Fracionamento do fósforo em sedimentos de reservatórios tropicais semiáridos

Abstract

The reduction of external loads of phosphorus (P) is the main action to promote the reduction of eutrophication in lakes. However, the elimination of these sources is not always sufficient for the recovery. This occurs because the phosphorus can be accumulated in the sediment and can be release for long time. Thus, to restore a lake, is necessary also to reduce the internal loading. For this, is important to know the composition of phosphorus in the sediment, for to evaluate the phosphorus availability potential, important data for restoration plans of eutrophic systems. In this study, the forms of phosphorus in the sediment of two reservoirs in the semi-arid tropical region was investigated. The determination of the forms of phosphorus was evaluated by fractionation, sorting out the forms in loosely sorbed P (P-Water), reductant soluble P (P-BD), metal oxide bound P (P-NaOH), P bound to organic matter (P-Humic), calcium bound P (P-HCl) and residual P (P-residual). The sediment was collected in September 2016 and sliced in situ every 2 cm from surface to 10 cm. The amount of P forms in the sediment varied of 5 mg.kg-1 to 349 mg.kg-1 for Gargalheiras reservoir. While in Cruzeta reservoir the forms varied of 12 mg.kg-1 to 371 mg.kg-1. Despite the variation of amount between the depths and the reservoirs, in general, the range of fractions in Gargalheiras and Cruzeta, was: P-BD > P-NaOH > P-HCl > P-water > P-Residual > P-Humic. In both reservoirs the predominant form was BD followed by NaOH and HCl. The first two forms are available forms and are released easily, becoming it bioavailable for phytoplankton growth.