Almost all Indian rivers are under severe despoliation caused by anthropogenic activities; the magnitude varies at various segments all along the rivers’ course
One of the crucial challenges of the 21st century is the restoration of degraded running-water ecosystems — streams, rivers, springs— besides preserving those that are still in good condition. The historical scientific databases on lotic ecosystems are generally poor with largely anecdotal or incomplete information. The ecosystem paradigms can serve as tools for evaluating the existing condition of running waters, surmising their likely antecedent condition and developing targets and strategies for their restoration. Because the majority of degraded streams and rivers has changed beyond our ability to return them to their original state, the call for their rehabilitation acquires significance. It often takes the form of returning certain organisms or processes to a condition that addresses societal objectives.
Restoration will dominate in more developed regions where modifications of running water systems and their watersheds have been more extensive. In lesser developed regions, preservation of many of these lotic systems may still be possible, but the distinction between pristine and degraded systems is disappearing rapidly. In the context of preserving and rehabilitating streams and rivers, it is important to enlist the best scientific understanding of the structure and function of running-water ecosystems. The regulations governing the protection and width of riparian buffer zone plays a vital role.
Riparian zones depict areas that are transitional between terrestrial and aquatic ecosystems. They are distinguished by gradients in biophysical conditions, ecological processes and biota. They connect surface and subsurface hydrology namely, water bodies with their adjacent uplands. Riparian areas are adjacent to perennial, intermittent and ephemeral streams, lakes and estuarine-marine shorelines. They usually extend from the edges of water bodies to the edges of upland communities and represent a zone of interactions between the aquatic and terrestrial component.
A river is more than a channel carrying water; it transports sediments, harbours various organisms, plants, animal and microbes. Hence it should be conceived as a natural resource comprising biotic and abiotic ingredients essential for management of hydrological and ecological system. Until recently, planning and management of rivers were largely oriented on the channels themselves and it is integrated with catchment management. However, there are many aspects of channel catchment linkages with ecological perspective of riparian zones and these are essential for maintaining the health of the lotic system.
In India, rivers are classified mainly into two types based on their geographical locations and origin — Himalayan rivers and peninsular ones. The former are glacier-fed and perennial, while the latter are altogether monsoon-fed. The perennial Himalayan rivers constitute three major river systems — the Ganga, Brahmaputra and Indus — which cover various types of catchments and provide a variety of microhabitats. The Ganga river system (major tributaries —Yamuna, Ghaghara, Gandak, Gomati, Sone and Tons), the Brahmaputra river system (Siang river as a main channel and major tributaries — Dibang, Lohit, Subansiri, Ranganadi, Manas, Kulsi, Dhansiri, Champamati, Sankhosh and Digaru rivers) and the Indus river system (consisting of the Beas and Sutlej as major tributaries in India) are the principal Himalayan rivers; however, a major stretch of the Indus flows in Pakistan, leaving back a small segment of its drainage basin in the Indian territory. The Himalayan rivers are antecedent rivers having deep gorges exhibiting practically vertical to convex valley walls; and slope failures have become very common particularly in the belts cut by active faults in their hilly stretch. They provide different gradient of habitat heterogeneity from its headwater to mouth for colonisation of aquatic fauna. Further, the fragility of geologic formations in the Himalayas and deforestation of riparian catchments, soil erosion in the upper stretch of rivers causes severe sedimentation to downstream and habitat destruction.
The ecological conditions of peninsular rivers depend on hydrological characteristics like water level, current velocity and discharge, which vary from very lean to very high depending on relative rainfall in the respective watershed and catchment areas. Among the peninsular rivers, majority of them are East Coast rivers viz, Mahanadi, Krishna, Godavari and Cauvery. These east-flowing rivers drain into the Bay of Bengal. The West Coast rivers comprising Narmada, Tapi, Sabarmati and Luni flow towards west and drain into the Arabian sea.
All peninsular rivers are monsoonal and display very poor water flow to heavy flood, displaying fluctuating ecological and biological conditions. However, almost all the Indian rivers are under severe despoliation caused by anthropogenic activities; though the magnitude varies at various segments of the rivers all along their course. Some serious issues arise — river pollution throughout the country caused by untreated urban sewage, industrial effluents, agricultural runoff, mining wastes, religious ceremonies and navigational operations; indiscriminate destruction of drainage basin because of clearing of riparian zone vegetation; huge load of suspended solid, causing increased magnitude and frequency of flood that changes the level of interaction between land and water and hence affects despoiling input of energy source; river regulation, lift irrigation and water allocation without considering the ecological consequences that have adversely influenced the density, diversity and productivity of aquatic bio-resources. The population of migratory fishes is also adversely affected.
The water accounting study suggests that there is less physical risk of meeting the existing or future water demands and quantity of the supplied water as well. However, water quality is an issue that poses a major threat to the river ecology, risking the livelihoods of people dependent on rivers. The alteration of flow regimes is the most serious contemporary threat to the ecological sustainability of rivers and their associated floodplains. There is a growing awareness about the pivotal role of the flow regime in maintaining the ecological integrity of riparian zones. There is still much to learn about the ecological significance of individual flow events and sequences of events.
There is a small set of overarching ecological principles that, if employed for river management, may alleviate many of the difficult flow regulation issues facing resource managers and policy makers. The following principles, derived on several spatially broad overviews of river and riparian characteristics, are simple to maintain — The flow regime determines the successional evolution of riparian plant communities and ecological processes; the river serves as a pathway for redistribution of organic and inorganic material that influences plant communities along rivers; every river has a characteristic flow regime and an associated riparian community; riparian zones are topographically unique in occupying nearly the lowest position in the landscape, thereby could be integrated with catchment-scale management.
The major challenge for riparian management is to place water resource development within the context of these fundamental ecological principles in order to maintain ecological vitality with long-term planning. Despite growing recognition of the relationships between riparian characteristics and flow regimes, ecologists still struggle to predict and quantify biotic responses to altered regimes.
An obvious difficulty is the inability to distinguish the direct effects of modified flow regimes from the effects associated with other changes that often accompany water resource development. One often encounters river systems affected by multiple stressors, making it nearly impossible to definitively separate the effects of altered flow regimes from those of myriad other factors and interactions associated with climate and land use changes.
The writer is a former IFS officer. The views expressed are personal.
