Oxygen regime of Lake Vendyurskoe in winter in response to trout farm operations

The article presents the results of an analysis of interannual variability (2007–2024) of the dissolved oxygen content in water of a small Lake Vendyurskoe (southern Karelia, Russia), where a trout farm has been operating since 2011. The data on water temperature мand dissolved oxygen content in the water column at 10–15 depths in the central deep-water part of the lake in the year-round mode are used. It is shown that immediately after ice-on, the dissolved oxygen content begins to decline, most significantly near the bottom, due to bacterial destruction of organic matter. Already a few weeks after ice-on, oxygen deficiency develops in the bottom layers of the central deep-water basin, мwhere the settling suspended organic matter accumulates. The ratio of the dissolved oxygen content in the water column on each day of the ice period Ct to its content on the first day of freeze-up C0 was analyzed. The Ct /C0 ratio is considered as a proxy of the proportion of oxygen consumption in the lake due to bacterial destruction of organic matter. To identify interannual variability in the volume of oxygen consumption in the lake in winter, we compared the Ct /C0 value on the 130th day of the ice period in different years. At the beginning of the measurement period, oxygen consumption in the lake in winter reached 34 % of the initial level on the first day of ice formation, while at the end of the measurement period it was 48 %, i.e., the increase in oxygen consumption over 16 years was more than 40 %. The increase in oxygen consumption in winter due to the increase in water temperature and acceleration of metabolism (9 %) explains only part of the identified trend. Along with water temperature, a мsignificant contribution to the increase in oxygen consumption is likely made by an increase in the amount of OM, associated, among other things, with the trout farm operations.