Biogeochemical Cycles HL – Nitrogen and Phosphorous

The Nitrogen Cycle http://cahnrs.wsu.edu/alumni/wp-content/uploads/sites/3/2011/10/nitrogen-cycle.jpg

Nitrogen Fixation http://www.micropia.nl/ While the atmosphere is 72% nitrogen gas (N2), plants cannot take up this form of the molecule. Process of converting atmospheric nitrogen into ammonia (NH3) which can be absorbed by plants Azotobacter and Rhizobium Rhizobium has a mutualistic symbiotic relationship with the roots of certain plants (legumes) Nitrogen is fixed by Rhizobium and the plant gives it carbohydrates

Nitrification Conversion of ammonia to nitrate Nitrosomonas convert ammonia to nitrite (NO2-) These are chemoautotrophs: they oxidize ammonia to produce energy resulting in nitrite. This energy is then used to fix carbon dioxide into organic carbon. Nitrobacter converts nitrite to nitrate (NO3-) Also chemoautotrophs, but they derive energy from nitrite for carbon fixation. Nitrate produced is available to be used by plants.

Denitrification Conversion of nitrate to nitrogen (via reduction) Pseudomonas denitrificans Only occurs in the absence of oxygen because bacteria will use nitrate as the final electron acceptor when oxygen is not available This process reduces the availability of nitrogen to living things Waterlogging (flooding, overwatering, etc.) can lead to this process

The Phosphorous Cycle http://reefkeeping.com/issues/2006-08/cj/images/image003LG.jpg

The Phosphorous Cycle Short term cycle Long term cycle Phosphorous is needed for many molecules (ATP, DNA, cell membranes) and is readily taken up into plants from the soils Long term cycle Much phosphorous is stored in rocks and is only slowly released into the environment through processes like weathering; thus, there is a relatively low turnover rate

Agriculture While phosphorous is naturally found in soils, it is often a limiting factor Farmers often add phosphorous through the use of fertilizers Phosphate is mined for the purpose of creating fertilizers Phosphate is a finite resource because most of it is found in our rock layer. This is of concern as it may limit our ability to continue to create the same crop yields.

Eutrophication Nutrient enrichment can lead to eutrophication Extra nutrients in water lead to algal growth which blocks the sun for plants below. Death of algae and plants leads to an increase in the amount of bacteria which are decomposing the dead material. These bacteria have high BOD (biological oxygen demand) which leads to less oxygen being available in the water for other living things

Eutrophication Waterlogging and poor irrigation leading to run-off events often cause this issue Phosphates can dissolve into the water Run-off takes phosphates to new locations Fertilizers, animal wastes and release of sewage are major contributors