The structure of the food web of a northern humified lake: seasonal features
N. A. BEREZINA1, A. A. MAXIMOV1, P. M. TERENTYEV2, S. M. TSURIKOV3
1Zoological Institute of the Russian Academy of Sciences, St. Petersburg, Russia
2Kola Scientific Center of the Russian Academy of Sciences, Institute of Industrial Ecology Problems of the North, Apatity, Russia
3A. N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences, Moscow, Russia
Keywords: isotope analysis, carbon, nitrogen, zooplankton, Eudiaptomus, benthos, Chaoborus, methane, small lakes, vegetation season, ice-covered period, Subarctic
Abstract
The relevance of studying the structure of food chains in high-latitude lakes characterized by oligotrophy and a significant influx of allochthonous organic matter from adjacent marshes is beyond doubt. In this study, an attempt was made to identify carbon sources in various trophic groups (zooplankton, zoobenthos, fish) and analyze trophic relationships between them, taking into account seasonal dynamics in a small subarctic humified lake located in the north of Karelia (White Sea coast). To achieve this goal, an isotopic analysis of stable carbon (δ13C) and nitrogen (δ15N) isotopes was carried out in the tissues of consumers and potential producers in different seasons (summer, autumn, winter and spring) of 2019-2020. The results of the study revealed significant differences in the structure of the lake food web between the open water and ice-covered periods, which is likely due to changes in the level of phytoplankton primary production, sources and rates of allochthonous organic matter input, and a significant energy contribution from heterotrophic organisms associated with methanotrophs. The important role of methane carbon in the formation of organic matter in this reservoir was indicated by low δ13C values (<-40 ‰) in consumers such as zooplankton (dominated by Eudiaptomus graciloides) and chaoborids (Chaoborus sp.), apparently actively involved in the transfer of methane carbon within food chains. In summer, a significant contribution of diazotrophic nitrogen fixed by planktonic cyanobacteria acted as an important source of nutrients. Seasonal variations in δ15N values and trophic position were determined for the common perch (Perca fluviatilis). The obtained data contribute to the understanding of the mechanisms of energy and trophic links formations in humified lake food web with an influence of allochthonous organic matter.
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