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Environmental monitoring in Africa


(*) Secretariat for International Ecology, Sweden (SIES) Sveavägen 166, 15th floor, S-113 46 Stockholm, Sweden.



According to a resolution in the U.N. General Assembly in December 1974, the Global Environment Monitoring System (GEMS) of the U.N. Environmental Programme should devote special attention to monitoring natural resources. Of importance in Africa is dust monitoring. Satellite imagery has shown that the African soil is blown away. The Sahel catastrophe was registered by dust in the West Indies. The ecological importance of this has not been investigated. In dry ecosystems, the nutrients and pollutants form dry sediments which are easily disturbed. In mining areas in dry regions, as in Zaire, Zambia and Botswana, heavy metals such as lead and cadmium might be accumulated in vegetation. A further accumulation may take place in grazing animals. Livestock industries must consider these risks. Special pilot projects should be developed to study these problems, both from the monitoring and the ecosystem points of view.

The word "monitoring" has different meanings, and it will be defined here as regular observations in a time series designed to give information about the environment so that past and existing states can be assessed and future trends predicted in any environmental features which may be important to man. This definition is partly from the report of a task force of the Man and the Biosphere (MAB) Programme dealing with monitoring research (MAB report 20).

From this definition it is clear that environmental monitoring must be problem-oriented. The problems must be important to man. These problems could be divided into three main categories:

1. Potentially adverse climatic changes resulting from human activities;
2. Potentially adverse changes in biota and man from contamination by toxic substances;
3. Potentially adverse changes in biological productivity caused by improper land use.

Those environmental parameters that describe and quantify these three problem areas can be classified under the following main headings:

1.a. Physical and chemical data from the atmosphere pertinent to climatic change potential,

b. Physical and chemical data from air, water soils, and biota pertinent to human health and welfare;

2.a. Physical, chemical, and biological data reflecting the state of human health.

b. Biological data reflecting the performance of biological systems.

In order to measure these variables, special monitoring systems must be set up. Recommendations for such systems were made to the 1972 U.N. Conference on the Human Environment held in Stockholm. Responsible for the global monitoring activities is the U.N. Environmental Programme (UNEP); and it has now been decided that a special Global Environmental Monitoring System, GEMS, should be established. An inter-governmental meeting on monitoring, convened by UNEP, was held in Nairobi during February 1974. The goals for GEMS were established as follows:

1. An expanded human health warning system;

2. An assessment of global atmospheric pollution and its impact on climate;

3. An assessment of the extent and distribution of contaminants in biological systems, particularly food chains;

4. An assessment of critical environmental problems related to agriculture and to land and water use;

5. An assessment of the response of terrestrial ecosystems to pressures exerted on the environment;

6. An assessment of the state of ocean pollution and its impact on marine ecosystems;

7. An improved international system allowing the monitoring of factors necessary for the understanding and forecasting of disasters and for the implementation of an efficient warning system.

At the same meeting a list of priority pollutants, starting with sulphur dioxide and radio-nuclides and followed by ozone and DDT, was accepted.

At the U.N. General Assembly at the end of last year, a resolution was passed that GEMS should not only concentrate on priority pollutants but should devote half of its capacity to monitoring the natural resources. This resolution was strongly supported by countries from the developing world.

In this paper I shall concentrate on aspects related to natural resources.

Imagery in Fig. 1 is taken from the geosynchronous satellite SMS 1 on July 8, 1974. It shows a large dust cloud over the Atlantic that left Africa on the 1st of July. The dust in the cloud is at a height of 3,0004,000 meters. Already in 1970 the Nimbus weather satellite picked up dust clouds over the Atlantic. The consequences of this dust transport from Africa over the Atlantic have recently been analyzed by Dr. Anders Rapp of the Secretariat for International Ecology, Sweden, in a report entitled "A Review of Desertization in Africa. Water, Vegetation, and Man". The facts presented here about the dust transport are from this report.

Fig. 1

Fig. 2

Dust fall into the Atlantic outside Africa has been known for a long time. Fig. 2 is a map of dust recorded by ships at sea based on data collected before 1942. In 1966, American scientists wanted to test clean air, and as a test site they picked Barbados in the West Indies. But the air was not clean; it contained dust transported by easterly winds. In 1966, the dust content was 6 micrograms per cubic meter. In 1967-68, it had increased to 8 micrograms. After 1968 it increased rapidly, and reached 15 micro grams in 1972 and 24 micrograms in the summer of 1973. Here is the Sahel catastrophe!

It is important however that the dust is not sand from the Sahara but African soil. During the summer months the dust is reddish-brown, probably coming from the northern margins of the Sahara; in winter the dust is black, coming from the burnt areas in the south. Deshler (1974) registered the extent of grass fires in the savannas of Africa along the southern side of the Sahara by using remote sensing and imagery from ERTS 1.

Fig. 3

Rapp has pointed out that it is possible to study erosion phenomena by using ERTS 1 imagery. This illustration shows erosion with loose sand dunes from Tunisia (Fig. 3). It is ERTS 1 imagery, processed in Sweden. The white ridge No. 3 corresponds to the dune in the previous picture. It has also been possible to trace the origin of specific dust storms from the Mojave Desert by using satellite imagery, as shown by Bowden et at. (1974). Thus, it should not only be possible to record the amount of dust blown away but also to pinpoint the location of origin.

Fig. 4

Rapp has worked out the amount of dust blown from Africa during the summer of 1969. For comparison it can be mentioned that the annual sediment transport in the Nile River has been estimated at 150-200 million tons at the inflow to Lake Nasser; they are of the same magnitude.

The conclusions in the SIES report were:

" The types, extent, and rates of desertization processes have to be surveyed and monitored in the future as a basis for both short-term and long-term actions against desertization and its destructive effects. "

In agreement with many authors and reports we strongly recommend careful sampling surveys on the ground combined with extrapolation using aerial photographs and satellite data. To such surveying/monitoring transects have to be added pilot trial plots for the purpose of research and demonstration of ecologically sound methods of land use in areas of potential or actual desertization.

Fig. 5

Recent discoveries show surprisingly large amounts and long transport distances of airborne soil dust from the Saharan and Sahelian zones into and over the Atlantic. This is probably the most destructive effect of desertization in a longer time perspective. We strongly recommend to UNEP and WMO to consider monitoring of airborne soil dust together with the use of satellite images, as an early warning system. Three suitable locations for ground stations would be:

1. The Cape Verde Islands (Sahelian west);

2. Jebel Marra Mountains, Sudan (Sahelian east);

3. Tenerife Island (northern Pre-Saharan belt of desertization).

SIES is now trying to formulate pilot projects to explore these possibilities, especially the technique for the measuring of dust.

Fig. 6

If one tries to assess the effects of this dust transport in Africa one must first consider the global aspects. It has been pointed out that increased turbidity in the atmosphere may be responsible for the present cooling of the earth that began about 1945. It was recently reported, for instance, that the snow and ice cover has increased by 12 percent during 196772 (G. and H. Kukla, 1974, Environmental Studies 6. 2/3, No. 79). Bryson pointed out that the increased turbidity was caused not only by industrial activities in temperate regions, but also to a large extent by improper land use in tropical and subtropical regions. It is thus reasonable to assume that the dust catastrophe in Africa must be studied when global climatic changes are considered.

The loss of topsoil is very important. It should be especially stressed that through water flow in arid areas the plant nutrients are placed in the surface layer. In this surface layer also are the microorganisms responsible for nitrogen fixation. However, the erosion process involves not only transportation but also sedimentation. The dry fallout over the Atlantic was shown in an earlier slide, and the sedimentation of nutrients over the Atlantic must be of importance for the productivity of the sea.

This dry fallout must also be of importance to the terrestrial ecosystems. It is well known that there is an accumulation of the dry sediment in vegetation, although very little is known about the importance of this redistribution of nutrients. It is also well known that the fertility of the Nile Basin depended on the sediment load brought by the annual floods. Some have now assumed that the fertility of the Nile Valley would decrease as the sediments accumulated in Lake Nasser. It has been claimed however that part of the fertility of the Nile Valley depends on nutrients blown in from the neighboring deserts. To verify this and to investigate the importance and the consequences of the sedimentation of wind-blown material must be regarded as very urgent in Africa. It is of special importance in relation to livestock problems. Here integrated ecosystem studies are needed to establish changes in productivity.

To follow changes in an ecosystem and to correlate these changes to productivity is difficult, as one must control both input and output. In humid areas, ecosystems in small watersheds can be used for such studies. Since water is the main carrier of nutrients to and from the watershed, this transport can be measured. The bio-geo-chemical processes can be studied in a limited, well-defined area. Such watersheds could be used not only for integrated studies of long-term trends but also for studies of short-term effects of human activities, such as clear cuttings.

In dry areas the boundaries of the local ecosystems are more diffuse. The wind as a transport medium is dominant. The unit is not the watershed, but the airshed. The airshed has more diffuse boundaries and is also in general much larger than the watershed. Studies of the ecology in such an area are more difficult to make and so far not very well developed. It is possible that the best results will be achieved by studies of transects through the air, which means studies over long distances. At every point in the transect both horizontal and vertical transport have to be followed.

There is a very close relationship between the use of natural renewable resources and pollution. The pollutant may decrease productivity by suppressing some vital processes; for instance, the acid rain over Europe may decrease the productivity in forests and fresh waters. The effects of the pollutants with the so-called biological magnification and their accumulation in the different compartments is well known in humid areas.

In Fig. 6 we see that the final sink for the pollutants is the sediment. The pollutants are trapped in the sediments and often sealed off. In certain cases the sediments are disturbed, and the pollutants get into circulation again. Pollutants following this pat tern are, for instance, the metals mercury, lead, and cadmium

Fig. 7

In a dry area the situation is quite different. The emissions are not washed out, but there is a dry fallout and sedimentation. These dry sediments are easily disturbed, especially by wind erosion, and pollutants again get into circulation. Fig. 7 shows erosion caused by overgrazing. These pollutants are accumulated in the grass and then finally deposited in the grazing animals.

This is a theoretical model, and very few investigations have been carried out to verify this model. We know some details well, however. It is known, for instance, that there is a dry fallout around industries emitting heavy metals. Well-established methods exist for the study of this phenomenon. It is even known that the pollutants can damage the vegetation. It is known that pollutants accumulate in grass and in grazing mammals. Thus the processes are known, but they have not been studied in a dry ecosystem.

However, are these speculations of any importance to Africa, where there are so few industries? I think that there may be a very real danger in relation to mining activities. In connection with copper mining, both lead and cadmium occur as emissions. In Zaire (Katanga), Zambia, and with the new mines in Selebi Pikwe in Botswana, these problems have to be watched. Emissions of heavy metals could thus be a very serious problem in range areas. Two effects must be considered: the productivity of the ecosystem is decreased and the quantity of the meat is affected by residues.

The pollutants and their interactions with dust particles carried by air are also important for man. Lead and cadmium especially may have serious effects on human health; and if these are carried together with particles, the effect may be synergistic. In an environment rich in airborne particles, the effects of pollutants may be more marked. Of interest in this connection is that health surveys in Botswana have shown very high frequencies of lung diseases. In present mining areas and especially when new mines are opened, health studies should be continuously undertaken as part of the monitoring.

To sum up: Studies of arid and semi-arid ecosystems have to be undertaken in order to develop monitoring methods. Of special importance is the study of global, regional, and local effects of dust transport. These studies should be of vital importance for livestock industries. The Secretariat for International Ecology, Sweden, is now planning pilot projects in this area, and any cooperation is welcome. We would also like to submit our plans to ILCA for consideration and, if the plans are acceptable, for approval.

Fig. 8

Fig. 9


1. BOWDEN, L.W., HONING, J.R., HUTCHINSON, C.F., and JOHNSON, C.V. - Satellite photograph presents first comprehensive view of local wind: the Santa Ana. Science, 1974, 184 (4141): 1077-78.

2. DESHLER, W.W. - An examination of the extent of grass fires in the savannahs of Africa along the southern side of the Sahara. Ninth International Symposium on Remote Sensing on Environment. ERIM, Ann Arbor, 1974.

3. KUENEN, H. - Marine Geology. New York, 1950, J. Wiley & Sons, Inc.

4. MAC LEOD, N.H. - Dust in the Sahel: Cause of drought? (Mimeogr.), 1974.

5. PROSPERO, J.M. and CARLSON, T.N. - 1972: Vertical and aerial distribution of Saharan dust over the western equatorial North Atlantic Ocean. J. of Geophysical Res., 77 (27): 5255-52-65.

6. RAPP, A. - A review of Desertization in Africa - Water, Vegetation, and Man. 1974, SIES report No. 1.

7. SCOPE - Global environmental monitoring. 1971, ISCV, SCOPE 1, Stockholm.

8. SCOPE - Global environmental monitoring systems (GEMS). 1973, ISCV, SCOPE 3, Toronto.

9. UNESCO - Pollution monitoring and research in the framework of the MAB-Programme. 1974 (MAB report series No. 20).

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