Lotic Ecosystems or Moving Water

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.
(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 m³/sec, ft³ 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.