**5.4 Maintaining the sustainability of watershed ecosystems**

Natural aquatic ecosystems are among the important water resources supporting life. It is very important to maintain the ecological flows of these systems. Ecological flows are usually determined by some practical statistical approaches, assumptions and methods supported by scientific research conducted at site. During these studies it must be considered that aquatic ecosystems are in interaction with terrestrial ecosystems. Thus, any change in aquatic or terrestrial ecosystem will have an effect on the other one. For example, the decrease in surface water levels will affect the groundwater levels and dependent ecosystems. Evapotranspitation increase due to climate change has also effect on the decrease of groundwater levels. As this condition may lead to change in the vegetation cover which in turn lead to habitat change regulation of groundwater use becomes more important. As renewal of groundwater lasts long, planning must be done prior to facing water scarcity.
