Tag: Animals

Minnesota’s lakes are running low on oxygen

This story originally featured on Nexus Media News, a nonprofit climate change news service.

On a sweltering morning in July of 2021, thousands of dead fish washed onto the northeastern shores of Pokegama Lake, 140 miles north of Minneapolis. 

Deb Vermeersch, an official with the Minnesota Department of Natural Resources, was called in to investigate. 

When she arrived, she saw a quarter-mile stretch of sand covered with the rotting carcass of walleye and Northern pike, which thrive in deep, cool waters, as well as crappies, sunfish and suckers—all warm water dwellers. “They were already pretty decomposed because of the warm water,” Vermeersch recalls. 

Because so many different types of fish had died, Vermeersch and her colleagues knew it wasn’t a species-specific parasite, a common cause of fish kills. They zeroed in on the culprit: dangerously low oxygen levels.

Oxygen is disappearing in freshwater lakes at a rate nine times that of oceans due to a combination of pollution and warming waters, according to a study published in Nature earlier this year. Lakes like Pokegama are warming earlier in the spring and staying warm into autumn, fueling algae blooms, which thrive in warm waters, and threaten native fish.

Minnesota, with its 14,380 lakes and temperatures that have risen faster than the national average, is a unique laboratory for studying how climate change is affecting temperate-zone lakes around the world. The state sits at the intersection of four biomes––two distinct prairie ecosystems and two ecologically different forest systems. This means scientists here are able to study how lakes in different ecosystems fare on a warming planet, and look for ways to stave off the worst effects of climate change. 

“If you start losing oxygen, you start losing species.“

“What’s going on at the surface is that warmer water holds less oxygen than cool water,” says Lesley Knoll, a University of Minnesota limnologist and one of the authors of the Nature report. She says that longer, hotter summers are interfering with two key processes that have historically kept lakes’ oxygen levels in check: mixing and stratification. In temperate climates, water at the surface of lakes mixes with deep waters in the spring and the fall, when both layers are similar in temperature. As the surface water warms during the summer, the water forms distinct layers based on temperature––cool water at the bottom, warm at the top. This is known as stratification. In the fall, when the surface waters cool again, the water mixes for a second time, replenishing oxygen in deeper waters. But as climate change makes surface water warmer, and keeps it warmer for longer, that mixing doesn’t happen when it should.

“As you have that stronger stratification, the water in the deep part of the lake is cut off from the oxygen at the top part of the lake. If you start losing oxygen, you start losing species,” says Kevin Rose, a biologist at Rensselaer Polytechnic Institute in New York and a coauthor of the Nature study.

Knoll, Rose and a team of 43 other researchers studied 400 temperate lakes from around the world. They found that, on average, surface waters warmed by 7 degrees Fahrenheit and have lost roughly 5 percent of oxygen since 1980; deep waters, which haven’t warmed much, have still lost an average of almost 20 percent of their oxygen. (Thanks to the state’s long-held lake monitoring programs, almost a quarter the lakes in the study were in Minnesota.)

Warming lakes emit methane

Fish kills aren’t the only reason scientists are concerned about lakes losing oxygen. In extreme cases, when deep waters go completely void of oxygen, something else happens: Methane-emitting bacteria begin to thrive.

“As lakes warm, they will produce more methane and most of that has to do with stratification,” says James Cotner, a limnologist at the University of Minnesota.

Lakes normally emit carbon dioxide as a natural part of breaking down the trees, plants and animals that decay in them, but plants in and around fresh water also absorb it, making healthy lakes carbon sinks. 

Lakes have historically emitted methane, too––about 10 to 20 percent of the world’s emissions––but the prospect of them releasing more of the greenhouse gas has Cotner and his colleagues alarmed. Methane is about 25 times more potent than CO2 when it comes to trapping heat in Earth’s atmosphere.

Cotner is leading a team of researchers who are studying what conditions allow methane-emitting bacteria to prosper in lakes and how conservationists can respond. 

“The key questions are understanding how much and when carbon dioxide and methane are emitted from lakes, and what are the key variables that can tell how much will be emitted. Certainly, oxygen is a big part of that, but stratification and warming also plays a role,” says Cotner. 

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Pollution plays a big role

It’s not just longer, hotter summers that are causing lakes to lose their oxygen. Polluted agricultural runoff (pesticides and fertilizers) and logging have long plagued Minnesota’s lakes. It’s a problem that’s getting worse worldwide as climate change pushes agriculture further away from the equator and into new territory, says Heather Baird, an official with Minnesota’s Department of Natural Resources.

In northern Minnesota, potatoes now grow where pine forests have thrived for years. Phosphorus, a common fertilizer, now runs off from the soil into the region’s lakes, Baird says. Though small amounts of phosphorus occur naturally in lake ecosystems, too much of it feeds harmful algae blooms. 

Those blooms, which thrive in warm, nutrient-rich water, set off a chain of events that remove oxygen from deep lake waters.

“When phosphorus builds in lakes and creates algae blooms, those blooms eventually die. As they do, they sink. Deeper down, bacteria break down the algae, using up the remaining oxygen at those lower depths,” said Baird.

A quarter of Minnesota lakes now have phosphorus levels that are so high that the state advises against swimming, fishing or boating in them. Fueled by these nutrients, algae blooms take over, covering the lake in sometimes toxic residue that thrives in warm, nutrient-rich water, as was the case in Pokegama Lake earlier this year. The protists choke out aquatic life, especially fish that thrive in cold, deep waters. This is all exacerbated by warming air temperatures. 

The 75 percent rule

Researchers and conservationists in Minnesota are now studying the best ways to protect temperate-climate lakes from the worst effects of climate change. They have found that preserving 75 percent of deep-water lakes’ watersheds appear to keep fish stocks healthy. 

“Having a forested watershed helps keep better water quality by filtering out nutrients, which in turn can buffer against the impacts of climate change, to a point,” Knoll said. However, she added, as temperatures continue to rise, “that 75 percent may not be high enough anymore.” 

Knoll and state conservationists are focusing their research and efforts on deep, cool lakes that have a better chance of staying oxygenated than warmer, shallower lakes, like Pokegama.

July 2021, when the Pokegama Lake fish kill occurred, was the hottest month ever recorded on Earth. Parts of Minnesota were also experiencing the worst drought in 40 years, a trend some climatologists expect to persist in future summers. 

Vermeersch, the Minnesota fisheries supervisor, said it’s unclear what this will mean for the future of lakes like Pokegama. “Hopefully it’s not going to be a linear thing,” she said, adding that fish kills are “probably going to happen more often,” depending on a combination of factors. “When you get lakes like Pokegama that are shallow and already impaired, I think we are going to see more and more conditions like this

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How big did ancient millipedes get? Bigger than you’d like.

A fossil found in sandstone near the England-Scotland border contains the largest millipede ever found—and the discovery was completely by accident.

In January 2018, Neil Davies, an Earth scientist at the University of Cambridge, had taken a group of PhD students on a “social trip” to Northumberland, England, where he had previously gone on holiday. The group noticed some rocks had crashed onto the beach where they were walking. One of those chunks happened to contain a paleontological surprise.

“The way the boulder had fallen, it had cracked open and perfectly exposed the fossil, which one of our former PhD students happened to spot when walking by,” Davies said in a statement. “It was a complete fluke of a discovery.”

Davies and his colleagues were at first unsure about what they had found. In May 2018, they extracted the fossil and brought it back to Cambridge for analysis. The specimen is just the third known example of an Arthropleura, a genus of giant millipede that roamed the Earth during the Carboniferous Period, between 359 million and 299 million years ago. But that’s not all: This Arthropleura fossil is also the oldest ever found, dating back to 326 million years ago, as well as the largest. It measures a whopping 30 inches by 14 inches.

That suggests a pretty impressive beast. The millipede itself was likely around 8.5 feet long and nearly two feet wide, and probably weighed about 110 pounds. The team’s results were published in the Journal of the Geological Society.

[Related: This eyeless millipede shattered the record for most legs]

“Finding these giant millipede fossils is rare, because once they died, their bodies tend to disarticulate,” Davies told BBC. This particular specimen is likely just part of a molted exoskeleton, rather than a piece of a millipede’s corpse. Such a sparse fossil record means that these bugs largely remain a mystery. To this day, “we have not yet found a fossilised [millipede] head,” Davies added, “so it’s difficult to know everything about them.”

For example, researchers are unsure how many legs these millipedes had. Current best guesses are either 32 or 64—a paltry set compared to the maximum 1,300 legs recently found on some living millipedes. Scientists also don’t know what these giant bugs ate to sustain their lumbering bodies, though they seem to have thrived due to an abundance of resources and little competition. But later, in the Permian Period, they went extinct—either because of a changing climate or due to new reptile species outcompeting them for food. To uncover the mysteries still lurking in giant millipedes’ history, researchers will need more examples of them to fill out the fossil record.

The area of Northumberland where the fossil was found is mostly sandstone, which “is normally not brilliant for preserving fossils,” Davies told NPR. So “the fact that this has been preserved is, on the one hand, surprising. But it just suggests that actually there might be a lot more and similar things in places where people haven’t really looked for fossils before.”

The fossil will go on public display at Cambridge’s Sedgwick Museum in the New Year.

These are the days in the year you’re more likely to hit a deer

Tom Langen is a professor of Biology at Clarkson University. This story originally featured on The Conversation.

Autumn is here, and that means the risk of hitting deer on rural roads and highways is rising, especially around dusk and during a full moon.

Deer cause over 1 million motor vehicle accidents in the US each year, resulting in more than $1 billion in property damage, about 200 human deaths and 29,000 serious injuries. Property damage insurance claims average around $2,600 per accident, and the overall average cost, including severe injuries or death, is over $6,000.

While avoiding deer—as well as moose, elk and other hoofed animals, known as ungulates—can seem impossible if you’re driving in rural areas, there are certain times and places that are most hazardous, and so warrant extra caution.

Transportation agencies, working with scientists, have been developing ways to predict where deer and other ungulates enter roads so they can post warning signs or install fencing or wildlife passages under or over the roadway. Just as important is knowing when these accidents occur.

My former students Victor Colino-Rabanal, Nimanthi Abeyrathna, and I have analyzed over 86,000 deer-vehicle collisions involving white-tailed deer in New York state using police records over a three-year period. Here’s what our research and other studies show about timing and risk.

Time of day, month and year matters

The risk of hitting a deer varies by time of day, day of the week, the monthly lunar cycle and seasons of the year.

These accident cycles are partly a function of driver behavior—they are highest when traffic is heavy, drivers are least alert and driving conditions are poorest for spotting animals. They are also affected by deer behavior. Not infrequently, deer-vehicle accidents involve multiple vehicles, as startled drivers swerve to miss a deer and collide with a vehicle in another lane, or they slam on the breaks and are rear-ended by the vehicle behind.

In analyzing thousands of deer-vehicle collisions, we found that these accidents occur most frequently at dusk and dawn, when deer are most active and drivers’ ability to spot them is poorest. Only about 20 percent of accidents occur during daylight hours. Deer-vehicle accidents are eight times more frequent per hour of dusk than daylight, and four times more frequent at dusk than after nightfall.

During the week, accidents occur most frequently on days that have the most drivers on the road at dawn or dusk, so they are associated with work commuter driving patterns and social factors such as Friday “date night” traffic.

Over the span of a month, the most deer-vehicle accidents occur during the full moon, and at the time of night that the moon is brightest. Deer move greater distances from cover and are more likely to enter roadways when there is more illumination at night. The pattern holds for deer and other ungulates in both North America and Europe.

Over a year, by far the highest numbers of deer-vehicle accidents are in autumn, and particularly during the rut, when bucks search and compete to mate with does. In New York state, the peak number of deer-vehicle accidents occurs in the last week of October and first weeks of November. There are over four times as many deer-vehicle accidents during that period than during spring. Moose-vehicle accidents show a similar pattern.

That high-risk period is also when daylight saving time ends—it happens on Nov. 7, 2021, in the US. Shifting the clock one hour back means more commuters are on the road during the high-risk dusk hours. The result is more cars driving at the peak time of day and during the peak time of the year for deer-vehicle accidents.

Overall, given that most US states and more than 70 countries have seasonal “daylight saving” clock shifts, elevated ungulate-vehicle accident rates caused by clock shift may be a widespread problem.

There is a longstanding debate about the benefit of a daylight saving clock shift, given how it disrupts humans’ circadian rhythms, causing short-term stress and fatigue. Risk of deer-vehicle accidents may be another reason to reconsider whether clock shifts are worthwhile.

Deer still cross roads at any time

It’s important to remember that deer-vehicle accidents can occur at any time of day or night, on any day of the year—and that deer can show up in urban areas as well as rural ones.

The insurance company State Farm found that on average, US drivers have a 1 in 116 chance of hitting an animal, with much higher rates in states such as West Virginia, Montana and Pennsylvania. Over the 12 months ending in June 2020, State Farm counted 1.9 million insurance claims for collisions with wildlife nationwide. Around 90 percent of those involved deer.

Where deer or other ungulates are likely to be present, drivers should always be alert and cautious, especially at dawn, dusk, on bright moonlit nights and during the fall rut.

The Conversation

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Wasps are the bee’s knees

Wasps are the forgotten cousin of their family tree. Bees have whole societies devoted to their conservation, while wasps, if thought of at all, pile up in yellowjacket traps.

But those wasps, doing what they do best—killing and eating other insects—are providing invaluable, if overlooked, benefits to the world, according to a recent review of decades of wasp research.

“Everybody recognizes that we have honey, and many fruits and vegetables because of honeybees,” says Alessandro Cini, an entomologist who studies insect socialization and an author of the study. “We’re trying to diffuse into society the idea that you should have a different perspective on wasps. They’re not just the ruiners of your picnic, but also allow you to eat food, to not have your garden or crops destroyed by beetles.”

The research, published in Biological Reviews, focuses on stinging wasps, a group that includes both social animals (like the hornet and yellowjacket) and solitary ones, many of which have evolved to prey on a particular kind of beetle, grasshopper, or spider.

The predatory, sometimes ravenous, nature of wasps mean that they’re playing a very different role than bees in an ecosystem. Social wasps are all-purpose carnivores, killing just about any large bug they can get their stingers into. (The adult wasps actually eat sugar, giving the meat to their offspring.) One yellowjacket colony might eat as much as a pound of bugs over a several-year period, although the exact amount depends heavily on the individual colony.

“That might not sound like so much,” Cini says. “But imagine how many individual insects it takes.”

Solitary wasps, on the other hand, might hunt dozens of the same kind of beetle. Although each species of solitary wasp usually targets a single type of prey, there are so many kinds—97 percent of the 33,000 stinging wasps studied—that they probably play a role in controlling bugs of all kinds.

That means, if you’re an agricultural scientist interested in controlling pests, wasps might look like a whole quiver of tools, some reducing overall bug numbers, others targeting specific problems.

As it happens, stinging wasps also pollinate, if only by accident. Since the adults live mostly on sugar, they visit flowers to collect nectar, moving pollen around on the way. (Some species even make honey.) But some plants have close relationships with solitary wasps that can’t be replaced by another species.

Many kinds of orchid are pollinated exclusively by wasps, and lure in the insects with chemicals that mimic the smell of prey. Other plants, including members of the asparagus family, lure in pollinators with flowers and nectar that appear specifically targeted to spider wasps.

For the most part, research on insect ecosystem services has focused on pollination, possibly because bees and butterflies are more charismatic, or because pollination is a service that we’re hard pressed to reinvent.

“To replace pollination is much more difficult than to replace predation. Pollination means an intimate relationship between an insect going from one flower to another,” Cini says. “To kill something is much easier.”

But the ways in which we’ve replaced predation—mostly with pesticides—clearly has huge downsides. “You have to pollute the environment. It’s not easy to find chemicals that are specific to taxa that you want to kill,” Cini says. “Also, you need money.”

Leaving wasps to munch their way through agricultural pests is free. And while many crop pests are quickly developing resistance to pesticides, they can’t become immune to a hungry mouth.

But wasps’ role in an ecosystem depends entirely on the species and habitat. And most research has been done on wasps in temperate climates. “We lack information about African species,” Cini says. “We have no idea if they’re well or not, if they’re growing or disappearing.“

Even the wasps we do know about look very differently in different parts of the world. Yellowjackets might be critical to eating other bugs in Europe, Cini points out, but in New Zealand, they’re an invasive species that threatens native insects. (Of course, the same thing can be true of North America’s honey bees, which are essentially domestic livestock introduced from Europe.)

Cini says that people have good reason to remove some wasps, especially if they’re allergic. “Obviously, if there’s a nest in my house, I will remove it,” though he’ll try to settle it elsewhere, rather than killing the insects entirely. “The point is to avoid killing them without any reason.”
And there are almost certainly connections between wasps and their surroundings that we haven’t even begun to understand yet. One series of studies found that European wasps even act as reservoirs for wild wine-makers yeast during the winter, and might even maintain the genetic diversity of that yeast. “The point is that you never know the ecological importance that something has, because the relationships are so complex,” Cini says. “Even things that you think are really different from one another can be linked.”

Philip Kiefer

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