Application of stable isotope studies in biogeochemistry: a case study off the Goa coast. CP-10

The field of biogeochemistry involves scientific study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment. Since this is a highly inter-disciplinary field, these are situated within a wide range of host disciplines including: atmospheric sciences, biology, ecology, environmental chemistry, geology, oceanography and soil science. Many researchers investigate the biogeochemical cycles of chemical elements such as carbon, oxygen, nitrogen, phosphorus and sulfur, as well as their stable isotopes. The cycles of trace elements such as the trace metals and the radionuclides are also studied. Biogeochemistry deals with how biological and geochemical processes affect element cycles in Nature, considering both space and time. Biogeochemical processes in sediment-water milieu in particular may be viewed as sets of inorganic and organic reactions, which involve enzymatically, mediated electron transfer from donors to acceptors. Bacteria play extremely important role in breaking down of organic molecules and transformation of inorganic compounds: eg., sulfate reduction and anaerobic methane oxidation like processes. Bacteria derive energy by transferring electrons from electron source or donor to an electron sink or terminal electron acceptor. Organic electron donors vary from monomers that support fermentation to simple compounds such as acetate and methane. Energy is harnessed by shuttling electrons through transport chains within a bacterial cell until a final transfer is made to a terminal electron acceptor. The common electron acceptor are O2 , NO3- , SO4 , Mn3+ , Fe3+ , CO2 . Bacterial processes in sediments may be classified as aerobic and anaerobic. The most fundamental difference between aerobic and anaerobic metabolism is energy yield