Phosphorus release and sediment geochemistry in a low-salinity water bay of the Gulf of Finland.

Sequestration of phosphorus in sediments is critical in controlling the availability of phosphate for algal growth in shallow bays of the Gulf of Finland (Baltic Sea). In the organic rich, low-salinity-water bay studied, the release of phosphorus from the sediments was sensitive to bio irrigation and oxygen conditions in the water. This was explained by the importance of hydrated iron oxides in binding phosphorus at the sediment surface, the sensitivity of iron-bound phosphorus to redox conditions, and the presence of soluble iron and sulphate. Chemical forms of phosphorus, especially phosphorus bound by redox-sensitive hydrated iron oxides, are regulated by the amount of degradable organic matter, availability of oxygen, iron and sulphate as well as bio irrigation by benthic fauna. To improve the short-term prediction of the water quality and particularly the dynamics of algal blooms in the coastal areas of the Gulf of Finland, sediment phosphorus and especially hydrated iron oxides should be included in water quality models. [ABSTRACT FROM AUTHOR]