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 atNYU 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.