Denitrification in constructed free-water surface wetlands: I. Very high nitrate removal rates in a macrocosm study

Six newly constructed experimental macrocosms (approximately 0.13 ha each) were built to study nitrogen transformation processes in the adjacent Prado Basin constructed wetland, southern California, USA. First year macrocosm data showed that nitrate was the dominant nitrogen species. Nitrate removal rates during September 1992 were measured at 2800 mg N m −2 d −1 while inorganic nitrogen and ammonia transformation rates were an order of magnitude less. Nitrogen trends and transformation rates within the macrocosms were similar to those found within the adjacent wetland. Based on calculated plant uptake rates and the absence of seepage losses, nitrate removal was attributed to denitrification.