Eutrophication
Eutrophication

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Eutrophication

3.1.2 Nitrogen

Nearly 80% of the atmosphere is nitrogen. Despite the huge supply potentially available, nitrogen gas is directly available as a nutrient to only a few organisms.

  • Why cannot the majority of organisms utilize gaseous nitrogen?

  • Nitrogen gas is very unreactive and only a limited number of bacterial species have evolved an enzyme capable of cleaving the molecule.

Once 'fixed' by these bacteria into an organic form, the nitrogen enters the active part of the nitrogen cycle. As the bacteria or the tissues of their mutualistic hosts die, the nitrogen is released in an available form such as nitrate or ammonium ions - a result of the decay process. Alternatively, the high temperatures generated during electrical storms can 'fix' atmospheric nitrogen as nitric oxide (NO). Further oxidation to nitric acid within the atmosphere, and scavenging by rainfall, provides an additional natural source of nitrate to terrestrial ecosystems. Nitrates and ammonium compounds are very soluble and are hence readily transported into waterways.

Nitrogen is only likely to become the main growth-limiting nutrient in aquatic systems where rocks are particularly phosphate-rich or where artificial phosphate enrichment has occurred. However, nitrogen is more likely to be the limiting nutrient in terrestrial ecosystems, where soils can typically retain phosphorus while nitrogen is leached away.

S216_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371