【推荐1】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.

【推荐2】For more than 50 years, seawater has flowed through the Hong Kong’s toilets. And in 2013, Hong Kong built a system that used seawater to cool part of the city. The system sends cold seawater to a factory with heat exchangers. The seawater takes in heat to cool pipes full of circulating (循环的) water. That cooled water then flows into buildings to cool rooms. The slightly warmed seawater is sent back to the ocean. Known as district cooling, this type of system tends to use far less energy than typical air conditioners.

How much water and energy had this strategy saved Hong Kong? And why weren’t other coastal cities doing this? A team at the Hong Kong University of Science and Technology set out for answers. They focused on Hong Kong and two other big coastal cities: Jeddah, Saudi Arabia, and Miami, Fla. The idea was to see what it might look like if all three adopted city-wide saltwater systems.

All three places would save lots of fresh water and energy, the researchers found. These savings came from the more efficient saltwater air conditioning. Though costly to build, saltwater-cooling systems could pay off in the long run for many cities.

The researchers figured out how emissions (排放) of greenhouse gases would drop if each city instead used seawater for cooling and flushing (冲刷). Next, they studied how much pollution would be created to build the new system. They compared these results to see how emissions of climate-warming gases would change for each city.

Hong Kong would see the biggest cut in greenhouse gases if the system were expanded to the whole city. It could drop by some 250,000 tons each year. Miami could see a drop of around 7,700 tons of carbon pollution per year. Saltwater cooling would cause more planet-warming gases in Jeddah than it would save. The reason: Jeddah’s unplanned urban expansion and all the pipes that would be needed to service it. The pollution coming from building such a large system would be higher than what the system would save.

【推荐3】Can staying up late make you fat? A growing body of research has suggested that poor sleep quality is linked to an increased risk of obesity (肥胖症). But a new study found that it’s not the sleep loss that leads to obesity, but rather that overweight can cause poor sleep.The researchers discovered their findings in a very small worm, called C.elegans.

Study co-author David Raizen stressed that while these findings in worms may not translate directly to humans, C. elegans offers a good model for studying humans' sleep. Like all other animals that have nervous systems, they need sleep. But unlike humans, who have complex neural circuitry (神经回路) and are difficult to study, a C. elegans has only 302 nerve cells，one of which scientists know for certain is a sleep regulator.

In humans, people who get fewer than six hours of sleep per night are more likely to be obese. Moreover, starvation in humans, fruit flies, and worms has been shown to affect sleep, indicating that it is regulated, at least in part, by nutrient availability. However, the way in which sleeping and eating work in tandem (协同地) has remained unclear.

The researchers genetically changed C.elegans to “turn off" a nerve cell that controls sleep. These worms could still eat, breathe, and reproduce, but they lost their ability to sleep.With this nerve cell turned off,the researchers saw a severe drop in ATP levels, which is the body's energy currency. “That suggests that sleep is an attempt to conserve energy; it's not actually causing the loss of energy,"Raizen explained.

The researchers knocked out the KIN-29 gene to create sleepless worms, and the mutant (突变的) C.elegans accumulated much fat. They assumed that the KIN-29 mutants did not sleep is because they were unable to release their fat.To test this guess, the researchers again controlled the KIN-29 mutant worms,this time expressing a chemical substance that freed their fat. With that operation,the worms were again able to sleep.