WATER QUALITY MANAGEMENT IN CONNECTED CATCHMENT- SHALLOW LAKE SYSTEMS - Integrating GIS, Remote Sensing, and Mathematical Modelling for Surface Water Quality Management - page 33

Figure (2-6): The relation between the watershed area and the lake area ratio and the nutrients loadings (After
Monson, 1992)

A number of issues affect lake water quality. These have mostly been identified and described in
industrialised regions, such as the North American Great Lakes, which have progressed from one issue
to another in a sequence parallel to social and industrial development (Meybeck et al., 1989).
Meybeck et al. (1989) have highlighted that the developing nations of today are responsible for
managing lakes which are being subjected to synchronous pollution from the simultaneous evolution
of rural, urban and industrial development, differently from the historical progression which occurred
in developed societies. This means that, in the developing world, multi-issue water quality problems
must be faced with greater cost and complexity in assessment design, implementation and data
interpretation. The current issues facing lake water quality can be summarized in the following:

Eutrophication

Health related issues and organic wastes

Contaminants

Lake acidification

Salinisation

In this presented research work, the main focus is on eutrophication of shallow lakes. The next section
describes characteristics of shallow lakes, the eutrophication as a water quality problem, its reasons
and impacts and the processes involved.

2.5. EUTROPHICATION OF SHALLOW LAKES

In order to define the eutrophication problems of shallow lakes, and how the problem originates from
the upstream activities and land uses in the watersheds, there are some definitions characteristics that
should be highlighted. First we have to define the Ecosystem , which is the unit of natural organization
in which all living organisms interact collectively with the physical chemical environment as one
physical system. Lakes are considered living ecosystems. Lake ecosystems are complex, involving
both terrestrial and aquatic photosynthesis, external and internal nutrients, grazer and detritus food
webs, and aerobic and anaerobic metabolism. The lake ecosystem consists of two major components:
the "aquatic" component which is the overall water body itself, and the "paralimnetic" component
which consists of the drainage basin or watershed. The paralimnetic component could be divided into
a variety of land-use. Likewise, the aquatic component could be divided into littoral zone, pelagic
zone, benthic boundary layer and sediments. Specific components of the lake ecosystem are shown in
figure (2-7) and could be distinguished as follows:

The littoral zone is the near shore area where sunlight penetrates all the way to the sediment
and allows aquatic plants (macrophytes) to grow.