Nowadays increase on needs for fossil fuel production in Kazakhstan are leaded to drought of Caspian Sea caused by industrial pollution. I totally agree with this statement and think that damaging of sea surface by oil exraction drive to death of underwater living creatures resulting on decrease of water ecosystem biomass, also processes such us getting petroleum from depth of sea by drilling made big carrers on bottom, which are filled by huge amount of hydroresources.
One of the reasons why Caspian Sea level was declined is destroyment of ecosystems. Such petroleum stations pollut water and reduce permeability of fotons, thus, photosyntesis of living organisms occur slowly or they could die. For example,if produced sulfuric oxides replace oxigen concentration in air or excess of the oil remain in sea surface ,because of density differencies , coefficient of surviving, variations of phytoplanktones, light and oxigen loving bacterias will considerably fall down.
Another important aspect is grow in depth. Fuel resources taken from the bottom of the sea are should be replaced by hydrogen oxide to keep a general balance. For example, drilling mechanism undergo by breaking down the tectonic plates covered with water and as a result, formed empty place was fulfilled.
To conclude, there are several reasons for Caspian Sea shrinkage ,that are connected with oil manifacturing. But I believe that the biomass concentration and producting technologies of the underland resources are the main key points of dissapearance of this big natural reservoir.