The Scenario base Calculation of Ecohidrological Water Needs for Sustainable Development of Water Resources (Case Study: Kaji Salt Wetland of Nehbandan)

Wetlands are actually the kidneys of the earth that lead to the environmental balance of the earth. Wetland is a unique environmental system with diverse performance and high biodiversity. Wetlands cover approximately 5 to 8 percent of the earth's surface (7-10 million square kilometers) and must be preserved in order to maintain their important functions as natural habitats and their role in the global carbon cycle. Wetlands have high primary productivity among all ecosystems and provide many ecological services, including environmental treatment, modification in the atmosphere and water cycle, wave intensity reduction and disasters resulting from them. However, a large proportion of wetlands in the transition zone from marine-river ecosystems lie in terrestrial ecosystems, making them a sensitive and fragile ecosystem. Due to changes in natural environments, over-exploitation of wetlands and irrational use of their resources, the structure of wetland ecosystems has been destroyed and the boundaries of wetlands are gradually shrinking, which leads to damage or their ecological performance is lost. Therefore, it is necessary to revive wetland systems through efficient engineering technologies and logical management approaches. In order to provide a scientific basis for protection and restoration, it is necessary to examine the ecological water requirement of the wetland. Researchers are trying to balance the ecological needs of the wetland with the rational allocation of water resources. Achieving this balance can ensure the natural flow of water in order to improve the overall ecological performance of the wetland system, with the aim of restoring its function and rebuilding its ecosystem.

In studies of calculating the water requirement of wetlands, the functions of the study wetland should be identified first and the index should be determined for each function. The indicators should be determined in such a way that in addition to maintaining the main functions of the wetland, its functions are also maintained. Due to the characteristics of Nehbandan wetland, including water with salinity and high salts, lack of aquatic animals, lack of endangered species related to wetland water, as well as special socio-economic and cultural factors related to wetlands such as special traditional ceremonies , This wetland does not have a special production, socio-economic and cultural function and its most important functions are from the point of view of physicochemical, biological and ecosystem services. After identifying these functions, an indicator was selected for each of them to calculate the amount of water required of the wetland. Maintaining the area of the main spot of the wetland in minimum and maximum amount as a physicochemical index, maintaining the area of the main spot of the wetland in medium size as a ecosystem services index and preserving plant and animal species related to the wetland were selected as biological indicators. The MNDWI index was used to identify the water area of the wetland. After determining the boundaries of the wetland, in a process using the detection of the wetland underwater surface and depth measurement with satellite images, the volume of water at different levels was calculated according to the shape of the wetland bed and water depth. The water balance formula was used to calculate the hydrological needs of the wetland. The average amount of precipitation in the region was calculated using the monthly data of TRMM satellite, the amount of evapotranspiration was calculated using Modis satellite data and the amount of runoff was calculated using Terra climate data. After calculating the hydrological water requirement, three species of tamarix aphylla, haloxylon aphyllum and phragmetes australis were selected as plant indicators and anas platyrhynchos were selected as animal indicators and the ecological water needs of the wetland were calculated. After calculating the indicators, the amount of water demand of Nehbandan wetland is examined during 6 scenarios so that while identifying the condition of the wetland in different scenarios, it is planned to achieve the ideal situation.

In this study, in order to preserve and revive the Nehbandan wetland, its hydrochloric water requirement was calculated in 6 different scenarios. The wetland water balance was used to calculate the hydrological water needs of the wetland and the species of Haloxylon aphyllum, Phragmetes australis, Tamarix aphylla and Anas platyrhynchos were used to calculate the ecological water needs of the wetland. The results showed that currently the water balance of the wetland is negative and the outflows of the wetland are 0.452 million cubic meters more than its inputs. Using the MNDWI index, the highest area of the wetland was calculated in May 2016 and amounted to 20 square kilometers, the average limit of the wetland in May 2017 was 8.8 square kilometers and the minimum limit of the wetland was 6 square kilometers in November 2018. Therefore, due to the depth of the wetland in different years, which varied between 10 and 30 cm, the volume of water in these three areas was calculated. Therefore, in order to maintain the main spot of the wetland in the cold months of the year, 0.65 million cubic meters of water is needed for minimum extent, which is 1.32 million cubic meters in average extent and 6 million cubic meters in maximum extent. According to the calculations, the amount of wetland water required in different scenarios is as follows.
scenario Annual Water Needs (MCM)
Real scenario of plant water needs 0.1026
Ideal scenario of plant water needs 0.12345
The water needs of the wetland in order to preserve the important animal species 0.0003479
Hydrological wetland water requirement according to the low spot level (drought situation) 13.3
Hydrological wetland water requirement according to the average spot level (normal condition) 13.97
Hydrological wetland water requirement according to the high spot level (wet years condition) 18.65

According to the obtained results, in order to provide the average level of water stain in the cold months of the year (the time of the presence of the wetland), Nehbandan saltwater wetland, with a water volume of 13.97 million cubic meters per year, needs water, which 12.2 million cubic meters are supplied via surface runoff. Therefore, there is a shortage of 1.77 million cubic meters, which must be met by reducing the area's groundwater abstraction by about 20 percent. Also, in order to maintain and develop the vegetation of the region in an ideal condition, the annual need for water is equal to 0.12 million cubic meters. This is equivalent to 0.000348 million cubic meters per year for the protection of waterfowl in the region. Therefore, by providing the water needs of ecosystem services in order to preserve fine dust, the ecosystem related to the wetland, including plant and animal species of the region, is also preserved. The results in the scenario of ecosystem services show that in the current situation, water balance of wetland is negative and considering that the area of the wetland is one of the wind erosion centers of the province, so the most important ecosystem services of Kaji wetland is to deal with dust. Due to the hot and dry climate of the region as well as the recent droughts, there is a concern that with the drying up of the region's wetland, it will become a center of dust. Salt and mineral in the lagoon also exacerbate this concern. Therefore, it is necessary to maintain and rehabilitate it, and determining the water needs of wetlands can restore their ecological conditions and play an important role in improving their environmental performance.