Model experiments using mangrove mesocosm tanks were performed two times at the campus of Kasetsart University, Thailand. Replicates of 13 mangrove (Sonneratia caseolaris) saplings were planted in 7 mesocosm tanks and water and soil samples were collected during the 2 experimental periods. The nitrogen removal rate showed 57 and 73 mgN/m²/day in the tanks where wastewater from shrimp aquaculture ponds was supplied and exchanged, and 164-425 mgN/m²/day in the tanks where the additional nutrients were provided. The phosphorus removal rate was 5.7 and 17 mgP/m²/day in tanks supplied and exchanged with wastewater, and 48 and 97 mgP/m²/day in the tanks provided with additional nutrients. Both nitrogen and phosphorus showed high removal rates in the mangrove mesocosm tanks. However, there was no marked increase in the bacterial community either in the water or surface soil, despite the organic matter-rich wastewater from shrimp aquaculture ponds or high concentrations of inorganic nutrients that were supplied.