The objectives are: a) measurement of potential and actual nitrification and denitrification rates at different stations in the brackish part of the estuary, followed by localization of the active organisms (attached-free living); b) measurement of production rates of nitrous oxide as well as experiments with specific inhibitors and stable isotops (15N) to trace the origin of this gas; and C) identification of bacterial populations using molecular techniques, i.e. denaturing gradient gel electrophorese (DGGE), and r-DNA targeted specific probes.