The political decision caused the drastic ecosystem shift of the Sivash Bay (the Sea of Azov)

Political and economic decisions have led to more drastic changes of aquatic ecosystems, than those caused by hydrological extremes (drought, floods). Examples of this are two transformations of the Sivash Bay (Sea of Azov); a review and analyses of them are given in the paper. Sivash Bay was a hypersaline lagoon before 1963. The North Crimean Canal was built to improve water supply to the Crimean peninsula by using the waters of the Dnieper River. After the initiation of Dnieper water via the North Crimean Canal and the subsequent development of irrigated agriculture, runoff waters from the fields began draining into Bay Sivash. The salinity began to drop. Pre 1997 the average salinity in Sivash Bay was 140 g L−1; in 1997 it had dropped to 17 g L−1. A fundamentally new brackish water ecosystem gradually formed in Sivash Bay. In April 2014, Ukraine made a political decision to stop supplying Dnieper water via the North Crimean Canal. Discharge of fresh water to the bay almost ceased. Salinity began to increase, and a new transformation of the Sivash ecosystem started. Six complex expeditions were conducted in the Sivash region; their results are described and analyzed in the article. The salinity of the lagoon has now risen to 55-75 g L−1, and drastic changes have occurred in the plankton, benthos, and aquatic vegetation.