Phosphorus characteristics of settling and suspended particles in Lake Erken.

The aim of the study was to determine proportions of phosphorus forms as well as total phosphorus content in suspended and settling particles during spring, summer and autumn in order to improve the understanding of particle composition and mineralization processes in moderately eutrophic, temperate lakes with summer stratification. The highest phosphorus content was found in epilimnetic suspended matter with maximum mean concentration in summer. There was a gradual decrease in total P content from suspended matter to settling particles and surficial sediment. Phosphorus extracted with sodium hydroxide was the dominant fraction showing organic phosphorus to be most important. Labile phosphorus was a significant fraction and contributed more in epilimnetic suspended matter and in material from the uppermost traps in comparison to hypolimnetic material and surficial sediment. There was a seasonal variation in P forms with maximal shares of labile P and organic P in summer. The findings clearly indicate a dominance of phytoplankton and detritus in the epilimnetic particulate matter during summer, while inorganic and resuspended material is more important during mixing periods. The P composition of settling particles and suspended matter show similar trends, but the total content and shares of labile and organic P are significantly higher in the latter.