Overview -
continuation
There is a great controversy about the amount of GHG
which is exchanged between the atmosphere and the earth,
mainly due to incipient methodology and incomplete
knowledge about the coupling of the different components
of each system. Research done in the last decade has
shown that the food chain of many aquatic environments
is not sustained by producing organisms (phytoplankton),
but rather by decomposers (bacteria) and by the input of
organic matter from the drainage basin (allochthonous
material). Taking this into regard, we may conclude that
photosynthesis is not the main source of carbon in these
environments, being superseded by the surrounding land.
And if primary production, based on photosynthesis, is
smaller than the respiratory activity of bacteria, then
these systems do not act as sinks of atmospheric carbon.
On the contrary, they become sources of carbon dioxide.
This approach on the functioning of aquatic environments
is still relatively new and many studies and equipments
are being developed for the measurement of the
respiration rates of bacteria in comparison to
photosynthetic production. As a result of this new
limnological outlook, the status of hydroelectric power
as “clean energy” has been questioned, since reservoirs
assimilate large amounts of plant biomass which is
flooded by them. It has been suggested that the
decomposition of this huge reservoir of carbon in the
aquatic environment is responsible for greenhouse gas
emissions comparable to that of thermoelectric power
plants of the same magnitude.
Indeed, recent research about the production and
emission of GHG in reservoirs has shown that these
systems have non-negligible emissions, particularly of
methane (CH4), carbon dioxide (CO2)
and nitrous oxide (N2O). Considering this,
Brazil has invested in the development of national
surveys of GHG emissions (www.mct.gov.br).
As regards the hydroelectric issue, at the first stage
only the CH4 emissions in the reservoirs were
taken into account, which are related to the
deforestation and land use changes. FURNAS, through a
partnership with COPPE, made a significant contribution
to this survey and to the understanding of reservoir
emissions, by studying the emissions in Serra da Mesa
reservoir still in the flooding phase. In that study not
only the CH4 emissions but also the dissolved
carbon dioxide emissions were measured, including the
measurement of dissolved gases in different depths. The
results established that the carbon dioxide emissions
are roughly ten times greater than the methane
emissions, and that large amounts of both gases were
retained in the hypolimnium, as a result of anaerobic
decomposition of flooded vegetation. Another important
contribution of that study was the use of the
surface-water level regression for the estimate of the
methane emission, since it was observed that no emission
took place in areas with a depth greater than 40 meters.
Due to this the estimates became more precise than the
simplistic extrapolation of the observed values for the
entire water body.
As well as COPPE, some other Brazilian research
institutions have examined the matter of GHG emissions
in reservoirs, most importantly the INPE-CENA (Lima &
Novo, 1999; Lima, 2002) and the INPA (Fearnside, 2002).
Due to the great variance in the average flow values
measured by the different teams, resulting, mainly, from
the diversity of methodology of data collection and by
the often non-linear nature of emission processes, it is
clear that research must be undertaken aiming to perfect
and standardize the different methods. The
state-of-the-art suggests that where the hydroelectric
power generation is smaller than 0,1 W per square meter
of reservoir área, there is the possibility that the GHG
emissions are greater than those produced by a
thermoelectric power plant of the same magnitude (Rosa &
dos Santos, 2000).
The World Commission on Dams (www.dams.org) has
underlined that in spite of the observation of GHG, one
must also take into account the ways in which the system
exchanged GHG with the atmosphere prior to the flooding
of the reservoir. Therefore, it is necessary to
establish a budget of how much carbon the reservoir will
release in its life cycle, and how much the pre-existing
system would release naturally in the same period.
Considering this, our project has the following main
questions to answer:
1 – What is the budget of GHG emissions in reservoirs?
2 – Does hydroelectric power act towards an increase in
the greenhouse effect?
3 – What are the differences in the methods of
estimating the flows of GHG?
4 – How great is our dependence upon the temporal and
spatial resolution of the processes for the development
of adequate models for understanding and predicting
these processes?
The project involves the Department of Environmental
Engineering (DEA.T) of Furnas Centrais Elétricas S.A,
the Alberto Luiz Coimbra Institute – Graduate School and
Research in Engineering – COPPE/UFRJ, the National
Institute for Space Resarch – INPE, the Federal
University of Juiz de Fora – UFJF, the International
Institute of Ecology – IEE, and a foreign consultant,
expert in measuring sediment exchanges of GHG with the
water column, with experience at Chile, Europe, Africa,
New Zealand, Canada and Japan.
This exchange of knowledge will open the door for the
transfer of technology for measuring emissions from the
sediment and for the development of models for the
evaluation of GHG emissions in reservoirs that flood
Cerrado areas. Each researcher will develop different
aspects related to the carbon cycle and to the
measurement of the emissions by reservoirs.
This project is designed to be developed over five
years, in which measurements will take place in most of
the reservoirs of the company. The studies will be
developed in two reservoirs in each year, in this order:
1st year: UHE Serra da Mesa and APM Manso;
2nd year: UHE Itumbiara and UHE Corumbá;
3th year: UHE L.C.B. de Carvalho and UHE
Mascarenhas de Morais; UHE Furnas;
4th year: UHE Funil and APM Manso;
5th year: development of models and final
report.
The carbon emissions at APM Manso will be measured once
again in the fifth year so that we may ascertain the
effect of the passage of the year over the emission
rates obtained earlier, while the reservoir was still in
its stabilization phase.
The following documents will result from the project:
• field reports, presenting the results of each field
trip, to be presented in January, May, and September;
• annual reports with conclusions about the emissions
and most important factors influencing the carbon cycle
in each reservoir; to be presented in March of each
year;
• final report presenting the general conclusions of the
project: the carbon budget in the reservoirs of FURNAS
Centrais Elétricas S.A,
The following diagram shows the different activities
that will take place in each reservoir.
Overview
