Determination of bioavailable phosphorus from water samples with low suspended sediment using an anion exchange resin method

Measurement of phosphorus in surface waters for eutrophication studies is common. Phosphorus is commonly adsorbed to suspended sediment, but can desorb under certain conditions. Only a fraction of measured total phosphorus is bioavailable to aquatic organisms like algae, and for assessment, monitoring, and regulatory applications, researchers need to understand what proportion of total phosphorus in mixed water-sediment samples is bioavailable. Ion exchange resins have high capability of taking up dissolved ions like phosphate (PO(4)(3−)) and a long history of use in examining bioavailable phosphorus in surface water runoff. Previous work using resins to quantify bioavailable phosphorus was undertaken in waters with high total suspended sediment (TSS) concentrations (200–2,240 mg TSS/L) and correspondingly high phosphorus. The work presented here was undertaken in watersheds where runoff TSS concentrations are an order of magnitude lower; since bioavailable phosphorus as low as a few micrograms per liter can be important to eutrophication, it was necessary to modify existing anion exchange resin methods for use in low TSS waters. Modifications of the original method and quality controls presented include: • A passive method to concentrate low TSS samples; • Elimination of P cross-contamination from reuse of anion exchange resin; and • Comparison to the original method and reproducibility of results.