Clogging the Earth´s arteries: River damming changes biogeochemical cycles (Part 2)

Clogging the Earth´s arteries: River damming changes biogeochemical cycles (Part 2)

My name is Sonia and I study GHG evasion from reservoirs. A few weeks ago, I wrote a blog post about the biogeochemical cycle of rivers and how it is affected by dams. This week, I wanted to explore further problems of dams, GHG emissions, and climate change.

What happens with Greenhouse gas emissions?

Greenhouse gases (GHG) (CO2, CH4, and N2O, among others) are responsible for the warming of the Earth, which allows life on the planet. Due to human actions, the concentration of GHG in the atmosphere has increased since the 1800s, and the Earth’s temperature has increased 1°C [1]. River damming increases the production of greenhouse gases compared to natural rivers and reservoirs emit up to 1.5% of the total human-related CO2-equivalent emissions from CO2, N2O and CH4 together [2].

Looking at the total GHG emission derived from construction, activation, and decommission of dams plus the actual reservoir emissions, there is controversy about how “green” is this energy source [3].  A recent review on global dam emissions shows that at higher latitudes the total GHG emission of dams is similar to other renewables energies. However, in the tropics, GHG emissions of dams are comparable to those of coal power plants [4]. Still, any additional emissions will contribute to climate change on Earth.

Image of dam construction site at Kalivac, Vjosa River. Image from G.Singer

Fish are not only threatened by migration barriers

An additional side effect of river reservoirs, which is related to biochemistry, is the increased production of the neurotoxin methylmercury in reservoirs. High methylmercury concentration has been found in fish downstream of dams in comparison with upstream [5]. Mercury is a volatile element. In the water, Mercury is uptaken by microorganisms and accumulated. One protection mechanism against mercury is to methylate it. This is done by anaerobic microorganisms and due to the anaerobic conditions in the reservoir sediments, more methylmercury is formed there than in natural rivers. Methylmercury is magnified in the bodies of zooplankton, fish, birds, and mammals and can lead to neurochemical, hormonal and reproductive changes [6].

Why I joined river intellectuals

Foto of Vjosa braided section. Own image.

In spring 2018, I joined a field expedition to the Vjosa River, which is a river that flows from the Northern Greek mountains, through Albania, and into the Adriatic sea. I helped measure GHG emissions from multiple sites along the river. From the very first moment, I felt a special connection with the river and its wilderness. Unfortunately, the Vjosa River is included in the dam-building plan for the Balkan region. This pristine river is a unique ecosystem with wild sediment dynamics that create braided sections. No study has been done to estimate the GHG emissions before and after damming on the Vjosa. We have now baseline data for the Vjosa River. This will help us and other scientists, managers, and politicians to make more informed decisions about dams in the Balkan region, and in particular for the Vjosa River. I find in the River Intellectuals a place where multidisciplinary experts and activists share a common goal and where fruitful projects and actions can be born, to study and increase awareness about (still) undammed rivers.

Picture of myself taking GHG samples from Vjosa River. Image from G.Singer.

– Sonia Herrero

References – links to  main scientific articles used to write the blog

[1] Allen, M.R., O.P. Dube, W. Solecki, F. Aragón-Durand, W. Cramer, S. Humphreys, M. Kainuma, J. Kala, N. Mahowald, Y. Mulugetta, R. Perez, M. Wairiu,  K. Zickfeld, 2018: Framing and Context. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. In Press.

[2] Deemer, B.R., Harrison, J.A., Li S., Beaulieu,  J.J.,  DelSontro, T., Barros, N., Bezerra-Neto, J.F., Powers, S.M., dos Santos, M.A., Arie Vonk, J. 2016. Greenhouse Gas Emissions from Reservoir Water Surfaces: A New Global Synthesis. BioScience, Volume 66, Issue 11, 949–964,

[3] Prairie, Y.T., Alm, J., Beaulieu, J. , Barron, N.,Battin,T., Cole, J., del Giorgio, P., DelSontro, T., Guérin, F., Harby, A., Harrison, J., Mercier-Blais, S., Serça, D., Sobek, S., Vachon D.2018. Greenhouse Gas Emissions from Freshwater Reservoirs: What Does the Atmosphere See?  Ecosystems, 21: 1058.

[4] Zarfl, C., Lumsdon, A.E., Berlekamp, J., Tydecks, L., Tockner, K.2015. A global boom in hydropower dam  construction. Aquatic sciences, 77: 161.

[5] Kasper D., Forsberg B.R, Amaral J.H., Leitão R.P., Py-Daniel S.S., Bastos W.R., Malm O. 2014. Reservoir stratification affects methylmercury levels in river water, plankton, and fish downstream from Balbina hydroelectric dam, Amazonas, Brazil.  Environmental Science and Technology 21;48(2):1032-40. doi: 10.1021/es4042644.

 [6] A.M. Scheuhammer, M.W. Meyer, M.B. Sandheinrich, and M.W. Murray, 2017. Effects of Environmental Methylmercury on the Health of Wild Birds, Mammals, and Fish, AMBIO: A Journal of the Human Environment 36(1), 12-19.[12:EOEMOT]2.0.CO;2