DIEL VARIABILITY OF WATER-QUALITY IN A TROPICAL POLLUTED BAY

The objective is to describe and quantify the diel variability of wate r quality in a tropical coastal system, Guanabara Bay, Brazil. Water s amples were collected in spring and neap tide cycles over 24 h periods at three strategic sites. A pollution gradient was evident between th e sampling sites, The average fecal coliform values decreased from 10( 6) (site 3, most polluted) to 10(1) (site 1, less polluted). Organic m atter mineralization was found in a similar gradient to organic pollut ion. However, complete nitrification was only found associated to regi ons where the water quality was better. Variability in this data set w as determined mostly by the pollution gradient observed, and by tidal influence as well. The poor water quality indicates that the bay under goes severe environmental stress. However water renewal promoted by ti dal action was an important mechanism in diluting the pollution, impro ving water quality even in ebb tides and in the inner channels. The si gnificance of micro-scale changes in water quality assessment in Guana bara Bay was confirmed, as well as the importance of these strategic s ampling sites, reinforcing the importance of these measurements in mon itoring programs.