Comparing the phosphorus regimes in soft sediments from two sub-systems of the Baltic sea with different redox conditions / En jämförelse mellan fosforbindningen i sediment från Bottenhavet och egentliga Östersjön och syrehaltens betydelse

The role of sediments in the phosphorus (P) dynamics of the Baltic Sea is often highlighted. The impact of the sediments on the water column is strictly limited by the amount of potentially mobile P available in the sediments. We present total P measurements for ten sediment cores from the Bothnian Sea and the Baltic Proper and detailed measurements of different P forms with different mobility in two cores. The Baltic Proper is characterized by anoxic conditions in the bottom waters overlying the accumulation sediments, whereas the bottom waters of the Bothnian Sea are generally oxidized which is also reflected in the sediments. Integrating the sediment concentrations over the depth profiles, amounts of mobile phosphorus were estimated in each sediment core. Average mobile P content in the sediments of the Bothnian Sea was found to be an order of magnitude higher than in the Baltic Proper. By contrast, the bottom waters of the Baltic Proper contained dramatically higher P concentrations indicating that the available mobile P was largely present above the sediments. An indicative distribution of P between deep water and sediment in the Bothnian Sea is 1:16, while the corresponding ratio in the Baltic Proper is 3:1.