Assessment of ecological water requirement of Dasht-e-Argan internationally important Wetland, Fars, Iran

Arjan wetland is one of the internationally important wetlands in Fars province, Iran. Despite its ecological and geological values as a typical polje, this wetland has lost its ecological services in the last two decades, except for short seasons in other dry seasons. The purpose of this study was to estimate the ecological water requirement of Arjan wetland. The amount of ecological (environmental) water requirement of the wetland was estimated based on the changes in the total population of migratory birds and also the selected species. Using satellite images, monthly and annual changes in the surface of the wetland as well as permanent and temporary water were estimated during the years 1990-2019.The selected species included one species of goose (gray goose) and 4 species of ducks (including shelduck, mallard, widgeon and teal). Satellite images show that in all the years studied, this wetland has been a temporary wetland, although the water level of the wetland has decreased more than 4 times in the last decade compared to the first studied decade. The abundance of gray-goose population showed the highest correlation with changes in the water level of the wetland. According to calculations, under normal conditions, the water level required to support more than 20,000 birds is between 200 and 400 hectares. Reducing the level of the wetland to less than 200 hectares creates critical conditions and the level of more than 500 hectares is desirable. Therefore, taking into account the hydrological and ecological conditions of the wetland basin, the water requirement of Arjan wetland to provide ecological services during different years  in terms of climatic conditions can be estimated as follows: Drought years: at least 3 Million cubic meters, normal years: 5.25 million  and wet years: 7.5 million cubic meters. Since the watershed has no permanent river to feed the wetland, protection of withdeawal from runoffs and aquifers are required to ensure the water requirement supply of wetland.