جستجوی مقالات مرتبط با کلیدواژه « دشت سیستان » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

The Sistan Plain for a long time has faced hazards of flood, drought and sandstorm. Also due to existence of abundant water resources it had been one of the important places for men’s placement. So far, no comprehensive study has been done on environmental hazards which would include ways to overcome or decrease their impacts in Achaemenid era. The present survey aims for studying the reciprocal relation between Achaemenid settlements and natural environment in areas based on environmental limitations. This research has been carried out through the descriptive- analytical- historical method using GIS software. After environmental conditions had been studied, variables types and distance from water resources, slope, soil type, Geology and wind were studied and the results indicate surface water resources effective role in settlements placement. The Water resources existence, gentle slope and consequently ease of waterflow down to plain and canals creation capacity to keep suitable distance to river and placement on Alluvial terrace to avoid flood hazards are among the factors turned area to population absorbing one despite shortage of aquifers and reliance on surface water resources. Being located on delta fans would lead to change of the direction of river canals, which causes relocations of settlements.

 Wetlands are valuable water resources that have different stakeholders due to the ecosystem services they provide. Since the dependence of these stakeholders on the wetland is higher in arid and semi-arid areas, changes in water supply in the wetland are more important. Analysis of changes in water resources in relation to wetland stakeholders, in addition, to supporting the life and sustainable management of the ecosystem, is used to address the importance of wetland protection. In this study, to highlight the importance of Hamoun wetland restoration as the only water source in the Sistan plain, the changes of this wetland in relation to stakeholders were investigated. 

 The land-cover classes were determined based on the importance of each class for the stockholders of the wetland. Then, the land-use/ land-cover map of the wetland in the years 2020, 2015, 2000, 1977 was created using Landsat satellite images. The SVM classification method was used to classify the images and produce the land-use/land-cover maps. The anomaly of the climate variables including mean annual temperature and mean annual precipitation were calculated to show the change in climate variables. The changes in water level of Hamoun wetland, temperature, and annual precipitation in relation to changes in the area of each land-use/land-cover class of each group of stockholders were investigated. 

 The results of the stakeholder-related classes show that in 1977 all stakeholders had a good condition in this region and the potential for soil erosion has decreased in this year. In natural conditions, the Sistan plain is a suitable area for residents despite locating in an arid area. But in 2000, due to the lack of water resources, the potential for soil eruption has increased the classes used by stakeholders have decreased and the ecosystem services of the wetland were limited. In 2015, the water body was increased in comparison to 2000, and the area of vegetation and agriculture were increased. The area of bare-land was decreased. Based on these results the stockholders had better conditions than 2000. In 2020, the area of the water body was more than 2000 and 2015. The vegetation and agriculture area were increased in this year. Therefore, the condition of life for stockholders was improved. These results show the importance of Hamoun wetland restoration as the only water source in the Sistan plain. As seen, the changes of this wetland affect the well-being of stakeholders.

 According to the results obtained in 1977, when the temperature and rainfall were better, a higher area of water resources existed. As a result, favorable conditions could be for farmers, livestock, and wildlife. The bare-lands have decreased, thus, the potential for soil erosion in the region has been decreased. In addition, the potential for soil erosion has decreased. Because the soil of the area was covered with water and vegetation. However, in 2000, when the drought occurred, due to the lack of water resources in Hamoun Wetland, the wetland body has changed to bare-lands, and the possibility of soil eruption has increased. In such a situation, because the water body did not exist, the conditions were not suitable for the stakeholders of the region. Especially agriculture, which is the most important occupation of the local people in this area. In case of drought and lack of water resources in Hamoun wetland, the potential of soil erosion increased and, as a result of which dust increases during storms. In addition to economic problems in the region, these factors also endanger the health of local communities. The results showed that after several years of dryness of the bed of Hamoun wetland, with the inundation of the Hamoun in 2020, the level of usable areas for the region's stakeholders has increased. Therefore, the living condition of the people and the wildlife have been improved. Because agriculture and vegetation have expanded, thus the potential for soil erosion has decreased due to the reduction of barren lands. The results of this study show the importance of wetland life in an arid and semi-arid region. With the change of wetland, the level of the lands that are related to each of the groups of users of the wetland also changes. Therefore, rehabilitation and protection of wetland, and water resources management is necessary for sustainable living conditions in the region.

Mapping of wetlands using remote sensing has faced challenges due to different land cover classes and similar reflectance across land cover classes. Synthetic aperture radar (SAR) data have a special ability to detect phenomena because of their penetration capacity, as well as their independence from time and weather conditionsIn this study, radar data were used to map the land cover of Hamoun wetlands in both wet and dry conditions. For this purpose, L-band capacity has been used to investigate land cover classes. Statistical indicators were used for assessing the separation between land cover classesThe images were classified using the method of the support vector machine. The results of the present study show the capacity of the L-band to separate different land cover classes. The results of the accuracy assessment show an overall accuracy of over 80% in preparing the land cover map of the region. Furthermore, because of the penetration of the L-band, it is possible to detect water in the underlying layer of plants. The results of this study showed that the difference between the reflectance of vegetation that their smaller portion is below the water, and vegetation, most of which is above the water is detectable by the L-band. The difference between their backscatter is 6 dB in the HV and about 2 dB in the HH polarization, which indicates the capaity of the HV polarization to separate these two classes.

Desertification phenomenon is not devoted to an especial climate, although its role in arid and semi-arid areas is clearer than other regions. In this research, four criterions of the wind erosion, soil, vegetation cover and climate have been considered for evaluating desertification potential and mapping of desertification intensity using to IMDPA model in ZAHAK Sistan region. Considering to evaluation of effective criterions in desertification of area in the IMDPA model, different indices of each criterion were evaluated and information layers of indices and criterion were provided. Results indicate that desertification intensity classified to information layer of wind erosion in two classes of the high (62205 ha) and very high (21309 ha), information layer of soil criteria in the two classes of the low (39121 ha) and moderate (44393 ha), data layer of vegetation cover criteria in the four classes of the low (24756 ha), moderate (5649 ha), high (14106 ha), and very high (39003 ha), and information layer of climate in the one class very high (83514 ha). Final map of the desertification intensity of area for information layers combination was provided using to geometric average. Evaluation results of the desertification potential of area indicate that 36.4 % equation 30405 hectare in the moderate level and 63.6 % equation 53109 hectare in the high level of desertification are included. Numerical value of criteria show climate criterion to numerical value 3.88 is the most effective factor in desertification intensity of area. Weighted average of desertification potential is related to severe class of desertification (2.74) in area of study.

Accessibility to a major portion of information about vegetation cover function of ecosystem is provided by the way of autecological study of plant species. Autecological study of Desmostachya bipinnata carried out in Sistan plain. This species is a perennial plant from Poaceae. For autecological study of D. bipinnata,at first vegetation habit of this species in Sistan plain was determined. Then, ecological characteristics such as climatic and edaphic characters of habitats, root system, phenology, reproduction, preference value and chemical compounds were assessed. The results showed that this species grows intensively in north eastern parts of study area. Based on the collected data in several years, annual rainfall of the study area is 60.8 mm and mean annual temperature is 22 0C. This species appears on soil with loam and sandy loam texture, pH of 8.03 – 8.31 and salinity of 10 – 60 ds.m-1. The plant has a adventitious root system and rhizome that penetrates in the soil about 2 meters. Root has a lot of subsidiary branches in soil surface. At different habitats, canopy cover of this species was about 14 – 28 %. Vegetation growth stage of Desmostachya bipinnata usually starts in late February and flowering complete at May and seed ripening start at July. Above ground materials of Desmostachya bipinnata contains 7.56 and 6.71% crude protein in their leaf and stem, respectively. Preference value of this plant is 25% for sheep and goats. This species has a high level of resistance against grazing and relatively harsh natural conditions. With above mentioned characteristics, this plant is a suitable species to be used in management and amendment programs for Sistan plain.