ACID PRECIPITATION
At the end of the 1800's you could notice the
effects of acid precipitation ("acid rain") in the south of Norway. The
catch of salmon gradually failed, and dying of other species of fish in
certain lakes was observed.
Due to two main reasons, Arendal and the rest
of southern Norway are especially affected by the acid
precipitation:
- The precipitation is brought by winds that
have passed the industrial areas in England and Central-Europe. When
these winds reach Norway, the acid rain will mostly fall down in our
part of the country. Actually, more than 90% of the acid rain in
Norway is caused by emissions from other countries.
- The ground in our region is hard and has a
lack of lime, and the layer of soil is thin. Therefore the soil has
little capability to neutralise the acid rain.
The causes of acid rain
We know that since the 1800's, the amount of
acid precipitation has strongly increased. More than 90% of the salmon
tribes have been eliminated in southern Norway, and 3 of 4 lakes are now
out of fish. The acid rain results in an increase of aluminium dissolved
from the ground. Experiments have shown that certain aluminium compounds
sticks to the gills of fish and thereby reduces the capacity of oxygen
exchange, leading to suffocation of fish.
Fortunately, the emissions from the
industrial areas of Europe have been reduced, and this has lead to a
decrease of acidity in the rain. Europe's emissions of sulphur have
nearly been halved. This has led to a reduction of 70% in the sulphur
part of the acid rain, while the precipitation of acid compounds due to
the emission of nitrogen compounds still is on a high level. In Lake
Rore, the nitrate content has doubled since the early 1960's, but has
not reached critical values.
Liming reduces the effects of
acidity
The only way to reduce the acidity in fresh
water is to add lime. The acid components are neutralised by the
lime.
The liming of the watercourse of Tovdal and
Nisser are two of the world's biggest liming projects. The results are
good. The salmon stock has increased several places, i.e. in
Nidelva.
The quality of the water in Lake Rore has
been improved by the liming of the two inflow rivers. The pH-value has
increased and the content of poisonous aluminium in the raw water has
decreased.
In the counties of Aust- and Vest-Agder there
are several organisations working on problems caused by acid
precipitation.
RUNOFF WATER FROM AGRICULTURE.
As a whole, this is not a big problem in the area of Arendal.
However, there are some places with runoff, which leads to
eutrophication of lakes and watercourses. The definition of
eutrophication is an increase of nutritive substances to a water
recipient, and the results of this increase. The most important
nutrients coming with the runoff water are nitrate and phosphate.
You would think this as a good thing, because more plants and algae
will grow and supply oxygen to the water. However, when the plants die
and sink to the bottom, bacteria break down the dead plants. During this
process the dissolved oxygen in the water can be so low that fish and
other animals near the bottom might die.
Sources to runoff problems:
- Natural processes in the fields cause most of
the runoff from the agriculture.
- Additional runoff comes from the grass tanks,
excessive use of fertilisers and from milking rooms. In Arendal, the
Moland- and Longum- watercourses (which are located in agricultural
areas) are effected by this runoff.
- Settlements. Usually caused by leaks in the sewage pipes.
In addition the landfill in Heftingsdalen may cause runoff problems.
Normally the runoff from here goes to the wastewater network, but a few
smaller overflow accidents have occurred.
Precautions to reduce the runoff to Lake Moland:
- Reduce the plowing in the fall.
- Establish protecting zones along the lakes
and the rivers.
- Better fertilising planning.
- Improve the standards on livestock manure
basements and the grass tanks.
- Find better solutions to avoid the emissions from households close
to the watercourse.
INDUSTRY AND OIL POLLUTION, A MINOR
PROBLEM.
The industrial pollution in Arendal is relatively low. However, a
former nitride plant at Eydehavn dumped for several years tar from the
processing of electrodes. Thus, aromatic hydrocarbons were sent to
dumping sites on land and into the sea. Some of this has accumulated in
the bottom sediments in Tromoysund.
Small amounts of aromatic hydrocarbons have also been observed in the
bottom sediments in Lake Moland and Lake Longum.
CAPACITY PROBLEMS MIGHT LEAD
TO RESTRICTIONS
:
In the summertime, the consumption of water
for the watering of gardens is high. At times the capacity of the water
network can not meet this demand. Therefore, watering restrictions are
imposed nearly every summer. Each subscriber of water is allowed to
use one garden water hose only in the evening, twice a
week.
POSSIBLE TECHNICAL FAILURE DEMANDS A SECURITY
SYSTEM.
The old waterworks are maintained, and they
function as a reserve delivery system of water. In addition, the
installation of an emergency electric power system at the new treatment
plant at Rore will secure the delivery of water.
