Avaliação dos impactos da atividade de piscicultura em tanques-rede sobre as emissões de gases de efeito estufa no reservatório da UHE de Balbina, Amazonas, Brasil

Abstract

The fish farming in artificial water tanks are increasing in the country and the impacts from this practice need to be evaluated to avoid damage to ecosystem. Impacts predicted are the increase of Green House Gases (GHGs) emissions, methane (CH4) and carbon gas (CO2) associate with the increase of organic sediments to the system. The Amazon government, since 2007, studies the implementation of fish farming in the Balbina hydroelectric power plant lake, Presidente Figueiredo county far 170 km of Manaus AM, where a pilot project is already going on with 8 water tanks. This work aims evaluate the impact of fish farming in the netting tank to CH4 and CO2 emission. To this study were procedures diffusivity and boiling emission mesurements of GHGs sampling between february and may of 2013. The diffusivity emission were carried on with floating static chambers, where temporal series sample (15 minutes in total) of gas were collected with 60 ml syringe and stored in 30 ml bottles. The boiling emission were proceeded with inverted hoppers, submerged and incubated for a period of 24 hours. All the samples were analysed to CH4 and CO2 using Gas Chromatography, at INPA in Manaus. The CH4 diffusive flux ranged from 0.003 to 189.000 mgC/m2/day, average of 8.473 mgC/m2/day, and the CO2 ranged from -1.650 mgC/m2/day to 183.518 mgC/ m2/day, average of 6.354 mgC/m2/day. The results do not indicate a significant difference in the diffusive fluxes between the control and netting tank area. The methane boiling flux ranged between 1.230 and 7.010 mgC/m2/day, and to CO2 ranged from 0.005 to 0.110 mgC/m2/day in the netting tank area. The methane boiling flux in the netting tank area was significantly higher than those measured in other parts of the reservoir, whilst the CO2 flux was not significantly. There were no anoxic zones in the water column on both locals (netting tank and control), or even significant concentration of CH4, CO2, Oxygen, temperature, pH and conductivity. The relative homogenity between the locals was due to the intense vertical and horizontal mixture and it explain the similarity of diffusivity emissions found. The major methane boiling emission in the netting tank reflect the major accumulation of organic debris in the local sedments. The results showed the importance of hydrodynamic in minimize the netting tank impacts in the water column. However, the solid sediments impact, which accumulate below the tanks were significant and should be considerate in the scheme of futures fish farming systems.