Dissolved and particulate phosphorus forms in a eutrophic shallow lake

Abstract.

Soluble and particulate phosphorus forms in the surface water of the eutrophic shallow Lake Bützow were investigated from March to November 1998. Soluble reactive phosphorus (SRP) and dissolved organic phosphorus (DOP) of the filtered water were analysed. Suspended particulate matter (SPM) was characterized by particulate organic matter (POM), particulate organic carbon (POC), particulate phosphorus (PP), particulate iron (PFe), phytoplankton biomass (PB) and Chl a. PP was investigated in more detail by means of sequential chemical extraction (Psenner et al., 1984) and the analysis of polyphosphates and phospholipids.¶ In spring, the lowest SRP values and highest PP values were recorded. Over the course of the year, SRP did not decline, whereas DOP increased and became the dominant P-pool in the lake in autumn. Polyphosphate, as a reserve compound in algae, was present only until July. Its decline was accompanied by an increase in phospholipids and a decrease in the easily available PP and the sorptive-bound PP. The levels of iron-bound phosphorus and the apatite-phosphorus remained stable over the year. The available phosphorus declined, although the SRP level never dropped below 0.015 mg L^-1. Thus, insufficient phosphorus was available in this eutrophic lake to allow formation of polyphosphate granules in algae in the second half of the year. Neither SRP nor the elemental composition of seston is suitable to describe the P-status and deficiency for algal growth in the shallow Lake Bützow.