Phosphorus sedimentation in seasonal anoxic Lake Scharmutzel, NE germany

The seasonal course of phosphorus (P) fractions of sinking particulate matter has been studied at the deepest location of dimictic eutrophic Lake Scharmutzel (29.5 m) by paired sediment traps at 9 and 27 m water depth from May 1996 to December 1997. Relatively large depositional fluxes and considerably variable P fluxes, mainly carried by allochthonous particles, diatoms in spring, and iron during overturns transport almost 60% of the average water column P pool to the sediment surface. The contribution of resuspension and sediment focusing (24-34%) is relatively small. A sequential chemical P extraction of the matter entrapped revealed that ,loosely adsorbed` P contributed to 5-14%, organic bound P to 55-68%, and Ca-associated P to 3-6% of the annual P flux, depending on season and depth. The redox-sensitive (iron bound) P ranged from only 12% of the annual P flux during anoxic sulfidic conditions to 28% during oxic conditions. On an annual basis, 16-18% of sedimenting P was recycled within the water column, and 71-75% of total primary P flux was recycled at the sediment surface. Ultimately, 10-23% of P became incorporated into recent sediments indicating the long residence time for P and a high internal resupply of P for primary production.