land degradation, desertification and combating desertification in the coastal area. Results of this study are consistent with Salehi et al., 2019; Halebian & Soltanian, 2017; Maher et al., 2018; Alijani et al., 2012.

The land-use change is one of the critical worldwide issues that has caused a problem in natural resource sustainability. The dynamics of land-use and land-cover change (LULC) affected by the anthropogenic activities and climate change in arid areas, were caused environmental degradation of these areas. This process has the negative effects on soil physicochemical properties. Soil degradation is the key component of land degradation that affected by land-use changes. So that it causes organic waste carbon, decreases the soil aggregate stability and structure and, consequently the raises of soil erodibility. So to understand the impacts related to these changes in land-use (LU), assessment of the effects of these changes on soil characteristics is important. Therefore, the current study aim was to investigate the effect of land-use change on physico-chemical characteristics of soil and erosion in Sistan area.

This research has done in Sistan area. This area laid southeastern border Iran and Afghanistan. The Sistan region forms a part of the Dasht-e-Lut and hence an exhibits extreme arid climatic regime. The region is nearly flat and featureless arid plain with an average height of 465–500m ASL in its eastern parts. In this study, at first spatial land-use changes in Sistan area determined. To achieve this purpose, used satellite images. By using the Landsat satellite images related to the years 2001 and 2019, the land use maps prepared, and by comparison approach in Idrisi Selva software, the map of land-use change was extraction. After that, the areas that converted from rangeland to flood-agri and bare land determined and that accuracy were assessed. Infield operation, 60 soil samples were collected from tow depths 0-25 and 25-50 cm in different land-use such as rangeland, flood-agri, and bare land. The Samples were collected in a completely randomized block design. To study the physical properties of soil, by hydrometer method, by the soil texture, and by measuring the mean weight diameter (MWD), the geometric mean diameter (GMD) and dry stable aggregates (DSA), the aggregate stability was determined. Also, the soil moisture and bulk density were measured. To investigate the chemical characteristics, the soil properties such as organic carbon, acidity (PH), electrical conductivity (EC), sodium absorption ratio (SAR), CaCO3, Na, and available K and P measured in the soil laboratory. The soil erodibility index calculated five characteristics, including sand, silt with fine sand, organic matter, soil structure class, and the infiltration rate class of the soil profile. To analysis the mean of parameters among different land uses were used the Duncan test.

The result of the study of physical properties showed that the percentages of sand, silt, and clay particles among the land-use that under study were significantly different. So that by the land-use change from rangeland to flood-agri and bare land, the distribution of soil particle size differently, that consequently the soil texture has changed from loam-silt-clay class in rangeland to lighter class loam-silt and loam-sand in flood-agri and bare land respectively. According to this change, the aggregate stability of soil inland converted from rangeland to flood-agri, and bare land 34 and 45 percent have decreased. Also by land-use change, the soil moisture 18% and 43 % has decreased respectively. The results also showed that the bulk density of soil, acidity, electrical conductivity, Na, CaCO3 and absorption ratio (SAR), increased in converted land-use whereas, the organic carbon and available K soil, have decreased significantly. In addition, after land-use change, the erodibility index has increased significantly (P < 0.05). So that the amount of this index in flood-agri and bare land compared to the rangeland land-use, more than equal 4 and 7 respectively.    

In this study, for the first time, has investigated the physico-chemistry characteristics of soil and erodibility in land converted from rangeland in Sistan area. The results revealed that the conversion of natural rangeland to flood-agri and bare land had negative effects on the measured soil properties. So that the percent of sand has increased, that changed the distribution of soil particle size, and according to that, the soil texture has changed also. This caused the aggregate stability soil to reduce. In addition, by decreasing the soil moisture, the plant growth has limited in this lands and given the high evaporation potential in Sistan area, the evaporation from land surface increased and according to that the electrical conductivity, acidity, Na and absorption ratio (SAR) in converted lands have increased, whereas, the organic carbon and available K soil, have decreased. This process has caused the Soil degradation, that affected by land-use changing. Therefore, the land-use change by destroying the soil structure and land-cover in converted lands, cause increases the potential of erodibility, that given exist environmental crises in Sistan area, has required the suitable planning to principle productivity of lands in Sistan area.