The importance of land use change analysis in the greenhouse gases emissions from hydroelectric reservoirs

摘要

Land use changes have become a major force driving ecosystem changes, such as native forest lost to crops or to construction of an artificial lake. Some external factors have been responsible for eutrophication processes in freshwater reservoirs, such as industrial, domestic, and agricultural waste discharge; agricultural residues; atmospheric pollution in precipitation form; and vegetation remaining in reservoirs not deforested before floodgates closed. These effects occur because reservoir construction disturbs the natural hydrological process and human activities change land cover. This has lead to numerous studies on land use / cover change (LUCC) caused by hydropower construction (LIMA et al. 2004, ZHENG et al. 2004). Nevertheless, these artificial water bodies often suffer influences from its environment such as degradation of upstream catchment areas due to land use change, such as development of large-scale irrigated areas and urbanization that cover far larger areas. However, it must be emphasized that these land use changes are considered in flux for about 20 years, after which they have reached a new equilibrium, as stated in the Intergovernmental Panel on Climate Change (IPCC) guidelines (IPPC 2006). There are some concerns about hydropower generation being a clean energy source because reservoirs flood large amounts of vegetation present in the drainage. Research on Brazilian hydroelectric reservoirs (Rosa et al. 1996, 2002) demonstrated that these systems have greenhouse gas (GHG) emissions, particularly methane (CH_4), carbon dioxide (CO_2), and nitrous oxide (N_2O) emissions. Measurements, studies and models for GHG emissions must take in account emissions or uptake from all kinds of land use, including reservoirs and river reaches as well as different terrestrial land use. Therefore, it is necessary to know and to quantify the contribution of land use change to the GHG emissions to evaluate the carbon budget better from the hydroelectric reservoirs. Several previous studies (CHANDRASEKERA 2000, PATTON 2005) showed that environments adjacent to the hydroelectric reservoirs should be appraised to quantify/establish the emission contributions from these sources. Thus, this study had as objective to estimate the influence of the land use change in order to improve GHG emission estimates and consequently to diminish carbon budget uncertainties from hydroelectric reservoir.