Effects of aerobic and anaerobic conditions on P, N, Fe, Mn, and Hg accumulation in waters overlaying profundal sediments of an oligo-mesotrophic lake.

Concentrations of key nutrients and metals in water overlaying profundal sediments were evaluated in replicate experimental chambers containing undisturbed sediment-water interface samples from Deer Lake, an oligo-mesotrophic lake in eastern Washington. Chambers were incubated under three sequential phases: aerobic (21d), anaerobic (27d), and second aerobic (14d). In general, nutrients and metals in chamber water were lower under aerobic versus anaerobic conditions. However, in some cases compounds anticipated to appear only under anaerobic conditions, including ammonia, phosphate, and manganese, were observed during aerobic conditions. Correlation analysis elucidated a number of interactions between compounds. Phosphate correlated significantly (p<0.05) with iron during all incubation phases, suggesting that phosphorus cycling was controlled by iron. Cycling of nitrate and ammonia was tightly and significantly coupled under aerobic conditions. During both aerobic phases, nitrate increased while ammonia decreased, likely as a result of biological nitrification. Finally, mercury appeared during mildly reducing conditions and showed a significant correlation with manganese during the anaerobic phase, suggesting that Mn oxide reduction was the source of Hg in chamber water.