Chapter 13 - Energy + productivity- (13.5) Environmental issues concerning nitrogen-containing fertilisers Flashcards
How does nitrogen increase plant growth?
Nitrogen is an essential component of biological molecules such as proteins and is needed for growth and therefore to increase in the area of leaves.
Increases the rate of photosynthesis and improves crop productivity.
What are the three main effects of using nitrogen-containing fertilisers:
Reduced species diversity: This is because nitrogen-rich soils favour the growth of grasses, nettles and other rapidly growing species. These out compete many other species. which die as a result. Species-rich hay meadow only survive when soil nitrogen concentrations are low enough to allow other species to compete with the grasses - without any additions of n-containing fertiliser.
Low species diversity in a field grown for silage ( corn) that used n-containing fertiliser.
Leaching: which may lead to pollution of watercourses
Eutrophication: caused by leaching of fertiliser into watercourses
What is Leaching?
Leaching is the process by which nutrients are removed from the soil.
Rainwater will dissolve any soluble nutrients, such as nitrate ions, and carry them deep into the soil, eventually beyond the reach of plants roots. The leached nitrate ions find their way into watercourses, such as streams and lakes that in turn may drain into freshwater lakes.
Due to this they may have a harmful effect on humans if the river or lake is a source of drinking water. Very high nitrate ion concentration in drinking water can prevent efficient oxygen transport in babies and a link to stomach cancer in humans has been suggested.
The leached nitrate ions are also harmful to the environment as they can cause eutrophication.
What is Eutrophication?
Eutrophication is the process by which concentrations increase in bodies of water.
It is a natural process that occurs mostly in freshwater lakes and the lower reaches of rivers.
What are the following events of Eutrophication?
In most lakes and rivers there is naturally a low concentration of nitrate and so nitrate ions are the limiting factor for plant and algae growth.
As the nitrate ion concentration increases as a result of leaching it ceases to be a limiting factor for the growth of plants and algae whose populations both grow.
What is the ‘algal bloom’
As algae mostly grows at the surface, the upper layers of the water become densely populated with algae.
What occurs from this occurence of algae?
The dense layer of algae absorbs light and prevents it from penetrating to the lower depths of the water.
Light then becomes the limiting factor for the growth of plants and algae at lower depths and so they eventually die.
The lack of dead plants and algae is no longer the limiting factor for the growth of
saprobiontic bacteria and so these populations too grow, using the dead organisms for food.
The saprobiontic bacteria requires oxygen for their respiration, which creates an increase demand for oxygen.
The concentration of oxygen is reduced and nitrates are released from decaying organisms.
Oxygen then becomes the limiting factor for the population of aerobic organisms, such as fish.
These organisms will die as the oxygen is all used up.
Without the occurrence of aerobic organisms, there is less competition for anaerobic organisms who population now rise.
The anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes, such as hydrogen sulphide, which make the water putrid (decaying/rotting)
