UK nitrogen feeds bacteria in the Arctic
18 November 2009, by Sara Coelho
A mass of air laden with industrial nitrogen pollution may be hardly noticed in Britain, but it can cause a flurry of activity in bacteria living in extreme environments as far as the Arctic Svalbard archipelago, north of Norway.
In June 1999 an unexpected, warm rain shower fell over the Spitsbergen Island in Svalbard, just before the seasonal summer thaw and annual glacier outburst. The rain was laden with nitrogen compounds, including ammonia (NH4+) and nitrate (NO3-) derived from human activities.
Dr Andy Hodson, from the University of Sheffield and colleagues from Norway and Sweden traced the origin of this early summer shower back to its origin in the UK. 'This was a cloud of "business as usual" industrial pollution that got to Svalbard very quickly, without being dispersed along the way,' he explains.
As rain fell on Spitsbergen's glaciers the water infiltrated the ice pack through a network of small cracks and crevasses until it reached the sediments at the bottom of the glacier. These sediments are not frozen, because the pressure of the glacier above melts the ice. Instead, they are home to a community of micro-organisms that have evolved to survive in extreme environments beneath up to 180m of overlying ice, with little or no light and oxygen.
The spike of nitrogen, which is a nutrient essential to all organisms, caused a surge of activity in the bacteria living underneath the glacier.
The nitrogen-rich rain cloud was an unexpected treat for Arctic ecosystems, which are extremely poor in essential nutrients. The sudden flurry of microbial activity "shows how starved the Arctic is for nitrogen," says Hodson.
Hodson and his team detected the increased bacterial activity beneath the ice when they analysed the water following an outburst flood, ten days after the rain shower. They measured an unusual amount of nitrate and ammonia in the glacier water. But the excess of nitrogen in the runoff was not enough to account for all the nitrate and ammonia estimated to have fallen during the rain shower.
In fact, 52 to 72 per cent of nitrogen was missing from the analysis, presumably used up by micro-organisms in the ten days between the rain shower and the glacier outburst. Hodson suggests in the Biogeochemistry report that most of the ammonia was picked up by the bacteria that live in the snow pack whilst the nitrate was used by the organisms living in the wet sediments beneath the glacier.
'This study shows that nitrogen pollution emitted as far south as the UK can have significant effects in remote Arctic ecosystems,' says Hodson.
Since the event happened before the annual summer thaw, when the soils were still frozen from the winter, it was the communities living in extreme environments, deep under the glacier, that responded and benefited the most from the extra nutrients brought by the rain.
Knowing that nitrogen emitted so far south 'has a profound effect in extreme Arctic ecosystems is important for understanding how micro organisms cope with nutrient scarcity and how coupled climate change and atmospheric pollution will affect them in the future,' says Hodson.
Andy Hodson, Tjarda Jane Roberts, Anne-Christin Engvall, Kim Holmén and Paul Mumford. Glacier ecosystem response to episodic nitrogen enrichment in Svalbard, European High Arctic. Biogeochemistry, published online 12 November 2009. doi:10.1007/s10533-009-9384-y
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