Role of micrometer sediment particles (SPLITT fractionation) in phosphorus speciation and its recycling in lakes

To study the potential of phosphorus (P) release from sediments in the lakes: Chelmzynskie and Wieczno Pld. was the aim of this study. The task was realized by carrying chemical sequential extractions. The novelty of our approach consists in adopting the SPLITT (split-flow lateral-transport thin) method of particles separation, which was used supplementary to sieving. Sieving provides following sediment fractions: 0.25–0.5, 0.125–0.25, 0.09–0.125 mm, whereas the SPLITT allows separation of particles which smaller than 30 μm, and which constituted >30 % of total sediment mass. The mass distribution of size fractions in sediments from both the lakes was very similar. P content, as the sum of HCl-P, NaOH-P, NH4Cl-P, was by ca. 20 % lower in the particle size fractions 0.25–0.5, 0.125–25 mm, whereas total P content in SPLIT sediment was much higher in all size fractions (<5, 5–10, 10–30 μm) in the Wieczno Pld. Lake. Although the ecological status is stated to be good in the Wieczno Pld. and moderate in the Chelmzynskie, the Wieczno Pld. experiences very extensive and frequent algal blooms which form scum on the lake’s surface. Based on our findings, we are of the opinion that shallowness of the Lake Wieczno Pld. favors water mixing causing resuspension of fine particles, which results in enhanced P internal cycling and thus P availability for primary producers. Much higher content of phosphorus in the fractions below 30 μm in the Wieczno Pld. than the Chelmzynskie Lake supports our statement.