An Introduction to Environmental Chemistry

controlled to limit algal growth in the receiving waters, even though the need for

this strategy arises from nitrate enrichment.

Nitrogen

Nitrogen (N) chemistry and cycling (Fig. 5.12) is complex because nitrogen exists

in several oxidation states (see Box 4.3), of which N(0) nitrogen gas (N 2 ), N(3-)

166 Chapter Five

1000

100

10

1

0.1

1 0.3 3 30

Total phosphorus

(mmol l–1, log scale)

Chlorophyll

a (

mg l

–1

, log scale)

Fig. 5.11Relationship between summer particulate chlorophyll alevels (as a measure of

phytoplankton abundance) and total phosphorus concentrations in various lakes, with data

plotted on log scales. After Moss (1988).

Phytoplankton Death/Cell lysis

NO– 2

Organic matter

(particulate and

dissolved)

Nitrogen

fixation

N 2 (N 2 O)

Oxidation Oxidation

NH 4 +

Oxidation

Denitrification

NO 3 – Photosynthesis

Fig. 5.12Nitrogen cycling in natural waters.