Greenhouse gas emissions (CO 2 , CH 4 , and N 2 O) from several perialpine and alpine hydropower reservoirs by diffusion
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Aquatic Sciences
RESEARCH ARTICLE
Greenhouse gas emissions (CO2, CH4, and N2O) from several perialpine and alpine hydropower reservoirs by diffusion and loss in turbines T. Diem • S. Koch • S. Schwarzenbach B. Wehrli • C. J. Schubert
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Received: 18 April 2011 / Accepted: 2 March 2012 / Published online: 11 April 2012 Ó Springer Basel AG 2012
Abstract We investigated greenhouse gas emissions (CO2, CH4, and N2O) from reservoirs located across an altitude gradient in Switzerland. These are the first results of greenhouse gas emissions from reservoirs at high elevations in the Alps. Depth profiles were taken in 11 reservoirs located at different altitudes between the years 2003 and 2006. Diffusive trace gas emissions were calculated using surface gas concentrations, wind speeds and transfer velocities. Additionally, methane entering with the inflowing water and methane loss at the turbine was assessed for a subset of the reservoirs. All reservoirs were emitters of carbon dioxide and methane with an average of 970 ± 340 mg m-2 day-1 (results only from four lowland and one subalpine reservoir) and 0.20 ± 0.15 mg m-2 day-1, respectively. One reservoir (Lake Wohlen) emitted methane at a much higher rate (1.8 ± 0.9 mg m-2 day-1) than the other investigated reservoirs. There was no significant difference in methane emissions across the altitude gradient, but average dissolved methane concentrations decreased with increasing elevation. Only lowland reservoirs were sources for N2O (72 ± 22 lg m-2 day-1),
Electronic supplementary material The online version of this article (doi:10.1007/s00027-012-0256-5) contains supplementary material, which is available to authorized users. T. Diem (&) S. Koch S. Schwarzenbach B. Wehrli C. J. Schubert Department of Surface Waters-Research and Management, EAWAG, Seestrasse 79, 6047 Kastanienbaum, Switzerland e-mail: [email protected] Present Address: T. Diem School of Geography and Geosciences, University of St. Andrews, Irvine Building, North Street, St. Andrews KY16 9AL, Scotland, UK
while the subalpine and alpine reservoirs were in equilibrium with atmospheric concentrations. These results indicate reservoirs from subalpine/alpine regions to be only minor contributors of greenhouse gases to the atmosphere compared to other reservoirs. Keywords Greenhouse gases Emissions Reservoirs Methane Alpine
Introduction In the early 1990s artificial lakes and reservoirs were discovered as potential greenhouse gas emitters (Rudd et al. 1993; Kelly et al. 1994). The question was put forward whether hydroelectric reservoirs, especially in the tropics, could still be considered cleaner energy sources compared to fossil alternatives (Fearnside 1997, 2002; Delmas et al. 2001; Pacca and Horvath 2002). Estimates suggest total emissions from reservoirs of about 70 Tg CH4 year-1 and 1,000 Tg CO2 year-1, accounting for 7 % of the anthropogenic emissions of these gases (St. Louis et al. 2000). Based on a much larger dataset, Barros et al. (2011) recently estimated reservoirs to emit only
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