|Title||A natural experiment reveals the impact of hydroelectric dams on the estuaries of tropical rivers|
|Publication Type||Journal Article|
|Year of Publication||2019|
|Authors||Ezcurra E., Barrios E., Ezcurra P., Ezcurra A., Vanderplank S., Vidal O., Villanueva-Almanza L., Aburto-Oropeza O|
|Type of Article||Article|
|Keywords||hydropower; mangroves; Science & Technology - Other Topics; Vegetation|
We tested how sediment trapping by hydroelectric dams affects tropical estuaries by comparing two dammed and two undammed rivers on Mexico's Pacific coast. We found that dams demonstrably affected the stability and productivity of the estuaries. The two rivers dammed for hydroelectricity had a rapid coastal recession (between 7.9 and 21.5 ha year(-1)) in what should otherwise be an accretional coastline. The economic consequences of this dam-induced coastal erosion include loss of habitat for fisheries, loss of coastal protection, release of carbon sequestered in coastal sediments, loss of biodiversity, and the decline of estuarine livelihoods. We estimate that the cost of the environmental damages a dam can cause in the lower part of basin almost doubles the purported benefits of emission reductions from hydroelectric generation.
The most important environmental argument frequently brought forth in favor of hydroelectric dams is that of emission reductions. These reductions, however, are often partially offset in tropical ecosystems by the emission of methane (CH4) and CO2 from decomposing organic matter from the forests submerged in the reservoir but can be, and often are, calculated in environmental studies around new hydroelectric projects.
However, the damages a hydroelectric project can cause in the coast and the lower part of tropical basins, in terms of loss of mangrove services and estuarine productivity, may add a significant amount to the environmental costs of a dam and are rarely calculated. These costs should be estimated and added to the many other well-known impacts of hydroelectric dams in both the reservoir itself and in the upper and mid-basin. The building of a dam on free rivers such as the San Pedro or the Acaponeta can imperil the livelihoods of fishing and rural communities in the floodable coastal plains, a social impact that should be added to the number of villagers that often lose their land and their sacred sites under the flooded reservoir. Last, although not easily quantifiable in economic terms, large dam projects imply the loss of important coastal biodiversity and imperil the continued formation and dynamics of accretional coastal landscapes.