Estimation of ammonia exchange at the land–ocean boundary condition of Sundarban mangrove, northeast coast of Bay of Bengal, India

Abstract

Abstract The Sundarban mangrove forest (4264 km 2 ) is about 3% of the total area of the world mangrove is interdependent on the coastal aquatic subecosystem (1781 km 2 ). Ammonia concentration and flux measurements in the mangrove ecosystem and measurements in such tropical land–ocean boundary conditions are few and far between. A micrometeorological method was used to measure ammonia exchange over Sundarban mangrove forest and aquatic subecosystem. Results showed both emission and gaseous dry deposition in the forest area at a rate 1.79×10 3 and 2.26×10 3 kg N km –2 yr −1 , respectively. Flux of ammonia in the aquatic subecosystem was found always from air to water with a rate of 775.7 kg N km –2 yr −1 . The annual particulate dry and wet atmospherically deposited ammonia flux were calculated to be 69.0 and 21.5 kg N km –2 yr −1 , respectively. Exchange of gaseous ammonia in the mangrove forest showed net deposition with a rate of 4.90×10 2 kg N km –2 yr −1 . Annual imported flux from the proximate terrestrial source to this virgin forest was found to be 4.26×10 6 kg N yr −1 out of which 32.9% was deposited to the coastal water. Ammonia compensation point for mangrove vegetation was found to occur between 51 and 421 nmol m −3 and its variation was related to wind velocity, temperature, and humidity.