Short answers, pulled from the story.
The Caspian Depression, also called the Caspian Lowland, is a low-lying flatland region encompassing the northern part of the Caspian Sea, the largest enclosed body of water on Earth. It covers parts of Kazakhstan (Atyrau Region, West Kazakhstan Region, and Mangystau Region) and Russia (Dagestan, Kalmykia, Astrakhan Oblast, and other regions), spanning roughly 200,000 square kilometers.
The lowest point in the Caspian Depression is Karagiye, near the city of Aktau, at 132 meters below sea level. The Caspian Sea itself sits at 28 meters below sea level, but several areas in the depression are even lower.
The Volga River and the Ural River both cross the Caspian Depression and empty into the Caspian Sea, forming extensive wetland deltas. Three other rivers also run through the lowland: the Emba, the Terek, and the Kuma.
Russian satellite photographs have revealed around 1,200 salt domes in the Caspian Depression in western Kazakhstan. One of the largest, the Chelkar Deposit, covers an area of 3,237 square kilometers and extends nearly 8 kilometers underground.
Water pollution, primarily from the Volga River, poses the most serious documented threat to biodiversity in the Caspian Depression. The pollution comes mainly from industrial, agricultural, and household discharges carried into the basin.
The Caspian Depression is rich in underground oil and natural gas reserves. Pipelines cross the region in both north-to-south and east-to-west directions to transport these resources. The area is also notable for its large deposits of salt domes.