Avaliação das formas e fracções do fósforo nos sedimentos superficiais do fundo do estuário Bons Sinais – Quelimane

Abstract

The identification of the chemical forms of phosphorus present in the sediments is a useful tool in the evaluation of the possible sources of this nutrient for estuarine regions, besides the identification of the biogeochemical processes that control the availability of phosphorus in tropical environments. The main objective of this work was to know the forms and concentrations of inorganic and organic phosphorus in the surface sediments of the Bons Sinais estuary, Quelimane province of Zambézia. To reach this objective, three points were selected which were georeferenced by a GPS, making a total of three samples collected at each point. These samples were collected on July 07, 2018 by a van (veen) type instrument (bottom sampler) ESCMC-UEM. The samples were submitted to the chemical fractionation of the sedimentary phosphorus where inorganic, organic, inorganic phosphorus and total phosphorus, PINA, PIA and PI, PO, PT fractions were extracted respectively using the modified Williams `method (Burrus et. al., 1990). The concentration of these fractions and forms were determined after extraction by photometric spectral analysis using specified reagents and wavelengths throughout the work. Where the estuary of the Good Signals indicated the concentration of PT from 270.03mg / kg to 620.68mg / kg. This allowed the classification of these sediments as unpolluted and moderately polluted because they present these concentrations, as a function of the phosphorus pollution index proposed by Cazati et al., 2008. While the inorganic form varied from 102.01 mg / kg to 241.08 mg / kg and the organic form from 803.66mg / kg to 1616.93mg / kg. The mobility of the inorganic fraction (PINA) was higher in contribution to both the inorganic form and the total phosphorus followed by the organic form that contributed with high concentrations for the total phosphorus in the sample of P3, this fraction is considered to be more labile, indicating that most of the phosphorus contained in the sediments of this estuary has the potential to migrate to the water column, this fraction also results from the intense anthropic activities. It was possible to observe a clear differentiation of the percentages of the PIA fraction in relation to the PT, since this low contribution is associated with the sample collection period. The observed difference between the points selected for sampling is likely to be derived from the differentiated inputs of material to which each point is subjected.