In the US, Western rivers may be allies in the fight against climate change

New study reveals underestimation of carbon uptake in rivers in arid areas, with global implications

Cary Institute of Ecosystem Studies

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Salt Creek in Death Valley, California. A new analysis reveals that rivers in arid landscapes are helping to soak up more carbon dioxide than previously thought. 

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Credit: Taylor Maavara

For decades, scientists have generally thought that rivers emit more carbon dioxide, a greenhouse gas, than they take in. But a new analysis of every river network in the contiguous United States — including underrepresented rivers in deserts and shrublands — challenges this assumption, uncovering hints that many Western waterways may be soaking up carbon dioxide from the atmosphere. The findings were published in Science and led by Taylor Maavara, an aquatic biogeochemist at Cary Institute of Ecosystem Studies.

“Rivers are one of the most uncertain parts of the global carbon cycle,” explained Maavara. “So in terms of balancing the global carbon budgets, figuring out where the carbon in rivers is coming from and and where it's going is essential.”

One of the biggest sources of uncertainty in rivers is metabolism — the balance between how much carbon dioxide rivers soak up through photosynthesis, and how much they emit through the respiration of plants, animals, and microbes. Historically, monitoring data on river metabolism has been biased toward forested rivers in temperate areas. Using machine learning, Maavara and colleagues upscaled large observational datasets for a more holistic view. The study is the largest analysis of river metabolism to date, including monthly and annual photosynthesis and respiration rates for all the streams and rivers in the US.

“Estimating stream metabolism at large scales has been an elusive problem despite its importance to understanding the food webs of these unique and biodiverse systems,” said co-author Pete Raymond of Yale University. “This work has advanced our understanding of how streams function, which will allow for better stewardship of these important ecosystems.”

The team used US Geological Survey data to establish photosynthesis and respiration rates at hundreds of sites across the country. Then they used those data to train a machine learning algorithm to rank the factors driving photosynthesis and respiration rates. Factors included light availability, water temperature, nutrient and organic matter, and river flow rates. The model was then able to estimate photosynthesis and respiration rates for river reaches where data hadn’t been collected.

Until now, scientific thinking about rivers’ role in the carbon cycle has been largely biased by studies in the Northeastern US, where rivers tend to flow through forests in temperate climates. In these environments, where there is less light to feed photosynthesis and lots of organic carbon washing into streams to feed respiration, rivers tend to emit more carbon dioxide than they absorb. Hence, scientists inferred that most rivers must be predominantly carbon emitters.

However, Maavara and team show that when models include understudied areas like deserts, arid environments, and shrub lands where there’s less canopy cover blocking sunlight, and less organic carbon washing into the stream, rivers can act as carbon sinks. 

“That's what we see happening out West, where there are more of these arid environments,” Maavara explained. Results indicate that about 25% of western river reaches take in more carbon than they emit on a yearly basis, compared to 11% of eastern reaches.

“Our work suggests rivers that were considered outliers in previous studies may be more common than we thought, especially in these understudied areas,” said Maavara. 

Taken as a whole, rivers in the US still emit more carbon than they absorb, but the new numbers suggest the deficit may be much lower than previously thought. And Maavara suspects that these trends may apply more broadly at a global scale, since 65% of the world’s land cover is arid or semi-arid. 

Intriguingly, climate change may be making rivers in the western US into better carbon sinks, at least for now. With hotter temperatures and lower precipitation, rivers are flowing more slowly, allowing sunlight to penetrate further into the water, allowing for more photosynthesis and hence more carbon absorption. However, if the rivers dry up entirely, this benefit goes away and the streams can instead become a source of carbon dioxide. 

Maavara cautions that much uncertainty remains in calculating the carbon budgets of rivers and streams. However, “this study takes us several steps closer to narrowing the big gap in terms of understanding in the carbon cycle, which in turn will help us manage and mitigate the CO2 in the atmosphere.”

FUNDING

Independent Research Fellowship, United Kingdom’s Natural Environment Research Council, grant number NE/V014277/1. United States Department of Energy award # DE-SC0024709. United States National Science Foundation NSF-DEB award # 2404575. Gaylord Donnelley Fellowship, Yale Institute for Biospheric Studies.

Cary Institute of Ecosystem Studies is an independent nonprofit center for environmental research. Since 1983, our scientists have been investigating the complex interactions that govern the natural world and the impacts of climate change on these systems. Our findings lead to more effective resource management, policy actions, and environmental literacy. Staff are global experts in the ecology of: cities, disease, forests, soils, and freshwater.

 

Taylor Maavara (front) samples the Gunnison River in Gunnison National Park, Colorado. 

Credit

Laura Logozzo

Cooler colors indicate rivers that are taking in more carbon dioxide than they’re emitting, acting as carbon sinks. Conversely, warmer colors indicate that respiration exceeds photosynthesis, and the rivers are a source of greenhouse gas emissions. Rivers in the arid West, which have traditionally been excluded from river metabolism studies, show markedly different patterns than the East — notably in the prevalence of carbon sinks in July. Including western rivers in the analysis showed that rivers may be a much smaller source of carbon emissions than previously thought, and because arid environments are prevalent around the world, they may even be a carbon sink at the global level. 

Credit

Credit: Maavara et al./Science 2025

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Journal

Science

DOI

10.1126/science.adu9843 

Article Title

River metabolism in the contiguous United States: A West of extremes

Article Publication Date

6-Nov-2025

 

Shopping data reveals ‘food desert’ hotspots in London, suggesting where nutritional needs are not be being met

University of Nottingham

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New research has used purchasing data to map areas of London where residents may be suffering from a nutritionally inadequate diet, pinpointing where there are ‘food deserts.’

Researchers from the University of Nottingham and Adelaide analysed Tesco food purchasing records from 1.6 million people across London to understand how food purchase patterns vary and what they reveal about health. Their results, published today in PLOS Complex Systems, show clear differences in the nutritional quality of food purchased in different areas of London and reveals where there are ‘food deserts’ - areas where residents may face barriers to a healthy and affordable diet.

The food and drink purchases were organised into 12 categories – grains, sweets, soft drinks, fruit and veg, fish, red meat, poultry, sauces, fats & oils, eggs, dairy and ready meals. The researchers analysed these against factors including household income, car ownership and black and minority populations.

The results showed area-specific adherence to high-sugar and high-carbohydrate purchases suggesting that residents in these areas are not accessing a nutritionally adequate diet. These behaviours are attributed to ‘food deserts’, and suggest possible barriers to people accessing nutritious foods such as high-fibre and high-protein options. Such areas are located in London’s east (e.g. Newham; Barking and Dagenham), and some areas of London’s north west (e.g. Ealing; Brent).

 

Poor diet and nutrition are a leading global risk to health, and accounts for 13% of deaths in the UK. Diets high in processed foods, sugars, and fats are known to cause obesity and are associated with a range of negative health outcomes including; hypertension, heart disease, and diabetes. In recent years, 61% of London’s adult population were classed as overweight or obese, and childhood obesity rates (for ages 10–11) were higher than the England average. Increased production of processed foods, rapid urbanisation, and changing lifestyles have led to a shift in dietary patterns.

Tayla Broadbridge is a PhD student from the School of Mathematics and is part of the joint Nottingham-Adelaide PhD program. She led the research and said: “We are re-thinking urban food deserts: purchase data, not supermarket locations, shows the reality of access to healthy food in London”. A map of food stores only shows potential access – food purchase data shows the reality, revealing where Londoner’s diets are nutritionally deficient.”

She continues: “Our findings emphasise the need for targeted interventions that address local food access issues according to specific socioeconomic characteristics. To be effective interventions should be strategically targeted to areas that show nutritionally deficient purchasing behaviours, and with sociodemographic characteristics in mind. A ‘one-size-fits-all’ approach is not the most effective way of addressing food deserts in London, and interventions should be tailored to the local level to maximise the effectiveness and compliance.”

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Journal

PLOS Complex Systems

DOI

10.1371/journal.pcsy.0000072 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Publication Date

6-Nov-2025

Grocery store records reveal London food deserts

Tesco loyalty-card data show unequal purchasing of nutritious food across the city

PLOS

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Researchers assess and model grocery store food purchases across London.

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Credit: Arthur Franklin, Unsplash (CC0, https://creativecommons.org/publicdomain/zero/1.0/)

A new study identified large clusters of food deserts, where residents have limited access to affordable, nutritious food, in East London—particularly Newham, Redbridge, and Barking and Dagenham—and in parts of west London such as Ealing and Brent. The findings were published November 6th in the open-access journal PLOS Complex Systems by Tayla Broadbridge of the University of Nottingham, UK, and colleagues.

Poor diet and unequal access to healthy food are linked to rising rates of obesity, diabetes, and heart disease. To effectively target interventions to areas where residents face barriers to accessing healthy food, identifying these food deserts is necessary.

In the new study, researchers used the Tesco Grocery 1.0 dataset, a record of 420 million food items purchased by 1.6 million Tesco Clubcard owners who shopped at 411 Tesco grocery stores across London in 2015. Transactions were linked to geographic areas of the residential address associated with the Tesco account, but otherwise anonymized.

The study revealed distinct geographic areas where residents purchased more high-sugar, high-carbohydrate and processed foods and less fresh, high-fiber and high-protein options. Inner north-west boroughs had the most nutritious purchase trends, while those in East London and the western boroughs had the least nutritious shopping records. The researchers developed a statistical model to analyze what sociodemographic factors could predict these food desert areas and found correlations that varied by region.

In the east and west of London, higher income was associated with nutrient deficient purchases while it was associated with more nutritious purchases in the inner-west. More car ownership was associated with more nutritious purchases in a small region of London’s north-west, but with nutrient deficient purchases in the east, west, and north-west. Higher proportions of Black, Asian, and minority ethnic residents were associated with nutrient deficient purchases in the west, northeast and inner-east food deserts.

Overall, the model explained much of London’s variation in food purchasing, highlighting areas most at risk of nutrient-deficient food purchases.

“Our findings demonstrate the potential of analyzing food purchase data to identify food deserts and their drivers, and suggest that area-specific, context-sensitive interventions are necessary for the implementation of local public health strategies,” the authors say.

The authors add, “We are rethinking food deserts: purchase data, not supermarket locations, shows the reality of access to healthy food in London.”

“A map of stores only shows potential access—our data shows reality, revealing where Londoners’ diets are nutritionally deficient.”

 

In your coverage, please use this URL to provide access to the freely available paper in PLOS Complex Systems: https://plos.io/4nfSdfN

Citation: Broadbridge TP, Green JEF, Preston SP, Fadai NT, Maclean J (2025) Food purchase data reveals the locations of London’s ‘food deserts’. PLOS Complex Syst 2(11): e0000072. https://doi.org/10.1371/journal.pcsy.0000072

Author countries: Australia, United Kingdom

Funding: The author(s) received no specific funding for this work.

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Journal

PLOS Complex Systems

DOI

10.1371/journal.pcsy.0000072 

Method of Research

Observational study

Subject of Research

People

 

West Coast mammal-eating killer whales are two distinct communities that rarely mix

AND THEY ARE DISTINCT FROM GREAT WHITE SHARK EATING ORCAS

University of British Columbia

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Inner coast transient killer whale hunting close to a Steller sea lion haulout off the outer coast of Washington.

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Credit: Credit by Jonathan Scordino Makah Fisheries Management.

New research has confirmed that West Coast transient killer whales who live between British Columbia and California are two distinct subpopulations: inner and outer coast transients.

Based on 16 years of data from more than 2,200 encounters, the study published in PLOS One challenges previous assumptions about this group of mammal-eating killer whales.

“I've been thinking about this possibility for 15 years,” says first author Josh McInnes, who conducted the research as part of his masters at UBC’s Institute for the Oceans and Fisheries (IOF). “Now our findings show the West Coast transients are two distinct groups, split along an east-west divide. They eat different things, hunt in different areas and very rarely spend time with each other.”

There are three ecotypes of killer whales which frequent the West Coast of North America: transients, residents and offshore, although a fourth potential ‘oceanic’ population was recently posited. The transients consist of six populations around the world, including the West Coast transients, which is the most studied and shares distinct DNA.

This West Coast group, which are found from southeast Alaska to southern California, were previously suspected to be split in a north-south divide, but the research found they differ in a number of ways.

“The inner coast killer whales are like city dwellers,” said co-author Dr. Andrew Trites, IOF professor and director of the Marine Mammal Research Unit. “They’re experts at navigating busy, maze-like streets of nearshore inlets, bays and sheltered waterways—whereas the outer coast killer whales are more like backcountry dwellers thriving in deep canyons and rugged underwater terrain along the edge of the continental shelf.”

The research team undertook a social network analysis of orca sightings using photos from a range of sources including scientific surveys and public sightings to identify specific animals from 2005 to 2021.  “We essentially drew friendship maps to see which whales spent time together, and then looked at where they were seen to figure out if they hung out in specific neighbourhoods,” said Dr. Trites.

The researchers found that the inner coast transients, numbering about 350 animals, were observed on average about six kilometres from shore and in significantly shallower waters than the outer coast whales, such as the Salish Sea. They ate a diet of smaller marine mammals such as harbour seals and harbour porpoises, and foraged in small groups of about five whales on average.

Outer coast transients, numbering about 210, are mainly found within 20 kilometres of the continental shelf break, frequently near submarine canyons. They were seen up to 120 kilometres from shore and travelled over extensive distances. They ate larger prey such as California sea lions, northern elephant seals, gray whale calves and Pacific white-sided dolphins and hunted in groups of about nine on average.

These differences could be due to the different habitats the animals occupy or human effects on the ecosystem, including culling and harvesting of key prey species.

Despite some overlap in their hunting grounds, which run from Southeast Alaska to southern California, the two subpopulations rarely associated with each other, with co-mingling seen in less than one per cent of encounters. “I have seen outer coast transients acting strangely around inner coast animals,” said McInnes, co-founder of the Oceanic Research Alliance. “One of the sightings reported a group of single male outer coast orcas slapping each other with their dorsal fins and charging at inner coast females.”

Given the difficulty of surveying in offshore waters, it’s possible there are even more subpopulations hunting beyond the reach of current observations.

In the meantime, the authors emphasize that their findings highlight the transboundary nature of transient killer whales and the importance of tailoring conservation and management efforts to the distinct ecological traits of each subpopulation. “These two communities of transient killer whale inhabit very different worlds and lead distinctly different lives,” said Dr. Trites. “Protecting them will take more than a one-size-fits-all approach. Each needs a tailored plan that reflects their unique needs and the specific threats they face.”

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Journal

PLOS One

DOI

10.1371/journal.pone.0325156