Ecological condition of marine waters in the area of dredging operations of the kashagan field, Kazakhstan

To determine the hydrophysical and hydrochemical parameters of sea water and their changes during dredging works in the north‐eastern part of the Caspian Sea along the Western Approach Route and near/inside block D, islands EPC‐2, EPC‐3, EPC‐4 and island A of the Kashagan field.Measurement of hydrophysical parameters: salinity, temperature, turbidity, dissolved oxygen concentration, electrical conductivity, pH of seawater was carried out using a portable multi‐parameter analyser "Horiba‐U53" directly in the water column. Water transparency was determined using a Secchi disc. The depth of the water layer was determined using a sounder. Hydrochemical investigations were carried out for seven parameters, with all components sampled in the near‐surface and benthic horizons. Water samples were taken using probes or bathometers: BM‐48, GR‐18 or their analogues.Hydrochemical analyses of seawater samples for: biogens (NO2, NO3, NH4, Ntotal, and Ptotal), synthetic surfactants, phenols, hydrocarbons including polyaromatic hydrocarbons (PAHS), heavy metals, chemical oxygen demand (COD) and biochemical oxygen demand (BOD5). These were carried out in laboratory conditions using analytical equipment according to scientifically accepted methods.The data obtained as a result of the research allow us to draw the following conclusion: changes in the amount of suspended sediment in sea water lead to changes in physical and chemical properties of water (increase in turbidity, disturbance of sediment composition and properties), changes in biotopes, deterioration of oxygen regime, optical properties of water and temperature regime.