Nitrogen Input in Rivers Causing Climate Change, New Study Finds

Climate change will have numerous effects on rivers. But could rivers also be a cause of climate change? A paper published in the most recent edition of the Proceedings of the National Academy of Sciences unravels the mysteries of river greenhouse gas emissions.

Specifically, a team led by researchers from the University of Notre Dame looked at nitrous oxide emissions. Interest in curbing nitrous oxide emissions stems from the fact that it has a global warming potential of 298. That means it’s almost 300 times more potent than carbon dioxide. Nitrous oxide emissions are currently accountable for about six percent of anthropogenic climate change.

Most research to date has focused on emissions from industrial and agricultural sources. The current research breaks new ground by looking at how rivers fit into the tapestry of global climate change causes. It also offers insights that could benefit watershed and land managers alike.

Rolling On The River

Researchers examined 72 rivers and streams in the US. They then ran their results through a global river model to come up with an emissions scenario. Their findings were surprising: they found that rivers account for at least 10% of total nitrogen oxide emissions. That’s three times more than the currently accepted estimate that the Intergovernmental Panel on Climate Change uses.

The research also shows that nitrous oxide emissions are higher from rivers in areas with agricultural or urban land uses when compared with less disturbed watersheds. Ultimately, rivers in urban watersheds win the prize as the biggest emitters.

Agricultural and urban landscapes contribute excess nitrogen to rivers in a variety of ways. This includes runoff from fertilizer and manure, tailpipe emissions, and untreated wastewater. The nitrogen from these activities flows into rivers where microbes then process it into nitrous dioxide.

Nitrogen runoff also has adverse local effects, particularly eutrophication. Large influxes of nitrogen and phosphorous increase algae growth, reducing oxygen and killing fish and advanced plant life. This process can continue downstream all the way to oceans. One notorious example is the dead zone in the Gulf of Mexico, causes by agricultural nitrogen runoff coming down the Mississippi River.

So human activities are not only poisoning rivers and estuaries but are also contributing to climate change. How do you mitigate these effects? The researchers from Notre Dame suggest starting at the source. One example would be using fertilizers more efficiently. Other research has documented how effective this can be both for the environment and farmers’ wallets.

By reducing nitrogen inputs at the source, emissions from terrestrial systems will also be reduced. For all the new interest in rivers, terrestrial nitrous oxide emissions are higher both in total emissions and emissions per nitrogen input. Getting a jump on those emissions will contribute to reducing one of the major causes of climate change.

Photo credit: Brian Kahn