Dynamics - Nitrogen Flashcards
What are the form of nitrogen in waters?
Dissolved molecular N2
Organic compounds
Nitrite, ammonia and nitrate
What are the deposition pathways of nitrogen into water?
Nitrogen fixation
Precipitation
Deposition of groundwater drainage
How is nitrogen lost?
Conversion into N2 by denitrification
Permanent sedimentation loss
Outflor from the basin
Prominent source of nitrogen…
Direct terrestial runoff
What is most atmospheric nitrogen in the form of?
Ammonia.
Where is N2 foudn mostly?
Colder waters, not water soluble.
Heterocysts
Differentiated cyanobacterial cells carrying out nitrogen fixation under aerobic conditions
How do cyanobacteria fixate nitrogen?
Heterocysts as filamentous cells with outrgwoths.
Denitrogenase Reductase
Transfers electrons from an electron donor to denitrogenase which then catalyses nitrogen reduction to ammonium
How does filamentous cyanobacteria form heterocysts?
Combined nitrogen present like nitrate or ammonium, whilst in absesne, heterocysts form in semi-regular intervals
What may destroy Nitrogenase?
Oxygen
How do nitrogenase prevent oxygen degradation?
Protection by microzone formation, redox conditions seperate of the surrounding water
How does turbulence reduce fixation?
Increasing diffusion
How are fixation rates based on lake type?
Low in oligo/mesotrophic whilst high in eutrophic (1-10% and 8-% nitrogen input rate for either)
What do N2 fixation enzymes requried?
Molybdenum and Iron trace elements thus higher fixation rates are dependent on these both
Molybdenum in oxygenated conditions…
Exist as molybdnate ions, where sulfate ions can competitvely inhibit fixation
What trees increase nitrogen levels?
Alnus and Myrica of trees bordering wetlands
Endophyte
An endosymbiont living within a plant for some part of its life cyycle without causing disases
Alnus and Myrica nitrogen fixation…
Fungi at or just below the soil
Where is alnus effective?
Glaciated regions in Alaska, where leaf litter nitrogen levels have 4x nitrogen levels
When are nitrogen fixation levels higher?
When phosphorous fertilization occurs
Fixation diurnal changes..
Maximises midday with maximum insolation…
Seasonal changes of nitrogen fixation…
Winters where CB are absent, so is nitrogen fixation
Fucntion of Mo in nitrogenase…
Cofactor catalysing redox reactions to convert N into ammonium ions.
