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What's the biggest threat to freshwater habitats?

What's the biggest threat to freshwater habitats?

No. 1 Threat to Freshwater Habitats: Agriculture

The biggest threat today to freshwater ecosys­tems is agricult­ure. Agriculture is the raising of crops and livestock for food. Obviously, we can't stop farming -- we have to farm to eat and we have to eat to survive. But unfortunately this vital institution hurts our freshwater systems. How?

Freshwater is a renewable resource -- through precipitation -- but it's not unlimited. If human consumption outpaces natural restoration, the quality and quantity of remaining freshwater sources suffers. Agriculture accounts for a whopping 70 percent of our freshwater use. Crops like rice, cotton and sugar are particularly thirsty and need a lot of water to grow. For example, it can take up to 1,300 gallons (5,000 liters) of water to grow just 2.2 pounds (1 kilo) of rice. To give you a sense of how much water that requires worldwide, the 2008 forecast for world rice production was 434.3 million tons (394 million metric tons) [source: USDA].

Water is indispensable for farming. But many countries grow crops that are unsuitable for the local climate and soil, often because government subsidies make growing those crops profitable. When overproduction occurs, the soil salinity (saltiness) increases and it becomes more difficult to grow hardy crops and raise cattle. In turn, farmers start using pesticides and chemicals to help their crops grow. The pesticide chemicals then wash into the remaining water sources, destroying freshwater habitats and the species that live there. In fact, the polluted runoff can wash all the way to the coast and even begin to affect the marine ecosystem.