Researchers have just completed the first worldwide record of lake color. Roughly one-third of them are blue but that number may drop if global temperatures rise. If average air temperatures in summer rose just a few degrees warmer, some of those crystal blue waters could turn green or brown.

Lake color offers clues to the stability of lake ecosystems. Factors such as water depth and how the nearby land is used also matter. Lake color depends in part, too, on what’s in the water. Compared with blue lakes, green or brown lakes have more algae (水藻) and organic matter. That’s according to Xiao Yang, a hydrologist who works at Southern Methodist University in Dallas, Texas. Changing lake colors, he says, could also change how people use those waters.

Yang was part of a team that analyzed the color of more than 85,000 lakes around the world. They used satellite photos from 2013 to 2020. Storms and seasons can temporarily affect a lake’s color. So the researchers focused on the most frequent color observed for each lake over the seven-year period. The scientists then looked at local climates during the same time period. They wanted to see how climate might be linked to lake color.

Average summer air temperatures and lake color were linked, the researchers found. Lakes were more likely to be blue in places where summer temperatures averaged less than 19℃. Up to 14 percent of lakes that are blue were near that threshold (门槛), though. That means just a bit more warming might tip them away from blue. Scientists think the planet could average 3 degrees Celsius warmer by 2100. If so, that could turn another 3,800 lakes green or brown.

Green or brown waters could be unappealing for play or it might cost more to clean it for drinking. But in fact, the color changes might not mean the lakes are any less healthy. If you were a certain type of fish species, you might think this is great.

【小题1】What is a feature of green or brown lakes?

A．Weak ecosystem.	B．High mineral content.
C．Increased organic matter.	D．Decreased water temperature.

【小题2】What does the research intend to find?

A．Why the color of most lakes is blue.

B．The consequences of lake color change.

C．How climate change affect creatures living in water.

D．The relationship between air temperature and lake color.

【小题3】What can be inferred from paragraph 4?

A．14 percent of the world’s lakes are blue.

B．3,800 lakes worldwide are green or brown.

C．Many lakes may experience severe ecological damage.

D．Some lakes are close to the critical point of color change.

【小题4】In which section of a website can this text be found?

A．Lifestyle.	B．Environment.
C．Technology.	D．Business.