DRYING-INDUCED STIMULATION OF AMMONIUM RELEASE AND NITRIFICATION IN REFLOODED LAKE SEDIMENT

Air drying of intact sediment cores from a shallow freshwater wetland caused the release of a substantial amount of ammonium following reflo oding. The increased ammonium concentration stimulated nitrification a t a rate 10 times higher than in the original waterlogged sediments un der aerated conditions. Under non-aerated conditions, nitrate concentr ations decreased more rapidly in reflooded systems than in the waterlo gged systems. Ammonium and nitrite had accumulated in the original wat erlogged systems, but this was rare in reflooded dried cores because o f 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. Dr ying and reflooding of wetland sediments may eventually increase loss through promotion of denitrification.