Original sentence: A dam also acts as a barrier between the upstream and downstream movement of migratory river animals, such as salmon and trout.Reservoirs can also contribute to greenhouse gas emissions.The decaying plant matter itself settles to the non-oxygenated bottom of the reservoir, and the decomposition—unmitigated by a flow pattern that would oxygenate the water—produces and eventually releases dissolved methane.The newly created reservoir has more surface area than the river would have had, and therefore more evaporation occurs than previously.This can lead to a loss of up to 2.1 meters in depth per year in some climates
Edited sentence: A dam also acts as a barrier between the upstream and downstream habitat of migratory river animals, such as Chinook salmon and steelhead trout in the USA, and Atlantic salmon in Europe.According to arguments of hydropower opponents, reservoirs contribute to greenhouse gas emissions as well.The decaying plant matter itself settles to the non-oxygenated bottom of the stagnant reservoir, and the decomposition—unmitigated by a flow pattern that would oxygenate the water—produces and eventually releases dissolved methane.The newly created reservoir has more surface area than the river would have had, and therefore more evaporation occurs than is normal.This argument however remains to be scientifically proven by empirical data.This can lead to a loss of up to 2.1 meters in depth per year