Flooding Depth and Timing Effects on Phosphorus Release from Flooded Biosolids in an End-of-Life Municipal Lagoon

Municipal biosolids in end-of-life lagoons can release phosphorus (P) to floodwater and contribute to P enrichment of receiving waters if the floodwater is released. Phosphorus release to floodwater is well-documented in agricultural and wetland soils, but information on flooding depth and timing effects on P release from flooded biosolids in end-of life municipal lagoons is currently lacking. This 42-day experiment utilized intact, cattail-(Typha latifolia L.) vegetated biosolids cores (45.7-cm diameter by 60-cm height) to investigate the effects of flooding depth (5, 15, and 25 cm) on P release from biosolids and on P fractionation in pore water, floodwater, and biosolids upon flooding of municipal biosolids. Averaged across flooding depths, TP rapidly increased from the onset of flooding (0.45 mg L−1) to day 14 (1.8 mg L−1) and remained relatively constant thereafter (1.8–1.9 mg L−1). Dissolved reactive P was the major fraction of P in pore water and floodwater. Flooding for more than 3 days resulted in the release of > 0.5 mg L−1 dissolved reactive P (DRP) to floodwater. Phosphorus release was positively correlated with Fe and Mn concentrations in pore water and with water-extractable inorganic P, labile inorganic P, and Fe/Al-bound organic P concentrations in biosolids. Results indicate that P release to floodwater; hence, risk to receiving water bodies, is minimal during the first 3 days of flooding. This suggests that release of floodwater from the lagoon presents minimal adverse impact to receiving surface waters if done during the early stages (< 3 days) of flooding.