Environmental Engineering Reference
In-Depth Information
comeback. The dissolved oxygen levels are improving, the algae are decreasing, and some game fish have
been reintroduced. Beaches that had been closed for decades have reopened. The improvement is great but not
complete.
St. James Bay Hydroelectric Dams
The St. James Project is a series of hydroelectric dams built in Quebec, Canada, since 1974. The eleven hydro-
electric power stations are built on four rivers.
The four rivers affected directly by dams, and several rivers' waters were diverted into the major rivers to in-
crease their flow. For example, the La Grande River's flow was substantially increased while the downstream
flow of diverted rivers was decreased by as much as 90 percent, drastically affecting ecosystems. Major por-
tions of the local boreal forest have been submerged behind the dams along the rivers. The waters in the affec-
ted areas fluctuate, filling shorelines with dead trees; shoreline plants are destroyed as well. The area is subject
to earth tremors caused by the weight of the artificial rivers and reservoirs behind the dams, resulting in a shift-
ing of rocks. There is the potential for great harm to the local population and the surrounding environment as
fault lines are now present in the valley.
Other changes to the ecosystem include the decline of salmon spawning in the area as dams built in some areas
block fish migrations, and other rivers' flow rates have been reduced, doing away with spawning sites altogeth-
er. Beaver habitats have been dislodged as the rivers and streams that fill the rivers have been altered. Migrat-
ing herds of caribou and flocks of Canadian geese and other migrating birds have been affected as the shores of
the James and Hudson bays have been altered.
Gulf of Mexico's Dead Zone
Both the Mississippi and Atchafalaya rivers empty into the Gulf of Mexico, carrying with them the pollutants
and nutrients they pick up along their courses. These pollutants include fertilizer, untreated sewage, deposition
from fossil-fuel combustion, runoff from streets, and discharge from industries.
Every spring, the wealth of nutrients introduced into the Gulf of Mexico creates a great bloom in algae and
plankton populations. However, with the increase in life is also an increase in death and decomposition, during
which bacteria use oxygen. Over time, this depletes an aquatic ecosystem of dissolved oxygen and the area be-
comes hypoxic. Lack of oxygen affects all other organisms in the area. So, the organisms die or leave the area.
Ultimately, this creates a dead zone, where there is no life.
Although one of the largest in the world, the Gulf of Mexico dead zone is not the only one. In fact, there are
now over 400 dead zones found throughout the world. This number has doubled since 2000. Since such an area
becomes devoid of life, the ecosystem ceases to function and must start over again when the oxygen levels re-
turn to normal levels. Economically, dead zones cost fishermen income and also can affect tourism dollars.
Aral Sea
In the middle of central Asia in both Uzbekistan and Kazakhstan (once part of the former Soviet Union), the
Aral Sea was once the fourth largest inland body of water in the world. Although it has always been a saline
lake, it has progressively become more saline and has also been dramatically depleted due to diversion of water
from the two rivers that empty into the lake, for use in irrigation in this hot, dry, drought-ridden region. The
lake's volume has decreased by 75 percent, and its salinity has increased dramatically. Instead of being one
large lake, the Aral Sea has been separated into three smaller lakes due to the extremely low water levels.
