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δ18O as a tracer of PO43- losses from agricultural landscapes
Journal article   Peer reviewed

δ18O as a tracer of PO43- losses from agricultural landscapes

Naomi S Wells, Daren C Gooddy, Mustefa Yasin Reshid, Peter J Williams, Andrew C Smith and Bradley D Eyre
Journal of Environmental Management, Vol.317, 115299
01/09/2022
DOI: https://doi.org/10.1016/j.jenvman.2022.115299
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δ18O as a tracer of PO43View
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Appendix A. Supplementary DataView
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Abstract

Agricultural industry Biogeochemistry Eutrophication Fertilizers International economic relations Leaching Livestock Livestock farms Point source pollution Sandy soils Soils Tracers (Biology) Phosphate leaching Stable isotope tracers Diffuse agricultural pollution Peel-Harvey catchment δ18O-PO43-
Accurately tracing the sources and fate of excess PO.sub.4.sup.3- in waterways is necessary for sustainable catchment management. The natural abundance isotopic composition of O in PO.sub.4.sup.3- ([delta].sup.18O.sub.P) is a promising tracer of point source pollution, but its ability to track diffuse agricultural pollution is unclear. We tested the hypothesis that [delta].sup.18O.sub.P could distinguish between agricultural PO.sub.4.sup.3- sources by measuring the integrated [delta].sup.18O.sub.P composition and P speciation of contrasting inorganic fertilisers (compound vs rock) and soil textures (sand, loam, clay) in southwestern Australia. [delta].sup.18O.sub.P composition differed between the three soil textures sampled across six livestock farms: sandy soils had lower overall [delta].sup.18O.sub.P values (21 [plus or minus] 10/00) than the loams (23 [plus or minus] 10/00), which corresponded with a smaller, but more readily leachable, PO.sub.4.sup.3- pool. Fertilisers had greater [delta].sup.18O.sub.P variability (~80/00), with fluctuations due to type and manufacturing year. Consequently, catchment 'agricultural soil leaching' [delta].sup.18O.sub.P signatures could span from 18 to 250/00 depending on both fertiliser type and timing (lag between application and leaching). These findings emphasise the potential of [delta].sup.18O.sub.P to untangle soil-fertiliser P dynamics under controlled conditions, but that its use to trace catchment-scale agricultural PO.sub.4.sup.3- losses is limited by uncertainties in soil biological P cycling and its associated isotopic fractionation.

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