Spatial and temporal variability in benthic processes along a mangrove-seagrass transect near the Bangrong Mangrove, Thailand

Benthic primary production and nutrient dynamics were examined along a transect in the Bangrong mangrove forest in Thailand. Six stations were established extending from a high-intertidal site within the mangrove forest to low-intertidal flats and seagrass beds in front of the mangrove forest. Benthic processes (O^sub 2^ and CO^sub 2^ fluxes) and nutrient dynamics (mineralization, sediment-water fluxes, pore water and sediment pools) were measured under light and dark conditions during wet and dry seasons over a 2-yr period. The sediments were mostly autotrophic, only the mangrove forest sites were net heterotrophic during the wet season. Maximum daily net primary production was found at the non-vegetated tidal flats (40-75 mmol O^sub 2^ m^sup -2^d^sup -1^), where light and nutrient availability were highest. The variation in benthic mineralization along the transect was minor (1.6-4.3 mmol CO^sub 2^ m^sup -2^h^sup -1^) and did not reflect the large changes inorganic matter content (organic carbon: 0.7-4.2% DW) and quality (C:N ratio varied from 25 to 100), suggesting that the mineralizable pool of organic matter was of similar magnitude at all sites. There was only minor seasonal variation in rates of mineralization. The net primary production showed more variation with lower rates in the mangrove forest (reduced with 74%) and higher rates at the tidal flats (increased with 172%) and in the seagrass beds (increased with 228%) during the wet season. The nutrient pools and fluxes across the sediment-water interface were generally low along the transect, and the sediments were efficient in retaining nitrogen in the nutrient limited mangrove/seagrass environment. Pools and fluxes of phosphorus were generally very low suggesting that benthic primary production was phosphorus limited along the transect.[PUBLICATION ABSTRACT]