Biogeochemical cycle of nitrogen in a tropical mangrove ecosystem, east coast of India

Like many coastal systems, nitrogen is the critical limiting factor for mangrove net production. This study used a box model approach to assess the nitrogen budget in the Sundarban mangrove ecosystem, which acts as a sink for atmospheric nitrogen in terms of NOx, NH3, N2, and water column dissolved inorganic nitrogen. The coupling of biosphere and atmosphere in terms of atmospheric NOx and NH3 uptake showed that uptake of ammonia (130 × 106 mol yr− 1) was about six fold as large as that of NOx, (22 × 106 mol yr− 1). The nitrogen stored by the processes such as plant uptake of NOx, NH3 from the atmosphere, nitrogen fixation (5 × 109 mol yr− 1), and sediment water exchange (8 × 106 mol yr− 1) was about two times as large as that of recycled nitrogen from litter (3 × 109 mol yr− 1), and could account 74% of the nitrogen required for mangrove net production. Most of the nitrogen was conserved in the living biomass (living biomass: 118 × 103 mol ha− 1 versus soil: 3 × 103 mol ha− 1). The loss of nitrogen was 23% of the total amount that was conserved from the external sources in the Sundarban mangrove system. Thus, the coastal ecosystem like Sundarban mangroves could retain only 0.2% (8 × 106 mol) of the annual river flux of nitrogen to the coastal waters and nitrogen is generally conserved within the system.