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Nitrate contamination isa serious problem worldwide. By providing an ample supply of carbon and an anaerobic environment, wetlands are a valuable low technology for treating nitrate-contaminated waters with low organic carbon concentrations. Denitrification is apparently limited by the C:N ratio. with ratios >5:1 resulting in >90% nitrate removal efficiencies. The denitrification rate constant, V-NO3, varies in direct proportion to carbon supply. Several novel or emerging applications of wetlands include renovation of nitrate-contaminated aquifers (a pump-and-treat strategy), denitrification of nitrified sewage effluents, and treatment of irrigation return flows. Treatment of dual sources is also discussed. In arid regions with limited supplies of high quality water, nitrate treatment wetlands may play a significant role in the development of water resources. (C) 1998 Published by Elsevier Science Ltd. All rights reserved