Human activity is responsible for a lot of the nitrogen finding its way into the sea from the atmosphere and influencing the nitrogen cycle, according to the latest findings by an international team of scientists.

The presence of nitrogen in the sea influences global climate as it increases marine biological activity and carbon dioxide uptake, which in turn produces the potent greenhouse gas nitrous oxide.
Although the effect of fertiliser use in agriculture and burning of fossil fuels on land have been studied extensively, this is the first the time nitrogen's impact on the ocean has been properly quantified.
'Anyone concerned about climate change will be alarmed at the scale of man's impact on the world's oceans, as revealed by our new study,' said Peter Liss of the University of East Anglia.
'The natural nitrogen cycle has been very heavily influenced by human activity over the last century - perhaps even more so than the carbon cycle - and we expect the damaging effects to continue to grow. It is vital that policymakers take action now to arrest this.
'The solution lies in controlling the use of nitrogen fertiliser and tackling pollution from the rapidly increasing numbers of cars, particularly in the developing world.'
The paper is the culmination of a project involving 30 researchers from Britain, the US, Germany, Italy, China, the Netherlands, Switzerland, Canada and Chile.
The study found that increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for around one third of the ocean's external (non-recycled) nitrogen supply and up to three percent of the annual new marine biological production.
The findings of the study have been published in the latest issue of the journal Science.