Hydroenvironmental State of the Agrakhan Bay and Means for Improvement

摘要

Significant degradation of the Agrakhan Bay on the eastern coast of the Terek River delta has occurred in the course of the 20th century as a result of the combined action of natural and anthropogenic factors. Comprehensive studies conducted by the authors in 2018-2020 have made it possible to describe the main causes of this degradation, characterize the current state of the reservoir, and establish scientific bases under recommendations for its improvement. It has been demonstrated that as a result of partial drying and reduction of water surface area the bay has lost its former importance as a spawning and rearing water body providing the West Caspian region with the younglings of valuable commercial fish species. By 2018, the catches decreased by ten times compared to the early 20th century with sturgeons having almost totally disappeared. The state of the northern part of the bay, which has transformed into a group of shallow water bodies almost entirely separated from each other and from the sea is particularly unfavourable. The study of hydrological and morphological, hydrobiological, fishery-related and hydrochemical parameters has shown that the improvement of the wetlands at the former bay site is possible. Detailed analysis of the water balance using multivariate limnological calculations has shown that there is enough water for watering and partial restoration of the water bodies of the Agrakhan Bay hydrographic system. Clearing of silted and overgrown canals, deepening and berming of the remaining water bodies, and directing the necessary amounts of river water into Northern and Southern Agrakhan Bay (in accordance with the calculated delivery schedule) will allow reduction of the overgrowing and siltation of water bodies, restore the water exchange between them, improve water quality, revive the fishery industry in the region, improve the habitats of many rare and protected animal species, and increase the recreational attractiveness of the region.