title: Phosphorus fractionation in volcanic lake sediments (Azores - Portugal).
abstract: The phosphorus distribution in volcanic sediments of three lakes that are under different anthropogenic pressures in São Miguel island (Azores - Portugal) was evaluated using a sequential extraction scheme. The P-fractionation scheme employs sequential extractions of sediment with NH4Cl, bicarbonate-dithionite (BD), NaOH (at room temperature), HCl and NaOH (at 85 degrees C) to obtain five P-fractions. The P-fractionation shows that in lakes with higher trophic status (Lake Furnas and Lake Sete Cidades), the NaOH extracted P is the dominant fraction, that contribute with more than 50% to total sedimentary phosphorus. The rank order of P-fractionation for these two lakes was NaOH>NaOH (85 degrees C)>HCl>BD>NH4Cl for Furnas lake and NaOH>HCl>NaOH (85 degrees C)>NH4Cl>BD for Sete Cidades lake. On the other hand, the trend of P contribution in the oligotrophic lake Fogo shows that the most inert P pools have the higher concentrations, with more than 50% of the P contribution from the last extraction step with NaOH at 85 degrees C. For this lake, the rank order of P-fractionation was NH4Cl>BD>NaOH>HCl>NaOH (85 degrees C). The Phosphorus Maximum Solubilization Potential (P-MSP) was also calculated and the results show that for the more bio-available P-fractions (first and second extraction step), the P-MSP values for Furnas and Sete Cidades lakes are sensibly higher than the results obtained in Fogo lake, an indication of the non-point diffuse load discharged in the first ones.
authors.affiliation: Institute for Biotechnology and Bioengineering, Centre for Biological Engineering--University of Minho, DEB, Campus de Gualtar 4700-057 Braga, Portugal.
authors.forename: D C
authors.initials: DC
authors.lastname: Ribeiro
authors.forename: G
authors.initials: G
authors.lastname: Martins
authors.forename: R
authors.initials: R
authors.lastname: Nogueira
authors.forename: J V
authors.initials: JV
authors.lastname: Cruz
authors.forename: A G
authors.initials: AG
authors.lastname: Brito
mesh_terms: D005591:Chemical Fractionation / Q000379:methods*; D004784:Environmental Monitoring; D005068:Eutrophication; D005618:Fresh Water / Q000737:chemistry*; D005843:Geography; D019015:Geologic Sediments / Q000737:chemistry*; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry; D011174:Portugal; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus