An Introduction to Environmental Chemistry

The Baltic contrasts with the nearby North Sea, where oxygen concentrations

rarely fall to low levels, despite large inputs of nutrients. This is because the

North Sea is shallow and its waters exchange freely with those of the North

Atlantic providing a constant supply of oxygen-rich surface water to the North

Sea deeper waters.

234 Chapter Six

1958 1963 1968 1973 1980

Year

4

3

2

DIP ( 1

mmol l

N –1)

Germany Poland

Baltic Sea

Denmark

Gulf of Finland

BothnianFinland

Bay

Norway

Sweden

Skagerrak

Katte-

gat

Bothnian

Sea

1900 1920 1940 1960 1980

0.4

0.2

O^2    0

(mmol l

–1) O 2

HS–

Year

Fig. 6.30Oxygen and phosphorus concentrations in the Baltic Sea. Dark line through data is

a regression line and thin line marks zero O 2 concentration. DIP, dissolved inorganic

phosphorus. Data plots after Fonselius (1981) and Nehring (1981), with permission from

Elsevier Science.