Environmental Engineering Reference
In-Depth Information
1966
100
United Kingdom
The Netherlands
Sweden
Australia
10
1.0
0.1
0
50
100
150
200
250
300
350
Distance from the sea (km)
Fig. 3.1
Chloride concentration in precipitation in
relation to distance from the coast (after Voigt 1980).
1mgl
−1
between coast and inland (Fig. 3.1). In more
human-affected landscapes air transport of pollutants
has become an important issue as well. Examples
include the transport of sulphur dioxide and mineral
nitrogen from industrial and agricultural sources,
but also the transport of radioactive gases after the
accident at Chernobyl in the former USSR. Distances
covered by wind transport can be large. The acidifica-
tion of Scandinavian lakes through the deposition
of sulphuric acids is mainly caused by industrial emis-
sions in western Europe, a distance of 500 -1000 km!
(Fig. 3.2). Not only can the distance covered be
significant, but also the quantity of material transported
by wind. Nitrogen deposition in the Netherlands has
increased from
c
.5 kg ha
−1
yr
−1
under natural con-
ditions to over 30 kg ha
−1
yr
−1
at present (see the
Dutch Rijksinstituut voor Volksgezondheid en Milieu
(RIVM) environmental data compendium at http://
arch.rivm.nl/environmentaldata). In nutrient-poor
soils this source accounts for more than 25% of the
nitrogen in the system (Verhagen
et al.
2003) and goes
beyond critical loads (Achermann & Bobbink 2003).
500 km
Fig. 3.2
pH of precipitation over Europe in 1966.
(after Likens
et al
. 1972). Reproduced by permission of
Helen Dwight Reidd Educational Foundation.
on the spatial structure of landscapes. For the Earth
as a whole the exchange between atmosphere and con-
tinents amounts to 106
10
12
kg of water yr
−1
while
about two-thirds (69 × 10
12
kg) of this precipitation
returns directly to the atmosphere by evaporation. The
remaining precipitation surplus of 37 × 10
9
m
3
yr
−1
is
divided very unevenly over the Earth but in most areas
there is - at least temporarily - water flow towards
seas and oceans. This flow can take place either
through rivers and lakes as surface water or through
the soil as groundwater. Eventually, the large major-
ity of groundwater flows do also discharge in surface-
water systems but this route may take a long time,
often centuries and sometimes even millennia. In the
meantime these systems may sustain wetlands outside
the limits of areas that are flooded regularly with sur-
face water. The size of groundwater systems differs
greatly from catchment to catchment and depends both
on the topography and the permeability of geological
strata, but most systems are at least several square kilo-
metres in size. Groundwater flow, especially in cases
×
Water flow
Only a minimal part of all the water on the planet
is found in the atmosphere and on the continents
(Table 3.1) but water is at the same time indispens-
able for all terrestrial life forms and has huge effects
