The article investigates the dynamics of the dissolved oxygen (DO) content, the water temperature, the chlorophyll «a» and the under-ice irradiation in the small mesotrophic lake during the springtime heating period. All data were obtained from long-term observations using high-precision autonomous equipment. In the convectively mixed layer (CML) were recorded the DO oscillations up to 1 mgO2/l with daily frequency. Assumedly, these fluctuations are due to the daytime intensification of the photosynthesis on the background of under-ice irradiation growth (reaching 120 W/m2 when snow melts from ice surface) and the destruction of newly formed organic matter. The CML also exhibits the high-frequency DO fluctuations (on scales from 2—3 minutes to 3—4 hours), presumably related to convective currents and seiche activity. The involvement of oxygen-depleted water portions from underlying stratified layer to convective mixing leads to decrease of DO concentration in CML, but the total oxygen content in the water column during the under-ice convection period increases at a rate ~0.1—0.4 gO2/m2 per day due to photosynthesis enhance.

Изучено распределение солнечной радиации в водной толще трех малых озер Южной Карелии в период ледостава и открытой воды. Измерения проведены в режиме автономных станций в период весенней подледной конвекции (с 27 марта по 6 апреля 2020 г.) на озерах Вендюрское и Голубая ламба. В период открытой воды 2020 г. на этапе раннего лета (июнь) и осенью (октябрь) выполнено зондирование водной толщи озер с использованием зонда RBR-Concerto. Установлено, что поток солнечной радиации быстро убывает с увеличением глубины в озерах Вендюрское и Риндозеро и практически равен нулю глубже 3-4 м в период открытой воды и 2-3 м в период ледостава. В прозрачной Голубой ламбе глубина фотической зоны может достигать дна в солнечные дни (> 6-7 м). По данным измерений оценены значения коэффициентов экстинкции, которые составили для периода открытой воды 0,99-1,97 м -1 в озере Вендюрском, 1,60-1,88 м -1 в озере Риндозеро, 0,12-0,14 м -1 в Голубой ламбе. В период весенней подледной конвекции в Голубой ламбе значения коэффициентов экстинкции, осредненные для слоя 0-2,9 м, составили 0,47-0,57 м -1 . Сравнение полученных нами показателей ослабления солнечной радиации с оцененными ранее позволяет заключить, что оптические свойства водной толщи озер не претерпели заметных изменений в течение последних 30-40 лет на фоне меняющегося регионального климата и антропогенного воздействия (форелевое хозяйство на озере Вендюрском). К л ю ч е в ы е с л о в а: малое озеро; солнечная радиация; фотосинтетическая активная радиация; период открытой воды; период ледостава; коэффициент экстинкции.

Parametrization of the formation of organic matter in ecological models is traditionally carried out by using the dependence of the Michaelis – Menten – Monod type [Monod, 1942], which describes the growth rate of algal biomass depending on the factor limiting their development. One of the biggest drawbacks of these dependences is the presence of empirical parameters in them, which in a complex way depend on environmental factors and are an individual characteristic of various types of algae. These parameters in the models actually become fitting coefficients that provide the best fit between observational data and modeling results, which does not allow for effective diagnostics and forecasting of the state of aquatic ecosystems. In this work, on the basis of dimensional analysis, a parametrization was obtained that describes the photosynthesis of algae depending on the parameters relatively easily measured in natural conditions - total solar radiation, phytoplankton biomass, and water transparency. Parametrization has been verified according to observations on more than 30 different types of lakes located in different regions of the world. The calculated data are in satisfactory agreement with the data of field observations, both qualitatively and quantitatively. Discrepancies in field and calculated data may be due to the fact that the species composition of algae in lakes of different trophic status is not taken into account, which can lead to errors in assessing the efficiency of using solar radiation. Discrepancies may also be related to the total solar radiation, rather than photosynthetic active radiation, which varies in different geographic and atmospheric conditions. The proposed parametrization can be used in the development of mathematical models of lake ecosystems, as well as to determine the trophic status of poorly studied water bodies.

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