Autochthonous and allochthonous organic matter in trophic chain of lake ecosystems

Abstract

This work presents analysis of mass–balance model simulating biotic flows of energy in pelagial of the large lakes of Russia (Ladoga, Onego, and Baikal) and small lake in northern part of the Karelia. The model had been developed on the basis of software package Stella and intended to predict an annual production of phytoplankton, bacterio plankton and consumers (non predatory and predatory zooplankton, planktivorous and piscivorous fishes). The input (independent) abiotic parameters of the model were latitude, mean lake depth, total phosphorus content and water color. The model analyzed an involvement of the autochthonous and allochthonous organic matter in the total energy flow through trophic chain. It was underlined that bacteria are important component of the planktonic community linking the dissolved organic matter (DOM) with organisms of the trophic chain. In high humic and oligotrophic boreal lakes the plankton respiration exceeds the primary production, therefore allochthonous DOM transformed to bacterial production replaces photosynthetic production in consumer feeding. The efficiency of bacterial growth (the ratio of bacterial production to consumed energy) depends on the ratio between autochthonous and allochthonous DOM. It had been shown that efficiency of bacterial growth in lakes with high primary production was higher than in oligotrophic waters with dominated allochthonous DOM. The author discussed different–type organic matter contribution to hydrobiont production depending on total phosphorus and humic matter content. Bacterioplankton consuming allochthonous DOM is additional energy source for zooplankton. For prediction of the total biological productivity it was recommended to take into account also production of heterotrophic bacterioplankton which is involved in utilization of allochthonous DOM.