Forms of phosphorus and its accumulation in coastal sediments of Kieler Bucht

Abstract

To study the fate of natural and anthropogenic phosphorus input to a coastal system, the removal of P by accumulation in fine-grained sediments of Kieler Bucht (Western Baltic) was investigated. A phosphorus fractionation scheme was applied to 12 cores from mud, sandy mud and muddy sand sediments. Most phosphorus is contained in the moderately reducible and organic fractions. Almost all excess P in the top enrichment zone is chemisorbed or bound to iron. Evaluation of dated cores from the different sediment types yielded a natural background accumulation of 702 × 10⁶ g P · yr⁻¹ for the whole Kieler Bucht from erosion of till and fluvial input. There is an additional accumulation of up to 538 × 10⁶ g P · yr⁻¹ in recent years which is partly due to diagenetic mobilization and redistribution. In any case, the accumulation of P in fine-grained sediments of Kieler Bucht is far less than published input rates from streams and sewage plants. Thus, in addition to sediment accumulation, a substantial part of the phosphorus input from land is entrained in nearshore sedimentary basins and is lost by currents flowing through Kieler Bucht. Accumulation in sand and lag sediments (16 cores) is of minor importance due to low P-contents and a slow accumulation rate.