Seasonal and vertical distributions of porewater phosphorus and iron concentrations in a macrophyte-dominated eutrophic lake.

In this study variations in total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP) and total iron (TFe) concentrations and pH values in the littoral sediment porewater of macrophyte-dominated eutrophic Mogan Lake (Turkey), were determined depth wise (0-20 cm, on a basis of 5 cm depths) over a period of eleven months. Additionally water temperature, dissolved oxygen, redox potential, TDP, SRP and TFe levels in the overlying water were measured. Especially in the spring and summer months constituting a large portion of the research period, seasonal variation of SRP at depths between 0-5 cm and 15-20 cm were not found to be statistically significant (p > 0.01). However in the fall and winter months, surface sediment (0-5 cm) SRP values were elevated in comparison with deeper sediment depths. As for TFe values, no clearseasonal variation was evident at different depths. Due to the fact that TFe concentrations in the overlying water (101.25-511.67 mg x m(-3)) were lower than iron concentrations in the porewater (104.00-783.00 mg x m(-3)), positive phosphorus release remained at low levels. In this eutrophic lake, in which action is continuing to reduce the external phosphorus load, monitoring SRP variations in the overlying water and porewater would be beneficial.