Case of missing nitrogen solved: It comes from the bedrock

A study says that the leaching of nitrogen from the bedrock could be the reason for elevated levels of nitrogen in groundwater

By Akshit Sangomla
Published: Tuesday 10 April 2018

The distribution of nitrogen rich bedrock and its weathering varies from one region to another. Credit: PxhereNitrogen is the most abundant element in the atmosphere at 78 per cent. When fixed into the soil by micro organisms and taken up by plants it becomes essential to all living organisms in the form of plant chlorophyll and proteins. For a long time, scientists thought that this was the only source of natural nitrogen for plants and, in turn, for animals who feed on them.

But a new study conducted at the University of California, Davis, suggests that 26 per cent of the nitrogen in vegetation comes from the bedrock deep inside Earth’s crust. This gets released by weathering of rocks – either physically through shifts in tectonic plates or through chemical reactions with water.

The distribution of nitrogen rich bedrock and its weathering varies from one region to another. According to the study published in the journal Science on April 6, the weathering is low in large regions of Africa, while it is high in the higher latitudes in Europe and North America. It is also high in the Himalayan and Andes mountain ranges, deserts, Tundra and grass lands.

The pre-industrial planetary nitrogen cycle.

This part of the nitrogen in the Earth’s system had been un-accountable until now and was considered as ‘missing nitrogen’ or the ‘mysterious gap’. Now, scientists say that the case of the missing nitrogen has been solved and it comes from the earth’s bedrock.

“We show that the paradox of nitrogen is written in stone,” co-leading author of the study Scott Morford told the media. “There’s enough nitrogen in the rocks, and it breaks down fast enough to explain the cases where there has been a mysterious gap,” he added.

The study also points out that cases of elevated levels of nitrogen in groundwater could also be caused by the leaching of nitrogen from the bedrock, apart from the trickling down of artificial nitrogen used in farms.

Nitrogen, with other nutrients such as phosphorus, is also required to bring down CO2 levels in the atmosphere through natural cycling. This helps maintain the carbon balance in nature. Previous work from the same scientists had shown that in temperate coniferous forests growing on top of bedrock which was rich in nitrogen carbon absorption doubled. They have also highlighted that the reason behind the extra ordinary ability of boreal forests to absorb CO2 from the atmosphere is to do with the rich nitrogen in the rocks below them.

In times to come, this discovery of a new source of nitrogen will help develop better models for the nitrogen cycle on the planet. It will also help us re-analyse our strategies for managing human generated CO2 in the atmosphere and the subsequent climate change being caused by it.

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