High oil prices and environmental and economic security concerns have triggered interest in using algae¹-derived oils as an alternative to fossil fuels. But growing algae（海藻） – or any other biofuel source – can require a lot of water. However, a new study shows that being smart about where we grow algae can drastically reduce how much water is needed for algal biofuel. Growing algae for biofuel, while being water-wise, could also help meet congressionally mandated² renewable fuel targets by replacing 17 percent of the nation's imported oil for transportation, according to a paper published in the journal Water Resources Research.

Researchers at the Department of Energy's Pacific Northwest National Laboratory found that water use is much less if algae are grown in the U.S. regions that have the sunniest and most humid climates: the Gulf³ Coast, the Southeastern Seaboard and the Great Lakes.

"Algae has been a hot topic of biofuel discussions recently, but no one has taken such a detailed⁴ look at how much America could make – and how much water and land it would require – until now," said Mark Wigmosta, lead author and a PNNL hydrologist（水文学者） . "This research provides the groundwork and initial estimates needed to better inform renewable energy decisions."

Algal biofuel can be made by extracting and refining the oils, called lipids, that algae produce as they grow. Policy makers⁵ and researchers are interested in developing biofuels because they can create fewer overall greenhouse gas emissions⁶ than fossil fuels. And biofuels can be made here in the United States. In 2009, slightly more than half of the petroleum⁷ consumed by the U.S. was from foreign oil.

Wigmosta and his co-authors provide the first in-depth assessment⁸ of America's algal biofuel potential given available land and water. The study also estimated how much water would need to be replaced due to evaporation⁹（蒸发，消失） over 30 years. The team analyzed¹⁰ previously¹¹ published data to determine how much algae can be grown in open, outdoor ponds of fresh water while using current technologies. Algae can also be grown in salt water and covered ponds. But the authors focused on open, freshwater ponds as a benchmark for this study. Much of today's commercial algae production is done in open ponds.

Crunching¹² the numbers

First, the scientists developed a comprehensive national geographic¹³ information system database that evaluated topography（地势） , population, land use and other information about the contiguous United States. That database contained information spaced every 100 feet throughout the U.S., which is a much more detailed view than previous research. This data allowed them to identify available areas that are better suited for algae growth, such as those with flat land that isn't used for farming and isn't near cities or environmentally sensitive areas like wetlands or national parks.

Next, the researchers gathered 30 years of meteorological information. That helped them determine the amount of sunlight that algae could realistically photosynthesize and how warm the ponds would become. Combined with a mathematical model on how much typical algae could grow under those specific conditions, the weather data allowed Wigmosta and team to calculate the amount of algae that could realistically be produced hourly at each specific site.