The effect of eutrophication on greenhouse gas emissions in three reservoirs of the Middle Tiete River, southeastern Brazil

摘要

Classic organic pollution, eutrophication, and hypolimnetic anoxia are some of the common water quality problems in reservoirs (STRASKRABA & TUNDISI 1999). In Brazil these problems are related mainly to the loading of untreated sewage to the water bodies; most of the sewage produced has no treatment. In addition to the known consequences, such as hygienic problems, formation of potentially toxic cyanobacterial blooms, and fish mortalities, these impacts may also contribute to greenhouse gas production in the reservoirs and emission to the atmosphere. Untreated sewage loading promotes high dissolved carbon, phosphorus, and nitrogen input, which results in increased autochtonous biomass in the water column; however, the sinking of the organic particles (dead organisms, fecal pellets) results in increased accumulation of organic matter in the sediments. Precipitation also makes an important contribution to the input of allochtonous dissolved and particulate organic matter from the watershed to the reservoirs. As the accumulated organic matter in the sediments is decomposed by microorganisms, increased gas production in the sediments and in the anoxic hypolimnion might occur. This study was designed to evaluate the sediment CH_4, CO_2 and N_2O concentrations of 3 tropical reservoirs in Brazil, as well as to determine the diffusive fluxes of these gases across the water-air interface. The trophic conditions for these reservoirs were also evaluated to determine the relationships between sediment gas accumulation, diffusive fluxes across the water-air interface, and changing conditions in the trophic status of these water bodies.