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Sea otters helped prevent widespread California kelp forest declines over the past century



Sea otters helped prevent widespread California kelp forest declines over the past century

Monterey Bay Aquarium researchers strengthen the link between sea otters and long-term health of California kelp forests in a new study released today. The paper, published in the journal PLOS Climate, finds that sea otter population growth during the last century enhanced kelp forest resilience in the state. This finding reinforces the importance of conservation and recovery of the threatened southern sea otter and highlights a potential nature-based solution for restoring kelp forests along the California coast, and perhaps beyond.

The study revealed dramatic regional kelp canopy changes over a 100-year period, from 1910 to 2016. During this time there was a significant increase in kelp forest canopy along the central coast, the only region of California where southern sea otters survived after being hunted nearly to extinction for their fur in the 1800s. At the century scale, the species’ favorable impact on kelp forests along the central coast nearly compensated for kelp losses along both northern and southern California resulting in a slight overall decline statewide during this period.

“Our study showed that kelp forests are more extensive and resilient to climate change where sea otters have reoccupied the California coastline during the last century. Where sea otters are absent, kelp forests have declined dramatically. In fact, we found sea otter population density as the strongest predictor of change in kelp canopy coverage across this hundred-year span,” said lead author Teri Nicholson, Senior Research Biologist with the Monterey Bay Aquarium Sea Otter Program.

Aquarium scientists used historical surveys of kelp forests dating back to the early 1900s to perform detailed estimates of canopy extent, biomass, and carbon storage — while correcting for annual variation and differences in survey methods. This allowed the scientists to examine California’s kelp forest trends over a longer time period, going back more than 60 years before available data from modern surveys based on aerial or satellite imagery. The team then compared the corrected and conservative historical estimates to contemporary datasets and used a machine learning framework to assess the dominant drivers of change over the last century.

“The use of historical maps provided an important opportunity to help us examine long-term kelp forest trends,” said Monterey Bay Aquarium Sea Otter Program Manager, Jess Fujii. “This broader view is important for understanding trends related to climate change, and developing effective science-based conservation strategies.”

Statewide, the data showed only a six percent decline in kelp canopy from 1910 to 2016. Regional changes, however, proved more sizable. Kelp canopy decreased in northern and southern regions by 63 and 52 percent, respectively. It increased nearly everywhere throughout the central coast, contrastingly, gaining an estimated 56 percent of kelp forest coverage.

While the modeling showed sea otter population density was the strongest predictor of change in kelp coverage, it also identified other factors, including extreme marine heat due to climate change.

“Today, extreme heat in the ocean is intense and persistent. Beginning a decade ago, this threat now affects more than half the ocean’s surface,” said Kyle Van Houtan, a Research Scientist at Duke University, and senior author of the study. “This is a major problem for kelp forests as chronic temperature stress undermines kelp growth and health. Ecosystems are complex, and to give them their best chance at surviving these extreme changes, they need all their component parts. Sea otters, of course, are hugely influential for Pacific kelp forests. Historical studies like this are a crucial demonstration of this dynamic over the long term.”

Healthy kelp forest ecosystems provide many benefits, including serving as nursery grounds for fisheries, reducing coastal erosion from storms, and contributing to carbon storage. The study indicates returning otters to areas of their historical range could help recover kelp forests and restore their benefits in more places along the California coast.

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Titan’s lakes may be shaped by waves




Titan’s lakes may be shaped by waves

Titan, Saturn’s largest moon, is the only other planetary body in the solar system that currently hosts active rivers, lakes, and seas. These otherworldly river systems are thought to be filled with liquid methane and ethane that flows into wide lakes and seas, some as large as the Great Lakes on Earth.

The existence of Titan’s large seas and smaller lakes was confirmed in 2007, with images taken by NASA’s Cassini spacecraft. Since then, scientists have pored over those and other images for clues to the moon’s mysterious liquid environment.

Now, MIT geologists have studied Titan’s shorelines and shown through simulations that the moon’s large seas have likely been shaped by waves. Until now, scientists have found indirect and conflicting signs of wave activity, based on remote images of Titan’s surface.

The MIT team took a different approach to investigate the presence of waves on Titan, by first modeling the ways in which a lake can erode on Earth. They then applied their modeling to Titan’s seas to determine what form of erosion could have produced the shorelines in Cassini’s images. Waves, they found, were the most likely explanation.

The researchers emphasize that their results are not definitive; to confirm that there are waves on Titan will require direct observations of wave activity on the moon’s surface.

“We can say, based on our results, that if the coastlines of Titan’s seas have eroded, waves are the most likely culprit,” says Taylor Perron, the Cecil and Ida Green Professor of Earth, Atmospheric and Planetary Sciences at MIT. “If we could stand at the edge of one of Titan’s seas, we might see waves of liquid methane and ethane lapping on the shore and crashing on the coasts during storms. And they would be capable of eroding the material that the coast is made of.”

Perron and his colleagues, including first author Rose Palermo, a former MIT-WHOI Joint Program graduate student and a research geologist at the U.S. Geological Survey, will publish their study in a forthcoming issue of Science Advances. Their co-authors include MIT research scientist Jason Soderblom, former MIT postdoc Sam Birch, now an assistant professor at Brown University, Andrew Ashton at the Woods Hole Oceanographic Institution, and Alexander Hayes of Cornell University.

“Taking a different tack”

The presence of waves on Titan has been a somewhat controversial topic ever since Cassini spotted bodies of liquid on the moon’s surface.

“Some people who tried to see evidence for waves didn’t see any, and said, ‘These seas are mirror-smooth,'” Palermo says. “Others said they did see some roughness on the liquid surface but weren’t sure if waves caused it.”

Knowing whether Titan’s seas host wave activity could give scientists information about the moon’s climate, such as the strength of the winds that could whip up such waves. Wave information could also help scientists predict how the shape of Titan’s seas might evolve over time.

Rather than look for direct signs of wave-like features in images of Titan, Perron says the team had to “take a different tack, and see, just by looking at the shape of the shoreline, if we could tell what’s been eroding the coasts.”

Titan’s seas are thought to have formed as rising levels of liquid flooded a landscape crisscrossed by river valleys. The researchers zeroed in on three scenarios for what could have happened next: no coastal erosion; erosion driven by waves; and “uniform erosion,” driven either by “dissolution,” in which liquid passively dissolves a coast’s material, or a mechanism in which the coast gradually sloughs off under its own weight.

The researchers simulated how various shoreline shapes would evolve under each of the three scenarios. To simulate wave-driven erosion, they took into account a variable known as “fetch,” which describes the physical distance from one point on a shoreline to the opposite side of a lake or sea.

“Wave erosion is driven by the height and angle of the wave,” Palermo explains. “We used fetch to approximate wave height because the bigger the fetch, the longer the distance over which wind can blow and waves can grow.”

To test how shoreline shapes would differ between the three scenarios, the researchers started with a simulated sea with flooded river valleys around its edges. For wave-driven erosion, they calculated the fetch distance from every single point along the shoreline to every other point, and converted these distances to wave heights. Then, they ran their simulation to see how waves would erode the starting shoreline over time. They compared this to how the same shoreline would evolve under erosion driven by uniform erosion. The team repeated this comparative modeling for hundreds of different starting shoreline shapes.

They found that the end shapes were very different depending on the underlying mechanism. Most notably, uniform erosion produced inflated shorelines that widened evenly all around, even in the flooded river valleys, whereas wave erosion mainly smoothed the parts of the shorelines exposed to long fetch distances, leaving the flooded valleys narrow and rough.

“We had the same starting shorelines, and we saw that you get a really different final shape under uniform erosion versus wave erosion,” Perron says. “They all kind of look like the flying spaghetti monster because of the flooded river valleys, but the two types of erosion produce very different endpoints.”

The team checked their results by comparing their simulations to actual lakes on Earth. They found the same difference in shape between Earth lakes known to have been eroded by waves and lakes affected by uniform erosion, such as dissolving limestone.

A shore’s shape

Their modeling revealed clear, characteristic shoreline shapes, depending on the mechanism by which they evolved. The team then wondered: Where would Titan’s shorelines fit, within these characteristic shapes?

In particular, they focused on four of Titan’s largest, most well-mapped seas: Kraken Mare, which is comparable in size to the Caspian Sea; Ligeia Mare, which is larger than Lake Superior; Punga Mare, which is longer than Lake Victoria; and Ontario Lacus, which is about 20 percent the size of its terrestrial namesake.

The team mapped the shorelines of each Titan sea using Cassini’s radar images, and then applied their modeling to each of the sea’s shorelines to see which erosion mechanism best explained their shape. They found that all four seas fit solidly in the wave-driven erosion model, meaning that waves produced shorelines that most closely resembled Titan’s four seas.

“We found that if the coastlines have eroded, their shapes are more consistent with erosion by waves than by uniform erosion or no erosion at all,” Perron says.

The researchers are working to determine how strong Titan’s winds must be in order to stir up waves that could repeatedly chip away at the coasts. They also hope to decipher, from the shape of Titan’s shorelines, from which directions the wind is predominantly blowing.

“Titan presents this case of a completely untouched system,” Palermo says. “It could help us learn more fundamental things about how coasts erode without the influence of people, and maybe that can help us better manage our coastlines on Earth in the future.”

This work was supported in part by NASA, the National Science Foundation, the USGS, and the Heising-Simons Foundation.

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At least one in four US residential yards exceed new EPA lead soil level guideline




At least one in four US residential yards exceed new EPA lead soil level guideline

Roughly one in four U.S. households have soil exceeding the new U.S. Environmental Protection Agency’s lead screening levels of 200 parts per million (ppm), halved from the previous level of 400 ppm, a new study found. For households with exposure from multiple sources, the EPA lowered the guidance to 100 ppm; nearly 40% of households exceed that level, the study also found.

“I was shocked at how many households were above the new 200 ppm guideline,” said Gabriel Filippelli, a biochemist at Indiana University who led the new study. “I assumed it was going to be a more modest number. And results for the 100 ppm guideline are even worse.”

Remediating the roughly 29 million affected households using traditional “dig and dump” soil removal methods could cost upward of $1 trillion, the study calculated. The study was published in GeoHealth, an open-access AGU journal that publishes research investigating the intersection of human and planetary health for a sustainable future. Filippelli is the former editor-in-chief of GeoHealth.

National lead problem “nowhere near over”

Lead is a heavy metal that can accumulate in the human body, with toxic effects. In children, exposure to lead is associated with lower educational outcomes. In the United States, the burden of lead exposure has historically fallen on lower-income communities and communities of color because of redlining and other discriminatory practices. Lead pollution can come from aging water pipes, old paint, and remnant gasoline and industrial pollution, but today, most lead exposure are from contaminated soils and dust, even after lead-containing infrastructure was removed.

The Centers for Disease Control and Prevention first set a limit on the concentration of lead in blood in 1991 at 10 micrograms per deciliter, and it lowered that limit several times until reaching the current limit of 3.5 micrograms per deciliter. But the EPA’s soil lead screening level remained unchanged for more than 30 years until the January announcement. Some states had established their own lower guidelines; California has the lowest screening level, at 80 ppm.

The lag is likely due to “the immensity and ubiquity of the problem,” the study authors wrote. “The scale is astounding, and the nation’s lead and remediation efforts just became substantially more complicated.” That’s because once the EPA lowers a screening limit, they need to tell people what to do if their soils exceed it.

When the EPA lowered the screening level, Filippelli and his co-authors decided to make use of the database of 15,595 residential soil samples from the contiguous United States that they’d collected over the years to find out how many exceeded the new guideline.

Household health hazard

About 25% of the residential soil samples, collected from yards, gardens, alleys, and other residential spots, exceeded the new 200 ppm level, the study found. (Only 12% of samples had exceeded the older, 400 ppm level.) Extrapolating across the country, that equates to roughly 29 million households.

The EPA issued separate guidance for households with multiple sources of exposure, such as both lead-contaminated soil and lead pipes, setting the level in those situations at 100 ppm. In practice, that’s most urban households, Filippelli said. Forty percent of households exceed that limit, increasing the number of affected households to nearly 50 million, the study found.

Typically, contaminated soils are remediated with removal — colloquially, “dig and dump.” But the practice is costly and typically only used after an area is placed on the National Priority List for remediation, a process that can take years. To remediate all contaminated households with “dig and dump” would cost between $290 billion and $1.2 trillion, the authors calculated.

A cheaper option is “capping”: burying the contaminated soil with about a foot of soil or mulch. A geotechnical fabric barrier can also be installed. Most lead contamination is in the top 10 to 12 inches of soil, Filippelli said, so this simple method either covers up the problem or dilutes it to an acceptable level.

“Urban gardeners have been doing this forever anyway, with raised beds, because they’re intuitively concerned about the history of land use at their house,” Filippelli said.

And capping is quicker.

“A huge advantage of capping is speed. It immediately reduces exposure,” Filippelli said. “You’re not waiting two years on a list to have your yard remediated while your child is getting poisoned. It’s done in a weekend.

Capping still requires time and effort; residents must find clean soil, transport it to their home and spread it out. But the health benefits likely outweigh those costs, Filippelli said.

Because capping has been done more informally, there’s still a lot to be learned about its lifespan and sustainability, Filippelli said. That’s where the research will go next.

Despite the “staggering” scale of the problem, “I’m really optimistic,” Filippelli said. “Lead is the most easily solvable problem that we have. We know where it is, and we know how to avoid it. It’s just a matter of taking action.”


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Jupiter’s great red spot is not the same one Cassini observed in 1600s




Jupiter’s great red spot is not the same one Cassini observed in 1600s

Jupiter’s iconic Great Red Spot has persisted for at least 190 years and is likely a different spot from the one observed by the astronomer Giovanni Domenico Cassini in 1665, a new study reports. The Great Red Spot we see today likely formed because of an instability in the planet’s intense atmospheric winds, producing a long, persistent atmospheric cell, the study also finds.

The Great Red Spot is the largest known planetary vortex within the solar system, but its age has long been debated, and the mechanism that led to its formation has remained obscure. The new study used historical observations from the 17th century onward and numerical models to explain the longevity and nature of this spectacular phenomenon.

“From the measurements of sizes and movements, we deduced that it is highly unlikely that the current Great Red Spot was the ‘Permanent Spot’ observed by Cassini,” said Agustín Sánchez-Lavega, a planetary scientist at the University of the Basque Country in Bilbao, Spain, who led this research. “The ‘Permanent Spot’ probably disappeared sometime between the mid-18th and 19th centuries, in which case we can now say that the longevity of the Red Spot exceeds 190 years.”

The study was published in Geophysical Research Letters, which is an open-access AGU journal that publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

A spotty history

Jupiter’s Great Red Spot is a massive atmospheric vortex, with a diameter approximately that of Earth’s. At its outer periphery, winds whip by at 450 kilometers per hour (280 miles per hour). Its red hue, which is due to atmospheric chemical reactions, stands in stark contrast with the gas giant’s other pale clouds.

The spot has intrigued scientists for centuries, in part because its large size makes it visible using even small telescopes. In 1665, Cassini discovered a dark oval at the same latitude as today’s Great Red Spot and named it the “Permanent Spot,” as he and other astronomers observed it until 1713, when they lost track of it. It was not until 1831 and later years that scientists once more observed a clear, oval structure at the same latitude as the Great Red Spot. Given the intermittent historical observations of Jupiter’s spots, scientists have long debated whether today’s Great Red Spot is the same one 17th-century scientists saw.

In the study, the authors used historical sources dating from the mid-1600s to analyze the evolution of the spot’s size, structure and location over time.

“It has been very motivating and inspiring to turn to the notes and drawings of Jupiter and its Permanent Spot made by the great astronomer Jean Dominique Cassini, and to his articles of the second half of the 17th century describing the phenomenon,” Sánchez-Lavega said. “Others before us had explored these observations, and now we have quantified the results.”

How the spot was formed

The Red Spot, which in 1879 was 39,000 kilometers (about 24,200 miles) at its longest axis, has been shrinking to about the current 14,000 kilometers (8,700 miles) and simultaneously becoming more rounded, the study reported. Since the 1970s, several space missions have studied this meteorological phenomenon; most recently, observations from instruments aboard Juno have revealed that the Great Red Spot is shallow and thin — useful information for scientists looking to explore the spot’s formation.

To explore how this immense vortex could have formed, the researchers carried out numerical simulations on supercomputers using two models of the behavior of thin vortices in Jupiter’s atmosphere. The spot could have formed as a result of a gigantic superstorm, similar to those occasionally observed on Jupiter’s twin planet Saturn; from the merging of multiple smaller vortices produced by wind shear from the intense wind currents that flow parallel to each other, but alternating in direction with latitude; or from an instability in the winds that could produce an elongated atmospheric cell, similar in shape to the Spot.

The results indicate that, although an anticyclone forms in the first two cases, it differs in terms of shape and dynamic properties from those of the present Great Red Spot. The cell-producing wind instability, on the other hand, could have produced a “proto-Great Red Spot” that then shrank over time, giving rise to the compact and rapidly rotating Great Red Spot observed in the late 19th century.

The formation mechanism is supported by observations of large, elongated cells in the genesis of other major vortices on Jupiter.

Future research will aim to reproduce the Great Red Spot’s shrinking over time to elucidate the physical mechanisms underlying the Spot’s relative stability. Researchers also aim to predict whether the Great Red Spot will disintegrate and disappear when it reaches a size limit, as might have occurred to Cassini’s Permanent Spot, or whether it will stabilize at a size limit at which it may last for many more years.

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