Warming rivers are starving the Arctic Ocean of usable nitrogen

Arctic rivers are sending a warning. Climate change is changing the type of nitrogen they carry. This shift matters because marine life depends on a specific form of nitrogen to survive.

A new study led by Bridger J. Ruyle at NYU Tandon reveals what’s going wrong. His team tracked the six largest Arctic rivers for 20 years. What they found: these rivers now deliver much less of the usable, inorganic nitrogen. Instead, they carry more of the harder-to-use, organic kind.

“This is a red flag for the Arctic,” said Ruyle. “Rapid changes in river nitrogen chemistry could completely transform how these marine ecosystems function.”

Arctic rivers have less useful nitrogen

From 2003 to 2023, Ruyle and his team measured nitrogen in rivers like the Ob’, Lena, Mackenzie, and Yukon. These rivers used to deliver enough inorganic nitrogen to feed coastal food webs. Now, not so much.

They found that the amount of inorganic nitrogen (DIN) is dropping. At the same time, dissolved organic nitrogen (DON) is rising. But organic nitrogen isn’t as helpful. Marine organisms struggle to use it.

The mix is shifting. In four of the six rivers, DON now dominates the nitrogen flow. That’s a problem for organisms that rely on nutrients that are easy to absorb and process.

Permafrost thaw and Arctic nitrogen

Permafrost is thawing. That’s one major reason behind the change. When frozen ground melts, it releases more organic matter. Rivers pick it up, but this process seems to suppress the delivery of inorganic nitrogen.

Models show that rivers in areas with thawing permafrost tend to carry more dissolved organic nitrogen and less inorganic nitrogen. That means the warming Arctic is feeding marine systems with the wrong kind of nitrogen.

Heavy rain adds more organic nitrogen

It’s not just heat. Extreme rain matters too. The study found that heavy rainfall days – not just total rainfall – increased nitrogen loads. These intense events now make up 24% to 42% of yearly rainfall across the six river basins.

As climate change continues, extreme rain will likely become more common. That will push even more nitrogen into rivers. But again, it’s mostly the organic type that rises.

Arctic nitrogen levels change each year

Some years, rivers discharge more water. Those years usually see higher organic nitrogen levels. Inorganic nitrogen, on the other hand, doesn’t follow the same pattern.

In the Ob’ River, fires also played a role. As the amount of land burned decreased between 2007 and 2013, so did DIN.

Wildfires can temporarily spike nitrogen levels, especially nitrate, but their long-term effect is unpredictable.

Land and soil affect nitrogen flow

Rivers that flow through wetlands and cultivated land carry more nitrogen overall. These features, along with the amount of thawed permafrost, explain why nitrogen levels vary between rivers.

Soils with long histories of warming show more variability in the kind of nitrogen they export. These areas may lose more inorganic nitrogen due to denitrification or other microbial processes.

Ruyle studies how environmental change affects water. That includes Arctic rivers and also urban drinking water.

“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.

Broader implications of the study

While the total amount of nitrogen flowing into the Arctic Ocean remains steady, levels of inorganic nitrogen are falling. That means marine life, especially species at the bottom of the food web, might struggle.

“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.”

Indigenous communities depend on these ecosystems. Less available nitrogen means weaker food webs. That could affect the fish, mammals, and people that rely on them.

The Arctic is heating up quickly. As permafrost thaws and storms intensify, Arctic rivers are already reflecting the strain – and they could become even more disrupted as climate change accelerates.

The study is published in the journal Global Biogeochemical Cycles.

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