Posted on March 26, 2026 in ASRC News, Environmental Sciences Initiative
Nitrogen is essential for plant growth, and modern agriculture depends heavily on fertilizers to sustain crop yields. But excess reactive nitrogen doesn’t always stay put. It can wash into rivers and coastal waters where it fuels harmful algal blooms and contributes to low-oxygen dead zones such as those in the Gulf of Mexico.
A new study published in Environmental Research Letters reveals that climate extremes—like droughts, heat waves, and intense rainfall—are reshaping how nitrogen moves from land into rivers across the United States, which has important consequences for ecosystems, agriculture, and human health.
Led by Nicolas Maxfield, a CUNY Graduate Center Ph.D. candidate with the CUNY ASRC Environmental Sciences Initiative, the research team examined how both average climate conditions and short-term extreme events influence nitrogen transport. Using a widely applied watershed model and data from hundreds of U.S. monitoring sites over two decades, they found that extremes can significantly alter nitrogen flows, sometimes even reversing expected trends.
“Most models focus on average temperature and rainfall, but our results show that extreme events can fundamentally change how nitrogen behaves,” Maxfield said. “In some regions, increases in extreme weather actually outweigh the effects of long-term climate trends, leading to more nitrogen entering rivers than we would otherwise predict.”
The study found that wet summers and unusually cool years tend to increase nitrogen delivery to rivers, while dry summers can reduce it. Surprisingly, short bursts of hot and dry conditions sometimes increased nitrogen runoff—likely due to disruptions in soil microbes that normally help retain nitrogen.
“These findings highlight that the timing and intensity of weather events matter just as much as long-term averages,” said Charles Vörösmarty, founding director of the ASRC Environmental Science Initiative and the study’s principal investigator. “If we ignore climate extremes, we risk underestimating future threats to water quality and coastal ecosystems.”
The research also has implications not only for coastal areas but also for agriculture. Farmers depend on nitrogen staying in soil to nourish crops, but climate-driven shifts in moisture and temperature can make that harder to manage. The researchers suggest that more diverse cropping systems and soil-friendly practices could help stabilize nitrogen in a changing climate. They also highlight the need to consider the impact of point source sewage and urban runoff, which further load river systems with pollutants.
As extreme weather becomes more common, understanding these dynamics will be key to protecting both food systems and waterways.