Nitrogen Cycle Flashcards
List the N-cycle processes
N2 fixation (biological and chemical), Ammonification, Nitrification, Denitrification, ANAMMOX reaction
What are the different forms of nitrogen
- N2 atmosphere: largest pool but biologically inactive (in air 78.1% by volume)
- Organic matter (detritus or living organism) in soils and aquatic systems: amino acids, proteins, bases of nucleic acids (adenine, quinine, cytosine, thymine, uracile)
- Inorganic nutrients in atmosphere, soils, and aquatic systems: NO (gas), N2O (gas), NO2-, NO3-, NH4+ and NH3 (gas)
General description of methodologies used to determine N-fluxes
Methods for measuring DIN(dissolved inorganic nitrogen)
- There are quick and cheap methods but less accurate like test strips, test kits, and color discs. There are more expensive methods which are more accurate like specific electrodes, ion chromatography and spectrophotometric methods.
Analysis of N concentration and isotopic ratios
- While measuring the concentrations of particulate and dissolved nitrogen in organic and inorganic fractions is important in order to assess the level of water quality and determine permissible values, the use of nitrogen isotope ratio helps to refine these measurements in order to:
- Understand the origin of nitrogen pollution
- Specify the importance of the microbial processes responsible for this pollution
- Quantify them
Measuring N-fluxes using 15N tracers in aquatic systems
- Tracer experiments – in which a quantity of isotopically enriched material is added to a system of interest and its fate is observed. Because tracers increase analytical sensitivity, often by several orders of magnitude, they allow the measurement of processes that are difficult or impossible to measure without them.
Possible impacts of nitrogen deposition
Ecosystems: Nitrogen additions to land and oceans can reduce species diversity and modify ecosystems. Direct exposure to toxic algae (toxins that are detrimental to fish and other animals, blocking out sunlight and clogging fish gills), Dead zones and hypoxia (areas in water with little or no oxygen), Acid rain (HNO3, HNO2), Air pollution (NO2-)
Precipitation: Nitrogen oxides react with water to form nitric acid, which along with sulfur dioxide is a major component of acid rain. Acid rain can damage and kill aquatic life and vegetation, as well as corrode buildings, bridges, and other structures.
Air quality: High concentrations of nitrogen oxides in the lower atmosphere are a precursor to tropospheric ozone, which is known to damage living tissues, including human lungs, and decrease plant production.
Water quality: Adding large amounts of nitrogen to rivers, lakes, and coastal systems results in eutrophication, a condition that occurs in aquatic ecosystems when excessive nutrient concentrations stimulate blooms of algae that deplete oxygen, killing fish and other organisms.
Human Health: direct exposure to toxic algae (rashes, stomach or liver illness, respiratory problems, neurological effects), nitrates in drinking water (binding to hemoglobin)
Economic: Drinking water costs, Tourism losses, Commercial fishing and shellfish losses, Real estate losses (clean water)
Major sources of N inputs to water bodies
soil leaching, N2 fixation, wastewater or sewage, atmospheric deposition
Atmospheric deposition: source of oxidised and reduced N forms (NOx and NH3) = importance linked to industrialization, intensive farming (animal breeding) and climate (rainfall and winds)
Fertilizers: through agriculture, strong regional differences
Sewage input: untreated wastewater has particulate and dissolved organic matter (organic N). Treated wastewater includes different form of N at different stages of treatment
Description of N-retention mechanisms
Nitrogen retention is of particular interest because it is through its combined processes (denitrification, nitrogen sedimentation and uptake by aquatic plants) that local and downstream nitrogen concentrations are reduced.
Countering nitrogen pollution in a cost-effective way requires a threefold approach:
- Implement impact-pathway analysis to better managing the risks of air, soil, water and ecosystem pollution
- Manage nitrous oxide as part of greenhouse gas mitigation policies
- Monitor and manage any residual nitrogen excess by measuring the effect of the above measures on the national budget
Describe N2 fixation
Biological: free nitrogen N2 which is a relatively inert gas plentiful in air, to combine chemically with other elements to form more-reactive nitrogen compounds
- Organic N can be produced by various microorganisms (mainly bacteria and cyanobacteria). This reaction is extremely energy consuming reactions - 12 to 15 mol of ATP are required for the reduction of 1 mol of N2. The produced ammonia is assimilated to organic N. When other more “usable” (demanding less energy to be assimilated) N sources are available (like NH4+, NO2-, NO3-), N2 fixation will not occur. Most N2 fixation will occur in oligotrophic (low concentration of N-nutrients) environments
Chemical: Chemical fixation of N2 produces inorganic nitrate, nitrite, and ammonium. This reaction occurs naturally in the atmosphere and is induced by man during artificial combustion processes and in the production of fertilizers. When there is a high energy source like lighting, fossil fuel burning, it splits the N2 bond and reacts with oxygen
Describe ammonification
Ammonification: transformation of organic N into ammonium after the death of organisms, mediated by bacteria and fungi. Large molecules are “cut” into amino acids (smaller units) and transported inside the cell where they are mineralized to ammonium. This is an “oxygen consuming” process. Mineralization produces energy that is used by heterotrophs to grow.
Describe nitrification and denitrification
Nitrification: oxidation of ammonium into nitrite and nitrite into nitrate. This reaction is mediated by nitrifying bacteria.
Denitrification: Transformation of nitrate into N2, strictly anaerobic conditions. Bacteria mineralize (oxidize) organic matter using nitrate as final electron acceptor. Denitrification is an important way for reactive terrestrial nitrogen to be lost to the original atmospheric N2 pool.
Describe the ANAMMOX reaction
Denitrification with NH4+ as electron donor (instead of organic matter). Significant in systems receiving treated wastewater effluents that are rich in ammonium and in nitrate. Can be used in tertiary ww treatment processes.
- pros: oxygen addition can be reduced (results in energy and cost savings), Anammox bacteria do not require organic carbon as they do in nitrification, Production of excess sludge is reduced, Reduces CO2 emissions
- cons: Not a lot of knowledge available (skilled operation and maintenance required), High construction costs if the Anammox process replaces the conventional nitrification/ denitrification in treatment plants, Slow process
