Phosphorus retention and release by sediments in the eutrophic Mai Po Marshes,Hong Kong |
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| Institution: | 1. Southern Cross GeoScience, Southern Cross University, PO Box 157, Lismore, New South Wales 2480, Australia;2. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States;3. Western Australian Organic and Isotope Geochemistry Centre (WA-OIGC), Department of Chemistry, The Institute for Geoscience Research, Curtin University, GPO Box U1987, Bentley, Western Australia 6845, Australia;4. Natural and Agricultural Sciences, Faculty of Science, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia;5. Stanford Synchrotron Radiation Lightsource, Menlo Park, CA 94025, United States |
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| Abstract: | This study examined the phosphorus retention and release characteristics of sediments in the eutrophic Mai Po Marshes in Hong Kong. Results of chemical fractionation show that the sum of inorganic P pools exceeded 50% of the total sediment P content, with the redox-sensitive iron-bound P (Fe(OOH) ≈ P) being the dominant P fraction. Given the considerable average Fe(OOH) ≈ P concentration of 912 μg g?1, Mai Po sediments demonstrated a great potential to release bioavailable P under low sediment redox potentials. This was further supported by the high mean anaerobic P flux of 31.8 mg m?2 d?1 recorded in Mai Po sediment cores, indicating the role of bottom sediments as a net P source. Although sediments in Mai Po had appreciable Langmuir adsorption maxima (1642–3582 mg kg?1), the high zero equilibrium P concentrations (0.02–0.51 mg L?1) obtained suggest that sediment sorption processes would contribute to sustaining the eutrophic conditions in overlying water column even with a further reduction in external P load. Concerted efforts should be made to reduce internal loading of P, especially under reducing conditions, to complement the implementation of zero discharge policy for Deep Bay for effective eutrophication abatement and long-term water quality improvement in the Mai Po Marshes. |
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