Sediment Phosphorus Equilibrium Concentration (EPC₀) Measured Using a Novel Dynamic Mesocosm System

The sediment equilibrium phosphorus concentration (EPC₀) is used to estimate phosphorus (P) flux at the sediment-water interface. This parameter is most commonly measured by the batch method which potentially disrupts natural sediment structure at sampling. This manuscript describes the use of a dynamic mesocosm system consisting of sediment cores modified to recirculate overlying waters from the cores through an external reservoir that is subject to experimental manipulation. The method allows EPC₀ to be determined on intact cores while preserving in-situ sediment structure. Calibration of the system demonstrated time to steady state after P-spiking to vary by spike concentration and temperature. Comparisons between EPC₀ from batch and mesocosms revealed higher EPC₀ in cores compared to batch methods. When sediment structure was disrupted by homogenization, technique differences were reduced.