Nitrogen is an essential component of important substances such amino acids, proteins, and nucleic acids (deoxyribonucleic acids and ribonucleic acid).
In plants, much of the nitrogen is used in chlorophyll molecules necessary for photosynthesis and growth. The processes of the nitrogen cycle are important to convert gaseous nitrogen into forms that can be used by living organisms.
The cycling of nutrients such as nitrogen, carbon, phosphorus, iron, sulphur and silica is important in the aquatic environment enabling the continual availability of such nutrients for use by living organisms. Human influences on some nutrient cycles were also stated.
Human Influences on the Nitrogen Cycle
1. Large scale growing of legumes, fertilizers production, pollution by vehicles and industrial plants, have increasingly changed nitrogen into biologically-available forms.
2. Fertilizer application, burning of biomass, livestock feed lots and industry increase nitrous oxide (N2O) in the air. N2O breaks down ozone in the stratosphere. N2O in the atmosphere is a greenhouse gas and contributes to global warming.
3. Increasing ammonia in the air decreases air quality. It is converted to nitric acid (HNO3), a part of acid deposition.
Ammonia is also toxic in the aquatic system. Both ammonia and nitric acid in the air cause respiratory damage to living organisms.
4. Burning of fossil fuels, biofuel and hydrogen produce nitrogen oxides (NOx). NH3 and NOx are involved in lower atmospheric ozone production.
Carbon is needed for the formation of all organic matter. It is present as carbon dioxide (CO2), bicarbonate (HCO3-), carbonic acid (H2CO3) and organic compounds in aquatic systems.
The atmosphere and sedimentary rocks are the major stores of carbon. Large amount of carbon is present in the aquatic system in form of organic and inorganic carbonates.
Organic forms result from biological and chemical breakdown of plants and animals. Major inorganic forms are carbon dioxide, bicarbonate and carbonate.
Dead plants and animals are broken down by biological and chemical activities into inorganic carbon or can be converted to part of the sediment after partial decay.
Exchange between carbon dioxide in the atmosphere and water produces an equilibrium concentration of carbon in water.
Plants absorb inorganic forms of carbon (e.g. carbon dioxide, CO2) and in the presence of light convert them into organic compounds.
Plants need carbon dioxide for photosynthesis and get carbon directly from the air but non rooted aquatic plants get carbon dioxide directly from the water.
CO2 produced by plants and animals during respiration is absorbed by water but if concentrations are too high, water gives up carbon dioxide to the atmosphere.
Inorganic and organic forms of carbon can be exchanged between sediment and water. Carbonate rock stores carbon and when dissolved, helps to control the pH of salt and freshwater ecosystems.
Organic carbon is present on the bottom of lakes and oceans. Biological and chemical breakdown of the organic carbon adds carbon to the water column. Sinking of dead plants and animals contributes carbon to the sediments.
Burning of fossil fuels and deforestation disturbs the carbon cycle.