Eastmain-1 Net GHG Emissions Project The Use of Automated Systems to Measure Greenhouse Gas Emissions from Reservoirs

Transcription

1 Eastmain-1 Net GHG Emissions Project The Use of Automated Systems to Measure Greenhouse Gas Emissions from Reservoirs By Alain Tremblay and Claude Demers, Hydro-Québec, Canada Julie Bastien, Environnement Illimité Inc., Canada Maud Demarty, Environnement Illimité Inc., Canada Claude Demers, Hydro-Québec, Canada ABSTRACT Hydro-Québec is the largest electric power company in Canada with more than MW installed for an annual generation of around 189 TWh. Hydro-Québec owns and operates over 57 powerhouses such as Eastmain-1 that was commissioned in The growing concern regarding the long-term contribution of freshwater reservoirs to atmospheric greenhouse gases (GHG), led Hydro-Québec, to study net GHG emissions from Eastmain-1 reservoir, which are the emissions related to the creation of a reservoir minus those that would have been emitted or absorbed by the natural systems over a 100-year period. This large study is realized in collaboration with Environnement IIlimité Inc., University du Quebec in Montreal and McGill University. Measurement of GHG fluxes were done with the used of a traditional technique, the floating chambers that measures GHG fluxes at the water-air interface and a new approach using automated systems measuring partial pressure of gas in the water column. Follow up of the CO 2 and CH 4 fluxes at EM-1 reservoir showed a rapid increase in both CO 2 and CH 4 emissions the first year after flooding and a rapid return to natural aquatic ecosystems values within 2 and 3 year for CH 4 and CO 2, respectively. Automated system and floating chambers show similar annual GHG mass balance. Overall GHG emissions from Eastmain-1 reservoir are very low in comparison to thermal power plant of the same capacity Introduction Hydropower represents about 66% of Canada and about 20% of the world s electricity generation capacity. Although hydroelectric power plants emit much lower amount of GHGs per terawatt-hour than thermal power plants (35 70 times less IAEA 1996), there is a growing concern to determine the contribution of freshwater reservoirs to the increase of GHGs in the atmosphere (e.g., St. Louis et al. 2000, Tremblay et al. 2004). The evaluation of GHG emissions from reservoirs is becoming more and more relevant to ensure that methods of energy production are compared adequately and for CO 2 credits evaluation (Tremblay et al. 2005). There are three greenhouse gases (GHGs) that are related to the creation of reservoirs and the exploitation of hydropower plant with reservoir which are carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O; IPCC 2001, Duchemin et al. 2006). In literature, most of the data available on GHG are gross emissions measured at the surface of the water bodies and from established reservoirs (>10 years old; e.g. 1

2 Tremblay et al. 2005). However, the energy sector should work towards the new approach based on net GHG emissions which are the emissions related to the creation of a reservoir minus those that would have been emitted or absorbed by the natural systems over a 100-year period. This is the goal of the Easmaint-1 (EM-1) net GHG emissions project ( Within the EM-1 project, we have used different ways of measuring GHG from the reservoirs such as Eddy Covariance Towers, gas partial pressure, floating chambers and automated systems. Here we present results of gross GHG emissions measured with both floating chambers and automated systems of a young boreal reservoir in the context of the first study evaluating net GHG emissions of a reservoir. Study area The Eastmain-1 reservoir is located in the boreal ecoregion of Quebec, Canada at 54 N about km north of Montreal as shown in Figure 1. The Eastmain-1 powerhouse was commissioned in 2006 and it is equipped with 3 turbines generating 160 MWh each for a total of 480 MWh. The main dam, along with 33 dikes, form the Eastmain-1 reservoir with a surface area of 603 km 2. Figure 1 Northern Quebec with the major reservoirs and associated powerhouses, including the new Eastmain-1 reservoir and powerhouse commissioned in

3 Automated systems In the Eastmain-1 project we have installed 5 automated systems. One system is installed at Eastmain-1 generating station and measure GHG year around. This system is connected to distribution pipes collecting water from the scroll case. During ice free period (mid June to end of October) we have four automated systems installed on rafts collecting surface water (30 cm below the surface). In the EM-1 reservoir, one system is located at the mouth of the Eastmain river (entrance to the reservoir), one over a flooded peat and a third one is located over flooded forest. One automated system is also installed on a reference lake, Lake Mitsumis (Figure 2) Figure 2. Position of the automated systems on the reservoir, Eastmain-1 powerhouse (station EM-1 Powerhouse), over flooded forest (Station Marie-Eve Island), over flooded peatland (Station Grand Détour), major water entrance to the EM-1 reservoir (station Prospère Gorge) and a reference lake (Station Mitsumis Lake). 3

4 As shown on Figure 3, solar panels or small wind turbine provide the energy for the automated systems installed on rafts or on stream's shore. Figure 4 shows an overview of the continuous GHG monitor. This automated system is built of commercially-available components and is based on the GHG partial pressure technique. CO 2, CH 4 and O 2 partial pressures are measured in water and in air using three different types of sensors (LICOR LI-820, Neodim, and Qubit Systems Inc respectively). A similar automated system should be commercially available soon from AXYS ( ). Figure 4 Design of the automated systems (A: dry box, B: wet box) 4

5 The sensors, which must remained dry, are housed in a Dry Box, while the pump, valves, and tubing are installed in the Wet Box.. While in monitoring mode, the device typically activates once every three hours. The monitoring operating cycle requires 22 minutes: one cycle of 20 minutes in water with two measurements (at 10 and 20 minutes) followed by one cycle of two minutes in air with one measurement. Water temperature, instrument temperature, and gas loop pressure are also recorded. Control of all electrical devices, and collection and storage of data are performed by an electronic data logger. Details of quality assurance, quality control methods and equation for fluxes calculations from partial pressure are described in Bastien et al. (2007) and Tremblay et al. (2009) Floating Chambers Figure 5 shows an overview of the floating systems connected to gas analysers and computers. The floating chambers technique is widely used for measurement of GHG fluxes over water bodies (e.g., Tremblay et al. 2005). The air is sampled through an opening at the top of the floating chamber (surface area of 0.2 m 2 ) and is returned at the opposite end of the chamber. This configuration allows the trapped air to be continuously mixed and enables a more representative measurement of gas concentrations (Lambert & Fréchette 2005). Figure 5 Design of the floating chambers with NDIR and FTIR instruments 5

6 The CO 2 is measured with a NDIR (Non-Dispersive Infrared) instrument (PP-System model Ciras-SC), and CH 4 and N 2 O are measured with a FTIR (Fourier Transform Infrared) instrument (Temet, Gasmet DX-4010). The gas measurement accuracy is 0.1% and 1% for the NDIR and FTIR instruments, respectively. The instrument takes continuous reading, and the data logger stores a value every 20 seconds over a period of 5 to 10 minutes. All samples are plotted on a graph to obtain a slope and to calculate the flux of CO 2, CH 4, or N 2 O per m 2. More details can be found in Lambert & Fréchette (2005) and Demarty et al. (2008a,b). Results Figure 6 shows the variation of the CO 2 concentration in water of the Eastmain-1 reservoir over 16 months measured with an automated system installed at Eastmain-1 powerhouse. We can observe an increase in the CO 2 concentration in the late fall as the ice cover starts to form and a decrease in the spring time after the ice breaks-up. Figure 6. Concentrations (µg. L -1 ) of CO 2 at the Eastmain-1 reservoir measured with an automated system installed in the power station. 6

7 From Figure 7 shows mean fluxes of CO 2, CH 4 and N 2 O measured with floating chambers over natural aquatic ecosystems and different reservoirs in the La Grande hydroelectric complex, Northern Quebec. We can observe a rapid increase in both mean CO 2 and CH 4 emissions from the newly flooded Eastmain-1 reservoir which were about 5 times higher the first year after flooding (2006, CO ± 3567 mg CO 2 m 2 d 1, CH ± 9.5 mg CH 4 m 2 d 1 ) than those of natural aquatic ecosystems before impoundment ( : mean CO ± 1431 mg CO 2 m 2 d 1, CH ± 1.8 mg CH 4 m 2 d 1 ). These emissions decreased rapidly the second year after flooding and returned to values not significantly different than natural aquatic ecosystems for CH 4 (2007: mean 3.2 ± 3.1 mg CH 4 m 2 d 1 ) and the third year after impoundment for CO 2 (2008: mean 1942 ± 1175 mg CO 2 m 2 d 1 ). We have not observed any difference before or after flooding for the N 2 O fluxes. CO 2, CH 4 and N 2 O fluxes measured in aquatic ecosystems of Eastmain-1 area are comparable to those reported in the literature for boreal natural lakes and reservoirs on the Cote-Nord and James Bay region of Quebec and Labrador (Demarty et al. 2008a,b, Bastien et al. 2009, Tremblay & Bastien 2009, Figure 7) Similar results were also observed the first few years after flooding in young Quebec's reservoirs. Many parameters can influenced the GHG fluxes such as water residence time, the type of flooded vegetation (peat, forest soils, agricultural lands, etc.) and the ratio of surface area flooded to water volume. These parameters influenced both the intensity (the maximum fluxes reached) and the duration of these emissions. Generally, in boreal ecosystems, the CO 2 maximum flux is reached within the first year and the time to return to natural values is always within the first 10 years after impoundment. The increased of GHG emission in the newly formed reservoir is always coupled to an overall increased biological production (fish communities, invertebrates, planktonic communities, etc., Tremblay et al. 2005). Because trees barely decomposed, the CO 2 emitted is related to the natural decomposition of a fraction of the labile organic matter of flooded soils. After this transition period (<10 years), CO 2 emissions are comparable to natural water bodies and are related to the carbon entering the reservoir as runoff from the watershed, the reservoir effect is over after that period. 7

8 Figure 7 Mean (dashed lines) CO 2 (A), CH 4 (B) and N 2 O (C) fluxes (mg CO 2 m 2 d 1 ), medians (solid lines), 25 th and 75 th percentiles (boxes), and 10 th and 90 th percentiles (error bars) measured in Québec aquatic ecosystems and reservoirs in the La Grande region. 8

9 We have done a mass balance analysis of the GHG using both the automated systems and the floating chambers techniques, and they show only a difference of 12% between the two techniques. The automated system technique is very interesting to measure GHG from reservoirs as it reduces the overall cost of measuring, it requires only one person for the maintenance, the systems can be accessed remotely and it reduces the costs related to the safety measures of sampling on water bodies with boats. In summary, the monitoring of natural aquatic ecosystems and the newly flooded Eastmain-1 reservoir with automated systems and floating chambers demonstrate the following: - CO 2 and CH 4 fluxes increase rapidly within the first year after flooding; - EM-1 reservoir CH 4 fluxes have returned to values similar to natural aquatic ecosystems the second year after flooding; - EM-1 reservoir CO 2 fluxes have returned to values similar to natural aquatic ecosystems the third year after flooding; which is well within the 10 years generally observed for boreal reservoirs; - Automated systems and floating chambers techniques give similar results on annual mass balance. With a relatively small surface area and a very short water residence time for an installed capacity of about to 500 MW, the Eastmain-1 reservoir is a good example of project emitting small amount of GHGs. The most efficient thermal power plant, natural gas combined cycle, emit about tons of CO 2 equivalent per TWh, which is 23 times more than EM-1 (Tremblay et al. 2005, Tremblay et al. 2008). These results are clearly indicating that boreal hydroelectric reservoirs are low GHG emitters. Boreal hydropower plants should therefore be considered as part of the solution to reduce the impact of climate change. Reference All reference can be obtained from Centre de documentation, Hydro-Québec, 75 René- Lévesque Ouest, 2 th floor, Montréal, Québec, Canada H2Z 1A4. fax : ) Bastien, J., A. Tremblay & L. LeDrew, Greenhouse Gases Fluxes from Smallwood Reservoir and natural water bodies in Labrador, Newfoundland, Canada. Limnology. Verh. Intern. Verein. Limnol. 30 (in press). Bastien, J., Fréchette, J-L. & R.H. Hesslein Continuous Greenhouse Gas Monitoring System Operating Manual. Report prepared by Environnement Illimité inc. for Manitoba Hydro and Hydro-Québec, 35 p. and appendices. Demarty, M., Bastien, J. & A. Tremblay, 2008a. Aménagement hydroélectrique de l'eastmain-1 Étude des flux de gaz à effet de serre Résultats été-automne 9

10 2008. Rapport conjoint d Environnement Illimité inc. et Hydro-Québec Production, Direction Barrages et Environnement. 63 p. et annexe Demarty, M., Bastien, J. & A. Tremblay, 2008b Étude des flux de gaz à effet de serre des milieux aquatiques de la Mauricie, de la Côte-Nord et du lac Péribonka Suivi Rapport conjoint d Environnement Illimité inc. et Hydro-Québec Production, Direction Barrages et Environnement. 47 p. et annexe.. Duchemin, E., J. T. Huttunen, A. Tremblay, R. Delmas & C. F. Silveira Menezes (Lead authors), Appendix 2 - Possible approach for estimating CO 2 emissions from lands converted to permanently flooded lands. Basis for future methodological development. In Eggletion, H.S., L. Buendia, K. Iwa, T. Ngara & K. Tanabe (eds.). Intergovernmental Panel on Climate Change (IPCC), National Greenhouse Gas Inventories Guidelines, Vol. 4 Agriculture, Forestry and Other Land Use, IGES, Kanagawa, Japan, pp. AP2.1-AP2.9. [IPCC] Intergovernmental Panel on Climate Change, Climate change: the scientific basis. Contribution of Working Group I to the Third Assessment Report of the IPCC. Cambridge University Press, NY.. Lambert, M. & J.-L. Fréchette, Analytical techniques for measuring fluxes of CO 2 and CH 4 from hydroelectric reservoirs and natural water bodies, p In A. Tremblay, L. Varfalvy, C. Roehm & M. Garneau [eds.]. Greenhouse gas emissions: fluxes and processes, hydroelectric reservoirs and natural environments. Environmental Science Series, Heidelberg. St.Louis, V.L., Kelly, C.A., Duchemin, E., Rudd, J.W.M. and Rosenberg, D.M., 2000 Reservoirs surfaces as sources of greenhouse gases to the atmosphere: a global estimate. BioScience 50, Tremblay, A., M. Lambert & L. Gagnon, CO 2 Fluxes from Natural Lakes and Hydroelectric Reservoirs in Canada. Environ. Manag. 33(1) S509-S517. Tremblay, A., L. Varfalvy, C. Roehm & M. Garneau [eds.], Greenhouse gas emissions: fluxes and processes, hydroelectric reservoirs and natural environments. Environmental Science Series, Heidelberg. Tremblay, A., L. Varfalvy & M. Lambert, Greenhouse Gases from Boreal Hydroelectric Reservoirs: 15 years of data? Proceedings of the 15 th International Seminar on Hydropower Plants, HydroPower Plants in the Context of the Climate Change, November, Conference Center Laxenburg, Vienna, Austria. Pages Tremblay, A. & J. Bastien, Greenhouse Gases Fluxes from a New Reservoir and Natural Water Bodies in Québec, Canada. Limnology. Verh. Intern. Verein. Limnol. 30 (in press). 10

11 Authors Alain Tremblay (Ph.D.) is a senior environment advisor at Hydro-Quebec Production (Generation). He is the manager of the Greenhouse research program. Julie Bastien (M.Sc.) is a biologist and project manager at Environnement Illimité Inc. Maud Demarty (Ph.D) is a biologist at Environnement Illimité Inc. Claude Demers (M.Sc.) is a senior science communicator at Hydro-Quebec Public Affairs. His primary responsibility at HQ includes communication of research program and impact assessments. 11