How green is hydropower? It used to be an easy question to answer, but the complex relationship between emissions of greenhouse gases (GHG) from reservoirs and their contribution to global warming has raised questions over the shade of hydro’s green credentials.

The assumption that hydropower schemes emit negligible amounts of GHG from reservoirs is no longer a widespread belief but it is a question of degrees. Although industry analysts agree that hydroelectricity has very little effect on global warming through GHG, the problem has been quantifying how much is considered to be ‘very little’ over the lifetime of a project.

Alain Tremblay, Hydro-Québec’s senior environment advisor in Canada, says that recent trends have focused on the life cycle of projects and land use change. “It has been the subject of much worldwide interest,” he says.

Netting the gain

For the past 10 years, Hydro-Québec has been narrowing the focus of its research into reservoir emissions. Worldwide studies carried out with various partners led to a need for further investigation. “It transpired that we really had to look more closely at net GHG emissions from reservoirs,” Tremblay says.

With current measurements only citing gross GHG emissions, it is difficult to give an accurate comparison between hydropower and other energy alternatives. This, in turn, can make it more difficult for hydroelectricity to fight its corner in the trading arena for carbon credits. But, as Tremblay explains, “Hydropower only emits small amounts of GHG, so this should put it in a good position to sell extra carbon credits and make money. It can mean an income of millions of dollars for companies.”

With such economic potential, carbon credit trading is an important mechanism for countries that need hydropower development but do not have the financial muscle to support it. The opportunity to trade credits from hydroelectricity should make it easier to finance, guarantee and build projects. Tremblay believes that such economic implications are paramount and it is the calculation of net GHG emissions that will enable projects to fully utilise carbon credits.

Major research

The construction of the 480MW Eastmain-1 (EM-1) development in Canada is providing Hydro-Québec with a window of opportunity in the GHG question as is the subject of one of the energy sector’s most ambitious scientific investigations to date. Reservoir emissions at this new project can be monitored before and after impoundment to give an accurate comparison of the levels of net GHG produced naturally, and those induced by human activity.

“The main objective of this project is to determine the net impact of creating a reservoir,” Tremblay says. “We can study the natural system to determine the quantity of emissions and then look at what happens when we put a reservoir into this natural system.”

The EM-1 project is the first large-scale field study of a boreal hydroelectric reservoir, and is being co-financed by Hydro-Québec and the Canadian Foundation for Climate and Atmospheric Sciences. McGill University and Université du Québec à Montréal (UQAM) are partners in the project, which has been described as a major, multi-disciplinary research comparison.

Hydro-Québec expects that EM-1 will illustrate, through the scientific research, the true environmental impact of hydroelectric reservoirs. The study is also the first time that GHG releases have been monitored immediately after the creation of a reservoir, it says.

Natural ecosystems such as lakes, rivers, forests and peat land emit GHG naturally. After impoundment of a reservoir, a rapid increase in the gross emissions of carbon dioxide and methane are generally observed. During the early years following impoundment, a large part of GHG emissions from the reservoir are from decomposition of organic material. The maximum limits are reached within four years and within a 10-year period there is a gradual decrease in emissions, and levels return to those comparable with natural lakes.

EM-1 project has been divided into five research areas:

• Aquatic systems – to quantify carbon dioxide and methane fluxes as well as the amount of carbon in the reservoir compared to natural lakes or rivers in the EM-1 area. Various environmental parameters are monitored to help estimate the global mass balance of carbon from the aquatic ecosystem.

• Terrestrial systems – carbon dioxide and methane fluxes are quantified as well as the amount of carbon in a natural forest in comparison to the flooded ecosystem. The influence of forest fires and the role of peat land is taken into consideration.

• Stable isotopes – these determine the source of organic matter.

• Eddy correlation – high frequency carbon dioxide fluxes are measured using eddy correlation towers.

• Modelling – a model will be created using all collected data to predict GHG emissions from either natural ecosystems or the EM-1 reservoir over a period of 100 years.

The goal of the EM-1 project is to determine the anthropogenic GHG emissions related to land use change from a forest to a reservoir. Field work started in mid-2003 in areas unaffected by the reservoir and the data give the reference values. Forests and peat land, located in the basin at a radius of approximately 20km and designated for flooding by the reservoir, were also investigated.

The effect of flooding

Fifteen percent of the land area in northern Québec is covered by peat bogs. As this complex vegetative matter is reputed to contain a great amount of GHG, the effect of flooding the peat covered land at Eastmain needed thorough investigation. Peat bogs are major carbon sinks that are likely to become a major source of carbon in the context of climate change.

It is important, therefore, to define the carbon stored and how much could eventually be emitted. Core sample drilling enabled researchers to study the state of decomposition and learn more about historic climatic changes over centuries, which also provides data to help in climate change modelling.

Researchers returned to the sites during the summers of 2004-5 before the reservoir started to be filled in November 2005. At the end of 2006 the reservoir was fully impounded and they returned again to start monitoring the reservoir. Creativity and resourcefulness were needed to adapt the technology to the difficult conditions in northern Québec. “Some of the field work studies turned into two-week camping expeditions in order to obtain data,” Tremblay says.

Surface emissions of GHG at the reservoir were measured using traditional methods such as floating chambers to monitor the flux of carbon dioxide, and techniques not employed before were also used. Automated systems at different locations measured carbon dioxide levels every three hours to help determine variability in the system. The eddy correlation tower, another new monitoring tool, measures the flux of carbon dioxide at high frequency, such as 10 measurements per second. One tower was placed on a small island to give a footprint of the reservoir, and a second was sited in unburnt forest to the west of the reservoir to help establish how much GHG the natural system absorbs and emits.

Measurements will be carried out in the field for five to seven years and the data put into the ecosystem model to assess net GHG emissions, enabling the verification of predicted levels against ongoing measurement. The drawdown zone of the reservoir will also be analysed in greater detail in the model to help investigate the implications of fluctuating water levels for GHG emissions, and help planning of reservoir management.

Preliminary findings

The EM-1 project is carry out monitoring of the reservoir and reference system until the end of 2009. Tremblay expects the research to be wrapped up by 2010. Information will be available on the EM-1 project website ( While there will be a time lag between the completion of field studies and the publication of data and findings, first results are due this year and some preliminary findings are available.

Some of the preliminary data from the EM-1 project were presented at the recent American Geophysical Union (AGU) conference. However, Michelle Garneau, from UQAM, noted that the data had yet to be integrated into the model, which could take up to a year to complete. However, Annie Lalonde and Jean-Francois Hélie, also from UQAM, gave further insight into the research by presenting a paper on carbon isotopes used in measurements.

Most of the work on monitoring GHG emissions from reservoirs has been at established sites more than 20 years old, the researchers said. Problems associated with a newly flooded reservoir are different, they explained, because after flooding the salts and nutrients from the submerged soils are released into the water column. It is anticipated that carbon dioxide fluxes will be higher in young reservoirs, but little is known of their magnitude and sources. Stable carbon isotopes were used to constrain carbon sources and cycling in the reservoir environment at EM-1.

Ultimately, the study aims to estimate annual carbon dioxide fluxes at the surface of the reservoir. Sampling was performed four times (June, August and October in 2006, and June 2007) to account for seasonality of the carbon cycle. Twelve sites were visited on the reservoir as well as a natural lake near the reservoir. Three sites were also sampled along a depth gradient.

In-situ measurements were taken at each site, including water and air temperatures, pH, alkalinity, wind speed, conductivity and dissolved oxygen content. Samples were collected for the analysis of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) and particulate organic carbon (POC) concentrations, for the analysis of the carbon isotopic compositions of DOC, DIC, POC and carbon dioxide at the reservoir surface, and finally for the ratios of carbon and nitrogen (C/N) of dissolved and particulate organic matter.

DOC concentrations are highest, averaging 6.86mg/l±1.40mg/l; DIC concentrations average 1.51mg/l±0.76mg/l; and POC concentrations are up to two orders of magnitude lower, averaging 0.036mg/l±0.018mg/l.

The stable carbon isotopic composition (d13C) values of DOC average –27.42±0.32% versus the main international reference system for measuring carbon 13 isotopic contents, called Vienna-Pee Dee Belemnite (V-PDB), which is close to average values of C3 plants (most common), and vary little throughout the year. The d13C-DIC values vary slightly throughout the reservoir but show large variations from one sampling campaign to the next.

Depth profiles show a small decrease in d13C-DIC with depth, in a well mixed water column. A strong relationship has been observed between d13C-DIC and DIC concentrations.

Although the research is ongoing, the scientists have not been surprised by the early findings. “We are quite sure that GHG emissions are very small but we need to demonstrate this through good science,” says Tremblay. “Overall, the gross surface reservoir measurements taken to date are very small and indicate that the net GHG emissions would be even smaller.”

Better assessments of future schemes

For companies such as Hydro-Québec, net emissions give greater insight into GHG and help facilitate better assessments of new build projects and future schemes. Existing installations will also be able to fully utilise carbon credits. Furthermore, Tremblay is hopeful that the net GHG project may even be used by the Intergovernmental Panel on Climate Change (IPCC) and integrated into its recommendations.

Although the EM-1 project is described as being a world first in its area of research, its focus is limited to boreal systems.

“We do have a lot of information about GHG emissions from boreal system but little data about other areas of the world, especially tropical climates,” Tremblay admits. “However, it is hoped that this research can be partly extrapolated to other countries. All of the processes that lead to GHG emissions are the same all over the world. The problem lies in understanding and quantifying them. Our experience from the boreal region could be used to the advantage of the rest of the world.”

Eastmain-1: Project Brief

Hydro-Quebec began construction of the 480MW Eastmain-1 development in the north of Québec in 2002. The project was commissioned in April 2007.
Powerhouse – three vertical Francis units have an average annual output of 2.7TWh. The design flow is 840m3/sec and the rated head 63m. A minimum flow of 140m3/sec will be maintained at the powerhouse outlet.
Dam – the rockfill dam is 890m long and 70m high.
Spillway – at maximum reservoir level the discharge capacity is 5500m3/sec.
Reservoir – 35km long covering a total area of 603km2. Active storage is 4.21km3 with drawdown of 9m.

Research in Tropical Reservoirs

The 2nd Workshop on the Greenhouse Status of Freshwater Reservoirs was held in October 2007, in Brazil, and hosted by UNESCO’s International Hydrological Programme, the World Bank, Itaipu Binacional and the International Hydropower Association (IHA).
Based on the information presented, it was described as being “evident” that some reservoirs in the tropics have higher GHG emissions than those in other parts of the such regions and in other climates. It was also clear there is a need to develop an analytical, predictive process for future reservoirs.
Such a process would determine whether GHG emissions from future reservoir sites were likely to be significant issues. A small number of key indicators were be used, such as hydrology, reservoir type, climate and organic load. Where this process indicates the potential for GHG emissions, more detailed analysis would be applied.
At least 20 representative tropical/sub-tropical reservoir schemes will be selected for data collection. A working group, chaired by Professor Dr Carlos Tucci of UNESCO-IOHP Brazil, is to develop the initial analytical process. The working group is scheduled to deliver a list of key parameters, site selection criteria, and a summary of methodologies for data collection this month.