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Human induced changes in large rivers

Sunday, Jun 28, 2020 14:45 [IST]

Last Update: Sunday, Jun 28, 2020 09:08 [IST]

Human induced changes in large rivers

Dr.DEBAPRIYA MUKHERJEE
The world’s great rivers are threatened by a range of anthropogenic stressors including  climate change that decrease resilience and increase vulnerability to extreme events like draught and flood. All the large rivers are hotspots of resources, agriculture, trade, and energy production and flow through developing nations, where much of the population is vulnerable to environmental and ecological stresses. The demands posed by burgeoning population growth are placing unprecedented stresses on the world’s great rivers. If appropriate policies are not framed with urgent interventions, humanity will face collapse of planet’s diverse ecosystem in the coming decades. Despite human-induced adverse change of many large rivers, the current coronavirus disease 2019 pandemic is already influencing regulatory frameworks as observed in United States.  The US government has eased its enforcement of pollution monitoring, enabling polluters to avoid penalties. This approach particularly by the governments to overcome economic recession is really political shock. Already negligence in supervision of industrial operations in some sectors during lockdown has caused increasing wastewater discharge.
These anthropogenic stressors function on a range of timescales, and their effects potentially amplify the risks posed by extreme climate events and thereby increase the likelihood that key resilience thresholds will be crossed. Most importantly the strong link between ecosystem services and livelihoods acts as severe stressors that cause major barriers towards meeting the UN Sustainable Development Goals by 2030. Among many major rivers in the world, river Ganges covering a distance of 2600 km eventually becomes one of the planet’s most polluted rivers, a mélange of urban sewage, animal waste, pesticides, fertilizers, industrial metals, rivulets of ashes from cremated bodies and many more. The bacterial levels are remarkably high. Its numerous watersheds in the mountains, across the Deccan Plateau and its vast delta serve 400 million people — a third of India’s population — as a source of drinking water for humans and animals, essential for crop irrigation, travel and fishing.
Rivers have assimilative capacity for responding  to upset of  equilibrium in water quality or sediment load  through self-adjusting processes of erosion and sedimentation. These responses typically involve feedbacks that impart some resilience, allowing rivers to absorb a degree of change. Climate change, as manifested through a complex global pattern of future floods and droughts, presents a background stress that is increasing through time and pushing this flexibility to its limits. River resilience can further be lowered by a range of other anthropogenic stressors that could present slow ongoing changes or extreme events that operate over short timescales. For example, the severity of flood in Kerala that killed at least 370 people, displaced 780,000 and caused Rs 30000-50000 crore worth of damage may be attributed to the ways in which river channels are engineered.  The disaster with signi?cant consequences may be attributed to poor water governance in India.  Thereby reduction in resilience makes river systems more vulnerable to the increasing magnitude and frequency of such extremes, which increases the likelihood that the tipping point for system resilience will be crossed. Such changes can have immediate consequences, such as hazardous riverbank erosion, which damages infrastructure and threatens lives, but could also impose a legacy of change that persists for centuries.
Changing river flows also modulate the movement of sediment to floodplains and deltas. Timescales of effects for climate related changes in river flows, and their extremes, range from decades to hundreds of years. In addition, land-use changes, such as deforestation or reforestation catchment hill slopes and floodplains, can modify the quantity of water and sediment entering rivers through soil and bank erosion over timescales of decades to centuries.
The construction of many large dams all the over world for hydropower, flood control, irrigation, and water supply is booming. Many of them are already constructed and many more dams are either    under construction or are being planned. If all the dams are constructed , the number of remaining free-flowing rivers  would not only be drastically reduced but also these dams trap sediment, alter flow regimes, trigger riverbed incision and bank instability, and in tropical regions, cause substantial of the potent greenhouse gas (GHG) methane as a result of vegetation decay. Such effects are compounded by water diversions and the interlinking of rivers within, and between, river basins. In this way the riverine ecology has been completely jeopardized. In addition to these destruction in the name of development sand and gravel mining are destroying riverbeds across the globe.  Further, the introduction of non-native species—such as fish, invertebrates, and vegetation—can have almost immediate ecological effects and economic consequences, potentially compounded by river interlinking.
Pollution from industrial, domestic, and agricultural sources could pose a near instantaneous threat. Water pollution is a problem that affects both rich and poor countries, however the cocktail of chemicals changes as countries develop. In poor countries it is faecal bacteria and as GDP increases then nitrogen and phosphorous  due to use of chemical fertilizer becomes the issue. Recently the researchers have revealed the  riverine antibiotic pollution originating from  human and animal waste and leaks from wastewater treatment plants and chemical factories. Such potent antibiotic pollution is present worldwide and aids the development of antimicrobial resistance.
Another major stressor is sediment starvation due to declining river sediment loads caused by  the changing frequency of extreme events; sediment trapping behind dams, large-scale mining of river sand. The combined impacts are so large that riverbed levels have lowered by  about 2–3 m in only the last decade, destabilizing river banks and enabling saltwater incursion at high tide , posing a severe threat to agricultural production.
With reference to above it may be mentioned that anthropogenic pressures are now so great and so rapid that there is a clear danger of imminent, and irreparable, environmental change. Environmental improvement all over the world we observed during  lockdown is the clear evidence  if effective interventions are made, cleanliness of river is possible.
A range of measures along the some rivers, including dredging plastic, relocating factories and  controlling waste discharge from industries and domestic sources and banning single-use plastic goods, are having major effects in reducing pollution. At the same time it is also true that in the centrally planned economies government officials were charged with protecting the national interest, which supposedly included environmental quality. However, bureaucratic incentives are such that more often than not the government officials maximized their job security and income by producing as much as possible and by ignoring environmental problems. Despite so must constraints,  effective international institutions must provide a channel for scientific advice and help support and enable the capability capacity of local, national, and transnational river-management organizations. Further,  river governance must include local stakeholders and incorporate issues of social equity, inclusivity, and gender. Creative financial instruments are also essential to delivering the investment necessary to fund restoration, protection, and management.
If we fail to recognize the timescales of change, incorporate the effects of extremes, and implement an appropriate international response, in 50 years’ time our despondent descendants will be baffled as to why. If governments failed to take effective measures, the environmental movement needs to be initiated for slowing down or stopping certain government policies that promised significant environmental damage.
E-mail:dpmcpcb@yahoo.com

Sikkim at a Glance

  • Area: 7096 Sq Kms
  • Capital: Gangtok
  • Altitude: 5,840 ft
  • Population: 6.10 Lakhs
  • Topography: Hilly terrain elevation from 600 to over 28,509 ft above sea level
  • Climate:
  • Summer: Min- 13°C - Max 21°C
  • Winter: Min- 0.48°C - Max 13°C
  • Rainfall: 325 cms per annum
  • Language Spoken: Nepali, Bhutia, Lepcha, Tibetan, English, Hindi