26 ENVIRONMENTAL SCIENCE
Physico-Chemical Properties of Lakes and Ponds
Lakes have the tendency to become thermally stratified during summer and winter to
undergo definite seasonal periodicity in depth, distribution of heat and oxygen. Light also
penetrates only to a certain depth, depending upon turbidity.
Kinds of Lakes
On the basis of physical factors and productivity, etc., different classifications of lakes
exist:
(1) Based on temperature
Hutchnson (1957) classified lakes into dimitic, monomictic and polemicist lake.
There are as under:
(i) The dimictic lakes exhibit two overturns every year, while monomictic lakes present
only a single overturn per year.
(ii) The monomictic lakes may be cold monomictic and monomictic.(2) Cold Monomictic
It is characterized by a circulation only during summer:
(i) Warm Monomictic: It has a circulation in winter as well.
(ii) Polomictic lakes present circulation throughout the year.
Based on the human acid content the lakes of world have been classified into clear
water lakes and brown water lakes,
(a) The brown water contains high humus content.
(b) Clear water takes may be divided into two types as under:(i) The oligotrophic type
Its water is poor in nutritive plant material and show nearly equal distribution of
oxygen during summer and winter months. Its mud bottom contains little organic material;
(ii) The eutrophic type
It is rich in nutrients. At greater depth below the thermo cline in summer eutrophic
lakes show a considerable reduction in oxygen content and their mud bottom is composed
of typical muck.
- Lotic Ecosystems or Moving Water
Moving water or lotic ecosystems include rivers, streams, and related environments.
They are of various sizes ranging from Ganga, Yamuna, Hindon, Kali Nadi, Sutlez, Gomti,
etc to the trickle of a small spring. Likewise, there is distinction on the basis of flow. On one
hand there are raging torrents and waterfalls and on the other hand, the rivers whose flow
is so smooth as to be almost unnoticeable. Every river varies considerably over its length,
as it charges from a mountain brook to a large river.
Main Characteristics of Lotic Environment: Moving water differ from lakes and
ponds as under:
(i) Current is a controlling and limiting factor.