Benthic bacterial diversity and nutrient processes in mangroves: impact of deforestation

The bacterial diversity and nutrient dynamics of mangrove sediments in Kisakasaka, Tanzania, was investigated in order to evaluate potential changes associated with deforestation of mangroves. Study sites included relatively undisturbed, recently protected mangroves and clear-cut mangrove areas that were sampled during both the wet and dry seasons. Physicochemical parameters, nitrogenase activity, pore water nutrient concentrations and bacterial diversity were measured in sediment depth profiles using both molecular and chemical techniques. Results show that there are significant differences in sediment pore water nutrient concentrations and bacterial diversity in sediments of mangrove areas which have been deforested compared to those which have been protected. Average measured values for protected and deforested areas, respectively, were: sulphide (S 2−), 1.9±0.5 mM at 30 cm depth; ammonium (NH 4 +), 58±2 μM and 113±12 μM at 4–5 cm depth; soluble reactive phosphate, 40.2±11 μM and 18.4±1.2 at 4–5 cm depth. Nitrogen fixation rates were lower in deforested areas during day and night, organic content was higher in protected areas (20±5%) compared to deforested areas (12±3%). The bacterial diversity was lower in deforested areas as determined by Shannon index using 16S rRNA gene analysis with terminal restriction fragment length polymorphism.