WATER QUALITY MANAGEMENT IN CONNECTED CATCHMENT- SHALLOW LAKE SYSTEMS - Integrating GIS, Remote Sensing, and Mathematical Modelling for Surface Water Quality Management - page 34

The limnetic zone is the open water area where light does not generally penetrate all the way
to the bottom.
The euphotic zone of the lake, which is the layer from the surface down to the depth where
light levels become too low for photosynthesis energy producers.
The benthic zone, which is the bottom sediment, it has a surface layer abundant with
organisms.
Figure (2-7): The typical lake distinct zones of biological communities
linked to the physical structure of the lake.
Shallow Lakes
In several parts of the world shallow lakes are more abundant than deep ones. Numerous shallow
lakes, for instance, are found at the edge of the ice cover during the Weichselian glaciation period.
Also, human activities such as digging for peat, sand, gravel, or clay have produced considerable
numbers of shallow lakes and ponds. The term 'wetlands' is often used to refer to shallow lakes and
adjacent marshy land. Such habitats are notoriously rich in wildlife. In densely populated areas even
small lakes can be very important from a recreational point of view. Fishing, swimming, boating and
bird watching attract a large public (Scheffer, 2001). In other areas the image is totally different where
the lakes could be mainly used for commercial fishing, discharging drainage and waste water from
catchments and fish ponds.
The pristine state of the shallowest lakes is probably one of clear water and rich aquatic vegetation.
Nutrient loading has changed this situation in many cases. The lakes have shifted from clear to turbid,
and with the increase in turbidity, submerged plants have largely disappeared. Efforts to restore the
clear state by means of reduction of the nutrient loading often are unsuccessful. This has invoked
experiments with additional methods such as temporary reduction of the fish stock. This has catalyzed
the development of insights into the mechanisms that govern the dynamics of shallow lake
communities (Scheffer, 2001).
Shallow lakes as defined earlier in this section are forced by wind mixing with depth of ten meters or
less. They typically, fall into the eutrophic category, although some might also be mesotrophic.
Shallow lakes can have the following general characteristics.
Vegetation:
Aquatic plant growth is abundant due to high nutrient content (phosphorous, nitrogen, and minerals)
and the shallowness of the water. Aquatic plants need both nutrients and sunlight to grow. These