Phosphorus Release from Lake Champlain Sediments Under Reducing and Oxidizing Conditions.

Phosphorus (P) release from lake sediments affects water quality and occurrence of algae blooms. The objective of this study was to quantify P release from lake sediment cores under reducing and oxidizing conditions. Duplicate cores (50 cm, 5-cm i.d.) were collected at four locations within Missisquoi Bay of Lake Champlain. Cores were transferred to vessels in the laboratory and incubated with constant delivery of nitrogen or oxygen gas to overlying lake water. Total P (TP), soluble reactive P (SRP), and unreactive P (URP) were measured at ten time points over 15-days. Relatively consistent P release among sites was found, with large differences between anoxic and oxic cores. Initial TP and SRP were low (12.1 and 3.7 μg L^-1) and increased curvilinearly with time. Mean TP at day-15 for anoxic and oxic cores was 293 ± 19 and 106 ± 11 μg L^-1, respectively; SRP was 137 ± 41 and 20 ± 8 μg L^-1, respectively. Data were pooled and cubic regression was used to estimate total mass of TP, SRP, and URP released over the incubation. Anoxic cores released 10.2-fold greater SRP than oxic cores, suggesting reductive dissolution of iron and/or manganese phosphates was an important P release mechanism. Total P and URP mass release from anoxic cores was 1.8 and 2.6-fold greater than oxidized cores, respectively. Results show that redox status strongly impacted both orthophosphate and organic P release, and demonstrate sediment legacy P could be an important P source to the bay.