عنوان مقاله [English]
Introduction: Global land use has significantly changed in recent decades. However, in order to monitor and survey of the ecological consequences of human interventions, quantification of land cover change is necessary. Wetlands are the most sensitive ecosystems to changes in land use and unique ecosystems with high diversity of flora and fauna. Ecological conditions and water quality of the wetlands are related to the characteristics of the land, including the type and ratio of land cover in the all watershed. Therefore, monitoring of land use and land cover changes is necessary in order to manage, control and take timely measures to reduce the threats and damage caused by the changes in the landscape. Whereas the land cover changes in Golpayegan Shoor Wetland have not been studied, so the main purpose of this study is to monitor land cover changes in this wetland in central of Iran. In fact, In the present study, the land cover of Golpayegan wetland for 1972, 1978, 1988, 1998, 2008 and 2018 was prepared using Landsat satellite images and the change was revealed during this period (46 years).
Methodology: Golpayegan Shoor Wetland, located in the northern plain of Golpayegan, is a part of the catchment area of Namak Lake and the only wetland ecosystem of Golpayegan city. Six land use classes were identified in the region: 1- Residential lands (urban, industrial, road, etc.), 2- Agricultural lands, 3- Water resources, 4- Dense rangeland, 5- Medium density rangeland 6- Low density rangeland - barren. Then the educational samples were digitized on the screen by digitizing the points. In the second stage, the resolution of educational samples was done. The third step is to classify satellite images using the maximum likelihood classification method. Six time periods of Landsat satellite imagery belonging to the mentioned years (1972, 1978, 1988, 1998, 2008 and 2018) were selected to analyze land cover changes. In order to geometrically correct the satellite images of the study area, topographic maps were used to perform the first-order polynomial equation with a scale of 1: 25000 and 20 ground control points. Atmospheric correction was performed using dark-object subtraction method. In order to detect and analyze changes during the studied periods, land change modeler was used in TerrSet software.
Conclusion: Kappa coefficient in 1972, 1978, 1988, 1998, 2008 and 2018 were 8.08%, 84.45%, 85.79%, 90.12%, 92.67% and 93.85%, respectively. In the study period, dense rangelands decreased during the years 1978-1972 with an annual rate of -1.86% percent (9795 hectares). Medium density rangelands and residential areas also showed an increase of 13,460 and 1,080 hectares with annual rates of 2.63 and 11.84 percent, respectively. The annual growth rate is 6.33 percent in irrigated areas, and the rate of increase is 142.2 hectares in this land use. The rate of reduction is 4050 hectares in low density pastures with an annual reduction rate of 16.3%. Between 1972 and 1978, there were 499, 394, and 194 hectares of net conversion of agricultural land use, dense pastures, and low-density-barren pastures to residential areas, respectively. The rate of net change is 70, 75 and 9 hectares from agricultural lands, medium density pastures and low density-barren pastures to irrigated areas, respectively. The highest net change is 13333 hectares from dense rangelands to medium density rangelands. Residential areas, agricultural lands and low-density-barren pastures also showed an increase of 1420, 14540 and 2860 hectares with annual rates of 5.1, 9.2 and 7.7 percent, respectively, during the studied years. Medium-density rangelands also decreased from 92,000 hectares in 1978 to 83100 hectares. Dense water areas and pastures have also decreased during this period, with annual rates of -7.87% and -1.12%. Dense pastures of 1545, 11246 and 3752 hectares were converted into residential areas, agricultural lands and low-density-barren pastures, respectively. The rate of net change is 119, 2018, 11246 and 751 hectares from irrigated areas, medium density pastures, dense pastures and low density-barren pastures to agriculture, respectively. 91, 1545 and 182 hectares of medium-density rangelands, dense rangelands and low-density-barren rangelands were converted to pure residential areas. During the years, the rate of net change is from medium, dense and low-density pastures to irrigated areas as 107, 10 and 1 hectare, respectively.
During this period, residential areas increased at an annual rate of 2.37 percent. Agricultural lands, irrigated areas and dense pastures also showed an increase of 4066, 90 and 13562 hectares with annual rates of 1.55, 3.65 and 1.68 percent, respectively. The annual reduction rate is in medium density rangelands and low-density rangelands - Bayer - 2.08 and -13.77 percent respectively. Between 1978 and 1988, there were 632, 6, 32, 266 and 29 hectares of net conversion of agricultural uses, irrigated areas, medium-density rangelands, dense rangelands and low-density-barren pastures to residential areas, respectively. During these years, 3279 hectares of net change was observed from dense rangelands to agricultural lands and the rate of net change is from low density densities to medium density rangelands 2698 hectares. Agricultural lands increased from 28,200 hectares in 1998 to 29,600 hectares in 2008 with an annual growth rate of 0.51 percent, with 90 hectares of medium-density rangelands and 932 hectares of dense rangelands converted. Rangelands decreased with average density of 2235 hectares and annual rate of -0.33%. The rate of net change was 1687 hectares from medium-density to low-density rangelands. The rate of increasing in low-density-barren pastures is 2565 hectares and the rate of net change is from dense rangelands to this land use 693 hectares. Water areas also decreased by 67 hectares from 1998 to 2008. An increasing of 743 hectares was observed in residential areas with an annual growth rate of 1.64 percent, which was the main net change from dense pastures to this use of 718 hectares. A large increasing was observed in medium density rangelands from 65,259 hectares in 2008 to 77,706 hectares in 2018 with an annual growth rate of 1.74%. The rate of increasing was in the water zones with 637 hectares, that it showed a net change from agricultural lands, medium density pastures and dense pastures to water zones 331, 217 and 120 hectares, respectively. In this period, the annual growth rate is 0.33% in agricultural lands. During the study period, residential areas, agricultural lands and water areas increased by 3857, 20261 and 558 hectares with annual rates of 3.35%, 2.34% and 2.24%, respectively. Dense rangelands decreased with medium and low density with annual rates of -0.5%, -0.02% and -3.3%. Agricultural lands, dense rangelands, with medium and low density at 771, 2335, 273 and 481 hectares were converted into pure residential areas. 224, 70 and 259 hectares of agricultural lands, dense and medium density pastures were converted to pure water areas, respectively. 2931 and 36 hectares were converted from dense pastures to medium and low-density pastures. The results of the spatial trend of changes from all land cover classes to residential areas revealed that the densely populated urban areas and human activities.