Monday, August 11, 2025

 

Strategically bringing back beavers could support healthy and climate-resilient watersheds



A new Stanford-led study uses high-resolution aerial imagery to map beaver dams and ponds, ultimately aiding managers in prioritizing areas for restoring wetlands and reintroducing beavers.



Stanford University





In brief:

  • Ponds created by beaver dams can help increase freshwater storage, boost biodiversity, contain wildfires, and improve water quality.

  • Beaver populations in North America have fallen from an estimated 60-400 million before European colonization to roughly 10-15 million today because of extensive hunting, habitat degradation, and trapping.

  • Better maps could help watershed managers prioritize areas for beaver reintroduction that would maximize benefits while highlighting trade-offs for water users.

After enduring centuries of hunting, habitat loss, and disease, North American beavers (Castor canadensis) are making a comeback – and bringing benefits for both humans and nature with them.

Equipped with findings from a new study published Aug. 11 in Communications Earth & Environment, a team of researchers from Stanford and the University of Minnesota aims to ensure that beavers return to or establish new homes in areas with the biggest bang for their buck (teeth).

Supported in part by a grant from the Stanford Woods Institute for the Environment’s Environmental Venture Projects program, the research reveals some of the factors that determine how well beavers can function within a given watershed. The findings could inform decisions about how to manage habitats, wildlife, and waterways.

“Our findings can help land managers figure out where beaver activity will have the biggest impact,” said lead study author Luwen Wan, a postdoctoral fellow in Earth system science at the Stanford Doerr School of Sustainability and the Institute for Human-Centered Artificial Intelligence. “It gives them a practical tool for using nature to solve water and climate problems.”

Although beavers often receive a bad reputation when their dams flood a farmer’s field or block drainage from a busy highway, their dynamic and rapid dam construction makes them superheroes in natural watershed management. Beaver dams create cool ponds that foster biodiversity, improve water quality, and even limit the spread of wildfires. They frequently construct multiple dams within an area, creating a wetland network of surface water and vegetation known as “beaver wetland complexes.”

These complexes provide long-term freshwater storage and recharge groundwater – a crucial benefit, especially in the American West, where dwindling surface water supplies are the result of years of sustained climate change-driven drought and over-allocation of surface water supplies, as seen in the Upper Colorado River Basin.

“Beavers are naturally doing a lot of the things that we try to do as humans to manage river corridors,” said study senior author Kate Maher, a professor of Earth system science at the Stanford Doerr School of Sustainability and a senior fellow at the Woods Institute for the Environment. “Humans will build one structure, leave it there, and hope it lasts for many decades. Beavers on the other hand, build little, tiny dams where they're needed and flexibly manage what's going on with the water in their environment.”

Maher and Wan collaborated with Emily Fairfax, a beaver expert at the University of Minnesota who has mapped beaver dams through topographic surveys and remote sensing imagery for years. However, traditional surveys in remote areas limit the scale and detail needed to holistically map beaver ponds and their impact on hydrology and ecology. Additionally, dams and ponds are often too small for satellite imagery to capture.

The new study details how the team mapped more than 80 beaver pond complexes across diverse regions in Colorado, Wyoming, Montana, and Oregon using high-resolution aerial imagery from the USDA National Agricultural Imagery Program. They then identified key factors influencing variations in  beaver dam length and pond area. 

Their approach allowed the researchers to link pond size to unique landscape features like topography, vegetation, climate, soil characteristics, and stream hydrology. For instance, they found that longer dams were correlated with larger ponds, which in turn could increase ecosystem benefits like cooler local air temperatures and more fish habitat.

Despite the potential for wetland resilience and restoration, beaver activity can create problems for nearby communities. New dams can temporarily reduce water flows, putting stress on downstream water users already struggling to find sufficient surface water supplies during drought conditions. Unmanaged beaver populations can pose a flooding threat to homes, crops, and infrastructure.

“There's definitely a lot of exuberance around reintroducing beavers, and it may not be that every beaver reintroduction project is the right one to pursue,” said Maher. “It’s important to understand those trade-offs and the risks and rewards from either intentionally reintroducing beavers, or just their natural return to watersheds.”

The team's research highlights the possibility of achieving dual benefits by relocating so-called “nuisance beavers” to watersheds with the capacity to support a beaver population and maximize the natural benefits beavers create. Wan also notes that the approach could help decision-makers understand the impact of beaver-inspired human structures like beaver dam analogues (BDAs) and other nature-based water management structures.

Moving forward, Wan and Maher are eager to collaborate with Jeannette Bohg, an assistant professor of computer science in the Stanford School of Engineering and co-investigator on the project, to apply machine learning methods to their mapping. Ultimately, the researchers envision dynamic risk maps that policymakers, watershed managers, and ecologists can use to quantitatively evaluate where, when, and how to bring back beavers.


Maher is a professor of Earth system science and a professor (by courtesy) of Earth and planetary sciences in the Stanford Doerr School of Sustainability, a senior fellow at the Stanford Woods Institute for the Environment, a faculty affiliate of the Institute for Human-Centered Artificial Intelligence, and an affiliate of the Precourt Institute for Energy.

This research was supported by a Stanford Woods Institute for the Environment Environmental Venture Projects grant and the Stanford HAI Postdoctoral Fellowship Program.

Co-author Emily Fairfax is an assistant professor of geography, environment, and society at the University of MinnesotaJeannette Bohg is also a member of Stanford Bio-X and a faculty affiliate at HAI.

 

Women who have been stalked may have a higher risk of heart disease, stroke



Women who experienced being stalked or who obtained restraining orders were more likely to develop heart disease and stroke than women who had not faced these events, finds a new study in the Circulation journal



American Heart Association





Research Highlights:

  • Women who reported being stalked by a current/former partner or other persons were more likely to develop heart disease and stroke during 20 years of follow-up than those who did not report those events.

  • Among women who obtained a restraining order for protection, their risk of developing cardiovascular disease was significantly higher than women who had not requested a restraining order.

  • The link between stalking and cardiovascular disease may be due to psychological distress, which may disrupt the nervous system, impair proper blood vessel function and negatively affect other biological mechanisms, the researchers said.

DALLAS, Aug. 11, 2025 — Women who reported having been stalked or obtained a restraining order were each more likely to experience a heart attack and/or stroke in later years compared to those who did not, according to new research published today in the American Heart Association’s flagship journal Circulation.

“Although violence against women is common, and evidence has linked violence with consequences for women’s later heart health, it is still not widely recognized or routinely considered by health care professionals as a potential cardiovascular risk factor among women,” said study author Rebecca B. Lawn, Ph.D., a research associate in epidemiology at Harvard T.H. Chan School of Public Health in Boston and at the School of Population and Public Health at the University of British Columbia in Vancouver, Canada.

“We felt it was essential to look beyond traditional cardiovascular risk factors in women and strengthen our understanding of the relationship between underexplored types of violence and heart health.”

About 1 in 3 women have been stalked at some point in their lives, according to data on intimate partner violence collected by the U.S. Centers for Disease Control and Prevention. The study notes that common forms of violence against women, such as stalking, are rarely discussed in cardiovascular research. Lawn’s previous research linked sexual assault and workplace harassment to higher blood pressure in women. Other studies report that people with restraining orders are more likely to experience poorer health.

Researchers analyzed stalking, restraining orders, and heart disease or stroke development among participants in the Nurses’ Health Study II, from 2001 to 2021. The analysis includes data for more than 66,000 women, average age 46 years in 2001. These women did not have cardiovascular disease in 2001, when they first shared whether they had experienced stalking or stalking harassment behaviors, such as receiving unsolicited correspondence, that made them fearful. The study also asked if participants had “ever taken out” a restraining order, which is a legal document that seeks to limit contact between a victim and perpetrator. Obtaining a restraining order was considered a sign of severe violence.

The analysis found:

  • Overall, nearly 12% of the women in the study reported that they had been stalked, while nearly 6% of them said they had obtained a restraining order.
  • About 3% of all women studied reported new-onset heart disease or stroke during the 20 years of the study.
  • Compared to women who had not been stalked, women who reported experiencing stalking were 41% more likely to have cardiovascular disease.
  • Women who had obtained a restraining order were 70% more likely to report cardiovascular disease versus those who had not.
  • Similarly, women whose medical records confirmed heart attacks or strokes were more likely to have reported being stalked or obtaining a restraining order.
  • The increased risks for heart attack and stroke associated with stalking and restraining orders remained despite the existence of other self-reported cardiovascular risk factors, such as health and lifestyle behaviors, medications, health conditions, childhood abuse and symptoms of depression.

“Stalking is often seen as a form of violence that does not involve physical contact, which may make it seem less serious,” Lawn said. “However, our findings suggest stalking should not be minimized. Stalking can be chronic, and women often report making significant changes in response such as moving.”

Harmony R. Reynolds, M.D., FAHA, immediate past  chair of the American Heart Association’s Clinical Cardiology & Stroke Women’s Health Science Committee, said she was surprised at the strong association this study found between stalking and cardiovascular disease.

“A variety of stressful life experiences are known to increase the risk of cardiovascular disease, including adverse childhood experiences, financial stressors, grief and other experiences,” Reynolds said. “People subjected to intimate partner violence face about a 30% higher risk of developing cardiovascular disease in the next few years compared to others. While this study shows a more moderate risk, given the long-time frame, it highlights how feeling unsafe can affect the body, in addition to the mind.”

Reynolds, the Joel and Joan Smilow Professor of Cardiology and Director of the Sarah Ross Soter Center for Women’s Cardiovascular Research at NYU Grossman School of Medicine in New York City, was not involved in this research, and noted that the effects of stress can be long-lasting. “Perhaps because it is our nature to re-think about things that happen to us, making us experience the situation over and over. However, social support may mitigate the effects of stress. It’s helpful to have people you can trust to talk with, whether they are family, friends, people in the community or professionals,” she said.

Study authors note that the link between stalking and cardiovascular disease may be due to  psychological distress, which may disrupt the nervous system, proper blood vessel function and other biological processes; however, these potential mechanisms were not examined in detail in this study.

Lawn said more research, as well as training for health care professionals, is needed to understand the link between stalking or obtaining a restraining order and women’s cardiovascular health.

“We also need to increase awareness about the potential health harms of experiencing violence and provide women with help and resources,” she said.

Among the study’s limitations are that participants—U.S. registered nurses—were mostly non-Hispanic white women. The findings may not apply to other populations or groups of people. The study notes that previous research indicated that, “violence history, including stalking, is more common among women from minority racial/ethnic backgrounds and those with low income.” In addition, the study relied on participants self-reporting their history of experiencing stalking and restraining orders.

Study Background:

  • The study included 66,270 U.S. women ages 36-56 years at enrollment in 2001 in the Nurses’ Health Study II, part of a larger, ongoing survey of U.S. female nurses that began in 1989.
  • Self-reported data on stalking was collected in 2001. Information about heart attacks and strokes was self-reported and verified with medical records.
  • The study used a prospective analysis, meaning researchers started with women who had never had a heart attack or stroke when asked about stalking or obtaining a restraining order. They then followed these women for more than 20 years to see if they reported experiencing stalking or obtaining a restraining order and were more likely to develop a heart attack or stroke compared to women who did not report these experiences.

Co-authors, disclosures and funding sources are listed in the manuscript.

Studies published in the American Heart Association’s scientific journals are peer-reviewed. The statements and conclusions in each manuscript are solely those of the study authors and do not necessarily reflect the Association’s policy or position. The Association makes no representation or guarantee as to their accuracy or reliability. The Association receives more than 85% of its revenue from sources other than corporations. These sources include contributions from individuals, foundations and estates, as well as investment earnings and revenue from the sale of our educational materials. Corporations (including pharmaceutical, device manufacturers and other companies) also make donations to the Association. The Association has strict policies to prevent any donations from influencing its science content and policy positions. Overall financial information is available here.

Additional Resources:

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About the American Heart Association

The American Heart Association is a relentless force for a world of longer, healthier lives. Dedicated to ensuring equitable health in all communities, the organization has been a leading source of health information for more than one hundred years. Supported by more than 35 million volunteers globally, we fund groundbreaking research, advocate for the public’s health, and provide critical resources to save and improve lives affected by cardiovascular disease and stroke. By driving breakthroughs and implementing proven solutions in science, policy, and care, we work tirelessly to advance health and transform lives every day. Connect with us on heart.orgFacebookX or by calling 1-800-AHA-USA1.

Conditional cash transfers significantly reduce AIDS incidence and mortality among Brazil’s most vulnerable women




A landmark study involving more than 12 million Brazilian women over nine years indicates that the Bolsa Família Programme significantly reduced AIDS incidence by up to 47% and AIDS-related mortality by up to 55%




Barcelona Institute for Global Health (ISGlobal)






The world's largest conditional cash transfer programme, the Bolsa Família Programme (BFP), is associated with a substantial reduction in AIDS cases and deaths, especially among brown and black women with lower income and limited education. This was the main conclusion of a study coordinated by the Barcelona Institute for Global Health (ISGlobal), a centre supported by ”la Caixa” Foundation, in collaboration with the National Institute of Allergy and Infectious Diseases (NAIDS/NIH). The results were published in Nature Human Behaviour.

Conditional cash transfer (CCT) programmes, which provide financial aid to low-income households in exchange for fulfilling health and education requirements, are a key policy tool for addressing the social determinants of health. Implemented in nearly all low- and middle-income countries, CCTs aim to improve the living conditions of families in vulnerable situations.

 

Education amplifies the impact of conditional cash transfer programmes

“We analyzed data from 2007 to 2015, focusing on mothers and daughters in households receiving Bolsa Família, using a causal inference framework and a robust quasi-experimental design,” explains Andréa F. Silva, PhD in the Institute of Collective Health, Federal University of Bahia (UFBA) (Salvador, Brazil) and lead author of the study. The analysis covered 12.3 million low-income women, and explored how intersecting vulnerabilities — such as poverty, race, and education — affected the programme's effectiveness.

Among daughters, the programme was associated with a 47% reduction in AIDS incidence and a 55% reduction in AIDS-related mortality. Among mothers, the reductions were 42% and 43%, respectively.

The programme’s impact was particularly significant among women facing multiple intersecting vulnerabilities. In particular, brown or black mothers living in extreme poverty and with higher levels of education experienced the greatest improvements: a 56% reduction in AIDS incidence. These findings suggest that education enhances the protective effects of cash transfers on health outcomes.

 

How Brazil is successfully reducing AIDS cases

Brazil has already reported a national decline in AIDS, with the relative incidence dropping by nearly 30% from 2007 to 2021, and over 40% among women. This study suggests that the BFP may be one of the reasons for this success, highlighting the importance of integrated social and health policy approaches.

Beyond financial aid, the BFP includes health and education conditionalities, such as mandatory school attendance, routine health checkups, and participation in health education activities, including sexual and reproductive health, which may further support HIV prevention and treatment. By improving nutrition, reducing food insecurity, and encouraging early engagement with healthcare services, these conditions create a multi-pronged approach to disease prevention.

This is the first large-scale study to assess the intersectional effectiveness of cash transfer programmes on HIV/AIDS outcomes. By linking massive socioeconomic and health datasets, the researchers were able to evaluate the effects of the Bolsa Família Programme across diverse subpopulations, many of whom are often underrepresented in traditional epidemiological studies or clinical trials. This is particularly relevant in policy evaluation: public interventions could have a very different impact according to the characteristics and baseline conditions, and of its beneficiaries.

“In the current global context of increasing inequalities and poverty rates, CCT programmes have the potential to significantly reduce morbidity and mortality from AIDS, especially among populations with multiple vulnerabilities,” says Davide Rasella, ICREA researcher at ISGlobal and coordinator of the study. “Our findings show that these programmes not only reduce HIV risks and AIDS-related deaths, but also support progress toward the Sustainable Development Goals in Brazil and beyond,” concludes.

 

Reference

Silva, A. F., Lua, I., Jesus, G. S., Gestal, P. F., Cavalcanti, D. M., Santos, C. A., Ichihara, M. Y., Barreto, M. L., Magno, L., Souza, L. E., Macinko, J., Dourado, I., & Rasella, D. (2025). Intersectional Impact of Cash Transfers on AIDS among 12.3 M Brazilian Women. Nature Human Behaviour10.1038/s41562-025-02278-3 

 

Ocean anomalies traveling North crucial for the Atlantic Meridional Overturning Circulation





Stockholm University

Léon Chafik aboard an oceanographic expedition 

image: 

Researcher Léon Chafik aboard an oceanographic expedition at the Greenland–Scotland Ridge, with a CTD rosette in the background used to measure temperature, salinity, and other water properties throughout the water column.

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Credit: Léon Chafik





Anomalies in temperature and salinity that originate in the midlatitude North Atlantic can affect the Atlantic Meridional Overturning Circulation (AMOC) in the Nordic Seas up to a decade later. The study published in Nature’s journal Communications Earth & Environment shows that the anomalies that travel northward with the Atlantic Water are an important part of the system, and actively modulate both the inflow of warm water into the Nordic Seas and the overflow of dense water back into the deep Atlantic.

“Rather than being passive signals, we find that these anomalies are an inherent part of the system — they help control the strength of the Nordic Seas branch of the AMOC. This research will likely open the door to many new studies on how upstream changes shape the overturning circulation at high latitudes — and how changes in the Nordic Seas may, in turn, influence conditions further south”, says Léon Chafik, first and corresponding author of the study and researcher at the Department of Meteorology, Stockholm University and the Bolin Centre for Climate Research.

The overturning circulation in the Nordic Seas is a key high-latitude branch of the larger Atlantic Meridional Overturning Circulation (AMOC), which moves heat northward and influences the climate of Europe and the Arctic. 

“In the study, we focus on what controls the strength of the AMOC in the Nordic Seas — something that has been poorly understood. Interestingly, all the time series we use in this study suggest that the Nordic Seas overturning is still stable, with no sign of long-term weakening. Understanding what drives variability in this region is essential, especially since it helps shape the future of the broader AMOC”, says Léon Chafik.

The research team reconstructed the northward transport of Atlantic Water into the Nordic Seas using 50 years of hydrographic observations — temperature and salinity profiles collected north and south of the Greenland–Scotland Ridge. 

“By combining these data with satellite altimetry and current meter records, we were able to piece together how thermohaline anomalies travel northward along the Atlantic Water pathway and influence the Nordic Seas overturning as they go. What’s unique about our approach is that we used variability in the inflow itself as a physical tracer — a way to follow these anomalies from their origin in the midlatitudes all the way to the Arctic gateways”, says Léon Chafik.

The results point to a slow but predictable chain of events, where changes in the North Atlantic can affect the high-latitude overturning circulation 5 to 10 years later. This makes thermohaline anomalies a potential source of climate predictability. 

“One important outcome of our study is that satellite data — particularly altimetry — can be used to monitor these changes as they unfold”, says Léon Chafik.

This offers a cost-effective way to track the state of this system in near real time. 

“We hope these satellite programs will continue to be supported and not be affected by government funding cuts, as is currently happening in some countries. In the long run, our findings could help improve forecasts of regional climate shifts, especially in northern Europe and the Arctic. They also highlight the need for sustained satellite and in-situ observations, and for better representation of high-latitude ocean processes in climate models”, says Léon Chafik.

Read more:
Find the study “The Nordic Seas overturning is modulated by northward-propagating thermohaline anomalies” in Communications Earth & Environment: https://www.nature.com/articles/s43247-025-02557-x
DOI: https://doi.org/10.1038/s43247-025-02557-x