Refinement of the Anion Exchange Membrane Method for Soluble Phosphorus Measurement

Abstract

AbstractThe proper use of anion exchange membranes (AEMs) to assess phosphorus availability in situ requires a more thorough understanding of their function under a wide range of soil biophysical conditions. We evaluated the ability of AEMs to sorb selected organic P compounds, determined possible interference of low‐molecular‐weight organic acids and humic substances on AEM‐P sorption, and assessed the efficiency of AEM‐P sorption in the presence of wetland sediments and soil‐sediment microbes. We collected soils, swamp water, and sediments from a cypress swamp‐pine flatwoods ecosystem in north central Florida. Membranes recovered nearly 100% of both ortho and organic P in a study using aqueous solutions of ortho P and organic P compounds. Membrane sorption of ortho P with varying concentrations of oxalate and protocatechuate was close to 100%. There was a reduction of 15 µg P per membrane when AEMs were placed inside low‐molecular‐weight‐cutoff dialysis tubing (<1000 MWCO) in P‐spiked swamp water; however, there was no significant tubing effect in non‐spiked swamp water. In an experiment exploring effects on AEM‐P sorption of P additions to swamp water with or without sediments, AEMs recovered six times more P than measured in non‐spiked swamp water with sediments. When swamp water was treated with chloroform, AEMs sorbed an equal or greater amount of ortho P than ortho P measured in swamp water with no AEMs. Results suggest that AEMs can be used to measure soluble and readily desorbable P in low‐P status soils and sediments with organic acids.