Analyse how human activities alter nitrogen stores and flows, then trace the resulting effects on ecosystems and compare nitrogen with carbon-cycle changes.
Explain how human activities can impact the nitrogen cycle.
Humans can impact the N cycle in a number of ways:
a. Burning fossil fuels releases nitrogen oxides into the atmosphere;
b. ...these oxides react with water to form nitric acid, which precipitates as acid rain;
c. Acidification / plastic/heavy metal/PAH/pesticide pollution of soils damage soil microbiota responsible for nitrogen cycling;
d. Deforestation/harvesting removes plants/animals from the environment as stores of organic nitrogen / can result in runoff/leaching of nitrogen into waterways / decreases dead organic material (which contains proteins) to be decomposed/;
e. Afforestation increases stores of organic nitrogen / increases organic material (containing nitrogen) to be decomposed;
f. Humans release nitrogenous waste entering environments through sewage effluent;
g. Inorganic fertilizers applied to crops, enter water bodies through runoff and leaching/cause eutrophication;
h. Haber(-Bosch) process fixes atmospheric nitrogen into ammonia to synthesize inorganic fertilizers;
i. Eutrophic waters develop nitrogen rich sediment that, through upwelling/positive feedback, repeats eutrophic event;
j. Overgrazing/mechanisation can cause compaction of soils damaging nitrogen-cycling microbiota;
k. Planting leguminous crops increases stores of nitrates in soils / through biological nitrogen fixation (Rhizobium living in root nodules);
I. Sustainable farming techniques / e.g.no/reduced tillage/mulching/cover crop/crop rotation enhances N retention in topsoil (reduces erosion) / increases microbial decomposition (through improved soil structure/moisture);
m. Intensive/industrial animal production systems emit nitrous oxides/ammonia to environment;
Note to examiners: Accept any other human activity along with valid and significant impact