Developing a stable isotope approach to trace the sources and metabolism
      of phosphorus in freshwaters
Creators: name: Davies, Ceri
Publisher: name: Lancaster University
Year: 2016
Subjects: Phosphorus
Stable isotopes
Freshwater

description: The oxygen isotope ratio of dissolved inorganic phosphate
      (δ<sup>18</sup>O<sub>p</sub>) represents a novel
      and potentially powerful stable isotope tracer for biogeochemical
      research. Analysis of δ<sup>18</sup>Op may offer new insights
      into the relative importance of different sources of phosphorus within
      natural ecosystems. Due to the isotope fractionations that occur alongside
      metabolism of phosphorus-containing compounds,
      δ<sup>18</sup>O<sub>p</sub> could also be used to
      better understand the intracellular and extracellular reaction mechanisms
      that control phosphorus cycling. 
      
      In this thesis, new methods were developed and tested for the extraction
      of dissolved inorganic phosphate (P<sub>i</sub>) from
      freshwaters and its isolation from other oxygen-containing compounds,
      including nitrate, sulfate and dissolved organic matter. Excluding
      contaminant sources of oxygen during
      δ<sup>18</sup>O<sub>p</sub> analysis is a critical
      analytical challenge that has constrained
      δ<sup>18</sup>O<sub>p</sub> research in
      freshwaters to date. These new methods were evaluated against existing
      protocols for analysis of
      δ<sup>18</sup>O<sub>p</sub>. While the protocol
      developed in this thesis exhibited greater accuracy and precision for
      freshwater matrices compared to the traditional approach reported by
      McLaughlin et al. (2004), further development work is required to increase
      the accuracy of this protocol compared to that reported by Gooddy et al.
      (2016).
      
      Through the application of
      δ<sup>18</sup>O<sub>p</sub> within two exemplar
      freshwater ecosystems in this thesis, the in-stream fate of Pi derived
      from the effluent of a wastewater treatment plant and from groundwater
      discharge was examined. Within both ecosystems,
      δ<sup>18</sup>O<sub>p</sub> revealed the
      occurrence of metabolic processes that influenced the in-stream fate of P
      yet were masked in the hydrochemical data. In addition, the data reported
      here increase the worldwide groundwater
      δ<sup>18</sup>O<sub>p</sub> dataset nearly
      threefold. These groundwater data highlight the important potential
      differences in δ<sup>18</sup>O<sub>p</sub> due to
      bedrock geology, alongside the potential to use
      δ<sup>18</sup>O<sub>p</sub> to better understand
      the importance of groundwater-derived P following discharge to surface
      water ecosystems. 
      
      
      -Gooddy, D.C., D.J. Lapworth, S.A. Bennett, T.H.E. Heaton, P.J. Williams
      &amp; B.W.J. Surridge. 2016. A multi-stable isotope framework to
      understand eutrophication in aquatic ecosystems. <i>Water
      Research.</i> <b>88</b>, 623
      
      -McLaughlin, K., S. Silva, C. Kendall, H. Stuart-Williams &amp; A.
      Paytan. 2004. A precise method for the analysis of δ18O of dissolved
      inorganic phosphate in seawater. <i>Limnology and Oceanography:
      Methods</i>. <b>2</b>, 202