The sand dunes in the Acaponeta river delta, which is unobstructed, remain stable. Photo by Ana Ezcurra/UCSD

Hydroelectric dams harm coastal ecosystems downstream

March 14 (UPI) -- According to a new study, coastal ecosystems suffer when hydroelectric dams are built upstream. Mangrove forests, wetlands and other estuarine habitats are already facing the threat of rising sea levels. Now, new research suggests these ecosystems are disrupted by upstream dam construction.

For the new study -- published in the journal Science Advances -- scientists studied four rivers in the Mexican Pacific states of Sinaloa and Nayarit, two dammed and two mostly unobstructed.

The Santiago and Fuerte rivers both feature large hydroelectric dams that produce large amounts of electricity. The two dams block 95 percent of the flow in each river. San Pedro and Acaponeta remain 75 percent unobstructed, making them relatively free-flowing. All four rivers follow parallel paths from the mountains to the Pacific and run through similar terrain.

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As the new research revealed, more than a million tons of sediment are blocked by the two hydroelectric dams. Sediment and fresh water are the life blood of coastal ecosystems. Since the Santiago and Fuerte became obstructed by dams, the rivers' annual rate of coastal land loss has increased 21 hectares.

Coastal lands in the mouths of the San Pedro and Acaponeta remained stable during the same time period.

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