Methodological biases in phosphate adsorption experiments

A review of the literature indicates that the methodology used in phosphate adsorption experiments varies greatly among researchers, especially in studies with freshwater sediments. We used sediments from three lakes with contrasting trophic status and geochemical characteristics to test the effect of sediment depth and experimental water to sediment ratios on phosphate adsorption isotherms and kinetics. We found that different sediment layers have different phosphate binding capacities and that these differences are not consistent among various types of sediments. We also found that sediments tested at higher solution to sediment ratios had lower adsorption rates, but higher phosphate binding capacity. This particle concentration effect suggests that applying laboratory results to field conditions where solution to sediment ratios vary (e.g. during sediment resuspension) may be complicated. A review of the literature suggests that storage and sieving of the sediments should be avoided, unless their effects on phosphate binding capacity are tested.