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Phosphorus Cycling under different redox conditions

Xiong, Yijun (2018) Phosphorus Cycling under different redox conditions. PhD thesis, University of Leeds.

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Xiong_Y_Earth and Environment_PhD_2018.pdf - Final eThesis - complete (pdf)
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Abstract

Phosphorus is a basic but essential nutrient element for life, as a major limiting nutrient, is also important for controlling primary productivity on geological timescales. However, P cycling is highly redox dependent through Earth history. The fate of P cycling in many environments is still not clear. This thesis is to investigate mineralogical controls on P cycling under different redox conditions. New geochemical data is reported in the low sulfate, euxinic Lake Cadagno, Switzerland, to investigate the behaviour of the phosphorus cycle. Sulfide-driven release of phosphorus from organic matter and Fe (oxyhydr)oxide minerals is re-trapped by Fe(II) phosphate to constrain the extent of P recycling, and this process is highly sulfate dependent. New experiments are designed to investigate what minerals control P cycling in the water column under different conditions. With the increase of P, Green rust is transformed to vivianite which shows that P concentrations exert first order controls on the mineralogy of Fe minerals, with strong implications for the availability of dissolved P in the water column. In order to quantify the extent of P cycling versus fixation in the sediments under different redox conditions, mass balance models are made based on 4 key redox scenarios. Analogous to those which were prevalent at various intervals in Earth history, under ancient episodes of ferruginous conditions, low flux of recycled P back to water column is controlled by both P re-uptake by Fe(III) (oxyhydr)oxide and the formation of Fe(II) phosphate. During the mid-Proterozoic and during Phanerozoic, under low sulfate euxinia, the flux of recycled P is constrained by Fe(II) phosphate formation. This study provides supporting evidence to the suggestion that the positive primary productivity feedback is constrained by these processes.

Item Type: Thesis (PhD)
Keywords: Phosphorus, P cycling, redox conditions, sulfate dependent, vivianite, Fe minerals, Earth history, primary productivity
Academic Units: The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Sciences (Leeds)
Depositing User: Mr YIJUN XIONG
Date Deposited: 13 Nov 2018 16:00
Last Modified: 13 Nov 2018 16:00
URI: http://etheses.whiterose.ac.uk/id/eprint/22045

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