V. V. Menshutkin

Development of Lake Ladoga ecosystem models: modeling of the phytoplankton succession in the eutrophication process. I

Abstract New models of Lake Ladoga ecosystem and the results of modeling are presented. In the first part the model of phytoplankton succession in the process of anthropogenic eutrophication of the lake is considered under the evolution of the phosphorus loading. The still continued anthropogenic eutrophication of the lake started in 1962 when the phosphorus load began to increase. Since 1962 during the evolution of the lake’s state from oligotrophic to developed mezotrophic one, the structure of phytoplankton community dominating species was significantly changed as well as its total productivity. The system state in the model is described by 14 parameters: nine phytoplankton complexes, zooplankton, dissolved organic matter, detritus, dissolved mineral phosphorus and dissolved oxygen. The number of parameters of this model is noticeably larger than that of previous models created by the authors. The relative dynamics of phytoplankton complexes in the lake’s ecosystem evolution was simulated by the new model. It is shown that the modeling results are adequately corresponding to the observation data. The results of phytoplankton structure modeling allow to estimate the impact of phytoplankton on the water quality as well as give the prediction of the lake’s ecosystem evolution with the changes of the phosphorus loading.

Mathematical model for the ecosystem response of Lake Ladoga to phosphorus loading

The ecosystem response model described in this paper combines an ecosystem model and a three-dimensional circulation model of Lake Ladoga developed earlier by the authors. The ecosystem model describes the process of Lake Ladoga eutrophication, and its biological submodel describes changes in the phyto- and zooplankton. In the earlier model version, lake circulation was determined using a two-dimensional hydrodynamical model which was not completely adequate. The present model allows calculation of the distributions of phyto- and zooplankton and mineral phosphorus and nitrogen. One of its main advantages is that reliable computations of the ecosystem dynamics over an extended period of time are possible. The response of the ecosystem to different levels of phosphorus pollution loading and to weather conditions is studied.

Ecosystem modeling of freshwater lakes (review): 2. Models of freshwater lake’s ecosystem

Mathematical models of ecosystems are considered, including models formulated as systems of differential equations and using up-to-date numerical methods for their implementation and models formulated and implemented using fuzzy logic and methods of artifical intellect. Logical-linguistic and cognitive models, which largely give qualitative description of ecological systems, are also considered.

Studying the Response of Lake Ladoga Ecosystem to a Decrease in Phosphorus Load

A study of the transformation of Lake Ladoga ecosystem in 1996–2005 shows that a decrease in the phosphorus load after 1995 has not cause a decrease in lake ecosystem productivity. Mathematical modeling provided an explanation of the observed phenomenon, thus justifying limnologists’ hypothesis that phosphorus turnover within a water body accelerates with increasing abundance of bacterioplankton and aquatic fungi. Computational experiments have shown that the additional amount of phosphorus that is required for maintaining phytoplankton productivity is additionally released by destructors (bacterioplankton and aquatic fungi) from detritus and organic matter dissolved in water.

Ecosystem modeling of freshwater lakes (Review): 1. Hydrodynamics of lakes

The development and use of lake ecosystem models are discussed as an essential part of integrated studies of lake ecosystem, the processes of eutrophication and matter transport and transformation for solving the problems of rational use of the natural resources of a water body, preservation of high water quality, prediction of the further development of lake ecosystems under the effect of anthropogenic and climate factors. Description is given to models that can be formulated as boundary value problems for systems of one-, two-, or three-dimensional transport differential equations for both reactive and nonreactive solutes in water. Those equations include nonlinear operators, describing the transformation of living and dead organic matter (phytoplankton, zooplankton, benthos, detritus) and dissolved biogenic substances (carbon, nitrogen, phosphorus, and silicon). The possibility to construct models including fish, macrophytes, and dissolved oxygen and its exchange with the atmosphere through water surface is discussed. Modern numerical methods are used to implement the models formulated as systems of differential equations. The need to introduce stochasticity is demonstrated. Additionally, models, whose formulation and implementation involves methods of fuzzy sets, artificial intellect, as well as logical-linguistic and cognitive models are described.