Surface and subsurface water coupled ecological model in a mangrove swamp, Ishigaki Island, Japan

•We model material cycling in a mangrove by combining surface water with groundwater.•Numerical simulation shows a good agreement with field observations of nutrients.•Ground water enhances material exchange between rivers and mangrove swamps.•Supply of dissolved nutrients from mangrove swamps depends on tidal flow.

A surface and subsurface water coupled ecological model is presented to describe material cycling in a mangrove area, to which an ecosystem model is applied in order to account for chemical and biological reactions as well as physical processes. In this model, the nutrient transport from the groundwater to the river is estimated by the combined use of field measurements and numerical simulation of subsurface flow. The water movement and temporal variations in nutrient concentration obtained from the numerical simulation show a good agreement with the field observations, indicating that this model is valid for simulating material cycling in a mangrove area. The numerical simulation reveals that the supply of dissolved nutrients from the mangrove to the coastal area during spring tides is about 1.6 to 5.5 times larger than that during neap tides.