STUDIES ON GREEN HOUSE GAS EMISSIONS FROM HYDROPOWER RESERVOIRS

Abstract

Now a day's GHG emissions from the hydropower reservoirs is a global issue because it causes global warming. For some years hydropower was regarded as green energy but now it is realized that it significantly contributing to global warming under climate change. Hydropower reservoirs are found to emit about 35-70 times less GHG compare thermal power plants. The amount of GHGs emitted at the air-water interface of reservoirs varies over time. The "fuel" for the methane, carbon dioxide and nitrous oxide emitted by dams is the rotting of the vegetation and soils flooded by reservoirs, and of the organic matter (plants, plankton, algae, etc.) that flows into, and is produced in, reservoirs over their lifespan. The gases are released at the reservoir surface, at turbines and spillways, and downstream of the dam. The trapping of sediments in reservoirs may act as a carbon sink; it may also indirectly increase the concentration of carbon dioxide in the atmosphere by reducing the amount of river-borne sediments available to fertilize oceanic plankton, which are important consumers of carbon dioxide. The magnitude of emissions not only depends on the type of eco-region in which the reservoir is located but also on the parameters like age, depth, temp, volume, input of organic matter, and water quality parameters such as DO, BOD, TP, nitrites-N, total alkalinity of the reservoirs and therefore, large variations in emissions are found. No data-is available on the emissions. and the factors affecting the emissions on hydropower reservoirs, so the baseline is required to be created of 154 reservoirs but it not appropriate for the prediction of GHG emissions from the Tehri reservoir because the R2 is less than 0.90. To study of impact of reservoir parameters on the GHG emissions, linear equations are developed but the regression coefficient is found very poor, the R2 range for CO2 is from 5 x 10-5 to 0.09 for tropical, 0.002-0.16 for temperate & 0.001-0.36 for boreal, and the R2 range for CH4 is from 0.004 to 0.217 for tropical, 0.012 to 0.244 for temperate and 0.024 to 0.121 for boreal reservoirs, Which is being far lower than 0.90 can not be accurately used for the prediction of GHG from the reservoirs . Thereafter, empirical regression equations are developed to see the combine impact of reservoir parameters and R2 is found as 0.48 for CO2 and 0.16 for CH4 for tropical, 0.34 and 0.37 for CO2 & CH4 respectively for temperate and 0.51 &0.26 for boreal reservoirs. The R2< 0.90 indicates that these equations can not be used to accurately predict the emissions, but can be used to get some idea about emissions from the reservoirs. The experimental results indicated that when the CO2 emission from Oyun reservoir were analysed for individual parameter then R2 is less than 0.90 for both site I and site II, When we combine the all parameters, then R2 0.91 for site I and 0.81 for site II so these multiple regression of site I is used for the prediction iii .The data analysis has indicated high uncertainty in water bodies due to the interferences of different pollutant and high variability in the aquatic environment. Result shows that if the number of parameter decreases, then R2 also decreases. Tropic index of Tehri reservoir shows that the reservoir is oligotrophic, i.e. low primary productivity, low nutrient cover. A deeper analysis shows that the TOC (Total organic carbon) of the Tehri reservoir emit less CO2 gas because of the TOC >93 μmol CL-1 i.e.825-960 μmol C L"1. So result shows that CO2 emission rate is affected by the TOC content.Total carbon (3.86 g year' x 109) and 40 g CO2 Eq. /MWh are compare with other temperate reservoirs and it is found that there `C' emissions in the Tehri reservoir are less than the other reservoirs even located in the same eco-region because of the layering of sediment into the reservoir and the less degradation of the organic material and huge variability in aquatic environment. The less `C' emissions are mainly due to age and mean depth, so it is a positive sign of the Tehri reservoir. The results concluded that common relationship can not be developed but these may be developed for each reservoir & can be used for prediction specific to the reservoir.