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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By Dr. Kate Raynes-Goldie
Of all the plastic we've ever produced, only 9% has been recycled. So what happened to all that plastic you've put in the recycling bin over the years?
Triangle of Mistruths<p>The myth created around plastic recycling has been one of simplicity. We look for the familiar triangle arrows, then pop the waste in the recycling bin so it can be reused.</p><p>But the true purpose of those triangles has been misunderstood by the general public ever since their invention in the 1980s.</p><p>These triangles were actually created by the plastics industry and, according to a report provided to them in July 1993, <a href="https://www.npr.org/transcripts/912150085" target="_blank">were creating "unrealistic expectations"</a> about what could be recycled. But they decided to keep using the codes.</p><p>Which is why many people still believe that these triangular symbols (also known as a <a href="https://sustainablepackaging.org/101-resin-identification-codes/" target="_blank" rel="noopener noreferrer">resin identifier code</a> or RIC) means something is recyclable.</p><p>But according to the American Society for Testing and Materials International (ASTM) – which controls the RIC system – the numbered triangles "<a href="https://www.astm.org/Standards/D7611.htm" target="_blank" rel="noopener noreferrer">are not recycle codes</a>." In fact, they weren't created for the general public at all. They were made for the post-consumer plastic industry.</p><p>In other words, the symbols make it easier to sort the different types of plastics, some of which cannot be recycled – <a href="https://www.ecobin.com.au/understand-recycling-codes/" target="_blank" rel="noopener noreferrer">depending on the recycling facility</a>.</p><p>"Unfortunately, just placing your plastic into the recycling bin doesn't mean it will get recycled," says Lara Camilla Pinho. She is an architect and lecturer at the UWA School of Design who is researching novel uses of plastic waste.</p><p>"The recycling system is complicated and often dictated by market demand. Not all plastic is recyclable. We cannot recycle plastic bags or straws for example."</p>
Behind the Scenes<p>So, what makes recycling plastics so difficult?</p><p>"Essentially, there are two types of plastics – thermoplastics and thermosets. While thermoplastics can be re-melted and re-molded, thermosets contain cross-linked polymers that cannot be separated meaning they cannot be recycled," says Lara.</p><p>"Even thermoplastics have a limit to the amount of times we can recycle them, as each time they are recycled they downgrade in quality."</p><p>Even when plastics are recyclable, it is <a href="https://www.theguardian.com/environment/2019/oct/13/war-on-plastic-waste-faces-setback-as-cost-of-recycled-material-soars" target="_blank">often more costly</a> than simply making new plastics.</p>
Sugar, Seaweed and Mushrooms<p>If the conventional recycling system isn't working, what else can we do with all the plastic we've created?</p><p>Lara is looking for ways to add value to recycled plastics such as using it in the design and development of architectural products. She hopes to use these architectural products to help underserved communities that are disproportionately affected by plastic waste.</p><p>In addition to recycling, we also need to find ways to reduce our use of virgin petroleum-based plastics.</p><p>Bioplastic is one such product that has been getting a lot of hype over the last few years. And although they're better than petroleum-based plastics, bioplastics also come with their own <a href="https://phys.org/news/2017-12-truth-bioplastics.html" target="_blank">set of challenges</a>.</p><p>"There are already a lot of bio-based alternatives to plastic, such as bagasse – a byproduct of sugar cane processing," says Lara.</p><p><a href="https://blogs.scientificamerican.com/observations/the-mycelium-revolution-is-upon-us/" target="_blank" rel="noopener noreferrer">Mycelium</a>, a type of fungi we most often associate with mushrooms, are also providing an interesting plastic alternative.</p><p>"In the field of architecture, mycelium is starting to be used as an alternative to plastic insulation, but also as compostable packaging and bricks," says Lara.</p><p>"The bricks take around five days to make and are strong, durable, water resistant and compostable at the end of their use."</p><p><a href="https://www.arup.com/news-and-events/hyfi-reinvents-the-brick" target="_blank" rel="noopener noreferrer">Hy-Fi Tower</a>, created by <a href="http://www.thelivingnewyork.com/living_about.html" target="_blank" rel="noopener noreferrer">The Living</a>, is an example of a building made from these bricks.</p><p>And finally, there's seaweed.</p><p>"[Seaweed is] cheap and can reproduce itself quickly without fertilizers. In architecture, there is use for seaweed as an alternative to plastic insulation but also as cladding," says Lara.</p>
More Money, More Problems<p>While all these alternatives are great, the main cause of our plastic dilemma is not scientific or technological, but economic.</p><p>As long as it remains <a href="https://engineering.mit.edu/engage/ask-an-engineer/why-is-it-cheaper-to-make-new-plastic-bottles-than-to-recycle-old-ones/" target="_blank">cheaper to create new plastics</a> from fossil fuels rather than from bioplastics or from recycling, we're going to be stuck with plastic garbage islands floating in our oceans.</p><p>The true cost to our health and our environment has yet to be included in the equation. But once it is, maybe that is when the real shift will happen.</p>
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Towards the end of the final presidential debate of the 2020 election season, the moderator asked both candidates how they would address both the climate crisis and job growth, leading to a nearly 12-minute discussion where Donald Trump did not acknowledge that the climate is changing and Joe Biden called the climate crisis an existential threat.
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By Zheng Chen and Darren H. S. Tan
As concern mounts over the impacts of climate change, many experts are calling for greater use of electricity as a substitute for fossil fuels. Powered by advancements in battery technology, the number of plug-in hybrid and electric vehicles on U.S. roads is increasing. And utilities are generating a growing share of their power from renewable fuels, supported by large-scale battery storage systems.