AbstractAn analytical registration of P‐transport processes in intact sediment cores from the shallow reservoir Radeburg II (near Dresden, Saxonia, Germany) was possible by application of KH232PO4and followed by sequential P‐fractionation (PSENNERet al.1984). Under oxygen free conditions and sufficient nitrate supply an activity accumulation was found in the uppermost sediment horizon. Nitrate influences above all the BD‐fraction (reductant soluble P), so that an interaction between nitrate and the iron binding system could be proved. It could be shown by means of activated sludge (a model object for microbial polyphosphate accumulation from a lab plant qualified for biological P‐ and N‐elimination) that added KH232PO4was bound within 5 h to about 75 % in the NaOH‐fraction. The saturation of iron compounds in the activated sludge took place immediately after KH232PO4had been added. In the same time the portion of the microbial immobilization of added32P amounted to 7 % in the high‐iron sediment from the Radeburg reservoir, whereas evidently in the heat‐ and HgCl2‐sterilized sediments this portion was additionally ascertained in the