Assessment of the current state of the coastal recreational zone of Sakhalin Island (case study of Lososey Bay): initial monitoring stage.

The first results of an environmental assessment of Lososey Bay (Aniva Bay, Sakhalin Island, Russia)-one of the region's most urbanized and recreationally significant aquatic areas-indicate the absence of acute anthropogenic pressure. No exceedances of maximum permissible concentrations for metals (V, Cr, Mn, Fe, Cu, Zn) were detected in the water. But Cu and Zn content in water exceeds the background levels many times. Elevated copper concentrations and borderline zinc levels were identified in the bottom sediments. The homogeneous spatial distribution of these metals, combined with the absence of historical concentration peaks in sediment cores, points to their predominantly natural origin. The most likely pathway for metal input into the bay is their leaching from ophiolites underlying the central part of the bay, characterized by occurrences of nickel, copper, and other metals. Sedimentation rate reconstruction using 210Pb revealed its temporal heterogeneity and suggested a shift in the bay's hydrological regime, possibly driven by climatic factors. Comparison of sedimentation rates with vertical suspended matter fluxes, assessed via the 210Pb-210Po pair, demonstrated a negligible contribution of lateral mass transport in the river estuaries and its increase towards the open part of the bay. The flux dynamics are also disrupted by the influence of local vortex currents in the open bay area. Quantitative assessment of 137Cs specific activity confirmed the absence of significant impact from the Fukushima-1 NPP accident on the radiological situation in the studied aquatic area.