Phosphorus fractions and their availability in the sediments of eight tropical semiarid reservoirs
2022
Lima, Daniel Jadson Noronha | Menezes, Rosemberg F. | Araújo, Fabiana Oliveira
PURPOSE: We quantified the phosphorus (P) fractions and oxide content in the sediment of eight tropical semiarid reservoirs to assess how water-level decreases affect the potential P internal loading. METHODS: Chemical fractionation analyses were carried out to determine the P fractions in the reservoirs’ sediment, and their chemical composition was evaluated via X-ray fluorescence. Linear regressions were performed to evaluate how changes in the oxide content in the reservoirs’ sediment and percentage of the maximum volume stored (%MVS) affected the P fractions. RESULTS: About 35 to 46% of the content of the sediment load of the total phosphorus (TP) was associated with potentially mobile P forms (NaOH-P and BD-P). The chemical composition of the sediments indicated a strong presence of Al₂O₃ and Fe₂O₃. The regressions showed that the lower the proportions of Al₂O₃ content, the lower was both P mobile (Total-P and BD-P) and non-mobile forms (HCl-P and Res-P) in the reservoirs sediment, whereas the proportions of Fe₂O₃ content were positively related to NaOH-P and Res-P. Moreover, the proportions of SiO₂ and CaO content in the sediment were respectively negatively related to NaOH-P and positively related to HCl-P. The decrease in the %MVS in the reservoirs favored both the accumulation of non-mobile forms of P (HCl-P and Res-P) and CaO in the sediments, whereas an opposite pattern was observed for Al₂O₃. CONCLUSION: The high P load in the sediments, associated with potentially mobile forms and low water level, indicates that an internal loading mechanism may be present in the environments observed.
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