Phosphorus fractions and their vertical distribution in seabed sediments of the eastern Baltic Sea

Phosphorus fractions and their vertical distribution in seabed sediments were studied in short cores from four coastal sites of western Estonia (Western Gulf of Finland, Väinameri Sea, Suur Strait, and Gulf of Riga) representing accumulation and erosion/transport settings. As a result of recent large-scale discharges of nutrients into the marine environment, abundant phosphorus has accumulated in the seabed sediments, from where it can, under the expansion of hypoxic or anoxic conditions, be remobilized and released back into the water column. A sequential extraction method with a neutral, a reducing, a basis, and an acidic solution was used to evaluate the distribution of phosphorous in pools of five different carrier fractions. Potentially mobile phosphorus is mostly associated with redox-sensitive iron- and manganese oxyhydroxides, and this fraction is significant in the Western Gulf of Finland and the Gulf of Riga. As oxygen conditions gradually deteriorate, the remobilization of a considerable amount of potentially mobile phosphorus from sediments can affect the entire Baltic Sea ecosystem.