ENVIRONMENTAL SCIENCE : NATURAL RESOURCES 27
(ii) Land water interchange is great because of the small size and depth of moving
water systems as compared with lakes.
(iii) Oxygen is almost always in abundant supply except when there is pollution.
(iv) Temperature extremes tend to be greater than in standing water.
(v) The most distinctive features of moving water ecosystems are those related to their
motion i.e. the rate of flow and the streams velocity. The rate of flow refers to the
volume of water passing a given observation point during a specific unit of time;
It is measured in units such as m^3 /sec, ft^3 or acre-feet/sec.(a) Rapidly flowing water
Rapidly flowing water can be defined as the portion of the streams in which the flow
is both rapid and turbulent. Consequently everything that is not attached or weighty is
swept away by the current. This includes organisms and sediment particles alike. The
substrate tends to be rock or gravel. The fragments are gradually rounded and smooth by
the water.
(b) Slowly flowing water
A slowly flowing water ecosystem is a very different type of system from the fast
streams. The flow is both slower and more likely to be laminar. The results are that the
erosive power of the stream is greatly reduced, hence, smaller sediment particles (sit) and
decaying organic debris, are deposited on the bottom. Besides, the slow streams have higher
temperature. Consequently, planktonic organisms, espeically protozoans, occur in large
number in this ecosytem. In some moving streams, the bottom muds contain more organic
material than mineral fragments. In slow water streams oxygen concentration is main
limiting factor. The high level of animal activity, along with an active detritus stream.
Besides, the low level of turbulence means that less oxygen is in corporate into the water
at surface. Thus the dissolved oxygen content of a slowly moving stream is likely to be much
lower than that of a fast-moving stream.
- Estuaries
Water of all streams and rivers eventually drain into the sea. Estuaries is the place
where this freshwater joins the salt water. As such estuaries are the transitional zones
between the sea and rivers and are the sites of unique ecological properties. They are
semienclosed coastal bodies of water that have a free connection with the open and within
which seawater is measurably diluted with freshwater from river. However, all the rivers
are not open into estuaries. Some rivers simply discharge their runoff into the ocean. Estuaries
are not alike. Instead they differ in size, shape and volume of water flow, they are influenced
by the geology of the region in which they occur. As the river reaches the encroaching sea,
the stream carried sediments are dropped in the quiet water. These accumulate to form
deltas in the upper reaches of the mouth and shorten the estuary.
The Position of Surface Water in the Country
India has been bestowed with substantial surface water resources. Overall water
resources of the country have been assessed at 1880 km^3 annually. Of thus, it may be
possible to harness about 690 km^3 of water for beneficial use. In addition, Ground Water
Resources of the Country are assessed at about 452 km^3.