Nitrate ​Pollution Poses ​a Big Threat to ​the Baltic Sea ​

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Nitrate ​Pollution Poses ​a Big Threat to ​the Baltic Sea ​

According to scientists, farming is now the biggest source of pollution in the Baltic Sea.

By: Eskild Heinemeier

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And since farming is the biggest source of nitrate, much more needs to be done to reduce this source of pollution. This is the message from scientists at the BONUS 2018 conference in Poland, where scientists from around Europe gathered to discuss the future of the Baltic Sea.

Farming releases large amounts of nitrogen and phosphorous. These nutrients come from fertilisers and are carried into the sea via streams and waterways. In the Baltic, they are a source of food for algae, which can grow and bloom to such an extent that they deplete the water of oxygen.

And no oxygen quite simply means no life, says Professor Jens Christian Refsgaard from the Geological Survey of Denmark and Greenland (GEUS). He is the leader of the SOILS2SEA research project, which is investigating how changes in climate and agricultural practices affect the transfer of such nutrients into the Baltic Sea.

Emissions from farming are invisible

Reducing nitrate emissions from farming is however, easier said than done.

Regulating emissions from farming is much trickier than other sources of nitrate, such as from industry or individual cities.

“Industrial and municipal waste comes out of a pipe. You can see it. And you know that you can put technology on that pipe to treat it,” says James Shortle, professor in agricultural and environmental economics at the Pennsylvania State University, USA. Shortle was one of the keynote speakers at the conference.

But unfortunately, finding the source of agricultural pollution is not so simple.

“Some people would call the agricultural problem ‘hidden’,” says Shortle.

“It seeps into the ground water, then it moves in ground water and flows into streams. You’ll never see it, it’s just percolating into the water. So there’s no pipe, it’s just coming out of the base flow into a stream,” he says.

This makes it extremely difficult to identify the polluter, he says.

Adapt farming to nature

According to Refsgaard, there is a way around this. It’s called spatial differentiation of agriculture.

This means that you organise production on the farm according to nature, such as choosing the right type of crops and fertilization for the individual fields.

In some places, nitrate is removed naturally. For example, if water flows through a part of the soil called the “reduced zone” (located some meters below ground surface) nitrate will be transformed to atmospheric nitrogen, and removed from the water.

So on these fields, restricting farmers’ choice of crops and fertilisation has no effect.

But such mitigation measures could be implemented on other fields, where nature removes less nitrate, says Refsgaard.

Read full article: Science Nordic

Read more in the Danish version of this article at Videnskab.dk

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