REGRESSIVE PHASE OF THE AYDAR-ARNASAY LAKE SYSTEM EVOLUTION (UZBEKISTAN)

Abstract

The article analyzes the regressive phase in the evolution of the Aidar-Arnasay lake system (AALS) in Uzbekistan, which began after 2006. Based on the synthesis and analysis of long-term hydrological monitoring data, satellite imagery, and collector-drainage flow information, it has been found that over the 15 years following 2006, the water level dropped by 3.12 m, the surface area shrank from 3,899 to 3,702 km², and the volume decreased from 42.1 to 34.2 km³. Seasonal water level fluctuations ranged from 0.56 to 1.17 m, peaking in May and reaching a minimum in November–December. It is shown that the main water source for the lake system is collector-drainage water (CDW), which contains high concentrations of conservative and non-conservative pollutants characterized by limiting hazard indicators and specific effects on aquatic communities. However, the CDW volume is insufficient to compensate for evaporative losses under conditions of climate warming and a sharp reduction in water discharges from the Chardara Reservoir on the Syr Darya River. Under these circumstances, the regressive phase is interpreted as a stage in the evolution of an anthropogenic water body during which the water balance structure changes: there occurs a general decrease in inflows and an increase in water losses due to evaporation from the lake surface, along with rising pollutant concentrations driven by the prevailing influence of CDW from irrigated areas within the former Hungry Steppe (Mirzachul). It is shown that the combined effect of these factors has led to a marked deterioration of environmental conditions in the lake system, manifested as increased eutrophication, reduced biodiversity, and other adverse changes. This situation calls for urgent water body reclamation measures. The obtained results can be used to justify optimal water use and water protection strategies in the AALS basin as a whole, including the need to maintain favorable hydrological and ecological conditions in the water body itself.