id="p0005">Can sources of aquatic PO4 be traced using its stable oxygen isotope ratio?
id="p0010">Various PO4 sources within a catchment were analysed for their δ18OPO4.
id="p0015">River δ18OPO4 indicated that rapid microbial cycling of PO4 was occurring.
id="p0020">This method appears inappropriate in systems where PO4 cycling is rapid.