New research demonstrates stability of phosphate oxygen isotope in lake sediments

Phosphorus is essential for all living organisms and plays a vital role in global food production. However, too much phosphorus from agriculture, waste water and industry can pollute lakes and rivers, contributing to harmful algal blooms and poor water quality.

Scientists use the phosphate oxygen isotope signature, δ¹⁸O-PO₄, to track how phosphorus moves through ecosystems. Normally, the bonds between phosphorus and oxygen in phosphate ions (PO₄^3-) are very stable and don’t break down easily. This means that the oxygen isotopes within PO₄^3- remain unchanged, unless biological processes are involved. Enzyme-driven reactions can break these bonds and allow oxygen isotope exchange with the surrounding water.

Until now, it has been unclear whether this isotope fingerprint remains stable in lake sediments over long periods of time. Researchers from BGS, Lancaster University, Loughborough University and the University of Copenhagen tested three sediment cores collected from one of the lagoons at Anglian Water’s Rutland Water Nature Reserve, with support from the Leicestershire and Rutland Wildlife Trust. One core was left untreated as a control, while the other two were stored for six months in water with a distinct oxygen isotope value at temperatures of 4 to 7 °C, to test whether δ¹⁸O-PO₄ is stable over time and therefore whether it can be used to reconstruct past phosphorus dynamics in freshwater lakes.

The results showed for the first time that δ¹⁸O-PO₄ signatures are preserved in lake sediments, even under conditions designed to encourage phosphorus cycling. The study gives scientists greater confidence that this technique can be used to reconstruct past environmental conditions, track nutrient pollution and support freshwater management.

Understanding how phosphorus has moved through lake ecosystems in the past is essential if we’re to understand these environments effectively in the future. Our results show that phosphate oxygen isotopes can preserve environmental information within lake sediments, which allows us to use this technique to reconstruct past nutrient dynamics and assess long-term environmental change.

Christopher Bengt, BGS-hosted PhD researcher who led the research.

The research paper, ‘Phosphate oxygen isotopes in lake sediments: stability and application for assessing palaeo-nutrient dynamics’, is now available to read.

This work was supported by the Natural Environment Research Council (grant number: NE/S007423/1), with Christopher Bengt’s studentship through the ENVISION Doctoral Training Partnership and the BGS University Funding Initiative.