conservation.html

Freshwater ecosystems have played an important role in human society since time immemorial. Most of the ancient civilisations developed on the banks of big river systems; they depended on the rivers for food, and sustenance and also to a large extent used it as a channel for trade and travel. Fisheries have been an important source of food for people living along these riverine ecosystems as well as those living farther away. Though marine fisheries are an important industry now, they were a major occupation of many sections of the society even before the development of modern trawlers. With the emergence of modern technology, most of the fishing methods have become mechanised all over the world and fishing is no longer the primary occupation of only a select group of the local inhabitants living along the aquatic habitats but rather other communities living close to water bodies have also started using this resource as a source of occupation. In riverine ecosystems, man has gone even further in tapping alternate sources of energy like hydropower, because of which a number of our major rivers have or are being altered and modified for the construction of dams and reservoirs. The effects of point pollution and habitat degradation have been felt and water quality standards have been set to meet the largely human oriented goals of reasonably clean drinking water, fishing etc. But most of these efforts do not, as yet, look into the effects of pollution on aquatic life other than those species that are directly useful to man.

Uttara Kannada district in Central Western Ghats

The river systems of Uttara Kannada are medium sized rivers which flow through one of the most pristine forest areas left in the Indian Subcontinent. Till recently, they were hardly affected much by human activities as since populations around the region mostly used the water resources for their basic needs like drinking water, washing and occasional fishing. The fishing was also not very intensive, since none of it was targeted at catering to larger markets. Fishes were mainly used by the local people for their own consumption and sometimes sales at the local market. Traditional fishing methods usually employ locally made nets like gill nets and cast nets. Some areas have, however, been dynamited in the recent times.
        The river Kali has a number of small and medium sized dams built on it. The development of the hydroelectric projects like the Supa and the Kaiga project on the river Kali are relatively new developments which have altered the habitats in the surrounding regions. Now, there are atleast six dams constructed all along this river and together with the West Coast paper mill at Dandeli (which dumps its industrial discharge into the waters of the Kali), the river ecosystem of the Kali has been badly affected.
        Studies like those by Birasal et al (1991) conducted on the river Kali have shown how the physicochemical properties of river water have changed since the construction of the Supa Dam on the upper reaches of the river. It has led to increased siltation, which has, in turn affected the growth of aquatic vegetation and thereby lead to decreased dissolved oxygen levels and increased carbon dioxide levels in the water.
            The river Bedti (or Gangavali, as it is called in the upghat areas) is so far unaffected by dams, but the site at Manchikeri might be affected by sewage discharge from Hubli town located some kilometers upstream. The river Aghanashini, which flows just south of the river Bedti, is the least affected as it flows mostly thorough relatively undisturbed forests and smaller settlements. The agricultural fields and plantations along the river at some places are sources of fertilizer pollution, but these are not many.
            On the upper reaches of the river Sharavati is built the large Linganmakki reservoir and dam which is the source of much of the hydroelectric power supply of the State of Karnataka. There is one other dam construction underway downstream of this river. The building of dams on river systems greatly alters the natural habitat conditions in it. A large area surrounding the river channel is cleared up for the reservoir – this causes a major change in the terrestrial ecosystem around it and, in addition, the flow regime of the river itself is highly altered. Current velocities are suddenly reduced and there is heavy siltation of the substratum due to the deposition of the sediments brought from the upstream regions. These grossly alter the habitats of the river from their original states. Fish communities, along with the other flora and fauna of that region, get affected by this alteration. In addition, a number of fishes are known to travel upstream as well as downstream at various times of their life cycle. Thus, a dam can itself act as a barrier for the passage of these fishes and can affect the fish communities both upstream as well downstream of the dammed areas. Apart from the Linganmakki project, there are new projects recently sanctioned near Gersoppa which are expected to submerge surrounding tracts of forest areas.