Flashcards in Environmental issues of nitrogen-containing fertilisers Deck (10):
What happens in natural ecosystems?
-in natural ecosystems minerals such as nitrate ions, which are removed from the soil by plants are mainly returned when the plant is decomposed
-however in artificial systems the crop is removed and so the nitrate is not returned an has to be replaced
-this is done by the addition of natural or artificial fertilisers
What are the effects of nitrogen-containing fertilisers?
-nitrogen is an essential component of biological molecules such as proteins and is needed for growth and therefore an increase in the area of leaves
-this increases the rate of photosynthesis and improved crop productivity
-nitrogen-containing fertilisers have benefited us providing us with cheaper food
What are the detrimental effects of the use of nitrogen-containing fertilisers?
-reduces species diversity
How do nitrogen-containing fertilisers reduce species diversity?
-because nitrogen-rich soils favour the growth of gasses, nettles and other rapidly growing species
-these out-compete many other species, which die as a result
-species-rich hay meadows, only survive when soil nitrogen concentrations are low enough to allow other species to compete with these gases
What causes 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 plant roots
-the leached nitrate ions find their way into watercourses, such as streams ands rivers, that in turn may drain into freshwater lakes
-here they may have a harmful effect on humans if the river or lake is a source of drinking water
-very high nitrate ion concentrations 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 the process of eutrophication?
-in most lakes and rivers there is naturally very low concentration of nitrate and so nitrate ions are a limiting factor for plant and algae growth
-as the nitrate ion concentration increases as a result of leaching, it ceases to be a limitation factor for the growth of plants and algae whose populations both grow
-as algae mostly grow at the surface, the upper layers of water become densely populated with algae, this is called an algal bloom
-this dense surface layer of algae absorbs light and prevents it from penetrating to lower depths
-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 a limiting factor for the growth of saprobiontic bacteria and so these populations too grow, using the dead organisms as food
-the saprobiontic bacteria require oxygen for their respiration creating an increased demand for oxygen
-the concentration of oxygen in the water is reduced and nitrates are released from the decaying organisms
-oxygen then becomes the limiting factor for the population of aerobic organisms, such as fish, these organisms ultimately die as the oxygen is used up altogether
-without the aerobic organisms, there is less competition for the anaerobic organisms whose populations 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
Which factors contribute to eutrophication?
-ploughing old grassland
-leaching of artificial fertilisers is the main cause
What are troubled waters?
-a farmer applied a large quantity of fertilisers toil fields next to a small lake
-a period of heavy rain followed
-after 10 days, scientists monitoring the lake noticed changes to the algal population, the clarity of the water and the levels of dissolved oxygen