Hydropower is a frequent target for criticism. Regardless of your views on global warming, turning a serene stretch of river into an artificial lake humming with electrical equipment can make you unpopular, and the announcement of any new hydropower project is often swiftly followed by outcries over habitat disruption and community displacement, among other concerns.

But hydropower’s clean energy bona fides are rarely questioned.

In fact, hydropower reservoirs do generate carbon emissions, and some scientists think these emissions could be substantial — maybe enough to cancel out the system’s green benefits.

Steven Bouillon, a carbon cycles researcher at the University of Leuven in Belgium, said the magnitude of emissions depends on the design of the reservoir. Bouillon is leading research in Africa to quantify emissions from inland water systems, including reservoirs.

“We’re quite convinced that for certain reservoirs, the effects on greenhouse gas emissions locally will offset the benefits of clean energy production,” he said.

When reservoirs are built — for hydropower or other purposes — the grass, vegetation and trees submerged underwater begin to slowly decompose, releasing the carbon dioxide they had been storing through photosynthesis for centuries.

How much of this carbon dioxide actually gets “outgassed” into the atmosphere is a product of several factors. The gas can bubble to the surface of the reservoir and escape; it can be released as the water passes through a dam’s hydroelectric turbines; and it can be released farther downstream. Some gas could also never make it out at all, buried in sediment in the reservoir or farther downstream, or carried all the way out to the ocean.

The size of the reservoir can make a difference. Shallow reservoirs with a wide surface area can emit more, because they’ve flooded more carbon-rich land, which can easily escape as gas out of the shallow water. Conversely, deep dams with a small surface area have much lower emissions.

The methane problem

Methane — a much more potent greenhouse gas than CO2 — may be a bigger concern, however.

Submerged vegetation emits some methane naturally, but stagnant reservoir water can also create an oxygen-deprived layer of water at the bottom of the lake, and this anoxic environment can turn some of the decomposing carbon into methane instead of CO2.

And to make matters worse, many hydropower stations draw water from the bottom layers of reservoirs to generate electricity, all but ensuring a portion of the methane gas is emitted downstream or as it passes through hydroelectric turbines.

A June 2012 commentary article in the journal Nature Climate Change claimed that the carbon emissions from all of Brazil’s hydroelectric reservoirs were equal to or greater than the annual emissions of São Paulo, the country’s largest city.

Richard Taylor, executive director of the International Hydropower Association, said these reports exaggerate reservoirs’ role in the natural carbon cycle. Indeed, the world over, carbon stored in forests and vegetation routinely seeps through groundwater into rivers and then outgases into the atmosphere (ClimateWire, Nov. 21).

“You have a natural system going on, unrelated anthropogenic activities going on,” Taylor said. “We know we can measure emissions on the surface of a reservoir, but the story is much, much more than that.”

With carbon constantly cycling through water and forest systems, and constantly flowing in and out of the atmosphere, do reservoirs really change anything? Or do they just emit carbon gas that would’ve found some other way into the atmosphere?

1 long-term study, mixed results

There has been only one study chronicling pre- and post-flood emissions from the same hydroelectric reservoir, a seven-year study of the Eastmain-1 dam in northern Quebec. Cristian Teodoru, a postdoctoral researcher at the University of Leuven, led the team that spent three years monitoring emissions from the landscape before it was flooded at the end of 2005. They then spent four more years measuring emissions from the flooded landscape.

Teodoru and his colleagues found that in its first post-flood year, the reservoir was a large net source of CO2 but a much smaller source of methane compared with pre-flood levels. In subsequent years, however, net carbon dioxide emissions declined steeply, while net methane emissions remained constant or increased slightly.

Another concern raised by scientists is that, while these emissions may decline over time, the big spike in outgassing early on is much higher than emissions from fossil fuel generation and could take decades to recover from.

Taylor, who’s read the study, described the methane emissions as so small they’re “negligible.” But in its paper, Teodoru’s team ultimately concluded that “the reservoir will continue to emit carbon gas over the long term at rates exceeding the carbon footprint of the pre-flood landscape.”

Teodoru said net emissions from reservoirs could be even greater in tropical and subtropical climates, since the bacteria in the water breaking down the carbon-rich vegetation work faster in higher temperatures. Northern reservoirs, including Eastmain-1, are also frozen for much of the year, he said, stifling potential emissions.

“If you compare the same surface in Canada to one in Brazil, you’d have totally different emissions,” Teodoru said.

The tropics and subtropics could also soon see a hydropower boom. Scientists believe up to two-thirds of the planet’s hydropower capacity is still undeveloped — the majority of it in the Southern Hemisphere — and forecast hydropower capacity to double by 2050.

With so many factors contributing to the natural carbon cycle, Taylor said research has yet to fully conclude what impact reservoirs have on this cycle.

He also argued that some research up to now has been flawed. Many studies investigating carbon emissions from reservoirs use the Balbina Dam in Brazil as a case study. The dam is wide and shallow, and it’s been shown to emit more methane than most coal plants.

Ways to build lower-emitting dams

Taylor called the dam an outlier, with a uniquely poor design and location contributing to exceptionally high emissions. Balbina has a 250-megawatt generating capacity yet has the same surface area as the deeper Itaipu Dam, whose 14,000 MW capacity is second in the world to China’s Three Gorges Dam.

Balbina, Taylor said, is “atypical, yet the most intensively studied project on greenhouse gas emissions.”

That said, there are steps hydropower developers can take to minimize reservoir emissions.

Developers should try to avoid building dams near major carbon sinks, for example, and should install an off-take system that draws water from the upper levels of the reservoir, not the methane-rich lower levels, Taylor said.

The International Hydropower Association has developed a sustainability assessment protocol that looks at more than 20 topics from the project planning stage to construction and production where emissions could be prevented.

“As we learn, we will evolve that practice,” he said. “Certainly, we would look at water quality. If that’s well-managed, I think the greenhouse gas issue’s well-managed.”

Ultimately, Taylor said he hopes the industry can move past this issue and focus on other things, saying he thinks the industry is “very tired of being the butt of this.”

“All renewables work together, and the storage of energy in hydro reservoirs is key to the increased utilization of renewables,” he said.

“We’re managing [emissions] the best we can,” he added. “I can’t say there’s going to be a perfect solution, but I

Missing Senate votes: Mick Keelty says lax WA standards to blame for lost ballots

Updated 13 minutes ago

An inquiry into Western Australia’s missing Senate votes has found significant failures in the handling, movement and storage of ballot papers.

The Australian Electoral Commission (AEC) asked the former commissioner of the Australian Federal Police, Mick Keelty, to conduct the inquiry after more than 1,300 ballot papers disappeared.

The bungle has left the Senate result up the air, with the AEC asking the High Court to order a fresh election in the New Year.

Mr Keelty found no evidence of any deliberate attempt to destroy or steal the ballot papers, but said the lax systems in WA made it difficult to reach a conclusive finding.

Mr Keelty has recommended the AEC introduce tamper-tracing materials for transferring and storing ballot papers.

He also recommends CCTV and alarms at the warehouses where ballot papers are stored.

Read Mr Keelty’s report into the missing WA Senate votes.

Topics: government-and-politics, elections, federal-elections, perth-6000, wa

MIT researchers report that with the loss of sea ice the Arctic Ocean is becoming more of a carbon sink and that the amount of carbon taken up by the Arctic is increasing by 1 megaton each year.

Click to enlarge. Courtesy: NOAA.

By Jennifer Chu, MIT News

For the past three decades, as the climate has warmed, the massive plates of sea ice in the Arctic Ocean have shrunk: In 2007, scientists observed nearly 50 percent less summer ice than had been seen in 1980.

Dramatic changes in ice cover have, in turn, altered the Arctic ecosystem — particularly in summer months, when ice recedes and sunlight penetrates surface waters, spurring life to grow. Satellite images have captured large blooms of phytoplankton in Arctic regions that were once relatively unproductive. When these organisms die, a small portion of their carbon sinks to the deep ocean, creating a sink, or reservoir, of carbon.

Now researchers at MIT have found that with the loss of sea ice, the Arctic Ocean is becoming more of a carbon sink. The team modeled changes in Arctic sea ice, temperatures, currents, and flow of carbon from 1996 to 2007, and found that the amount of carbon taken up by the Arctic increased by 1 megaton each year.

But the group also observed a somewhat paradoxical effect: A few Arctic regions where waters were warmest were actually less able to store carbon. Instead, these regions — such as the Barents Sea, near Greenland — were a carbon source, emitting carbon dioxide to the atmosphere.

While the Arctic Ocean as a whole remains a carbon sink, MIT principal research scientist Stephanie Dutkiewicz says places like the Barents Sea paint a more complex picture of how the Arctic is changing with global warming.

“People have suggested that the Arctic is having higher productivity, and therefore higher uptake of carbon,” Dutkiewicz says. “What’s nice about this study is, it says that’s not the whole story. We’ve begun to pull apart the actual bits and pieces that are going on.”

A paper by Dutkiewicz and co-authors Mick Follows and Christopher Hill of MIT, Manfredi Manizza of the Scripps Institute of Oceanography, and Dimitris Menemenlis of NASA’s Jet Propulsion Laboratory is published in the journal Global Biogeochemical Cycles.

The ocean’s carbon cycle

The cycling of carbon in the oceans is relatively straightforward: As organisms like phytoplankton grow in surface waters, they absorb sunlight and carbon dioxide from the atmosphere. Through photosynthesis, carbon dioxide builds cell walls and other structures; when organisms die, some portion of the plankton sink as organic carbon to the deep ocean. Over time, bacteria eat away at the detritus, converting it back into carbon dioxide that, when stirred up by ocean currents, can escape into the atmosphere. The MIT group developed a model to trace the flow of carbon in the Arctic, looking at conditions in which carbon was either stored or released from the ocean. To do this, the researchers combined three models: a physical model that integrates temperature and salinity data, along with the direction of currents in a region; a sea ice model that estimates ice growth and shrinkage from year to year; and a biogeochemistry model, which simulates the flow of nutrients and carbon, given the parameters of the other two models. The researchers modeled the changing Arctic between 1996 and 2007 and found that the ocean stored, on average, about 58 megatons of carbon each year — a figure that increased by an average of 1 megaton annually over this time period. These numbers, Dutkiewicz says, are not surprising, as the Arctic has long been known to be a carbon sink. The group’s results confirm a widely held theory: With less sea ice, more organisms grow, eventually creating a bigger carbon sink.

A new counterbalance

However, one finding from the group muddies this seemingly linear relationship. Manizza found a discrepancy between 2005 and 2007, the most severe periods of sea ice shrinkage. While the Arctic lost more ice cover in 2007 than in 2005, less carbon was taken up by the ocean in 2007 — an unexpected finding, in light of the theory that less sea ice leads to more carbon stored. Manizza traced the discrepancy to the Greenland and Barents seas, regions of the Arctic Ocean that take in warmer waters from the Atlantic. (In warmer environments, carbon is less soluble in seawater.) Manizza observed this scenario in the Barents Sea in 2007, when warmer temperatures caused more carbon dioxide to be released than stored. The results point to a subtle balance: An ocean’s carbon flow depends on both water temperature and biological activity. In warmer waters, carbon is more likely to be expelled into the atmosphere; in waters with more biological growth — for example, due to less sea ice — carbon is more likely to be stored in ocean organisms. In short, while the Arctic Ocean as a whole seems to be storing more carbon than in previous years, the increase in the carbon sink may not be as large as scientists had previously thought.“The Arctic is special in that it’s certainly a place where we see changes happening faster than anywhere else,” Dutkiewicz says. “Because of that, there are bigger changes in the sea ice and biology, and therefore possibly to the carbon sink.”Manizza adds that while the remoteness of the Arctic makes it difficult for scientists to obtain accurate measurements, more data from this region “can both inform us about the change
in the polar area and make our models highly reliable
for policymaking decisions.” This research was supported by the National Science Foundation and the National Oceanic and Atmospheric Administration.

Abstract

The rapid recent decline of Arctic Ocean sea ice area increases the flux of solar radiation available for primary production and the area of open water for air-sea gas exchange. We use a regional physical-biogeochemical model of the Arctic Ocean, forced by the National Centers for Environmental Prediction/National Center for Atmospheric Research atmospheric reanalysis, to evaluate the mean present-day CO₂ sink and its temporal evolution. During the 1996–2007 period, the model suggests that the Arctic average sea surface temperature warmed by 0.04°C a⁻¹, that sea ice area decreased by ∼0.1 × 106 km2 a⁻¹, and that the biological drawdown of dissolved inorganic carbon increased. The simulated 1996–2007 time-mean Arctic Ocean CO₂ sink is 58 ± 6 Tg C a⁻¹. The increase in ice-free ocean area and consequent carbon drawdown during this period enhances the CO2 sink by ∼1.4 Tg C a⁻¹, consistent with estimates based on extrapolations of sparse data. A regional analysis suggests that during the 1996–2007 period, the shelf regions of the Laptev, East Siberian, Chukchi, and Beaufort Seas experienced an increase in the efficiency of their biological pump due to decreased sea ice area, especially during the 2004–2007 period, consistent with independently published estimates of primary production. In contrast, the CO₂ sink in the Barents Sea is reduced during the 2004–2007 period due to a dominant control by warming and decreasing solubility. Thus, the effect of decreasing sea ice area and increasing sea surface temperature partially cancel, though the former is dominant.

Citation

“Changes in the Arctic Ocean CO2 sink (1996–2007): A regional model analysis” by M. Manizza, M. J. Follows, S. Dutkiewicz, D. Menemenlis, C. N. Hill R. M. Key published in Global Biogeochemical Cycles

DOI: 10.1002/2012GB004491