Drying-induced stimulation of ammonium release and nitrification in reflooded lake sediment

Abstract

Air drying of intact sediment cores from a shallow freshwater wetland caused the release of a substantial amount of ammonium following reflooding. The increased ammonium concentration stimulated nitrification at a rate 10 times higher than in the original waterlogged sediments under aerated conditions. Under non-aerated conditions, nitrate concentrations decreased more rapidly in reflooded systems than in the waterlogged systems. Ammonium and nitrite had accumulated in the original waterlogged systems, but this was rare in reflooded dried cores because of the depletion of bioavailable organic carbon. These results suggest that drawdown and drying of wetlands can accelerate mineralization of the organic matter in sediment, and can temporarily increase ammonium and nitrate concentrations in the water column during reinundation. Drying and reflooding of wetland sediments may eventually increase N loss through promotion of denitrification.