Bottom Sediments as a Potential Source of Phosphorus in the Riverine-Lacustrine System of the Kośna River (Northeastern Poland)

Sediments from hypereutrophic Lake Łajskie localized in northeastern Poland were examined on the basis of P-fraction. The sediments were collected at five sampling sites. In the investigated lake, the rank order of P-fractions was HCl-P > BD-P > NH₄Cl-P > NaOH-nrP. The loosely sorbed phosphorus NH₄Cl-P represented < 3% of the sedimentary inorganic phosphorus, while the reductant phosphorus (BD-P) ranged from 2 to 10%. The calcium bound phosphorus (HCl-P) showed considerable contribution (59–74%) to the sedimentary inorganic P-loads. BDP was the most reactive fraction in Lake Łajskie. Iron compounds and organic matter seem to play a significant role in regulating this labile P-budget.