Environmental Engineering Reference
In-Depth Information
1960
1999
2002
Aralsk
KAZAKHSTAN
NORTH
ARAL SEA
dam
dam
SOUTH
ARAL SEA
ARAL SEA
Muynak
UZBEKISTAN
100 km
Fig. 3.5
The changed shape of the Aral Sea since 1960 (from Jones 2003). Reproduced by permission of
New Scientist
.
growth. Examples can be found in the south-western
USA where water from the Colorado River is used for
irrigation so intensively that the river dries up com-
pletely before it reaches the Salten Sea. Another,
well-known example is that of the shrinking Aral Sea
(Jones 2003; Fig. 3.5). In recent times there is also a
development towards transporting water to areas
where there are only temporal water shortages, i.e. dur-
ing the dry season. For example, in the Netherlands
huge canals enable the transport of water from the
River Rhine to all corners of the country in order to
optimize conditions for crop growth throughout the
year. The impact this may have on the re-arrangement
of aquatic plant and animal communities is still
largely unexplored; see also Chapter 11 in this volume.
Not only a redistribution of water, also the use of
fertilizers has enabled an enormous increase in crop
production in previously marginal areas. The average
nitrogen gift in the Netherlands increased from
15 -30 to 150 kg ha
−1
yr
−1
between 1900 and 1960 for
meadows (Bakker & Olff 1995) and from 200 to
450 kg between 1950 and 1985 for intensively used
arable fields (Keuning 1994). The same trend can be
witnessed all over western Europe and resulted on
average for the whole European Union in a product-
ivity increase in commercial crops of 1.9% ha
−1
yr
−1
between 1950 and 1991 (Strijker 2000). The effects of
these developments are not restricted to agricultural
areas; the yearly nitrogen load from agricultural
sources into the River Rhine at the German-Dutch
border has increased from
c
. 100 × 10
6
kg of N in the
period 1954-7 to more than 150
10
6
kg of N in the
period 1993-5 (Behrendt 1997). Similar developments
also occurred in other parts of the western world.
Despite its dry climate and nutrient-poor soils, Israel
has become one of the world's major exporters of
citrus fruits due to an improved water redistribution
and nutrient application. At the same time this has
led to a severe pollution of groundwater and created
large problems for the production of drinking water
(Ronen & Magaritz 1991).
In densely populated regions deliberate transport of
matter is probably quantitatively more important
than natural flows. As a result, natural differences
between landscapes fade away and the boundaries
between different areas of countryside become
increasingly blurred. Broadly stated, organisms that
are adapted to moist and eutrophic conditions are
×
