Biogeochemical cycling of N in tropical coastal zones: molecular microbial ecology of trace gas production.

The coastal zone is extremely important in the biogeochemical processes which control the natural cycle of elements of the Earth. In particular, the coastal zone contributes significantly to the nitrogen cycle, removing nitrogen washed in from the land by rivers and so reducing its fertilizing impact on the coastal seas. However, these removal processes, driven by microorganisms, also contribute to the formation of nitrogen gases, some of which (N2O, NO, NO2) are important in global warming. While a lot of work has been done to measure these processes in temperate coastal regions, there is little known about how they occur in the tropical coastal zone nor whether the microorganisms bringing about the processes are the same or different to those in temperate regions. Recent information suggests that there may be significant differences between these regions which we need to know about if we are to be able to understand their importance globally. We intend to measure the rates of these important processes in several tropical coastal sediments, and the relative importance of the different endproducts of N cycling, using stable isotope tracers of N. In addition, we will apply the techniques of molecular microbiology of N cycling, developed in the Colne estuary, to tropical sediments to determine whether the microorganisms are different or the same as in temperate estuaries; and whether different groups of microorganisms predominate in the two regions.