A recent study demonstrates the widespread environmental consequences of large dam reservoirs in Mexico — ScienceDaily

Researchers at the University of California, San Diego, and the Scripps Institute of Oceanography at the University of California, Riverside, found that inland dams have a highly devastating impact on the stability and productivity of coastline and estuary habitats. The study was published on March 13th at Science Advances .

The researchers analyzed the downstream ecosystems of four rivers in the states of Sinaloa and Nayarit in the Pacific Ocean, two of which were two and two were unobstructed. They found a severe coastal decline along the river's blocked estuary, including important ecosystems such as mangroves, which provide protection against storms, commercial fisheries and underground carbon storage.

The rivers studied by researchers have been parallel to each other through similarly developed land into large coastal lagoon systems. There are dams in the San Diego and Fuerte rivers that provide hydroelectric power to the area, but retain 95% of these rivers. At the same time, the San Pedro and Aktapota rivers are relatively free-flowing and unspoiled, with more than 75% of the rivers still unimpeded.

More than one million tons of sediment per year are trapped in the dams of the Fuerte and San Diego rivers, causing a coastal economic recession in the estuary. This sediment usually leads to the estuary and accumulates along the coast, allowing ecosystems such as mangroves to grow. Since the dam was built, the San Diego and Fulth rivers have lost 21 hectares (about 40 American football fields) each year. In contrast, the coast around the estuary of the San Pedro and Akpota rivers did not retreat, but stabilized and even showed sediment growth during the same period of time.

"A similar process of stopping the river and controlling the flow of water is destroying the estuaries and coasts of many parts of the world," said Exequiel Ezcurra, a former professor of the University of California, and a part-time professor at Scripps. “Although the impact on ecosystem protection is enormous, the process of coastal degradation due to large dams has not been fully studied or quantified through rigorous comparative methods.”

The coastal economic recession has had widespread economic impacts on the region, including loss of fishery habitats, reduced coastal protection of storm events, reduced biodiversity, loss of estuary livelihoods, and previous storage in coastal sediments. Carbon release increases. Researchers calculate the economic consequences of these losses for more than $10 million a year, of which $1.3 million comes from natural capital in the region that relies solely on fisheries services.

"The benefits of short-lived work around dam construction need to be weighed against the long-term costs of the dam's local livelihoods," said Octavio Aburto-Oropeza, a collaborator and professor at Scripps.

In addition, the co-author of this article, botanist Sula Vanderplank from San Diego State University and Lorena Villanueva of the University of California, Riverside, found that this instability directly affected the floral biodiversity of coastal areas. The unmodified San Pedro and the apex of the Acaponeta River are much richer in species than the Fuerte and San Diego rivers. Many species that have disappeared from the estuary estuary are not found elsewhere and are of high conservation value.

Hydropower dams are considered a source of alternatives to renewable energy and low-emission fossil fuels. However, hydropower projects may cause losses to coastal and tropical basins, and in terms of mangrove service losses and estuary productivity, the environmental costs of dams may be significantly increased and rarely calculated.

"This study reveals the need to consider the environmental and economic impacts of hydroelectric dams on coastal and basin ecosystems," Aburto-Oropeza said. “We need to fully explain the impact of upstream on the entire region.”

This study was funded by David and the Lucile Packard Foundation, UC MEXUS, and the Leona M. and Harry B. Helmsley Charitable Trust. Aburto-Oropeza and Ezcurra are both winners of Pew Fellowship.

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