Hydrologic Sustainability Of The Sultan Marshes In Turkey

Hydrologic changes in the Sultan Marshes ecosystem, a closed-basin wetland in the semi-arid Develi Basin in south-central Turkey, are analyzed and related to intensification of irrigated agriculture in the catchment. Relationships between water-level changes in the marsh, and inflows and outflows of surface water and groundwater are examined. Since the 1980s, surface runoff from the surrounding mountains into the Develi Basin has been captured in three major reservoirs and used for flood irrigation. Substantial declines in seasonally-fluctuating water levels were recorded in the Sultan Marshes from 1993 to 2003. Our analysis shows that these trends are related to decreases in inflows from groundwater and springs, not to climatic changes. Simulations with a deterministic hydrologic model for the Ortuluakar Marsh, a sub-system of the Sultan Marshes, as well as statistical analyses, showed that it is necessary to reduce water use from groundwater and springs to maintain pre-1995 marsh water levels. Alternative groundwater management scenarios to sustain both the wetland and irrigated agriculture in the Develi Basin were tested. A 50% reduction in groundwater and spring-water use for irrigation showed promising results for the Sultan Marshes. Irrigation in the basin uses 66% surface water and 34 % groundwater. A 50% reduction in groundwater use for irrigation therefore represents less than 20 % of total irrigation water used. Reduction in groundwater use is, however, linked to social and economic conditions in the Develi Basin, and incentives that encourage farmers to adopt sustainable groundwater use practices need to be developed.