STOICHIOMETRIC COMPOSITION OF SESTON IN LITTORAL AND PELAGIAL ZONES OF SHALLOW LAKE OBSTERNO (BELARUS)

We estimated the seston elemental composition (C, N, P) and its ratio in pelagic and littoral zones of mesotrophic shallow Lake Obsterno during two contrasting seasons, as well as the influence of macrophyte beds on the seston stoichiometry. In the both pelagial and littoral zones in summer the C: N ratio was small, 4.62 and 7.05 respectively. But it increased slightly during autumn to 5.66 in pelagic samples against 8.33 in littoral ones. The large N : P ratio and the small phosphorus content specially in the macrophyte covered littoral zone equal to 57.7 in July against 22.47 in September suggest a high level of phosphorus limitation in the littoral locations as a possible mediated reason suppressing zooplankton abundance in sumabundance in sum in summer. Our results in the both pelagial and littoral habitat showed a highly P limited situation in which the N : P ratio was larger in littoral with macrophyte than in pelagial zones. The obtained data of littoral seston stoichiometry were recorded for the first time and exceeded the classical Redfield ratio. The elemental imbalance between macrophyte covered littoral and pelagial suggest that nutrients, especially P, are more limiting in macrophyte beds in summer due to the resource competition between phytoplankton and macrophytes for nutrients, a poor food quality, low zooplankton abundance, as well as its poor taxon-specific elemental ratio in summer.