RECONSTRUCTION OF WATER BALANCE COMPONENTS BASED ON FIELD OBSERVATIONS AND MODEL ESTIMATES FOR A SMALL CLOSED COASTAL LAKE

Abstract

Based on a comprehensive analysis of field data (2023–2024) and numerical estimations, the water balance of a closed coastal water body in the south-eastern Baltic – the Yantarny Pond (Kaliningrad Oblast, Russia) – has been calculated. Quantitative characteristics were obtained for all major balance components: precipitation, evaporation, surface runoff, and groundwater flow. Three empirical evaporation formulae (Meyer, Rohwer, and Vikulina– Braslavsky) were tested for the conditions of the study area; the Rohwer equation was shown to provide the most physically sound results. Annual evaporation according to this formula amounted to 680 mm in 2023 and 600 mm in 2024 (for a partial year). Surface runoff from the catchment, estimated using the HYPE model, exhibits pronounced seasonal variation, ranging from 70 mm/month in winter to 3–7 mm/month during the summer low-flow period. For the first time, a quantitative assessment of the groundwater component of the water balance was obtained for this water body using the residual method. A pronounced interannual variability of groundwater exchange was revealed: in 2023, groundwater outflow from the pond prevailed (–420 mm), while in 2024, groundwater inflow was recorded (+130 mm). This difference is attributed to the inertia of filtration processes and the buffering capacity of the “lake – groundwater” system. Correlation analysis revealed a lagged response of the water level to changes in groundwater flow, with a characteristic response time of about two months. The results obtained may serve as a methodological framework for regional assessments of water balance in other coastal water bodies of the Kaliningrad Oblast’.