Seasonal Translocations of Nitrogen and Phosphorus in Two Lobelian Lakes in the Vicinity of Bytów, (West Pomeranian Lake District)
A. Jarosiewicz, Z. Witek
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Institute of Biology and Environmental Protection, Pomeranian Academy, Arciszewskiego 22b, 76-200 Słupsk, Poland
Pol. J. Environ. Stud. 2009;18(5):827–836
The aim of this paper was to determine the nutrient translocations between different chemical forms (mineral and organic), as well as between different parts of a lake system (pelagic and benthic; epi- meta- and hypolimnion) in an annual cycle. Nitrogen and phosphorus content in lakes Jeleń and Mały Borek were estimated in monthly intervals (except periods of ice cover). In both lakes the biggest amounts of pelagic P and N were recorded in autumn. With the beginning of the growth season the quick decrease of P-total in both lakes was observed, attributed to the sedimentation of the particulate organic material. At the end of spring phosphorus resources dropped by about 50%, and the biggest reduction was observed in epilimnion. Translocations of nitrogen during the vegetative period were poorly synchronized with phosphorus translocations. N-total stocks in water column during spring were increasing or stable. The increase was especially intensive in lake Jeleń and was associated with cyanobacterial nitrogen fixation. This process was stopped and nitrogen resources started to decrease when phosphorus resources attained a minimum level. In the second half of summer (before autumn overturn) the amounts of N and P started to increase, due to enhanced migration of nutrients from sediments. During the winter period extensive nitrification was manifested by the downfall of ammonium and simultaneous growth of nitrate stocks. The lakes differ substantially in such features as the levels of ammonium concentration, rate of phosphate and ammonium accumulation in hypolimnion, or intensity of nitrogen fixation. Symptoms of internal loading with phosphorus and extensive nitrogen fixation were found in lake Jeleń, one of the clearest lakes in Poland.