Featured Science

Ecosystem Restoration of Ganga River Basin

30th July 2021

In 1972, the UN General Assembly designated 5th June as World Environment Day. The first celebration, under the slogan “Only One Earth” took place in 1974. In the following years, WED has developed as a platform to raise awareness on the problems facing our environment such as water pollution, air pollution, plastic pollution, illegal wildlife trade, sustainable consumption, sea-level increase, and food security, among others. Furthermore, WED helps drive change in consumption patterns and in national and international environmental policy. The theme for World Environment Day 2021 is “Ecosystem Restoration”.

Ecosystem Restoration

Ecosystem restoration means assisting in the recovery of ecosystems that have been degraded or destroyed, as well as conserving the ecosystems that are still intact. Healthier ecosystems, with richer biodiversity, yield greater benefits such as more fertile soils, bigger yields of timber and fish, and larger stores of greenhouse gases. Restoration can happen in many ways – for example through actively planting or by removing pressures so that nature can recover on its own. It is not always possible – or desirable – to return an ecosystem to its original state. We still need farmland and infrastructure on land that was once forest, for instance, and ecosystems, like societies, need to adapt to a changing climate. Between now and 2030, the restoration of 350 million hectares of degraded terrestrial and aquatic ecosystems could generate US$9 trillion in ecosystem services. Restoration could also remove 13 to 26 gigatons of greenhouse gases from the atmosphere. The economic benefits of such interventions exceed nine times the cost of investment, whereas inaction is at least three times more costly than ecosystem restoration. All kinds of ecosystems can be restored, including river ecosystems, forests, farmlands, cities, wetlands and oceans.


Significant loss of species biodiversity in the Ganga river network has been observed over the past many decades, with many important aquatic species (fishes, dolphins, ghariyals, turtles, etc.) having dwindled or disappeared from river stretches in recent history. Now, a river ecosystem – with its intrinsic biodiversity – plays a crucial role in the functional health of the river basin and the ecosystem services provided by the river. To grasp the biodiversity changes in National River Ganga and devise suitable means to restore her ecological balance, it is necessary to understand the dynamics of the Ganga river ecosystem and assess the possible anthropogenic and non-anthropogenic factors affecting it. Broadly, an ecosystem is a community of living organisms (plants, animals and microbes) in conjunction and interacting with non-living components of their environment. The biotic and abiotic components are linked together through nutrient cycles and energy flows: energy and carbon enter the ecosystems through photosynthesis, while mineral nutrients are mostly recycled within the ecosystems. Now ecosystems are controlled both by external factors (or “state factors, such as climate underlying geological material, topography and time) and internal factors (such as decomposition, periodic disturbances, species competition and human activities). Since ecosystem processes are driven by the types and number of species in an ecosystem and the relative abundance of organisms within these species, hence species biodiversity plays an important role in ecosystem functioning. In general, ecosystems can be assessed either in terms of the services (or goods and services) they provide to humans, or in terms of “ecosystem structure” (i.e. measurable attributes of a least impacted or reference state of the ecosystem). The Ganga river is a diverse landscape-scale ecosystem. To start with, the river traverses three distinct climatic-geographical zones from the snow-clad and alpine Himalayan reaches to the tropical alluvial plains until it enters the estuarine zone and meets the sea. Ecologically, the diversity of the basin within each climatic zone plays an overarching role on River Ganga. For while a river’s ecosystem boundary may be nominally demarcated by the river banks, there are varying degrees of (but often close) biotic and abiotic interactions of the river with her riparian zones, flood plains and drainage basin. The saturated subsurface zone under the river bed also forms a unique habitat (termed “hyporheic biotope”) for a diverse group of fauna, which also provides temporary refuge for aquatic organisms in times of adversity and plays an important role in the processing of river nutrients and interacting with groundwater. National River Ganga and her tributaries are home to a wide variety of aquatic organisms (from microscopic flora and fauna to higher invertebrates and vertebrates) and visited periodically by many other creatures from far and near.

Criteria for measuring success of eco-restoration steps referred to as standards for ecologically successful river restoration



Role and Impact of Riparian Vegetation in Ecosystem restoration

Riparian ecosystem is a connecting link between the stream environment and terrestrial catchment. Riparian forest is an area of trees accompanied by shrubs and herbs that is adjacent to the water body. It influences the structure of both aquatic and upland terrestrial communities. The components influenced by the riparian ecosystem are modifying storage capacity and aquifer recharge, in-channel primary and secondary productivity, organic matter quality and quantity, biodiversity and migratory patterns, and biogeochemical pathways and rates. Riparian flora also helps in trapping pollution, filtering and converting sediments, nutrients and other chemicals. They absorb periodic flood fluxes and supply food cover and thermal protection to the biota. Ecological buffers that are important to the riparian ecosystem. Ecological buffers are as predominant as the wood plant community, presence of surface water and abundant soil moisture, diversity interspersion of habitat features, & Corridor for dispersal and migration. The Riparian ecosystem has many functional characteristics. They are highly productive because of convergence of energy and material, and unique hydrological conditions. Degradation of riparian zones and streams diminishes their capacity to provide critical ecosystem functions, including the cycling and chemical transformation of nutrients, purification of water, attenuation of floods, maintenance of stream flows and stream temperatures, recharging of groundwater, and establishment and maintenance of habitats for fish and wildlife.

Threats to Biodiversity of National River Ganga

The riverine ecosystem has been exploited for meeting human needs. Major threats to the Ganga basin as well as other river basins in the country are affecting/disturbing ecological integrity.

1. Habitat Fragmentation & Changes in the Flow Regime: The flow patterns in the river Ganga have been altered due to the number of run-of-the-river (ROR) hydro-electric projects in the head streams. These hydro-electric projects have fragmented the river and obliterated the migration routes of some important fishes viz., Schizothorax sp. and Tor sp. It is necessary to ensure longitudinal connectivity – along with adequate water and sediment flows – throughout the Ganga river network.

2. Habitat Alteration: In addition to changes in the flow regime, the river morphology and habitat are also altered steadily. Large scale gravel and sand mining, dumping of construction wastes and other solid wastes have led to changes in flow direction causing erosion, channelization and river realignment. This reduces stream width, altering flood plains and riparian vegetation. The ecology is seriously impaired with changes in habitat. The alteration in habitat, changes benthic flora and fauna, fish breeding sites and egg laying sites, for soft and hard shell turtles.

3. Habitat Shrinkage: Large anthropogenic water abstractions are being affected from the Ganga River Network all over the basin, thereby considerably shrinking the aquatic space of river species. Many of the dams and barrages on the rivers are used to divert river flows. River water abstractions are generally high during lean flow seasons but low (or nil) during the wet seasons. This results in the river channel carrying extremely low flows during the dry season but with the original high flows of the wet season almost intact. In fact, peak runoff rates from the basin into the rivers may have increased in many places due to urbanization and land-use changes over the past one or two centuries, thereby increasing the river flood peaks from their earlier levels. Overall, the extremes of the river’s natural hydrological regime have certainly accentuated, thus exerting considerable further survival pressures on the biota.

4. Habitat Pollution: Pollution from domestic and industrial wastes is extensive in the Ganga river downstream of Haridwar, and it assumes alarming proportions below Kannauj (after the confluence of Ramganga and Kali rivers) at least up to Varanasi. High levels of pollutants in the river have fatal effects on river biota.

5. Habitat Invasion by Alien Species: Exotic species of fish especially common carp Cyprinus carpio and Tilapia Oreochromis niloticus have invaded Ganga water downstream of Prayagraj. These fishes have gained access through water of Yamuna at Sangam. Downstream Prayagraj up to Bhagalpur and beyond they have grown in large numbers. They compete with Indian Major Carps (IMC) and have outgrown them due to their adaptability in variable flows. Seven species of exotic fish have been reported in river Ganga including Thai magur, (Clarias gariepinus) and Grass carp (Ctenopharyngodon idella). But it is not only the middle and lower reaches that have been invaded. The sighting of another exotic fish – the brown trout (Salmo trutta fario) downstream of Jhala – is an important signal of the presence of invasive species reaching up to Bhagirathi. Now, invasion of ecosystems by alien species can occur only after their introduction into the ecosystem, which is often anthropogenic. But, even after their introduction, alien species have to out-compete the native species in the ecosystem. Often, this competitive advantage in river ecosystems accrues from manmade changes in rivers to which indigenous species are not well adapted. Habitat invasion of the Ganga River Network by alien species is also essentially of anthropogenic origin. The adverse consequences of such invasions include the propagation of new diseases and parasitic organisms, and disruption of the river’s ecological balance. It is, therefore, imperative that exotic species that have invaded the river network be eliminated and appropriate control measures be devised against introduction of any new alien species.

6. Habitat Encroachment: Human beings have been encroaching upon rivers since long ago especially by occupying much of the flood plains and parts of river banks for various purposes. In modern times, however, the encroachments have become extensive with widespread construction activities on floodplains and even farming on river beds during lean flow seasons. On the one hand, the increased constructions on flood plains have led to altered runoff patterns into rivers, increased pollution inflows with runoff, reduced groundwater recharge and, hence, decreased base flows in rivers, and curtailed ecological linkages between the river, its floodplains, and floodplain wetlands. On the other hand, river bed farming together with modern chemical pesticides such as DDT and HCH, have polluted the river bed, thus affecting the health of aquatic creatures, especially the hyporheic biota, and disturbing the breeding sites of higher aquatic animals.

8. Habitat Malnutrition: While anthropogenic pollution or increase of harmful substances in the Ganga river habitat is a matter of grave concern, the reverse phenomenon of anthropogenic nutrient deprivation in the river has received little attention. The general notion of anthropogenic effects on nutrient concentrations in rivers is that of nutrient enrichment, i.e. increased concentrations of nitrogen (N), phosphorous (P) and other nutritional elements commonly present in agricultural, domestic and industrial wastewaters. But the opposite phenomenon of nutrient depletion is often overlooked.


Ecosystem Restoration Measures under Namami Gange

Namami Gange programme, implemented by National Mission for Clean Ganga (NMCG) is an integrated mission for conservation of Ganga and its tributaries. NMCG’s vision is to restore the wholesomeness of the River by ensuring Aviral and Nirmal Dhara, and maintaining its geo-hydrological and ecological integrity. The holistic approach and innovative features in policy making, project management, financial planning, sustainability of investment, scientific research, knowledge management, institutional development, basin management and planning has helped Namami Gange program to evolve as a pioneering river rejuvenation programme. One of the bottlenecks for a comprehensive planning for a river rejuvenation is the lack of scientific data, which requires detailed research studies. To overcome these issues, NMCG has sanctioned different research projects touching different aspects of river rejuvenation using basin approach. These research projects cover the historical part, cultural part, Ecological part as well as scientific and technological part.

River basin plan

NMCG is ensuring several activities as restoration of longitudinal connectivity along with E-flows across dams/ barrages; maintenance of lateral connectivity across floodplains; restoration of unpolluted river flows; restrictions on river bed farming, gravel and sand mining, plying of vessels, dredging, and bed and bank modifications; control of alien species invasions, overfishing and fishing during spawning seasons; river nutrient assessment and release of dammed sediments into the river; bio-monitoring of Ganga river network etc. NMCG is leading to the development of Arth Ganga model linking economic development of Ganga Basin with ecological improvement and Ganga Rejuvenation. Nature has capacity to rejuvenate itself if human interventions are controlled and the same was witnessed during the national lockdown period. The lesson to be learnt is that we need to have better enforcement and also keep working for behavioural change as everything cannot be achieved by regulatory approach only. People’s participation is key to transformation. Sustainable development increasingly depends upon successful management of urban growth and water resources. Ganga Rejuvenation is critical for implementation of 2030 agenda of Sustainable Development Goals (SDGs). Namami Gange has developed a framework for river rejuvenation which is now being followed for several rivers beyond Ganga basin.

Ganga is in the heart of millions who have been drawn to it since time immemorial. In essence, Ganga represents all rivers and several river streams are also named after Ganga. It has always been and will remain a great unifying force. Its rejuvenation requires the efforts of all and its rejuvenation is needed by all.

Er  Peeyush Gupta
Real Time Information Specialist
National Mission for Clean Ganga,,
Ministry of Jal Shakti,
Email: peeyush.gupta@nmcg.nic.in.