Environmental Engineering Reference
In-Depth Information
The impacts of overexploitation are sometimes coupled to harvesting techniques
that destroy habitat. A stark example is provided by the dynamiting of coral reef to
stun and collect fi sh. The effects of bottom trawling are less visible but may some-
times be equally destructive. Take the cold-water coral reefs that occur down to
depths of 3 km in the offshore waters of at least 41 nations. The technology to study
these in close-up recently became available, only to fi nd, for example, that heavy
trawling gear has already destroyed up to 40% of the reef off the west coast of
Ireland. Managers face the double task of developing harvesting policies that respond
to the risk of overexploitation and the threat of physical damage to habitat.
1.2.7
Habitat
degradation - laying
waste
Like the other drivers of biodiversity loss, degradation of habitat by human pollut-
ants continues to show an alarming increase. The chemicals that we release into the
atmosphere return to Earth as gases, particles or dissolved in rain, snow and fog.
But in the process the pollutants may be carried in the wind for hundreds or thou-
sands of kilometers. Sulfur dioxide (SO
2
) and oxides of nitrogen (NO
X
) (associated
with the burning of fossil fuels) interact with water and oxygen in the atmosphere
to produce sulfuric and nitric acids, creating atmospheric pollution which falls as
'acid rain'. Rainwater has a pH of about 5.6, but pollutants lower it to below 5.0 and
values as low as 2.1 have been recorded in various industrial areas of the world.
Acid rain acidifi es the water in lakes and streams, and many species of algae, inver-
tebrates and fi sh cannot tolerate the extreme conditions. Forest trees can be affected
just as badly. Other atmospheric pollutants, including the carbon dioxide produced
by the burning of fossil fuels, are now known to cause disturbingly far-reaching
climatic effects, with expected changes to global patterns of temperature and pre-
cipitation. This will be dealt with in Section 1.2.8.
Our dependence on fossil fuels has other consequences too. More than 4 million
tonnes of oil fi nd their way into waterways every year, some seeping naturally from
the ocean fl oor, some from industry, and a large proportion from oil wells and oil
tankers. Oil prevents light from reaching aquatic plants and reduces aeration of the
water, with adverse effects for seaweeds and invertebrates such as molluscs and
crustaceans. Feathers of seabirds become choked with oil and fi sh gills cease to
function. The infamous incident in 1989, when the oil tanker
Exxon Valdez
ran
aground in Alaska, spread oil along the coast for a thousand kilometers, contaminat-
ing the shores of state parks and other protected areas, and killing an estimated 300
harbor seals, 2800 sea otters and 250,000 birds.
Among the various categories of habitat degradation, agricultural development is
set to pose the greatest problems in future. Between 3 and 6% of natural ecosystems
around the world have been converted to agriculture since 1950, and this has con-
sequences both for natural habitat loss and for the pollution and degradation of what
remains. The scale of the problem is not uniform. As our use of habitat becomes
ever more intensive (from protected land, through light grazing of natural grass-
lands, to cultivation and urban development), biodiversity loss increases for all
animal and plant groups (Figure 1.12).
Increasing agricultural intensity is associated with increases in soil erosion, sali-
nization (loss of productive capacity because of salt intrusion) and desertifi cation,
and with increased removal of surface and ground water for irrigation. River fl ow
has been reduced so dramatically that, for example, the Nile in Africa, the Yellow
River in China and the Colorado River in North America, for parts of the year dry
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