The variability of phosphorus fractions in sediments of a shallow, restored Antoninek Reservoir (Poznań, Poland)

Spatial and temporal variability of phosphorus (P) fractions content in bottom sediments of a shallow preliminary reservoir was studied in Antoninek, situated in Poznań. Fractions were analyzed at least once in a season (more often in spring and summer) between August 2004 and November 2005 according to the fractioning protocol proposed by Psenner et al. (1988). Circa 10 cm thick sediment layers were collected from three study sites, situated along the main axis of the reservoir. The contribution of NH4Cl-P and BD-P, i.e. the most accessible fractions biologically was similar at all stations (usually below 10%). The share of other fractions increased according to the sequence NaOH-RP < NaOH-NRP < HCl-P < Res-P. Only at station 1 the amount of phosphorus related to organic matter was lower than with aluminum. The domination of Res-P fraction indicated that the main part of phosphorus in sediment is biologically unavailable, therefore the intensity of phosphorus loading from sediments shall be low. However, high organic matter content, noted in sediments of Antoninek Reservoir, determined great amount of NaOH-NRP fraction. Both parameters remained under the influence of mats of macroalgae, growing intensively in the reservoir during vegetation season. The role of sediments as a source of phosphorus for water column enlarged, due to increased organic matter decomposition, especially in periods of high water temperature in this shallow reservoir.