Environmental impacts of nitrate-accumulating sulfur oxidizing bacteria on coastal ecosystems : Population dynamics and nitrogen metabolism

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The following studies have been conducted to clarify the relationships between eutrophication in coastal marine environments and nitrate-accumulating sulfur oxidizing bacteria (NA-SOB); 1. Field investigation of spatial and temporal dynamics of NA-SOB populations, 2. Field investigation of environmental factors controlling the population dynamics of NA-SOB, 3. Laboratory investigation of nitrogen-metabolism of NA-SOB, 4. Field (laboratory) investigation of quantitative effects of NA-SOB on benthic respiration and nitrogen cycling at sediment-water interface and 5. Development of mathematical model of benthic respiration and nitrogen cycling in coastal marine sediments where NA-SOB dwells on or in. To investigate the spatial and temporal dynamics of NA-SOB populations, methods to enumerate biomass of each NA-SOB population and to estimate intracellular-NO_3- concentration in a single filament had been developed. Quantitative PCR based on clone library and FISH analysis had also been dev … More eloped for biomass enumeration. To investigate the environmental factors controlling the population dynamics of NA-SOB, an in situ micro-profiling system with micro-sensors had been developed to measure micro-environments at sediment-water interface. To investigate the quantitative effects of NA-SOB on benthic respiration and nitrogen cycling at sediment-water interface, an in situ flux chamber was constructed. With those methods and instruments, seasonal filed investigation had been performed at one or two months intervals for two years at two stations in Tokyo Bay. Regarding the nitrogen -metabolism of NA-SOB, ^<15>N technique was applied to the experimental sediment core with NA-SOB established under laboratory conditions and showed that more than 80% of the intracellular-NO_3- is reduced NH_4+. The mathematical model of benthic respiration and nitrogen cycling in coastal marine sediments with NA-SOB was based on two parallel calculation procedures (modules); i. a biogeochemical module and ii. A biological module describing the movement of NA-SOB and their intracellular pools of NO_3- in particular. Thus, the NA-SOB-model was built by coupling the biogeochemical module to the biological module. In the biological NA-SOB module a NA-SOB filament was described as a "self-operating particle" (automaton) responding to external micro-environments. It has been quantitatively shown with the model that NA-SOB is deeply concerned in the increase in the internal nitrogen loading from the sediment and in the decrease in the sediment denitrification. Less