, Volume 472, Issue 1-3, pp 53-65

Phosphorus sedimentation in seasonal anoxic Lake Scharmützel, NE Germany

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The seasonal course of phosphorus (P) fractions of sinking particulate matter has been studied at the deepest location of dimictic eutrophic Lake Scharmützel (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.