Spatial distribution of sedimentary P pools in a Mediterranean coastal lagoon ‘Albufera d’es Grau’ (Minorca Island, Spain)

Abstract

The method for the sequential extraction of P proposed by Jensen et al. [Mcglathery, K.J., Marino, R., Howarth, R.W. (1998) Limnol. Oceanogr. 43, 799–810] was used to study the spatial distribution of sedimentary P in superficial sediments of a mesohaline coastal lagoon located in a watershed formed by carboniferous sandstone in the Western Mediterranean (Minorca Island, Spain). Dissolved inorganic phosphate (IP), dissolved organic phosphate (OP), Fe, Ca, Al, and F were analyzed in the extractions to assess adequacy of this method to clay sediments. The elemental composition of the solid phase (Al, Fe, K, Ti, Si, Mg and Ca) was also analyzed to relate concentrations of P pools to the mineral composition. Samples from marine carbonated sediments, rock and some materials of biological origin (tubes of polychaete Ficopomatus enigmaticus, bivalve shell debris) were analyzed for comparative purposes. The sequential procedure allowed to extract almost all sedimentary P from carbonate sediments and biogenic debris, but only 70% of total phosphorus (TP) from clay sediments and rock. Main IP pools in the lagoon were Fe-bound P (16.6% of TP), CaCO 3-bound P mainly from Ficopomatus tubes (12.0% of TP), and detrital carbonate fluorapatite (7.8% of TP). The most abundant P pool was refractory P (20.3% of TP), which appeared associated to the (Fe,K)Al-silicate fraction and to humic P. This indicated that clay–humic–organic P complexes were the main P reservoir in the lagoon. Spatial distribution of P pools reflected differential sedimentation of allochthonous materials, authigenic precipitation of Fe-oxides, and Fe-bound P as well as the differential distribution of organisms such as Ficopomatus.