by Arushi Arora
Climate change is one of the most pressing global issue in contemporary times, and dams play a substantial role in aggravating it by becoming feeding grounds for methane-producing microbes. In addition, dams fragment rivers and disrupt their natural flow, threatening the survival of aquatic fauna, especially migratory species. Dams are also culpable for disrupting the biogeochemical cycles of river ecosystems, thereby impacting their function and structure. Taking all the environmental impacts of dams into account, the apparent economic gain from them may not be worth it. —
In 2014, the dam in Canada’s Mount Polley mine gave way without warning, releasing 21 million cubic meters of mining sludge into British Columbia’s famed Quesnel Lake. In May 2020, Midland County in Michigan, US, was threatened with unprecedented flooding when two of its ageing dams – Edenville and Sanford – breached due to heavy rainfall. The unexpected flooding of downtown Midland resulted in the immediate evacuation of 10,000 people. In July 2020, China witnessed record-breaking rains that led a small reservoir in the Guangxi district to collapse. This incident was considered to be a harbinger, a “black swan” of future collapses in the country’s 94,000 ageing dams.
As disquieting as they may seem, dam failures are relatively common catastrophes in the 21st century, impacting the lives of hundreds of thousands of people and taking an irredeemable toll on the environment. This raises a pertinent question about their efficacy: “Is the environmental price of economic development through dams too high?”
Dams have often been referred to as the “temples of the modern economy’’ since they supplement agriculture, irrigation, water storage, flood control, and electricity generation. Considered symbols of economic prosperity, dams were constructed with great gusto in developing societies throughout the 1900s. However, this approach might have been slightly near-sighted, conveniently disregarding the ecological footprint of these massive reservoirs. Dams can directly or indirectly be responsible for soil erosion, species extinction, spread of diseases, sedimentation, salinisation, and waterlogging. Large dams may even be able to alter the Earth’s orbit, given the massive shifts in water distribution across several major river systems. As the world tries to make economic sustenance and environmental sustainability synchronous, it is imperative to accept the fact that dams may be fruitless, if not detrimental, to this attempt.
The Environmental Impacts of Dams
Dams are massive structures that retain water for domestic use, irrigation, hydroelectricity generation, and for use in industrial processes. However, when dams block the flow of water across a river, they trap enormous amounts of lake sediments in their reservoirs. Underwater microbes feed on the organic matter that gets accumulated in these sediments and produce methane, a potent greenhouse gas that significantly contributes to global warming. Additionally, dams lead to the fragmentation of rivers and the destruction of surrounding forests, inevitably eliminating valuable carbon sinks.
Bridgit Deemer, a research associate at Washington State University, along with John Harrison, associate professor at the WSU Vancouver School of the Environment, wrote for the journal BioScience (2016) and concluded that “while reservoirs are often thought of as ‘green’ or carbon-neutral sources of energy, a growing body of work has documented their role as greenhouse gas sources.” Vincent St. Louis, a biogeochemist at the University of Alberta, Canada, was the first to calculate the total contribution of reservoirs around the world to greenhouse gas (GHG) emissions. “Whatever dam builders may say, reservoirs are not greenhouse-gas neutral,” said St. Louis. As per his calculations, reservoirs all over the world collectively contribute roughly 1.3% of the world’s annual GHG emissions, as much as the entire nation of Canada.
Impact on Natural Flow and Riverine Biodiversity
Imagine this: a pod of emaciated Gangetic dolphins swimming lethargically along the Brahmaputra. The pod has been reduced to a mere few individuals and even those that remain barely manage to rise to the surface to breathe. The dolphins’ once lustrous skin, full bellies, and frequent leaps out of the water have been replaced with the struggle for survival. Those perpetual “smiles” on their faces effortlessly betray their ordeal within. Such is the life of India’s national aquatic animal as the country unceasingly builds dams on the Ganga and the Brahmaputra, the dolphin’s natural habitats.
Dams alter the natural flow of the river, thereby fracturing the migratory routes of most fish. As fish are unable to spawn, predators like the dolphin cannot eat. However, this phenomenon extends beyond just the Gangetic dolphin; the Royal Bengal tigers, Indian rhinoceroses, Irrawaddy dolphins, Siberian cranes, Yangtze sturgeons, and countless other threatened species depend on an undisturbed river ecosystem for survival.
As dams impede the flow of rivers, they also deter the flow of vital nutrients like carbon, nitrogen, silicon, and phosphorus along the nexus of the river and its tributaries. Sedimentation in the reservoir leads to increased nutrient retention upstream, depriving the downstream areas of nutrient-rich sediment altogether.
Carbon is the primary constituent of all life on Earth, and a disruption in the flow between continental and oceanic carbon could have disastrous results. At the start of the 21st century, in-reservoir sedimentation wiped out 13% of the total riverine export of carbon to the oceans, and this value is expected to rise to 19% by 2030. The Amazon River, which supports the largest rainforest in the world, is expected to have 184 new dams by 2030, thereby increasing upstream carbon sedimentation 38-fold or 7% of global reservoir carbon accumulation. This could have disastrous impacts on the Amazonian ecosystem. As the downstream areas receive fewer nutrients, the soil gradually loses its fertility and is unable to support the flora and fauna of the region. Moreover, as fewer quantities of these nutrients flow into the ocean, algae, which are major carbon sinks, fail to bloom. This indirectly aggravates climate change.
The environmental impacts of dams range far beyond those articulated above. The construction of large dams may even modify geo-environmental conditions, as in the case of the large-scale canyon deformations caused by the Xiluodu dam on the Jinsha River in China. Dams located in seismologically active geological zones, such as the Himalayas, pose a severe threat of flooding due to earthquakes, affecting millions of people and deteriorating land in their wake. All these reasons reaffirm that, unlike popular belief, dams are not “green”.
Supporters of these projects would argue that dams allow for the preservation and storage of water, which, given the increasing pressure on the world’s freshwater resources, has become a necessity. Reservoirs created by dams can collect water for irrigation, industrial use, and human consumption. They might also argue that dams facilitate the generation of hydroelectricity, which is a much cleaner energy source compared to fossil fuels. Furthermore, tailing dams store toxic mining waste, thereby preventing it from leaching into the surrounding land. However, these arguments can be easily dismantled.
Dams and reservoirs have a much greater surface area than the rivers that feed them and the nutrient-rich water in the reservoirs promotes plant growth. The water exposed to the sun and the plants’ transpiration speed up the process of evaporation, leading to immense loss of precious water. The world’s reservoirs lose about 170 cubic kilometres of water to evaporation every year, the equivalent of 7% of all freshwater consumed by human activities. Thus, the belief that dams help in the preservation of water is erroneous.
What’s more, hydroelectricity is not as clean as it seems. Decaying vegetation and nutrient sedimentation in the reservoir lead to increased microbial activity, which results in massive GHG emissions. “It would be a grave mistake to continue to finance those [dams] with the impression that they were part of the solution to the climate crisis,” said Kate Horner, executive director of the environmental group International Rivers.
Another counterargument is that, although tailing dams store noxious mining sludge, they have a very high failure rate. Dam breaches are more frequent than one might think, and toxic metals often escape into the soil via microbial action or acid drainage, thereby undermining the utility of the dam.
Many would argue that economic growth should be a nation’s foremost priority, and hence, any means adopted to achieve that stands justified. However, as the world currently deals with global warming – one of the most challenging battles in human history – it is imperative that we not only reconciles with the long-due ramifications of our actions but also works towards a more sustainable relationship with nature.
Undoubtedly, dams have numerous short-term economic benefits, but these stand null and void if they come at the expense of the environment. These water bodies were formed and have sustained over millions of years. Perhaps, it is time to acknowledge the fact that they survived for reasons far beyond human comprehension. Everything in nature is so intricately balanced that a massive imposition like a dam could have unimaginable consequences. What use is economic development if people forever remain susceptible to catastrophes and animals struggle for existence? The irreparable damage inflicted upon the environment will ultimately befall humanity in the years to come, reversing decades of economic growth in mere seconds. This utilitarian approach to our planet is terrifying and must change, now more than ever.
The dam failure in Canada’s Mount Polley mine, the unexpected flooding of Midland County in Michigan, and the breach of the reservoir in China’s Guangxi district are not a set of sporadic incidents. Dam failures have always been in tandem with the construction of dams and will continue to be as long as their environmental costs are not given due consideration.
Nevertheless, there is light at the end of the tunnel. Strategically planning the construction of dams on rivers, such that human needs are met with minimal damage to the environment, is the way forward. Significant change can also stem at an individual level. Simply voicing concerns regarding the construction of new dams by signing petitions will build pressure on the authorities concerned to take cognisance of the environmental impacts of these projects.
Dams are established to meet the ever-increasing energy and water demands of the population; therefore, small efforts to conserve power and water can go a long way. By refusing to contribute to recreational economic activities like boating and fishing, we can dissuade their growth in the future. Although the ultimate goal may seem daunting, it is crucial to remember that every contribution, no matter how small, makes a difference.
SOURCE: EARTH ORG https://earth.org/dams-economic-assets-or-ecological-liabilities