Document Type : Original Article
1 Desert Research Department, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran
2 Department of Desert Sciences, Faculty of Natural Resources and Earth Sciences, Kashan University, Kashan, Iran
3 Rangeland Research Department, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran
Introduction: Water depletion in wetlands, due to both natural and unnatural reasons, leads to the extinction and death of living organisms. After successive droughts, if flooding and rehydration occur, their recovery is highly unlikely. According to the Ramsar Agreement, the area of Shadegan Wetland is 537731 hectares and includes freshwater area, tidal zone, Mousa creek, and marginal lands. The freshwater area of the wetland is about 164 thousand hectares based on the Landsat satellite image during flooding and is equivalent to 28% of the total area of the wetland. This wetland is extremely important due to various functions such as flood control, air conditioning, soil erosion control, plant and animal habitat, and providing livelihood. The purpose of this study is to monitor the trend of changes in the freshwater area of the wetland using satellite images and identify the factors affecting changes in its area.
Material and methods: Landsat TM, ETM +, and OLI satellite data from 1998 to 2017 were used to monitor the water area of Shadegan Wetland. Various climatic, hydro-climatic, and water management factors were extracted for the study period in the whole watershed. The trend of changes and their relationship with changes in the wetland water area were investigated using the principal component analysis (PCA) method, and the factors that explained the highest variance of water changes were identified and analyzed.
Results and discussion: The trend of changes in the water area of Shadegan Wetland was increasing. Data using KMO and Bartlett statistics showed that the studied elements were suitable for changes in water area based on factor analysis. The results of factor analysis showed that five factors played an important role in changing the water area of Shadegan Wetland. In total, five factors were able to explain 88.9% of the variance of the data; the first factor was the temperature, the area under cultivation, the number of earthen dams and drains entering the sugarcane, which explained approximately 36% of the variance. The second factor was the humidity of the basin which explained 15% of the variance. The third factor was the instant discharge’s drought that explained 14.9% of the total variance. The fourth factor was discharge and precipitation with 11.8%, and the fifth factor was wetland moisture, which explained 11.2% of the variance of water area changes.
Conclusion: Wetlands that are situated at the foothills of watersheds are affected by the factors in the watershed. In total, five factors were able to explain 88.9% of the variance of the changes. In the first factor, apart from temperature, three factors that result from human activities were the most important: the area under cultivation due to the development of large irrigation projects, use of water sources of Jarahi River, which is the source of 90% of water input to the lagoon and numerous dams, dams upstream of the wetland that prevent the arrival of flood and seasonal runoff, and sugarcane drainage as inlet water to the wetland. In order to manage the wetland, reduction of human activities and utilization of water resources in order to provide the natural water of the wetland should be considered so that the wetland can continue as a living ecosystem.