Hydroelectricity - Energy Policy Analysis: A Conceptual Framework - page 151

Atlantic and Pacific coasts of the United States have reduced salmon populations by preventing
their access to spawning grounds upstream. Salmon spawn are also harmed on their migration
downstream when they must pass through turbines. When young salmon travel downstream toward
the ocean, they may be killed by turbine blades at hydropower plants. When adult salmon attempt
to swim upstream to reproduce, they may not be able to get past the dams (USEPA 2011). More-
over, lake species often replace river species of fish in reservoirs, either naturally or with artificial
stocking for sports fishing. Hydropower facilities can damage fish, restrict or delay migration,
increase predation, and degrade water quality (Schilt 2007).
Supersaturation. Supersaturation occurs when air becomes trapped in water spilled over a
dam as it hits a pool below, creating turbulence. Because air is comprised of 78 percent nitrogen,
the level of nitrogen dissolved in water can increase dramatically. Affected water does not lose
the excess nitrogen quickly. Supersaturated water can enter tissues of fish and other species. If
fish swim from an area supersaturated with nitrogen to a lower pressure area, a condition similar
to “the bends” in scuba divers can occur. This effect causes injury and can cause death to fish
(FWEE 2011).
Methane Emissions. Hydroelectricity generation has different impacts on climate change,
depending on the climate where a hydro project is located. Decaying plant matter from flooded
areas releases methane and carbon dioxide (Guerin et al. 2006). Hydro facilities located in tropi-
cal climates may produce substantial amounts of methane and are therefore likely to have more
severe impacts on climate change than facilities located in temperate climates, which may actually
sequester methane (FWEE 2011).
Water Quality. Mercury is mobilized and released into the environment for twenty to thirty years
by decaying organic matter undergoing anaerobic decomposition in reservoirs (Dillon 2010). A
fivefold to sixfold increase in mercury concentrations has been observed in fish in hydroelectric
impoundments as compared to natural reservoirs (Tremblay, Lucotte, and Hillaire-Marcel 1993).
Mercury is picked up by fish that humans like to catch and eat, and it bioaccumulates in both fish
and human body tissues. Too much mercury is especially harmful to development of the nervous
systems of small children (Dillon 2010).
Dam Failures. Because large dams hold back large volumes of water, a failure due to poor
construction, earthquakes (Armaroli and Balzani 2011, 234), terrorism, or other causes can be
catastrophic to downriver settlements. In an unstable political world, large dams upstream of
population centers constitute attractive targets for terrorism. Sound design and construction are
not adequate guarantees of safety. Smaller dams and micro hydro facilities create less risk, but
may constitute continuing hazards even after being decommissioned. Small dams can fail many
years after decommissioning, causing death and property destruction downstream.
Multiple Uses of a Reservoir. Reservoirs created by hydroelectric schemes often provide fa-
cilities for water sports and sport fishing, becoming tourist attractions. Multiple-use dams serve
multiple goals of providing water for agricultural irrigation, municipal water supply, and flood
control to protect people and property downstream (FWEE 2011).
Cultural Impacts. Large dam construction may require relocation of human populations from
a reservoir area and destruction of archeological and cultural resources of value to local popula-