MAP Technical Reports Series No. 106 UNEP

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conditions, the geochemical dynamics, which also include the flow of nitrogen and phosphorus,
are regulated by natural processes that depend on the specific geological, orographic,
sedimentological, geochemical, climatic and biotic environment in which these processes take
place. Thermic and hydrological conditions are of primary importance. However, historically all
these factors have been seriously affected or changed by man to various degree. A majority of
present-day landscapes, even of some where man's influence is not immediately apparent (e.g.,
the Mediterranean macchia), are to be classified under the category of anthropogenically
transformed landscapes, in which natural expanses remain as disjunct pockets only.
A breakdown into land use categories, and their implied relationship to pollution and
nutrient sources, is given in Figures 2 and 3. This breakdown has been kept as complete as
possible as a reminder, although in reality every situation differs from each other, and
accordingly must be evaluated and assessed separately.
Besides the still natural landscapes, which are listed for completeness but will not be
treated further, the main anthropogenically transformed land use categories of interest in the
context of eutrophication are:
- Urban Settlements and Communications Areas
- Farm Lands
- Industrial Areas
Urban Development. With the rapid expansion of population centres that began in the last
century in developed countries, and now involves also developing countries, new technologies
and facilities have been introduced. Of greatest hygienic and environmental consequences was
the almost general introduction in developed countries of water supply and water disposal
systems, i.e., sewers that often were discharged directly to rivers and/or lakes and other
stagnant waters. With the improvement of centralized treatment facilities and secondary
treatment during this century, some of the worst pollution effects resulting from the discharge
of untreated sewage to waterways have been alleviated. Still, secondary treated urban sewage
contains substantial amounts of phosphorus and nitrogen, which became the main cause of
eutrophication at the turn of the century. With the introduction of household and industrial
detergents containing polyphosphates after World War II the problem was further aggravated.
Following the adoption of tertiary sewage treatment and due to a substantial reduction of
polyphosphates in household detergents in some countries further development of the problem
has been halted or slowed down in recent decades. Still, secondary and in particular tertiary
treatment of urban sewage is not general, specially in countries bordering the Mediterranean.
Accordingly, urban sewage remains a major source responsible for the continuing eutrophication
of fresh and marine waters.
Further to direct discharges of insufficiently treated sewage, run-offs from urban streets
and highways, and connected areas continue to cause concern, in particular in situations of
combined sewer systems that receive both urban sewage and urban run-offs. This causes
difficulties of effective treatment in conditions of storm-run-offs because of excessive sewage
dilution that reduces and endangers the correct biodynamic functioning of treatment plants.
Farming. The relative role of various farming practices regarding their effects on
eutrophication, instead, depends largely on whether farming is extensive or intensive. Extensive
farming may have a low impact on eutrophication, even if animal stock raising is involved. As
long as the uptake capacity of soils remains high, extensive farmlands may act