Radium Isotopes and Hydrochemical Signatures of Surface Water-Groundwater Interaction in the Salt-Wedge Razdolnaya River Estuary (Sea of Japan) in the Ice-Covered Period

The interaction of surface water and groundwater is important in the ecology coastal basins, affecting hydrological conditions, oxygen regime, carbon, nutrient exchange. This study demonstrates a dynamic connection between salt-wedge region its underlying aquifer eutrophic estuary. In winter, this estuary covered with ice, river flow at lowest; that why specific response to discharge best marked season. Groundwater admixture was detected by highly active radium isotopes: 223Ra—4.80 ± 0.42 dpm 100 L−1, 224Ra—55.37 1.1 228Ra—189.71 4.66 L−1. temperature about +4 °C 0 °C, respectively; seawater −1.6 increased up +2.3 water–groundwater region. accompanied lower level concentration 52 μmol/kg; time, maximum 567 μmol/kg. waters high activity isotopes, there partial pressure CO2—4454 μatm range 100–150 also observed extremum NH4+, NO2−, dissolved phosphorus. through anoxic sediment can form localized anaerobic areas despite general supersaturation cause local recycling nutrients from bottom sediments.