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Lake trout are making a comeback — no one knows why

Trout in a bucket. Photo: Joshua Brown / University of Vermont

Erin Ross writes: Scientists have spent their entire careers trying to understand why some trout no longer survive in Lake Champlain and the Great Lakes. Now, they've returned and researchers don’t know why.

Why it matters: Around the world, large lake ecosystems, which drive the economies of cities that border them, are being threatened. “One thing [this return] demonstrates is that these lakes have enormous recuperative powers,” says Dave Fielder, fisheries research biologist at the Michigan Department of Natural Resources. “If we can provide relief from some of the stressors, the lake will respond. Sometimes, very quickly."

What they're studying: Lake Champlain serves as a microcosm for the Great Lakes, which are extremely hard to study in their entirety, explains Ellen Marsden, a professor at the University of Vermont who has spent decades studying Champlain’s ecosystem. In the years since the trout first became locally extinct, the lake has been through a lot – various invasive species, pollution and overfishing.

The bottom line: Regardless of why the trout came back, the biggest ecosystem changes in the last several years had to do with invasive species. “We’re at a point where we’ve endured so many invasive species in the Great Lakes ecosystem, they’re starting to interact and affect each other,” Fielder says. Those interactions may have opened up a niche — allowing the native fish back in.

Read the full story here.

Where health and education are improving — and failing — in Africa
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Reproduced from Osgood-Zimmerman, et al., 2018, "Mapping child growth failure in Africa between 2000 and 2015"; Map: Axios Visuals

Steady progress has been made in many parts of Africa on children's health and education, but stark inequalities remain in some regions, according to precision maps from two new studies, Eileen Drage O'Reilly reports. The researchers, writing Wednesday in Nature, add that none of the continent's countries are likely to end childhood malnutrition by the United Nations' goal of 2030.

Why it matters:

"Such fine-grained insight brings tremendous responsibility to act. It shows governments, international agencies and donors exactly where to direct resources and support. ... Without good data, we’re flying blind. If you can’t see it, you can’t solve it."
Kofi Annan, former secretary-general of the United Nations, wrote in Nature

Read the full story here.

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What we're reading elsewhere
  • Guns: A new study found gun injury rates were, on average, 20% lower on days of NRA conventions, Melinda Wenner Moyer reports for Scientific American. However, there was no corresponding dip in firearm crime rates, suggesting "NRA meeting attendees are not responsible for a large proportion of U.S. gun crimes — just gun injuries, many of which may be accidental."
  • Tree sex: Striped maples can change from male to female when damaged, per Amy Ellis Nutt in the Washington Post. Why? A study author told her "[i]f the branch is going to die anyway, it might make sense to be female and produce seeds before dying."
  • First light: Scientists report detecting a signal left by the universe's first stars — born just 180 million years after the Big Bang. The new technique they used could open the earliest moments of the universe to new study, Emily Conover writes in Science News.
Something wondrous

The land before plants: 550 million-year-old sandstone rocks in Brittany, France. Photo: William McMahon / University of Cambridge

Life arrived on the Earth scene at least 3.5 billion years ago, irreversibly changing the planet. Photosynthesizing organisms, for example, gave Earth's atmosphere oxygen about 2.5 billion years ago (seriously, pause for a quick thanks). And, around the time algae moved onto land and became plants 500 million years ago, a lot more mud shows up in the geological record.

"You could argue it is one of the most important shifts in Earth’s history. We went from a barren landscape to the lush one we see today," says William McMahon, a graduate student at the University of Cambridge and an author of a study published today in Science that hones in on exactly when things got muddy.

What they found: McMahon and his co-author Neil Davies spent four years traveling to rock formations all over the world and studied nearly 1,200 published reports of 704 others spanning 3 billion of Earth's 4.5 billion-year history. They looked at rocks from the land before plants, during their evolution and after vegetation was established, and found that when mosses and other bryophytes — "plants that tickle your feet on the ground” — came around, the amount of mud in the record increased at least 10-fold, McMahon says.

What happened: The researchers suggest even the earliest plants with their tiny anchors broke sedimentary rock down into clay, which is mud's main constituent. They and their rooted successors could have helped to retain mud by holding it in place or by slowing down the speed of moving water, making it more likely for mud to be deposited on the bottom of a river than carried to the ocean. Caltech's Woody Fischer, who studies the co-evolution of Earth's geology and biology, says it's unlikely Earth’s overall mud budget has changed much over its lifetime but that plants are really changing where mud goes.

Why mud matters: Understanding the movement of mud and other sediments throughout the planet's history is important for modeling the ocean's chemistry, how it regulates climate, and making predictions about how Earth will look, Fischer says.