Bridger Ruyle

Climate change is starving the Arctic Ocean of essential nutrients, with the region's six largest rivers now delivering far less of the type of nitrogen that marine ecosystems need to survive, according to new research in one of Earth's most vulnerable regions.

The study, led by Bridger J. Ruyle of NYU Tandon School of Engineering, is published in Global Biogeochemical Cycles, where it has been selected as an Editor's Choice. Ruyle completed the research as a Postdoctoral Fellow at the Carnegie Institution for Science.

The study found that warming temperatures and thawing permafrost are fundamentally altering the chemistry of Arctic rivers. The result is that coastal food webs that have sustained Indigenous communities for millennia are being deprived of inorganic nitrogen, an essential nutrient, potentially triggering cascading effects throughout the Arctic Ocean ecosystem.

"This is a red flag for the Arctic," said Ruyle, who joined NYU Tandon in the summer of 2025 as an Assistant Professor in the Civil and Urban Engineering Department. "Rapid changes in river nitrogen chemistry could completely transform how these marine ecosystems function."

The research analyzed 20 years of data from six major Arctic rivers — the Yenisey, Lena, Ob', Mackenzie, Yukon, and Kolyma — which collectively drain two-thirds of the land area flowing into the Arctic Ocean. These rivers transport nitrogen that supports up to 66% of the ecosystem's primary production in coastal Arctic regions.

Between 2003 and 2023, Ruyle and colleagues documented declines in inorganic nitrogen accompanied by simultaneous increases in dissolved organic nitrogen, a far less bioavailable form of the element, in four of the six rivers. The findings reveal that warmer temperatures and increased precipitation caused by climate change are driving the shift in nitrogen composition through their effects on river discharge and permafrost thaw.

Using sophisticated statistical modeling, the researchers identified permafrost loss as the key factor explaining the diverging trends between organic and inorganic nitrogen in these rivers. The study combined 20 years of water chemistry data with environmental variables including temperature, precipitation, land cover, and permafrost extent to pinpoint the climate drivers behind the chemical shifts.

This Arctic rivers research represents Ruyle's broader research mission to understand how human activity, climate change, and natural processes interact to affect water quality globally. Among other areas of focus, his work includes tracking "forever chemicals" and pharmaceuticals in wastewater.

"Whether we're looking at PFAS contamination in drinking water or nitrogen cycling in Arctic rivers, the common thread is understanding how environmental changes propagate through water systems," Ruyle explained. His research explores how human activity, the biosphere, and climate change affect water quality, with particular focus on developing analytical tools to quantify chemical contamination and developing models using remote sensing data to assess climate impacts.

The Arctic findings have implications for ecosystem management and climate adaptation strategies. River transport of nitrogen is estimated to support up to 66% of primary production in Arctic coastal regions, making these compositional changes important for marine food webs and the Indigenous communities that depend on these resources.

The research also highlights the interconnected nature of global environmental challenges. As Ruyle noted in previous work on pharmaceutical contamination, climate-driven water scarcity could exacerbate water quality problems, as there's less dilution of contaminants during drought conditions. The Arctic study similarly shows how temperature and precipitation changes cascade through complex biogeochemical systems, resulting in water quality and ecosystem impacts

"This work demonstrates why we need to think about water quality and climate change as fundamentally linked challenges," Ruyle said. " As climate change intensifies, we must understand these interconnections to protect both human health and ecosystem integrity."

Along with Ruyle, the paper's authors are Julian Merder of the University of Canterbury, New Zealand; Robert G.M. Spencer of Florida State University; James W. McClelland of the Marine Biological Laboratory, Woods Hole; Suzanne E. Tank of the University of Alberta; and Anna M. Michalak of Carnegie Institution for Science.

The study was supported by the National Science Foundation through grants for the Arctic Great Rivers Observatory.

Ruyle, B. J., Merder, J., Spencer, R. G. M., McClelland, J. W., Tank, S. E., & Michalak, A. M. (2025). Changes in the composition of nitrogen yields in large Arctic rivers linked to temperature and precipitation. Global Biogeochemical Cycles, 39, e2025GB008639. https://doi.org/10.1029/2025GB008639

The "forever chemicals" flowing from U.S. wastewater treatment plants are not only more abundant than previously thought, but also largely consist of pharmaceuticals that have received little scientific or regulatory attention, a new multi-university study reveals.  

The research, published in PNAS – and covered by The New York Times and The Washington Post, among other outlets – found that common prescription drugs make up about 75% of the organic fluorine in wastewater entering treatment plants, and 62% in treated water released to the environment.

These findings suggest millions of Americans could be exposed to these persistent chemicals through their drinking water.

"We've been focused on a small subset of these chemicals, but that's just the tip of the iceberg," said Bridger J. Ruyle, an incoming Assistant Professor in NYU Tandon School of Engineering’s Civil and Urban Engineering department and the study’s lead author. “The research shows that even advanced wastewater treatment removes less than 25% of these compounds before they're discharged into rivers and streams.”

Of particular concern is that six forever chemicals recently regulated by the Environmental Protection Agency in drinking water make up only about 8% of the organic fluorine found in wastewater effluent. The remainder consists largely of fluorinated pharmaceuticals and other compounds that aren't currently regulated.

Using a national model that tracks how wastewater moves through U.S. waterways, the researchers estimate that during normal river conditions, about 15 million Americans receive drinking water containing levels of these compounds above regulatory limits. During drought conditions, that number could rise to 23 million people.

The study examined eight large wastewater treatment facilities serving metropolitan areas across the United States. These facilities are similar to those serving about 70% of the U.S. population, suggesting the findings have broad national implications.

"What's particularly troubling is that these fluorinated pharmaceuticals are designed to be biologically active at very low doses," said Ruyle. "We don't yet understand the public health implications of long-term exposure to these compounds through drinking water."

The research comes at a critical time, as about 20% of all pharmaceuticals now contain fluorine. While this chemical element makes drugs more effective by helping them persist in the body longer, that same persistence means they don't break down in the environment.

The findings suggest that current regulatory approaches focusing on individual chemicals may be insufficient to address the complex mixture of fluorinated compounds in wastewater. The study also highlights how water scarcity could exacerbate the problem. In regions experiencing drought or implementing water conservation measures through wastewater reuse, there's less dilution of these chemicals before they reach drinking water intakes.

"These results emphasize the urgent need to reduce ongoing sources of these chemicals and evaluate the long-term effects of fluorinated pharmaceuticals in our water supply," said Ruyle. "We can't just focus on the handful of compounds we've studied extensively while ignoring the majority of what's actually out there. We need a more comprehensive approach to regulation and increased attention to the ecological and public health impacts of fluorinated pharmaceuticals."

The paper’s publication comes on the heels of Ruyle's November 2024 testimony to New York State lawmakers warning about the threats of forever chemicals passing through water treatment plants. The new findings provide detailed evidence supporting his concerns about the potential prevalence of these compounds in downstream drinking water supplies.

In addition to Ruyle, the paper's authors are Emily Pennoyer, Thomas Webster, and Wendy Heiger-Bernays from Boston University School of Public Health; Simon Vojta, Jitka Becanova, and Rainer Lohmann from the University of Rhode Island's Graduate School of Oceanography; Minhazul Islam and Paul Westerhoff from Arizona State University; Charles Schaefer from CDM Smith in New Jersey; and Elsie Sunderland, who holds appointments at Harvard's School of Engineering and Applied Sciences, Department of Earth and Planetary Sciences, and School of Public Health.

Financial support for this work was provided by the National Institute for Environmental Health Science Superfund Research Program (P42ES027706) and the Water Research Foundation (Project 5031). This study was also supported by contributions from the anonymous participating wastewater treatment facilities.

B.J. Ruyle, E.H. Pennoyer, S. Vojta, J. Becanova, M. Islam, T.F. Webster, W. Heiger-Bernays, R. Lohmann, P. Westerhoff, C.E. Schaefer, E.M. Sunderland, High organofluorine concentrations in municipal wastewater affect downstream drinking water supplies for millions of Americans, Proc. Natl. Acad. Sci. U.S.A.