Variations in the amount and composition of phosphorus in settling particles in the northern Baltic Sea archipelagos

Quantification of the downward flux of phosphorus (P) in the water column is essential for understanding the fates and pathways of different P forms and to establish mass-balances in aquatic systems such as the Baltic Sea. In this study, we investigated the amount and composition of settling P in sediment trap material, as well as the seasonal and spatial variation of the material in four archipelago areas along the Swedish and Finnish coasts of the Baltic Proper. It was found that potentially mobile and immobile forms of P make up roughly equal shares of the total P in settling material, implying that, over time, around half of the settling P will be mobilized in the sediments. We also found substantial temporal and spatial variation in terms of amounts and composition of settling P that may partly be explained by differences in primary production and resuspension.