jueves, 23 de junio de 2011

Small Hydro could add up to Big Damage on Environmental Expert

Small Hydro could add up to Big Damage

Source: SciDev.Net

Environmental engineers Tasneem Abbasi and S. A. Abbasi warn that widespread adoption of small hydro could repeat a history of environmental damage

A belief that small hydropower systems are a source of clean energy with little or no environmental problems is driving the growing interest in mini, micro, and pico hydro systems that generate from less than 5 kilowatts up to 10 megawatts of energy.
Hydropower appears to be the cleanest and most versatile of renewable energy sources. But experience shows that optimism about its potential can be misplaced.
Lessons of large hydro
Hydropower uses water and gravity (a totally carbon-free and inexhaustible resource) to drive turbines and generate electricity.
Unlike fossil-fuelled power plants, hydropower plants produce no gases or fly ash emissions (fine particles generated by burning coal). And, unlike nuclear power plants, there is no radioactive waste to contend with. Nor is any resource consumed, because water is neither lost nor polluted. Reservoirs can also enhance the scenery, attracting picnickers and tourists.
As soon as the world took note of these virtues in the 1950s, hydropower became popular. Developing countries including Brazil, China, India, Malaysia, Thailand, and Turkey built increasingly larger dams, generating anywhere from a few hundred megawatts to more than 10 gigawatts.
Egypt's High Aswan Dam has become an iconic symbol of these projects — and their environmental impacts.
Projects like these fundamentally altered river ecosystems, often fragmenting channels and changing river flows. Natural lakes take hundreds of years to evolve from oligotrophic (low in nutrients) to eutrophic (rich in nutrients) status. But man-made reservoirs underwent this transition within a few years, degrading water quality, harming fisheries, bringing siltation and invasion by weeds, and creating environments suitable for mosquitoes and other disease vectors.
And where reservoirs displaced people or suddenly changed resource availability or agricultural capacity, they brought major socio-economic problems.
It was during the mid-1970s, some 20 years after a number of major hydropower projects had been commissioned, that reports of their adverse environmental impacts began to emerge.
By the end of 1970s it had become clear that the very optimistic, almost reverential, attitude towards hydropower projects that had prevailed during the early 1950s was misplaced. These projects damaged the environment as seriously as did fossil-fuelled power projects.
The mistake had been to see only the virtues, and to not prepare for possible problems, some of which surfaced only once a large number of projects had been commissioned at different locations.
The big question is: are we set to repeat the same mistake with 'small' hydro?
No evidence
Nearly everyone seems to believe that small hydro is a safe substitute for large hydro. Some assert it is entirely benign; others acknowledge some problems similar to the ones associated with large hydropower, but say these are too small to be of concern.
In a report on the environmental implications of renewable energy sources, the International Energy Agency (IEA) notes: 'Small-scale hydro schemes (SHS) tend to have a relatively modest and localised impact on the environment. These arise mainly from construction activities and from changes in water quality and flow on ecosystems (aquatic ecosystems and fisheries) and on water use'.
After the reassuring first sentence, the IEA goes on to list a number of environmental impacts and concludes: 'The impacts of small-scale hydro schemes are likely to be small and localised, providing best practice and effective site planning are used'.
But the fact is, it gives no evidence whatsoever to support the conclusion that the impacts will be 'small and localized'. [1]
Cumulative problems
So far, the world has not experienced any major problems from 'small' hydro simply because the world has used 'small' hydro very sparingly.
A turbine here or there may not affect the river noticeably; but if we are to use the technology extensively and put turbines in every other waterfall in a river, and make small dams on most of its tributaries or feeder streams, the environmental degradation — per kilowatt of power generated — will likely be much higher than that caused by large hydropower systems.
The factors that harm a river habitat with large hydropower projects are also at play with small projects: interrupted water flow, barriers to animal movement, water loss from evaporation and loss of biodiversity from the sacrificed portion of river are some examples.
With smaller dams, storage is an increasingly important problem that may require construction of more low-head systems (hydraulic heads that require a fall of water less than 5 metres) than anticipated. Reservoirs silting up or becoming overloaded with nutrients are common problems with major reservoirs that could be at least as serious where smaller and shallower bodies of water are created — the shallower a water-body, the more easily eutrophic it can become.
Likewise, methane generation occurs largely where water and sediment meet, and this means that a shallower water body is likely to release more methane per unit area than a deeper water body. Shallow reservoirs are not unlike paddy fields which are known to contribute substantially to methane emissions, a greenhouse gas 25 times more potent than carbon dioxide.
Disruption from building roads and power lines is less for small hydropower than for large hydropower projects in absolute terms — but on the basis of disruption per kilowatt of power generated, the impact may be at least as severe, if not more severe.
By using small hydro extensively we could be on course to repeat the environmentally damaging history of large hydropower projects. Countries considering the technology should invest in research into the potential problems, and proceed with caution.
Tasneem Abbasi is assistant professor and S. A. Abbasi is head of the Centre for Pollution Control and Environmental Engineering, Pondicherry University, India. More information about their work is available at www.prof-abbasi.com

viernes, 3 de junio de 2011

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ScienceDaily (2011-05-30) -- Whale sharks are often thought to be solitary behemoths that live and feed in the open ocean. However, scientists have now found that this is not necessarily the case, finding that whale sharks can be gregarious and amass in the hundreds to feed in coastal waters.

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ScienceDaily (2011-05-28) -- Students who struggle to learn mathematics may have a neurocognitive disorder that inhibits the acquisition of basic numerical and arithmetic concepts, according to a new article. Specialized teaching for individuals with dyscalculia, the mathematical equivalent of dyslexia, should be made widely available in mainstream education, according to a new review.

Mapping ocean surface currents: West coast radar network is world's largest

ScienceDaily (2011-05-29) -- A network of high-frequency radar systems designed for mapping ocean surface currents now provides detail of coastal ocean dynamics along the US West Coast never before available.

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Mushroom compound suppresses prostate tumors

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Octopuses make some pretty good moves

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Breaking rules makes you seem powerful

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Wolbachia bacteria reduce parasite levels and kill the mosquito that spreads malaria

ScienceDaily (2011-05-20) -- Researchers found that artificial infection with different Wolbachia bacteria strains can significantly reduce levels of the human malaria parasite, Plasmodium falciparum, in the mosquito, Anopheles gambiae. The investigators also determined that one of the Wolbachia strains rapidly killed the mosquito after it fed on blood. According to the researchers, Wolbachia could potentially be used as part of a strategy to control malaria if stable infections can be established in Anopheles.

jueves, 2 de junio de 2011

'Apple a day' advice rooted in science

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Rotational grazing in native pasturelands benefits wildlife

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First rainforests arose when plants solved plumbing problem

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Curtains that block noise

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Robots learn to share: Why we go out of our way to help one another

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Living with a smoker may raise blood pressure in boys

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Media multitasking is really multi-distracting

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Who needs motivation? The rewards of doing 'something'

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Aspirin reduces the risk of cancer recurrence in prostate cancer patients, study suggests

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Seeking happiness? Remember the good times, forget the regrets

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Washing with contaminated soap increases bacteria on hands, research finds

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Work-related 'burnout' more likely to affect the best lecturers, study suggests

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Antioxidant may prevent alcohol-induced liver disease, study suggests

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Traveler's alert: Business travel linked to obesity and poor health

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Winners of mass extinction: With predators gone, prey thrive

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miércoles, 1 de junio de 2011

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Earth's dust and plankton from space: New views from Envisat satellite

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Africa the birthplace of human language, analysis suggests

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440-year-old document sheds new light on native population decline under Spanish colonial rule

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Japan's 9.0 Tohoku-Oki earthquake: Surprising findings about energy distribution over fault slip and stress accumulation

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Happiness has a dark side

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Teens use peers as gauge in search for autonomy, and consistently assume others have more freedoms than they do

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Prolonged breastfeeding may be linked to fewer behavior problems

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Sexy clothes -- too much, too young: Study reveals that a significant proportion of young girls' clothing is sexualized

We actually 'become' happy vampires or contented wizards when reading a book

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Malaria mosquitoes accurately find their way to smelly feet

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Succulent plants waited for cool, dry Earth to make their mark

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Database on environmental impact of major urban ecosystems created

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Researcher use trees to detect contaminants and health threats

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Clumsy avatars: Perfection versus mortality in games and simulation

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