The oxygen isotope composition of phosphate: a potential tool in UK freshwater studies?

The proposal is for a small, 'pilot' research project to look at the isotopic composition of oxygen atoms in phosphate in river systems. High concentrations of phosphate in rivers and lakes are a primary cause of 'eutrophication': an over-enrichment in nutrients leading to conditions which can result in severe environmental damage (reduced biodiversity, oxygen starvation, fish deaths), health issues (toxic algae), and economic problems (expensive water treatment). Many rivers in the UK, and other parts of the world suffer from this problem because phosphate-rich waters from sewage works or from farming activities are pumped or leak into the rivers. Dealing with this problem involves knowing where the phosphate comes from, and understanding what happens to it when it gets into the river. The phosphate ion consists of a phosphorus atom and four oxygen atoms, and the oxygen atoms can be of different isotope types: oxygen of atomic mass 18 and oxygen of atomic mass 16 (both are naturally-occurring, non-radioactive isotopes). Preliminary studies have shown that the proportions of these two isotopes differ depending on where the phosphate came from (e.g. sewage compared with agricultural fertilizer), and that changes in the proportion of the two isotopes indicates the way in which the phosphate is being used in the water. However, this preliminary work is very limited, and has been mainly done in saline waters in estuaries and coastal areas in other countries. We want to see if it might work in fresh water environments in the UK. The plan is therefore two-fold: 1) to analyse the proportions of oxygen-18 and oxygen-16 in phosphate from a small number of sewage and agricultural effluents, to see if they differ. If they do, we may be able to use measurements of river water to determine where phosphate pollution is coming from. 2) to see if the proportion of oxygen-18 and oxygen-16 in phosphate coming from a particular source (e.g. the outfall of a sewage works into a river) changes as the phosphate is carried downstream. If it does, we may be able to use such measurements to determine the phosphorus demand or 'limitation' of the system - an important factor in controlling eutrophication.