PHOTODEGRADATION OF DISSOLVED ORGANIC CARBON IN HUMIC COASTAL LAGOONS(RJ,BRAZIL)

摘要

Dissolved organic carbon(DOC)accounts for most of the carbon in lakes and represents a dynamic link between the geosphere,the hydrosphere and the biosphere(Graneli et al.,1998).Heterotrophic bacteria are the major consumers of DOC,reintroducing it into the food web through the microbial loop(Azam et al.,1983).DOC is composed mainly by humic substances in the majority of aquatic ecosystems(Thomas,1997).Due to their biologically refractory nature,these substances acumulate in aquatic ecosystems,unless other processes remove them from the water.Sunlight oxidize DOC directly to CO_2 or break it down into smaller molecules,generally labile bacterial substrates(Moran & Zepp,1997).This process of photodegradation enhances the removal of refractory DOC(i.e.humic substances)from aquatic ecosystems through 1)direct mineralization(photo-oxidation)and 2)increase in the bacterial consumption and consequent respiration(Graneli et al.,1998).Thus,any attempt to understand the interaction of light,DOC and bacteria in humic aquatic ecosystems,assumes a great importance for the understanding of the carbon cycle and ecological functioning of these ecosystems.