A manipulated river
The Ili River delta, a sprawling 8,000-square-kilometer wetland in southeastern Kazakhstan, is an ecological buffer for Lake Balkhash, one of Asia's largest lakes. This vast expanse of channels, small lakes, and riparian forests is dominated by immense stands of common reed, Phragmites australis. These reed beds, historically one of the most extensive on the planet, are the base of the delta's ecosystem. The river itself stretches for 1,439 kilometers, originating from glaciers in China's Tian Shan mountains and supplying 70-80% of the inflow to Lake Balkhash.
The natural rhythm of the delta was fundamentally altered with the construction of the Kapchagay Hydroelectric Power Plant and its reservoir, which began filling in 1970. The dam was built to generate electricity and support irrigated agriculture. This structure dramatically changed the river's hydrology downstream. Before the dam, the average flow rate was 468 cubic meters per second; during the reservoir's initial filling period, this dropped by 22% to an average of 366 cubic meters per second. The dam eliminated the spring and summer floods, which historically submerged the reed beds and saturated the soil, replacing them with a more uniform, and reduced, year-round flow.
A cascade of consequences
The stabilization and reduction of water flow had a direct, negative effect on the Phragmites australis beds. These plants, while tolerant of fluctuating water, depend on a high water table to sustain their perennial rhizomes—the thick underground stems from which new shoots grow. Hydrological models show that the water level dropped below the critical depth of these rhizomes. Without the seasonal inundation, soils began to dry out and increase in salinity. This water deficit stress is the primary driver of the massive die-off, which eliminated an estimated 60% of the reed biomass in just a decade.
The loss of these vast reed ecosystems has severe ecological repercussions. The delta is a designated Ramsar Wetland of International Importance and a Key Biodiversity Area, home to 345 animal species and 427 plant species. It provides habitat for numerous bird species, including colonies of Dalmatian and Great White Pelicans. The dense reed beds also supported populations of wild boar (Sus scrofa) and were spawning grounds for fish. The degradation of the reeds threatens this biodiversity. The die-off also impacts Lake Balkhash itself, as the reed beds serve as a natural filter, trapping sediment and pollutants before they enter the lake.