Nitrogen removal through N cycling from sediments in a constructed coastal marsh as assessed by 15N isotope dilution.
Constructed coastal marsh regulates land born nitrogen (N) loadings through salinity dependent microbial N transformation processes. A hypothesis that salinity predominantly controls N removal in marsh was tested through incubation in a closed system with added 15NH4+ using sediments collected from five sub marshes in Shihwa marsh, Korea. Time course patterns of concentrations and 15N atom% of soil N pools were analyzed. Sediments having higher salinity and lower soil organic C and acid extractable organic N exhibited slower rates of N mineralization and immobilization, nitrification, and denitrification. Rates of denitrification were not predicted well by sediment salinity but by its organic C, indicating heterotrophic denitrification. Denitrification dominated N loss from this marsh, and nitrogen removal capacity of this marsh was estimated at 337 kg N day 1 (9.9% of the daily N loadings) considering the current rooting depth of common reeds (1.0 m) We showed that sediment N removal decreases with increasing salinity and can increase with increasing organic C for heterotrophic denitrification.
Marine pollution bulletin