فصلنامه پژوهش های فرسایش محیطی
سال دهم شماره 3 (پیاپی 39، پاییز 1399)

Coastal environments are one of the most sensitive environmental systems under the influence of dominant hydrodynamic processes. Coastal changes and evolution are occurring very fast. Coastal areas are now gradually becoming known as severe natural and man-made disturbances, including sea levels rising, coastal erosion and sedimentation, and over-exploitation of resources. A deep understanding of the regionchr('39')s coastline dynamics (erosion and sedimentation) is essential for the proper planning, land use, and conservation strategies to reduce potential losses. Development of the southern coast of Iran has not only destroying the geomorphological landforms but also led to a change in the process of erosion and sedimentation in coastal areas. Understanding the behavior of the coastline would assist the management and planning of coastal facilities construction and determining the margins of the coast. Today, remote sensing methods, while being economical and promoting high accuracy, make it possible to continuously observe and manage beaches. These benefits have led to the increasing use of satellite imagery to determine the accurate position of the coastline in the world. The goal of this research is the investigation of periodic change of the Oman sea coastline from 2000 to 2109 using the Landsat time-series dataset.

The study area in this article is related to the coastal line between Gwatr port and the Strait of Hormuz. The years of 2000, 2009, and 2019 were selected for the periodical coastal changes analysis in the last two decades. According to the time interval, the images of two Landsat 5 and 8 sensors were selected. The numbers of images that were mosaiced in each period are 15 scenes. Then, to discrete the water and land border, the modified normalized difference water index (MNDWI) in ENVI 5.3 software was used. This indicator is a combination of Green and Mid-Infrared bands. After applying the water and land boundary discrimination index, shoreline digitization in ArcGIS software has been done manually and with high accuracy. Thus shoreline from satellite images extracts by the Digital Shoreline Analysis System (DSAS). This method calculates the shoreline mobility and its changes based on satellite imagery. DSAS v4.3 is an extension developed by the US Geological Survey, which is adding to the ESRI ArcGIS 10.3 software. It is calculated the number of shoreline shifts from the past to the present. In this study, shoreline shifts are calculated using four data analysis methods (e.g., EPR, LRR, LMS, and NSM).

Identification of erosion and sedimentation transects indicates that the shoreline has been progressing ahead in most areas of coastline. During the last twenty years, 172.47 km of coastline length increased which is indicated by coastline sedimentation. These changes are apparent in most transects; 49% of transects were sediment, and 36% were erosive transects. The highest progress of coastlines observed in the Yekboni estuary (river mouth) area, western Jask Kohneh area which the sedimentation rate has reached 295.25 m/y. The sedimentation rate in the area of Chakha estuary, Gurdim, Gwadar port, and Bahu estuary has been above 100 meters per year. Also, the area between Brys to Pasabander and the upper area of Gashmi and Kartan estuaries has been high. The reasons for this can be attributed to the dock construction and the large volume of sediment in the estuaries by rivers. The highest amount of erosion rate in the nose of Jask port was 178.15 meters per year. The construction of stone walls in this area is the main cause of severe erosion. The length of the coastline in the year 2000, 2009, and 2019 were 1228.54, 1397.56 and 1394.08 km, respectively. The change of beach length is observed from 2000 to 2009; 169 km, from 2009 to 2019; 3.47 km, and from 2000 to 2019; 172.47 km.

The nature of coastlines is dynamic; therefore, the management of such sensitive ecological environments requires accurate time-series data. In this research, Landsat satellite imagery of TM and ETM sensors in the three periods of 2000, 2009, and 2019 have been used to detect shoreline changes. Coastal changes and spatial analysis are extracted by using the DSAS Extension in ArcGIS software. The length of the coastline in the year 2000, 2009, and 2019 were 1228.54, 1397.56, and 1394.08 km, respectively. Maximum sediment/erosion rates have been observed 290.25 and -178.15 m per year in the Yekboni estuary area and the cape of Jask port respectively along the coast of the Oman Sea. During twenty years, the eroded areas have experienced a recession, an average of 11.28 meters per year. The reasons are the rocky shores of the Oman Sea, desert landforms of some beaches and their exposure to severe wind erosion, dunes movement, and human activities. The areas of the coast where sedimentation was higher had an average of 9.74 meters per year. Human activities such as port construction and large volumes of sediment at the mouth of rivers have caused part of the coast to move toward the sea. In general, 36% of the study area has been eroded, and 49%  has been more sedimented. Remote sensing and geological techniques with DSAS will be useful methods for monitoring long-term coastal changes and provide a comprehensive view of coastal erosion and sedimentation patterns. Continuing the coastline monitoring is necessary to observe future changes and is economically significant.

Erosion and sedimentation in watersheds has caused many problems in healthy and sustainable use of water and soil resources, and is considered as one of the major threats to global economic and environmental sustainability. The increase of sediment yield in watersheds has consequences such as dam filling, river diversion, conductivity capacity reduction of waterways and water facilities, and changes water quality for drinking and agriculture. So, spatial modeling and prediction of sediment yield in watersheds is very important, especially in arid and semiarid environments. In this regard, we should consider the whole process of erosion (destruction, transport and deposition), so that the relationship between inputs and outputs of the system are understood well. The Systematic view of geomorphology on the issue of erosion and sediment yield can be very effective and useful, considering the relationship between forms, materials and processes in the context of landform components. Recognizing the different processes of erosion and sediment production in the range of landform components can provide a more comprehensive and practical view of these processes in watersheds. Given the importance of the issue and the need to use digital elevation models in order to model the sediment yield variations, which have been recently considered, this study intends to analyze the relationship between the Landform components distribution and sediment yield in the Qarasu watershed, N.W. Iran. 

We use extensive and integrated statistical analysis of non-parametric (χ2) and parametric (regression) methods to understand the relationships between sediment yield (S.Y) variation (dependent variable) and distribution of components or classes of landforms (independent variable). 19 sub-watersheds, which have sufficient and reliable data of sediment yield (ton/y), were selected for analysis. As catchment area acts as a misleading variable in the  relationships between sediment yield and physiographic variables, a specific sediment yield (S.S.Y) ​​ (ton/km2/y) was used as a dependent variable. Also, an independent variable (landform components) was extracted of digital elevation model (DEM) with a resolution of 30 m. 6 landform classes, including 1- ridge 2- upperslope 3- midslope 4- toeslope 5- flat 6- valley, were delineated in the geographic information system (GIS) environment. Then, the percentage area of the landform classes was calulated as an independent variable. In order to perform the nonparametric test, it was necessary to convert the variables from quantitative to categorical and qualitative form. Classification of S.S.Y was done in 2 categories (low, high) and 3 categories (low, medium, high). Also, the classification (categorization) was done for the independent variable. These transformations and statistical tests were performed in the SPSS environment. The significance level of qualitative and quantitative tests were ≤ 0.05. It should be noted that the classes can be assumed to be both nominal and ordinal, ie low (1), medium (2) and high (3). Therefore, statistics related to the crosstabs can be obtained for both nominal and ordinal scales, indicating the quality and quantity of the relationships. On the other hand, the correlation test can be done in two ways, Pearson and Spearman.

In the first step, results of the non-parametric analysis showed that there are significant relationships between the distribution of S.S.Y classes and the Landform components classes expect 2 landforms: valley and ridge. meanwhile, the importance and certainty of the relationship between midslope and S.S.Y was determined in respect to repetition of significant relations during three χ2 tests. In the next step, the results of Pearson correlation analysis showed the positive correlation between ridge, midslope, valley landforms and S.S.Y. On one hand, and the negative correlation between upperslope, lowerslope and flat ladforms and S.S.Y on the other hand. The highest and lowest correlation coefficients were observed in midslope (R = 0.4) and upperslope (R = -0.03) components, respectively. The Results of the latest test, the Spearman correlation test, were indicative of similarities with the χ2 test, showing the significant relationships between flat, toeslope, midslope landforms and S.S.Y. Although more contribution of the midslope in sub-watersheds area and higher difference among sub-watersheds in terms of midslope contribution influence its relations with S.S.Y,("but" not needed) close and direct relationship between the midslope area and S.S.Y is attributed to high sediment supply and the occurence of dynamic sediment transport within this landform component.

Erosion and sediment yield (S.Y) within watersheds due to their extensive environmental dimensions as well as the complexity of the erosion process (destruction, transpotation and sedimentation) are the focus of systematic approach of geomorphology to provide useful and comprehensive knowledge of the inputs and outputs of the watershed system. Dividing the catchments into landform components and establishing a relationship between their distribution and S.Y of the catchments can be a key solution in this regard. In this research, applying the approach through both parametric (Regression) and non-parametric (Croostabs) statistical analyzes showed that important information about the relationships between landforms and S.Y can be acquireed at synthetic statistical method. Although the relationship between the independent and dependent variables in the qualitative test had superiority to the quantitative test in terms of the significance of the relationship, the type and strength of the relationship was determined by regression analysis. Meanwhile, the existence of a close and definite relationship between miidslope distribution and S.S.Y refred the necsessity for geomorphic prioritization of watershed management and soil protection measures in this landform class. In general, it seems that the classification of variables nominally and ordinally reduces the effects of residuals and makes the relationships of variables more meaningful. Furthermore, the distribution of landform components among the catchments and the existence of homogeneity/heterogeneity in this regard affect the quality and quantity of relationships, which is necessary to pay attention to in regional analysis of S.Y variations.

Natural hazards are naturally occurring phenomena that have disastrous effects on humans and have different categories, but the one that concerns us and has posed significant problems is “erosion”. Sedimentation in water resources and reservoirs of dams, loss of agricultural lands and loss of fertile soil are among the effects of erosion. As a result of the negative impacts of erosion, extensive research is being carried out in different parts of the world regarding different erosion protection methods and the use of insulated and semi-insulated surfaces. Water is a non-renewable resource that is used for many different purposes (from agriculture to afforestation to domestic use), and unfortunately many countries are facing water shortage due to the decline in groundwater availability. As a result, a sustainable groundwater and rainwater management is required. One of the sustainable plans made, is rain water harvesting (RWH) and the purpose of this study is to investigate the performance of different levels of catchment in rainwater harvesting. Based on the results, the best level that creates the most runoff can be selected and introduced to produce runoff. In RWH system, rainwater is stored during wet periods and used efficiently during dry periods as a supplementary irrigation to eliminate water shortage of the plants. This issue is of great importance in Iran as the climate is arid and semi-arid and the annual rainfall is very little.

In this study, three types of catchment surfaces were selected to collect rain water and in return three replications were considered for each of them. The areas selected were all square in shape and 49 m2 in size and were all build on a slope of 20%. The three reservoir surface treatments included 1) Impermeable surface 2) Natural surface with filter 3) Natural surface (control) A total of 9 plots were created, which were put together in a completely randomized statistical design. To measure rainfall runoff, a 200-liter barrel was installed downstream of each plot and the runoff generated by the pipe was directed into the barrel. A rain gauge was installed on the site to measure the depth of rainfall. After each storm leading to runoff production, the height of the runoff and the volume of water collected inside each barrel were accurately measured. The surface runoff coefficient in each of the treatments used was determined by dividing the runoff volume to the system level. Statistical analysis of data including mean comparison test along with descriptive analysis of data and comparison of results was performed. Correlation coefficient and regression analysis were used to investigate between rainfall depth as an independent variable and runoff depth as a dependent variable.

The results of the correlation between the amount and intensity of rainfall with the amount of runoff produced in the treatments shows that the reaction of all treatments to the storms was almost the same, although impermeable treatments were more correlated than the other two treatments. In each rainfall, the highest amount of runoff was collected in the impermeable treatment and the lowest in the natural land treatment. The results of this study show that with increasing the depth of daily precipitation in the region, their frequency decreases so that only 1% of the frequency of daily precipitation is related to precipitation of more than 25 mm. Rainfall of less than 5 mm, on the other hand, has only led to runoff production at impermeable surfaces. This shows the significant impact of impermeable surfaces on runoff from shallow rainfall. Occurrence of rainfall with shallow depth and intensity at natural levels is mainly absorbed by the soil and its runoff production is minimal. That is, the natural surfaces of the earth, depending on the texture of its soil, store part of the rainfall. Therefore, one of the advantages of using insulation surfaces can be considered in the production of runoff at minimum rainfall.

In conclusion, this study was conducted to investigate the effect of using different management methods in the context of catchment surface systems in reducing sediment erosion and increasing vegetation. The results of this study showed that by making the surface of water intake systems impermeable, sediment erosion would be reduced. In order to model the depth of extracted runoff in catchment areas in semi-arid climatic conditions, the average runoff coefficient was calculated in different treatments of catchment surface systems. The results showed that the average runoff coefficient in the impermeable treatment during the studied rainfall was 66.4. In other words, 2125 cubic meters of water can be extracted from each hectare of impermeable surface in an area with an annual average of the research site (320 mm), which can provide the required water for 15 hectares of rain-fed almond orchard with supplementary irrigation. Occurrence of rainfall with shallow depth and intensity at natural levels is mainly absorbed by the soil and its runoff production is minimized. Therefore, the advantage of using impermeable surfaces can be considered in the production of runoff at minimum rainfall. This issue, due to the frequency of rainfall events with amounts of less than 5 mm in semi-arid regions of the country, necessitates the use of insulation surfaces.

Dust has a significant impact on radiation budget, global biogeochemical cycles, soil structure, atmospheric chemical composition, air quality and public health. Natural and human factors have increased the frequency and severity of dust storms in the country in recent years. The most important natural factors are rainfall, drought persistence and global warming, and human factors include surface water control, agricultural development and uncontrolled groundwater consumption, land degradation and excessive use of climatic and ecological potential of the region. These factors can lead to the development of dust centers and increase their activity.

This study was conducted in Central Iran, where one of the most important environmental problems in this region is the occurrence of destructive dust storms. Arid and semi-arid climate, bare soil with sparse vegetation and severe storms are the characteristics of the central region of Iran that prepare the conditions for the occurrence of dust storms. The provinces of Kerman, Yazd, Isfahan, western parts of Sistan and Baluchestan, Semnan province, Khorasan Razavi are directly affected by the consequences of these events. In order to analyze the frequency of dust days, dust codes taken from 37 synoptic meteorological stations with longer statistics were used. For each station, the number of dust days on an annual scale in the statistical period 1999 to 2018 was extracted. In order to analyze the frequency of dust days, Professional5 Easyfit statistical software was used, based on which the most appropriate statistical distribution function for each synoptic station was selected. EasyFit Professional software fits data into 61 distribution functions. Then, using the Kolmogorov-Smirnov test, the most appropriate probability distribution function was determined.

The results show that the statistical distribution of Johnson SB was found to have the highest frequency in the study area. The Log-Logistic (3P) statistical distribution ranks next. A number of stations such as Bam, Kerman, Nain, Arak, Saveh, Mahallat, Zabol, Semnan, Qom, Zahedan, Yazd and Tabas can have more than 100 days of dust in the return period of 50 or 100 years. Also, Tabas, Qom, Yazd, Zabol, Zahedan and Arak stations show at least 50 days of dust every year. The zoning of dust days with a return period of 5 years also shows that the southeastern parts of the study area, as well as areas in the center and northwest of the basin, can be identified as sources of internal dust. The zoning of dust days with a return period of 25 years shows that the southeastern parts of the study area below the Loot basin and also the northeastern parts of the study area below the central desert basin (desert plain) can have a maximum of 225 dust days in the return period. The results of frequency analysis of dust days with a return period of 50 years show that in some areas of the study area, more than 276 days of dust per year can occur and these areas are identified as dust sources in the study area.

In recent years, dust events in the West Asian region have occurred with greater frequency and intensity. Dust phenomenon in Sistan and Baluchestan, Kerman, Yazd, Isfahan, Semnan and Khorasan Razavi provinces is one of the most important challenges.  Identifying and predicting dust source in these areas are of great importance.One of the most important forecasting methods in different return periods is the use of statistical distributions. In this study, using 61 statistical distributions and Easyfit Professional 5.5 software, the most appropriate statistical distributions were determined using the Kolmogorov-Smirnov test, the most appropriate probability distribution function in the study area. Johnson SB statistical distribution was found to have the highest frequency in the study area; also, Log-Logistic (3P) statistical distribution is in the next rank. Then, using statistical distributions to identify indicator stations, the number of dust days in the return period was estimated from 2 to 100. The results showed that Bam, Kerman, Naein, Arak, Saveh, Mahallat, Zabol, Semnan, Qom, Zahedan, Khoor and Biabanak, Yazd and Tabas stations according to the analysis of the frequency and number of dust days estimated in the annual return period to Index station were identified in the study area. Also, changes in the spatial pattern of dust in the return periods of 5, 25 and 50 showed that the southeastern parts of the study area of Kerman, Sistan and Baluchestan provinces due to the proximity of Hamoon and Jazmourian wetlands and 120-day winds of Sistan as one of the dust centers have been identified.

Main portion of organic wastes usually is burned or left in fields or landfills, which leads to pollution of soil, water, and air. The use of organic wastes for biochar production can be considered as a solution for the above-mentioned problems. Biochar is a rich carbon material which is produced via pyrolysis of various biomasses in anaerobic or limited oxygen condition. Inspire of world attention to biochar application in soil, effects of particle size, and method of biochar application has also been studied in a few pieces of research. Biochar is mixed with surface soil without the selection of a given class of particle size in most researches. Furthermore, olive kernel is considered as the main waste in agro-industrial integration, which often has no special use and is left in nature. Therefore, the use of olive kernel as a feedstock for biochar production can be a great approach for the management of these wastes and improvement of soil quality. Therefore, the purpose of this research is: 1- biochar production of olive kernel and its characterization and 2- A study of biochar addition effects with different particle sizes as the suspension on soil physical and erosion related properties of an erosion- prune soil.

An erosion-prone slit clay soil was sampled as undisturbed via metal cylinders (diameter and height of 25 and 15 cm, respectively) from 0 to 10 cm of soil located at Rudbar, Southern of Guilan, Biochar was produced of olive kernel at 650 C○ and 2 hours and 45 minutes. Biochar yield was calculated based on produced biochar per unit weight of feedstock (olive kernel). pH and electrical conductivity of olive kernel was determined at 1:5 (olive kernel powder : water) and 1:20 (biochar : water). Carbon, hydrogen, and nitrogen content and Fourier Transform Infrared Spectroscopy of olive kernel and biochar were assessed through Elemental Analysis and Fourier Transform Infrared Spectroscopmeter, respectively. Biochar was milled, and with particle size of 53-250 and 250-500 micron at 1 and 2 weight percent as a water suspension was injected to cylinder containing undisturbed soil. Four cylinders without biochar was also considered as a control treatment. Soil cylinders were located at a greenhouse at 20-25 C○ for 10 months (300 days) and their moisture was held approximately at 70 percent of field capacity. At the end of the tenth-mont of incubation, samples were provided of cylinders, and some soil properties and soil loss were studied.

The studied soil had a silt clay texture. Containing an abundant amount of silt can increase sensitivity of soil to surface crust formation. Carbon and hydrogen content was increased and decreased 44 and 69 percent, respectively as a result of olive kernel transformation to biochar. Result of Fourier transform infrared spectroscopy also showed olive kernel transformation to biochar has led to decrease of volatile organic components and increase of carbon and nitrogen content.
Results of this study showed that biochar with coarser particle size (250-500 micron) led to more increase of hydraulic conductivity compared to ones with finer particle size (53-250 micron). Although, biochar application result in aggregate stability improvement and runoff production decrease, biochar with particle size of 53 to 250 and 250 to 500 micron had no significant difference compared to each other. Runoff delay time and sediment yield were more and less, respectively in all biochar treatments in comparison with control (without biochar). The most increase of runoff delay time (5.65 minutes) was also was observed at 2 percent biochar application level of 250 to 500 micron. Biochar with particle size of 53 to 250 and 250 to 500 micron result in more decrease of sediment yield at 1 and 2 percent biochar application levels, respectively.

Generally, the results of this research showed that the transformation of organic wastes such as olive kernel can be considered as a useful approach to manage this kind of wastes. Olive kernel biochar with having less hydrogen to carbon molar ratio compared to feedstock (olive kernel) has long-term persistence in soil.  Furthermore, olive kernel biochar application as a suspension in an erosion-prone clay slit has positive effects on improvement of aggregation and hydraulic conductivity, and potential erosion decline.  Therefore, biochar production of olive kernel and its application as a suspension not only prevent soil degradation in time of application in soil but also lead to long-term carbon sequestration, improvement of important properties influencing soil quality, and sustainable use of unused wastes. A Study of biochar particle size and application-level also showed a specific type of biochar does not exert similar effects on different properties of a given soil, and particle size and level of biochar application must prescribe according to the desired goal.

The most suitable method to reduce wind erosion is to create and increase land cover vegetation. Vegetation increases the surface roughness, which reduces wind speed and the sediment carrying capacity. Therefore, the sediments transported by wind are deposited on the ground and in the vicinity of the vegetation. However, each plant species, according to its characteristics, has a special effect on the reduction and control of wind erosion. Selection of compatible and resistant plant species in dry and desert conditions is necessary for this purpose. But, it is necessary to determine the impact of each vegetation type on it. Therefore, in areas where vegetation has been used to control and reduce wind erosion, it is necessary to determine the impact and role of each type of vegetation on the amount and control of wind erosion to identify the most effective type of cover.

In this research, the effect of plant species that are used in non-desertification projects has been investigated in the critical area of wind erosion in the Nodeh Pashang region of Gonabad county with an area of 94818 hectares. For this purpose, according to the species type, time of planting, area of planting, amount of canopy, species density, and physical and climatic conditions, six homogeneous areas were selected. These six areas were covered by Haloxylon sp, Seidlitzia rosmarinus, Nitraria schoberi, Atriplex canescens, mixed of the species and not covered. The changes in the soil surface profiles were measured by installing 18 erosion pins in two replicates in an area of 100 m2 in each area for 81 dust and sand storm events during the 2018 and 2019 years. Also, the events were divided into two groups of dust storms (severe events) and blowing dust events (ordinary events). In the final, the changes in the soil surface profile were investigated in each area and event type. Also, statistical comparisons were made between areas for each event type.

Base on the results, the area of Haloxylon sp had the highest percentage of canopy cover (18.4 % ). Also, the mixed species-area had the highest plant density. The results confirmed the effect of vegetation in desert areas in reducing wind erosion. The greatest effect on reducing wind erosion was observed in the areas covered with Haloxylon sp, Seidlitzia rosmarinus, mixed of the species, Atriplex canescens, and Nitraria schoberi, respectively. Based on the results, the mean of wind erosion in the uncovered area was 83.6 ton/h; whereas, sedimentation has taken place in the covered areas except for Nitraria schoberi area. This difference was also statistically significant at the level of one percent. In the severe events, the mean wind erosion in areas with vegetation cover was 23.4 ton/h and in the uncovered area was 118 ton/h. In this type of event, the protective role of Haloxylon sp was higher than others, and as a result, erosion and sedimentation values were equal. In the ordinary events, the most protective role was observed in S.rosmarinus and N.schoberi area with 52 and 37.5 ton/h, respectively. Based on the results, increasing the canopy is an effective measure to control and reduce wind erosion.One of the main causes for more impact of the Haloxylon sp on wind erosion can be for more canopy cover area than other species in the studied area. Because the role of wind erosion control is more related to the percentage of vegetation canopy cover. Also, the results of this study showed that species type could be effective in wind erosion control. Based on the results, the protective effect of different species varies with the event intensity. In the severe events, the protective role of Haloxylon sp and mixed of the species was higher than other areas in the studied area; whereas, in the ordinary events, the protective role of Seidlitzia and Nitraria areas was higher than other areas. These results showed the role of species height in reducing wind erosion.

The results showed the best way to control and reduce wind erosion is to create and develop the vegetation in the critical area of wind erosion. The most important reason for this result is to increase the surface roughness due to the vegetation development, which reduces the velocity and sediment carrying capacity of the wind. The results showed that increasing the amount of vegetation canopy increases the control role in wind erosion. However, the control role of plant species in wind erosion is not the same. Therefore, the selection of suitable species to control wind erosion and sediment is required. Among the effective species in controlling wind erosion, the role of Haloxylon sp in controlling wind erosion and soil stabilization has been observed more than other resistant species. Furthermore, the control role of one species in wind erosion is not the same on all events. In ordinary events, shorter and broader species on the land surface have a greater impact on wind erosion control. These species reduce the wind velocity near the ground surface and causing the sedimentation of wind sediment; whereas, taller species will have a greater impact on wind erosion control in severe events.