Environmental Engineering Reference
In-Depth Information
90
60
Nitrate- pristine groundwater
30
0
1200
60
Nitrate- stream influenced by cropland
D ischarge
50
800
40
30
400
20
10
0
0
1996
1997
Year
FIGURE 13.5 Concentrations of nitrate in groundwater flowing from undisturbed prairie
(top, solid line), nitrate in Kings Creek, Kansas (bottom), and discharge in Kings Creek. High
nitrate is related to input of groundwater from under fertilized cropland that dominates dur-
ing periods of low discharge, not nitrate variations in groundwater from under prairie (data
courtesy of Konza Prairie Long-Term Ecological Research site).
tion of nitrate in streams can be large, given the complex interactions be-
tween precipitation and groundwater sources (Fig. 13.5), whereas concen-
trations in groundwaters may be more stable. Understanding processes that
control nitrate in streams generally requires understanding nitrogen dy-
namics in the surrounding terrestrial ecosystem. For example, riparian
zones decrease inorganic nitrogen and increase the ratio of NH 4 :NO 3 in
watersheds of the Amazon (McClain et al., 1994).
Oxic processes
Lightning,
Industrial fertilizer
production
Remineralization
Nitrification
N 2
Heterotrophy
As si m ilation
Ammonium
Assimilation
Nitrite
Assimilation
Nitrate
NO 3 -
Organic N
NH 4 +
NO 2 -
Dissimilatory reduction
Fermentation
Nitrous oxide, N 2 O
Nitrogen fixation
Denitrification
Nitrogen gas, N 2
Anoxic processes
FIGURE 13.6
A conceptual diagram of the nitrogen cycle.
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