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I. Significance: Humans need fifty liters of water per person per day on average (World Commission on Dams, 2000). Less than .007% of the water on earth is liquid freshwater that is regularly cycled and renewed (Human Appropriation). 
The world population is increasing at an unprecedented rate and urbanization is occurring at a similarly impressive scale. These increases will result in a larger demand for limited water resources; due to uneven water distribution, it is expected that one-third of water stressed countries will experience severe water shortages in the next century (WCD, 2000). Currently, most water is used for agricultural purposes, especially in developing countries. Currently, dams are a major factor in obtaining the water we so desperately need.
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Invasive species are non-native species that have been introduced to a water-way and that have been able to establish themselves in that ecosystem at the expense of other species. Increase in invasive species is correlated with a decrease in overall biodiversity and loss of ecosystem services and is a major concern in coastal ecosystems (Worm et al, 2006). Invasive species often upset the entire ecosystem balance, driving less competitive species into extinction and fundamentally altering the food web. High profile examples include the proliferation of zebra mussels in the Great Lakes--which have caused the decline in many native species and caused many industrial problems--and the Nile perch, which caused the extinction of hundreds of aquatic species in Lake Victoria. Invasive species are listed as the second greatest source of species extinctions (Wilcove et al, 1998).The figures at the right illustrate the interrelations between biodiversity, ecosystem services, and risks; species invasions is shown at the far right under "risks." 
Invasive species are often transported via ballast water, or water taken on-board ships to keep it level in water. The water is taken from the starting point and then released at the end point--along with any organisms living inside. High risk ballast in regards to transport of invasives is water taken onboard in a freshwater or estuarine port as those organisms have a high chance of surviving in their new environment (Portland University, 2006). Invasives are also released intentially-as with unwanted pet release or through aquarium dumping--such as the release of the red-eared slider in the United States.
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