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Unformatted text preview: 4C] in
atmosphere should ... decline 1 4C How do we know that it is anthropogenic factors?
Model predictions based on...
natural factors only combination of natural and
anthropogenic factors anthropogenic factors only Nitrogen:
Atmosphere is largest reservoir (78% of atmosphere is N), but....
... inaccessible for most organisms
N enters cycle only via
micro-organisms or lightning
N2 ➡ NH3 ( Ammonia)
free-living bacteria, cyanobacteria;
symbionts (e.g., legumes, alders) Rhizobium
(cyanobacteria + fungi) atmospheric ﬁxation:
N2 ➡ NO, dissolve in water
& form nitrates
(5-8% of total ﬁxation) Nitrogen cycle Atmosphere
N 2, N2 ➡ Organisms
Plants NO Denitriﬁcation Fixation
N H3 N 2 ➡ N O NO3- specialized bacteria, Nitrate
(esp. in ocean, wetlands)
removal of excess nitrate from groundwater
(excessive agricultural or residential
fertilizer) => sewage treatment, wetlands NO2Nitrite Decay
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