Sedimentation and diagenetic transformation of particulate organic phosphorus in a stratified eutrophic lake

For decades limnologists have known about the key role of sediments on the interna! cycle of phosphorus (P) in lakes. High P release rates in eutrophic lakes are often attributed to anaerobic conditions and excessive P accumulation in lake sediments (NüRNBERG 1988, S0NDERGAARD et al. 2003). In eutrophic lakes, a substantial portion of P settles as biogenic P, but its contribution to hypolimnetic P accumulation is often neglected in conceptual and predictive models. The present study was carried out in eutrophic Lake Arendsee, Germany, where a high hypolimnetic P accumulation was observed during summer stratification. Mass balance calculations and sediment core investigations indicated that hypolimnetic P accumulation cannot be solely explained by the potentially mobile P inventory in the sediment (HUPFER & LEWANDOWSKI 2005). Without an additional supply from freshly settled particulate P and its rapid remobilization, the temporary P pool in the sediment would be exhausted in less than 3 months. The objective of the study was to determine particulate organic P species during and after sedimentation and their importance on P recycling. For that purpose, the P-binding forms of seston, trap material, and the uppermost sediment layer was investigated at a high temporal resolution during spring 2005. ,Phosphorus associated with a variety of biogenic compounds was resolved and quantified by P NMR spectroscopy. This analytical too l has been increasingly used for limnological studies ofthe interna! P cycle (AHLGREN et al. 2006, REITZEL et al. 2006).