ION CONCENTRATIONS IN INTERSTITIAL WATER AS INDICATORS FOR PHOSPHORUS RELEASE PROCESSES AND REACTIONS

Sediment composition and interstitial water concentrations of soluble reactive phosphorus (SRP), dissolved iron, ammonia nitrogen and dissolved organic carbon and pH were monitored at five sampling stations in the shallow Lake Loosdrecht (The Netherlands). The differences in concentrations between the sediments were much larger than the differences in overall sediment composition. The concentration of SRP and ammonia were strongly correlated, the ratio between them was close to that predicted from a mineralization model. Possibly, the high concentration of refractory organic material in the sediments affect the availability of iron. The pore water was calculated to be frequently supersaturated with respect to vivianite. This, however, did not seem to affect the phosphate concentrations in the pore water.