Leading Factors of the Dynamics of Lake Ecosystems under a Changing Nutrient Load: Analysis of Long-Term Monitoring Data of Naroch Lakes

Abstract

Since the second half of the 1970s, the ecosystems of lakes Batorino, Myastro, and Naroch have undergone anthropogenic eutrophication, targeted deeutrophication, and benthification caused by the introduction of the filter-feeding mollusk Dreissena polymorpha Pallas. The set of continuous series of seasonal mean values of eight parameters of each ecosystem obtained in 1978–2015 have been analyzed by mathematical-statistical methods of principal components (PCA) and singular spectra (SSA). The analysis showed that the complicated long-term dynamics of the set of the chosen parameters of the ecosystems was described during this period of time by three principal components by 92% and 90% for Lake Batorino and Lake Myastro, respectively, and by five principal components by 94% for Lake Naroch. We propose a biological interpretation of these principal components, i.e., a hypothesis of the factors exerting the greatest effect on the ecosystem dynamics during those years. The first main factor, which determines the dynamics of the ecosystems of lakes Batorino, Myastro, and Naroch by 63, 65, and 43%, respectively, is interpreted as the resistance of the lake ecosystem to a variable biogenic load, which is inversely related to the trophicity of the reservoir. The second main factor, which contributes 21, 15, and 22% to the dynamics of the ecosystem parameters of Naroch lakes (in the same order), was interpreted as solar radiation activity. The interpretation of the third main factor depends on the properties of a particular ecosystem. For ecosystems that are not deficient in biogenic elements (lakes Batorino and Myastro, with a contribution of the factor to the ecosystem dynamics of 8 and 10%), this may be the transfer of the primary organic matter to consumers of the next trophic level related to the structure of the food chain in the ecosystem. For an ecosystem in which the process of primary production formation is limited by the available amount of biogenic elements (Lake Naroch, in which the contribution of the third main factor to ecosystem dynamics is 13%), this very factor is the third main one, affecting the ecosystem long-term dynamics. The fourth main factor, which determines the dynamics of the Lake Naroch ecosystem by 9%, is also related to the process of primary production formation. Only the fifth main factor, which determined 7% of the dynamics of the ecosystem of Lake Naroch during the analyzed time period, controls the transfer of primary production to consumers of the first trophic level. Thus, our statistical study not only confirmed empirical regularities of the functioning of lake ecosystems, but for the first time enabled us to obtain quantitative assessments of the importance of each main factor for ecosystem development under specific conditions, depending on the trophicity of the water body.