Understanding Chemical Sequential Extraction Method by Using Nuclear Magnetic Resonance and X–Ray Absorption Near Edge Spectroscopies for Phosphorus Fractionation of Lake Sediments
Phosphorus release from sediments contributes significantly to high phosphorus level in lake water and provides nutrient support to promote algal growth. To speed up the recovery of eutrophic lakes, it is necessary to limit phosphorus release from sediments. Accurate sedimentary phosphorus fractionation is a strong basis for understanding phosphorus release from sediments. There are several techniques to study sedimentary phosphorus fractionation. Chemical sequential extraction (CSE) techniques are commonly used by industrial practitioners. However, it is doubtful that the P fractionation of the lake sediments studied using the Jensen and Thamdrup (1993) method is reliable. The reason is that the phosphorus fractions do not exactly correspond to the chemically defined compounds in the sequential phosphorus extraction. In order to further understand the Jensen and Thamdrup (1993) method, it is necessary to study P species in the supernatant and residue of each fraction. X-ray absorption near-edge structure (XANES) can provide direct information about the mineral phase of phosphorus in the sediments. Solution phosphorus nuclear magnetic resonance (31P NMR) reveals direct molecular and structural characterization of organic phosphorus in the sediments. This study enhanced the understanding of the Jensen and Thamdrup (1993) chemical sequential extraction method for studying the sedimentary phosphorus fractionation by using solution 31P NMR spectroscopy and phosphorus K-edge XANES spectroscopy. The research using the chemical sequential extraction indicated that inorganic P was dominant in all sediments samples. Also, it suggested that calcium-bound P accounted for the largest proportion of the total P in every sediments sample. The solution 31P NMR spectroscopy clearly identified orthophosphate, phytic acid, pyrophosphate, and polyphosphate in the sediments samples. The P K-edge XANES spectroscopy showed all of the sediments samples contained apatite and phytic acid. In addition, the study using the XANES identified apatite in the residue after the HCl extraction of Blackstrap #6; however it indicated no apatite in the supernatant of HCl fraction of both Blackstrap #3 and Pond #11.
DegreeMaster of Science (M.Sc.)
DepartmentCivil and Geological Engineering
SupervisorPeng, Jian; Xiong, Wenhui
CommitteeHu, Yongfeng; Nemati, Mehdi; Boulfiza, Moh; Wang, Hui
Copyright DateOctober 2015
Chemical Sequential Extraction