Assessment of the environmental situation in Blagopoluchiya Bay (the Solovetsky Archipelago, White Sea) based on hydrochemical, hydrobiological and microbiological studies in 2025

Blagopoluchiya Bay (the Solovetsky Archipelago, White Sea) is a recipient of wastewater from the Solovetsky settlement and is susceptible to pollution by nutrients and organic matter. Anthropogenic impact leads to decreasing of the recreational value of the Bay and deterioration in water quality as a result of intensive growth of green macroalgae, so-called “green tides”. The aim of the work was to assess the environmental situation in the Bay. The aseesment was perfomed on the basis of hydrochemical, hydrobiological and microbiological studies in June and August 2025 during various phases of the tidal cycle. Blagopoluchiya Bay is a relatively shallow area with depths in the northern and southern parts of no more than 2 m, while at the entrance to the bay, the depths reach 8–9 m. The tidal range in the bay varies between 0.5 and 0.7 m. The current velocities at different tidal phases are relatively slow, not exceeding 10–15 cm/s. High concentrations of nutrients (121–1058 μg/L total phosphorus and 1.21–1.58 mg/L total nitrogen), as well as total coliform bacteria (up to 90000 CFU/100 cm³) were detected in the area of the Solovetsky settlement wastewater discharge. The data characterize the sanitary situation as critical. At other stations in Blagopoluchiya Bay, the content of nutrients was 2–20 times lower, and the number of total coliform bacteria was 4–1800 times lower. Despite the high concentrations of total phosphorus, indicating the eutrophic and even hypertrophic status of the Bay, chlorophyll “a” concentrations in the wastewater discharge area were low and corresponded to the mesotrophic level (2.07–3.29 μg/l). At the exit from the bay, the concentrations of chlorophyll “a” corresponded to the oligotrophic level (0.97–2.0 μg/l). This situation is explained by the widespread development of macroalgae in the bay, including representatives of the genus Ulva, which contribute to the formation of “green tides”. Phosphorus content in macroalgae mass at different stations in Blagopoluchiya Bay varied between 0.24–0.36 % (of dry weight). The interception of nutrients by macroalgae results in low concentrations of their mineral forms, which hinders the intensive development of phytoplankton. Consequently, low levels of chlorophyll “a” are observed. The monitoring results indicate an unfavorable environmental situation in Blagopoluchiya Bay, requiring immediate wastewater treatment. An important measure to improve the situation in the Bay is the removal of macroalgae from the areas where they grow.

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