فهرست مطالب لقمان شیرزادی

The annual loss of soil in the world is about 75 billion tons. In Iran, soil erosion is one of the most important environmental problems, and in Iran's catchments, soil erosion increased by 800% between 1951 and 2002. The significant decrease in the performance of Iran's catchments due to a large amount of erosion indicates the increasing necessity of monitoring and following up on this destructive phenomenon. Dendrogeomorphology is a technique that has been very successful in describing and determining geomorphological processes. Dendrogeomorphology is a very flexible method to assess soil erosion and can be used as a data source to determine the reliability of data obtained from direct estimation techniques. The purpose of this research is to investigate the state of sheet erosion in the Nachi watershed using the dendrogeomorphology technique on the oak tree's protruding roots as the region's dominant species. Considering the limited nature of such studies in Iran and the very fragile situation of the studied area, and the risk of filling up the reservoir of Zrebar Lake, which is very important from the point of view of the environment, it is necessary to study the situation of sheet erosion and soil wastage and sediment trans.

In order to achieve the research objectives, after collecting and preparing the primary information, including written information, statistical data, maps, and pictures, a preliminary area survey was carried out, and sampling sites were selected. The samples were prepared according to the program, based on the status of the catchment (according to the land use of the catchment and the direction of the range, the desired work units were selected in places with exposed roots). Based on this, different samples were taken in two different forests, agriculture uses, and western, eastern, and southern directions. All the samples were prepared from the oak tree species, which is the absolute majority in the study area. Finally, 64 samples were selected from the collected samples that could analyze the growth rings' anatomy. Discs harvested from the roots were used to reveal the vegetative rings of the discs by polishing and cutting the surfaces. Using a sanding machine, it was gradually polished with different grades to clear the growth ring border. Then, the disks were measured in the laboratory to determine the first year of root emergence and to determine the width of vegetative rings using a Lin-Tab 5 device equipped with a binocular microscope and specialized T-Sap chronology software with an accuracy of 0.01 mm.

This research showed that in the Nachi catchment, surface soil erosion in agricultural use (average erosion rate 2.43 mm per year) compared to forest use (average erosion rate 0.6 mm per year) is about 4 times. The results of the statistical tests also showed that the type of land use affects the average annual surface erosion rate in the studied basin. Also, this study found that different geographical directions do not affect the average annual surface erosion rate of the Nachi catchment. Comparing erosion values in agricultural and forest use shows the importance of natural covers' protective and important role in preserving the soil and preventing its erosion and wastage. Various studies in the world and Iran have shown that in recent decades, there has been an increasing increase in land use changes, that these changes have the basis of increasing runoff and affecting the amount of soil loss, comparing erosion in the agricultural area with the forest area, showing the protective and important role of the covers. Natural and forests have a valuable role in preserving the soil and preventing erosion and wastage of soil.

The results of this research reveal the necessity of paying more attention to studies on the possibility of modification and change of land use in these areas. The change in land use and the negative effects caused by human interference are not only in the basin itself but also in places outside the occurrence of erosion in the form of accumulation on high-quality agricultural lands, pastures, water storage sources, and irrigated canals. Also, the creation of pollution by sediments and heavy metals and accompanying chemicals, especially the threat to the very fragile ecosystem of Zrebar Lake, is more evident today than ever before. It is suggested to use another method parallel to this method in future works to validate the obtained erosion rate. In future studies, sampling should also be done from the northern slopes for a more detailed investigation of the effect of the slope directions on soil erosion.

One of the most important factors in the development of a region is the availability of sufficient water resources and its quality status for various uses. Due to Iran's arid and semi-arid climate and water shortage, it is essential to pay attention to the water quality of its rivers. Pishkooh-Taft Basin is an important watershed inthe east of Yazd province and located between 54º 15’- 53º 40’ east and 31º 50’- 31º 30’ north. Tezerjan fault of Taft Continues to the west with the northsouth trend. There are 3 gauging hydrometric stations in this area. TM images13 October 1991 and ETM+ 15 October 2011 of Landsat 7 were used to change the detection of the land use. In addition, to examine the physical and chemical properties of water in Taft, Islamiyah and Feyz-abad stations during 1361 to 1390 years were used. First of all, the method which was performed included geometric correction for fixing errors and adapting the images by the Digital topographic map scale of 1: 25,000. Then, land use was extracted by supervised classification, training samples, and maximum likelihood techniques. Next, to report the physical and chemical properties of anions and cations, TDS, conductivity and pH of the water, the stations were investigated during 1361 to 1370 and 1371 to 1390 years, and the data was evaluated using Mann-Whitney statistic. The finding of land use showed that the wasteland and pastures were dominated and there was an increase in pastures compared to 1370, but there was a decline in covered meadows in 1390. To examine the relationship between land use changes and water quality, the elements of the water was dealt with. For this purpose, the physical and chemical properties of anions and cations, TDS, conductivity, and pH of the water between the years 1361 and 1370 and 1371 and 1390 were studied. The results of Mann-Whitney statistic in different elements and three stations showed that the difference between these two periods was significant in Taft station. Discussion and conclusion: The effect of land use on water quality change over the period of 30 years showed a relative decline of water quality in Taft station and to some extent in Islamiyah station. This can be attributed to the increase in land occupancy and the existence of agricultural lands in Taft and Islamiyah Stations. However, in Feyz-abad station, due to the lack of habitat and agricultural lands and an increase in water flow, there was no decrease in water quality. On the other hand, the examination of the changes in the height of the stations showed that Taft station was in the outlet of the basin and had the minimum height which could affect the quality of the water. Several researchers (Townsend & Popcorn, 2009; Kazi et al., 2009; Travka, 2004; Orion, 1390) have studied the effect of reduction of water quality on increasing agricultural lands and urban areas which are in line with Taft station.

As one of the fauna and flora reservation sites, hyrcanian forest ecosystems have experienced sever destruction during recent decades because of the improper land uses. Use of fallout radionuclide, particularly Cs137, is one of the trusty methods in soil erosion rate. The purpose of this research was to estimate soil erosion rate in Hyrcanian forest heights in Ziarat catchment using radioactive element Cs137. Therefore, first Cs137 inventory was calculated in three land uses including forest, rangeland, and cultivate lands. After that, the erosion and sedimentation rates for each land use were determined using mass balance II model for cultivate areas and intuition and diffusion model for uncultivated area. The impact of land use on the soil erosion and sedimentation rate and organic carbon storage were investigated using ANOVA. The research found that the annual Cs137 inventory estimated was 575, 286, and 258 Bq/m2 in the forest, rangeland, and cultivate lands respectively. The maximum and minimum erosion rate had occurred in cultivated land by 39.8 and forest land by 5.2 ton/ha/y respectively. In addition, there was a positive correlation between erosion and sediment rate and organic carbon storage. The findings of this research can be used for sustainable management of Ziarat Catchment.