Hydropower Dams Can Harm Coastal Areas Far Downstream
By Paula Ezcurra and Octavio Aburto
Thousands of hydroelectric dams are under construction around the world, mainly in developing countries. These enormous structures are one of the world's largest sources of renewable energy, but they also cause environmental problems.
Hydropower dams degrade water quality along rivers. Water that flows downstream from the dams is depleted of oxygen, which harms many aquatic animals. The reservoirs above dams are susceptible to harmful algal blooms, and can leach toxic metals such as mercury from submerged soil.
We wanted to know whether dams also impact river systems farther away, at the coastlines where rivers flow into the sea. So we performed a natural experiment comparing four rivers along Mexico's Pacific coast — two that are dammed and two that remain free-flowing. We found that damming rivers has measurable negative ecologic and economic effects on coastal regions more than 60 miles downstream.
Feeding or Starving Coastlines
We studied four river outflows along the Pacific Coast of Mexico in the states of Sinaloa and Nayarit. Two of these were from the San Pedro and Acaponeta rivers, which are relatively unrestricted, with over 75% of their flow unobstructed.
The other two outflows came from the nearby Santiago and Fuerte rivers, which have over 95% of their flow retained in reservoirs. In addition to restricting water flow, these reservoirs trap sediments — over 1 million tons per year along the two rivers combined.
In unobstructed rivers, sediment flows downstream and is eventually deposited along the coast, helping to stabilize the shoreline and sometimes even to build it up. We found that this was happening along the free-flowing Acaponeta and San Pedro rivers.
However, because the sediment from the dammed Santiago and Fuerte rivers is no longer carried downstream, wave action takes over at the coast. At the mouths of these two rivers, we found that waves were eroding up to 33 hectares of combined land — equivalent to about 62 football fields — each year, with widespread ecologic and economic effects on the surrounding regions.
The dammed Fuerto and Santiago Rivers show greater erosion where they reach the Pacific coast than the free-flowing San Pedro and Acaponeta rivers. Images at right show coastline changes during the two periods: blue indicates land accretion, red indicates erosion.
Ezcurra et al., 2019., CC BY-NC
The Ecology of Healthy Coasts
Our field research clearly showed that coastal instability resulting from sediment loss at the mouths of the dammed rivers was harming ecosystems along the shore. For example, we found that coastal regions downstream of free-flowing rivers had significantly more plant diversity. Many of these plants were found only in coastal areas, and therefore had high conservation value.
Coastal erosion due to lack of sediment input from the rivers also reduces critical nursery habitat, such as mangrove forest, where many commercially important fish species spend their juvenile stage. We found that fishing activity at the mouth of the free-flowing San Pedro River was much higher than around the mouth of the dammed Fuerte River. This loss of fishing potential comes at a cost of around $1.3 million every year.
Reduced sediment flow also deprives coastal estuaries of nutrients. Lucrative shrimp and oyster fisheries in the region we studied rely heavily on nutrient inputs from rivers. In the San Pedro River region, these fisheries generate around $5.8 million yearly; near the dammed rivers, they have been all but abandoned.
Coastal mangrove wetlands also protect shorelines from hurricanes and tropical storms, and serve as recreational areas and conservation habitat for wildlife. Knowing this, we calculated that the loss of these ecosystem services around the dammed rivers totals $3.9 million annually.
Vegetation profile of sandbars of the free-flowing San Pedro River (A) and dammed Santiago River (B), where receding black mangrove forest is being eroded away into the advancing coastline
Ezcurra et al., 2019, CC BY-NC
Still another valuable function that mangrove wetlands perform is storing "blue carbon" in plant tissue and soils, reducing the effects of climate change. But when coastlines recede and mangroves are destroyed, this carbon is released. We calculated that mangrove loss in our study region represented a loss of around $130,000 in annual carbon trading potential for this region.
Adding up all of the ecological services that coastal ecosystems provide, we estimate that the economic consequences of shoreline loss around the Santiago and Fuerte rivers related to hydroelectric damming totaled well over $10 million yearly.
Letting More Sediment Flow
Because sediments are so essential to areas around river mouths, reducing sediment trapping behind dams could mitigate some harmful impacts on coastal areas. There are several ways to do this — notably, sediment bypassing, or diverting a portion of the sediments flowing from upriver around dams and allowing it to rejoin the river downstream.
This strategy can be included in new construction or incorporated into existing dams. In addition to reducing dams' environmental impacts, it also increases dams' service lives by reducing the rate at which their reservoirs fill up with silt.
To date, environmental impact assessments of large inland dams have often failed to properly analyze the impacts that these dams will have downriver on coastlines, estuaries, deltas and lagoons. Our study shows how important it is to fully account for dams' environmental and economic impacts along coasts and basins.
Mexico may be at a juncture in its approach to hydropower. The Mexican government recently contracted with Hydro-Quebec, the world's largest hydroelectric power producer, to revamp existing dams across the country. And a recent study by a Mexican nongovernment organization, SuMar-Voces por la Naturaleza, reported that a long-disputed proposal to build a new hydroelectric dam at Las Cruces is neither financially feasible nor needed to meet energy demand for the region, prompting national groups to call for the final cancellation of the project.
We believe that Mexico and all nations working to develop efficient, low-impact energy sources should take a holistic approach to future dam-related projects, so they can weigh their potentially harmful consequences. The coastal effects that we documented should be part of those reviews.
Paula Ezcurra is a digital communications specialist with the Gulf of California Marine Program, University of California San Diego.
Octavio Aburto is an assistant professor of marine biology with the the Scripps Institute of Oceanography, University of California San Diego.
Disclosure statement: Octavio Aburto receives funding from the David and Lucile Packard Foundation, UC MEXUS and the Leona M. and Harry B. Helmsley Charitable Trust. Paula Ezcurra does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond her academic appointment.
Reposted with permission from our media associate The Conversation.
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They also encounter what some call an "infodemic," an outbreak of misinformation that's making it more difficult to treat patients.
When Leaders and Doctors Spread Misinformation<p>When people in charge of towns, cities, states, and countries spread misinformation, the potential for belief in misinformation to result in policies can have harmful effects.</p><p><a href="https://www.northwell.edu/find-care/find-a-doctor?q=Bruce+E.+Hirsch%2C+MD&insurance=&location=&query_type=provider&physician_partners=false&default_view=list&gender=&language=&sort=relevancy" target="_blank">Dr. Bruce E. Hirsch</a>, attending physician and assistant professor in the infectious disease division of Northwell Health in Manhasset, New York, says an example of this is when President Trump informed the public he was taking hydroxychloroquine as a preventive measure.</p><p>"To approach this enormous challenge, we need some intellectual honesty and clarity, and to disregard expertise and to make decisions and model decisions based on hunches is inviting us to handle challenges on the basis of rumor and uninformed opinion. The magnitude of that error is epic," Hirsch told Healthline.</p><p>Stukus agrees, noting that the harm of this proclamation is documented.</p><p>"Early on when the president touted the benefits of hydroxychloroquine and azithromycin, people started to hoard this medicine, and state boards had to shut it down because they were getting so many prescriptions for this unproven therapy that it was not available for those who truly needed it, such as those who have lupus and autoimmune conditions," Stukus said.</p><p>He adds that calls to poison control centers increased after the president suggested using disinfectant to prevent contracting the new coronavirus.</p>
Listen to Science, Even When it Changes<p>When recommendations change or evidence flip-flops, skepticism may arise. However, Stukus says change is the beauty of science.</p><p>"That shows us that we can evolve, and if the evidence shows that our prior thoughts were incorrect, we need to be able to change our recommendations and advice based upon the best quality of evidence at the time," he said.</p><p>Pierre agrees.</p><p>"Science is an iterative process, whereby we arrive at facts and truth through repeated and controlled observations. That means that it's inherently self-correcting as we revise conclusions based on ongoing research. Scientific facts aren't immutable dogma chiseled on a tablet. They change based on the best available evidence we have at a given point in time," he said.</p><p>Because research of COVID-19 has only been underway for 6 months, information is evolving rapidly, and new information may contradict old.</p><p>"There's still much we don't know about exactly how [COVID-19] spreads, what effects it has on the body, or how to best treat it. That means that the best available evidence is preliminary, but that doesn't mean that we should ignore it or turn to other sources of information or opinion as if they're just as valid," Pierre said.</p><p>He explains that conspiracy theories based on mistrust lead to vulnerability to misinformation.</p><p>If people mistrust science because it sometimes "changes its mind," Pierre said, "that shouldn't be used to embrace other opinions based on no evidence at all, which are typically selected based on confirmation bias: what we want to believe rather than what the objective evidence supports."</p>
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