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| Titel |
Distinguishing phosphate from fertilizers and wastewater treatment plant effluents in Western Canada using oxygen isotope measurements |
| VerfasserIn |
Veronique Fau, Michael Nightingale, Frederica Tamburini, Bernhard Mayer |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088201
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| Publikation (Nr.) |
 EGU/EGU2014-2288.pdf |
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| Zusammenfassung |
| The successful application of oxygen isotope ratios as a tracer for phosphate in aquatic
ecosystems requires that different sources of phosphate are isotopically distinct. The
objective of this study was to determine whether the oxygen isotope ratios of phosphate from
fertilizers and effluents from wastewater treatment plants in Western Canada are isotopically
distinct. Therefore, we carried out oxygen isotope analyses on phosphate in effluent from five
different wastewater treatment plants (WWTP) in the Bow River watershed of Alberta,
Canada. Samples were collected directly from the final effluent (post-UV) in Banff
and Canmore upstream of Calgary, and from effluents of Calgary’s WWTPs at
Bonnybrook, Fish Creek and Pine Creek. We also carried out oxygen isotope analyses on a
variety of phosphate-containing fertilizers that are widely used in Western Canada.
Historically, most of the phosphate contained in manufactured fertilizers sold in
Alberta came from two distinct deposits: 1) a weathered Pliocene igneous carbonatite
located in eastern Canada, and 2) the Permian Phosphoria Formation in the western
USA.
Phosphate (PO43-) contained in the water or the fertilizer was concentrated and
quantitatively converted to pure silver phosphate (Ag3PO4). The silver phosphate was then
reduced with carbon in an oxygen free environment using a TC/EA pyrolysis reactor linked to
a mass spectrometer where 18O/16O ratios of CO were measured in continuous flow mode.
Preparation of samples for δ18OPO4 analyses was conducted using the Magnesium Induced
Coprecipitation (MAGIC) method. Expected oxygen isotope ratios for phosphate in
equilibrium with water (δ18Oeq) were calculated using the Longinelli and Nuti equation: T (Ë
C) = 111.4 - 4.3 (δ18Oeq - δ18Owater).
Measured δ18O values of phosphate for fertilizer samples varied from 8 to 25 oÈ®n
average, fertilizer samples of sedimentary origin had higher δ18O values (15.8) than those of
igneous origin (11.5). Phosphate isotopic analyses on samples from WWTP effluents are
currently being conducted. We hypothesize that δ18O values in phosphates of WWTP
effluents are controlled by equilibrium oxygen isotope exchange with water. Since water in
the Bow River has remarkably low ?18O values ranging between -21 and -18o
we expect δ18Oeq of phosphate of approximately +4 oÄ°f confirmed by ongoing
measurements, the δ18OPO4 values for WWTP effluents would be much lower than those of
fertilizers. Oxygen isotope compositions of phosphate would consequently be a
useful tool to trace phosphate sources affecting riverine systems in Western Canada. |
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