Chemical Composition of Water along the Seashore and Front Delta of the Don River under Low-Water Conditions (20th–21st Centuries)

This study is based on the results of targeted water sampling undertaken at different weather conditions and water levels in the Don River delta and the seashore. The main experiment covered the period from November 20, 2020, to March 18, 2021. Water for chemical analyses was sampled at maximal water surges: an easterly wind-driven decline in the water level and a westerly wind-driven rise in the water level; in some cases, layer by layer. At the same time, to clarify the nature of water (ground, riverine, or marine), and its dependence on the surge regimes of water was sampled from the main water pipeline in the city of Azov. The data were recorded under various conditions: in normal conditions, extreme fluctuations in the sea level, with a sharp increase in the proportion of groundwater under ice in the water balance, on a shallow seashore, and in delta arms during negative surges. In 2020, at the Donskoi hydrometric station, directly in the Don River channel, the measurements of water salinity (which depends on the underground runoff to a lesser extent) were started. The study data gave grounds to subdivide (classify) the transformed waters in the estuarine zone of the Azov–Don basin.