L4 - Nutrient cycling, nitrogen and phosphorus Flashcards
Why is nitrogen (N) essential for living organisms?
N is a key component of amino acids and nucleic acids (DNA and RNA)
What is phosphorus (P) critical for in organisms?
P forms the structural link in genetic material and is essential for producing Adenosine Triosphosphate (ATP), the energy currency of calls
What are the unreactive and reactive forms of nitrogen?
Unreactive form: N2 gas (78% of the atmos with a triple covalent bond)
Reactive forms: Organic N (found in tissues like DNA and proteins)
Inorganic N (ammonia, ammonium, nitrite and nitrate)
Why is N2 gas unavailable to most living organisms?
N2 gas is chemically inert and cannot react with biological forms, making it inaccessible for use without biological nitrogen fixation
what is the most oxidised form of nitrogen in lakes?
Nitrate (NO3) which is abundant and used by bacteria, fungi and plants
how does phosphorus enter freshwater ecosystems?
through external loading (e.g. weathering of rocks, fertilisers and detergents) and internal loading (e.g. nutrient cycling from sediments)
what are common sources of nitrogen and phosphorus in freshwater systems?
Nitrogen: rainfall, atmospheric deposition, fertilisers, fossil fuel combustion and wastewater
Phosphorus: weathered rocks, human pollution (e.g. detergents and fertilisers)
what organisms fix atmospheric nitrogen (N2)?
Diazotrophs such as bacteria, azotobacter, rhizobia and cyanobacteria, using heterocysts under anaerobic conditions
what happens during nitrogen fixation
PHASE 1: N2 gas is converted to ammonium (NH4+) is oxidised to nitrite (NO2) by nitrosomonas bacteria
PHASE 2: Nitrite is oxidised to nitrate (NO3) by nitrobacter bacteria
What is denitrification
the process where nitrate (NO3) is reduced back to N2 gas by denitrifying bacteria (e.g. pseudomonas) in anaerobic conditions
how is ammonium (NH4+) converted in the nitrogen cycle
it is directly converted to nitrate (NO3) by decomposers or undergoes nitrification to form nitrite (NO2) and then nitrate
why is P growth-limiting in freshwater systems?
it is often bound to soil and rock, and its biologically available forms (e.g. PO4) are released in small amounts through rock weathering.
how is P recycled in ecosystems?
through decomposition, where organic P dissociated into inorganic forms, making it available for plants, fungi and bacteria
what are the main challenges of increased nitrogen and phosphorus in ecosystems
SPECIES SHIFT - including harmful algae blooms causing aesthetic and ecological issues
INCREASED ORGANIC MATTER REDUCES WATER CLARITY - lowers oxygen levels, and harms aquatic life
how can nitrate (NO3) be removed from water systems?
through wastewater treatment and wetlands, where anoxic conditions encourage denitrification
