Pushed to the limit
Effects of unchecked human activity have overwhelmed the resilience of rivers to absorb changes — bringing adverse and drastic changes to large rivers across the world
The demands posed by burgeoning population growth are placing unprecedented stress on the world's great rivers. 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. If appropriate policies are not framed with urgent interventions, humanity will face the collapse of the planet's diverse ecosystem in the coming decades. Despite the human-induced adverse change of many large rivers, the current coronavirus disease 2019 pandemic is already influencing regulatory frameworks as observed in India, the United States and also in other countries. In India, the changes made in the draft EIA 2020 are completely contrary to the principles of environmental protection and sustainable development regarding EIA notification 2006. The US Government has eased its enforcement of pollution monitoring, enabling polluters to avoid penalties.
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 2,600 km, eventually becomes one of the planet's most polluted rivers, a mélange of urban sewage, animal waste, pesticides, fertilisers, industrial metals, rivulets of ashes from cremated bodies and much more. The bacterial levels are remarkably high. Despite so much pollution, 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 an assimilative capacity for responding to disturbances in the equilibrium in water quality or sediment load through self-adjusting processes of erosion and sedimentation. These responses typically involve feedback 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 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.
Changing river flows also modulates the movement of sediment to floodplains and deltas. Timescales of effects for climate-related changes in river flows, and their extremes, ranging from decades to hundreds of years. Also, land-use changes, such as deforestation or reforestation catchment hill slopes and floodplains, can modify the quantity of water and sediment entering rivers through the soil and bank erosion over timescales of decades to centuries.
The construction of many large dams across the world for hydropower, flood control, irrigation, and water supply is booming. With more dams being constructed, the number of remaining free-flowing rivers would be drastically reduced. These dams also trap sediment, alter flow regimes, trigger riverbed incision and bank instability, and in tropical regions, cause a substantial release of the potent greenhouse gas 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 jeopardised. In addition to this 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. The water quality is severely deteriorated on account of pollution from nitrogen, phosphorus and sediment, three ingredients that in high quantities can cause numerous environmental problems in streams, rivers and bays. 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 phosphorus become the issue. Recently, the researchers have revealed the presence of riverine antibiotic pollution originating from human and animal waste. 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. Riverbed levels have now been lowered by about 2-3 m in only the last decade, destabilising river banks and enabling saltwater incursion at high tide, posing a severe threat to agricultural production.
Environmental improvement across the world that was observed during the lockdown is clear evidence that if effective interventions are made, cleanliness of rivers is possible.
A range of measures along certain rivers, including dredging up plastic, relocating factories and controlling waste discharge from industries and domestic sources, while also banning single-use plastic goods, are having a major effect 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 maximised their job security and income by producing as much as possible and by ignoring environmental problems. Despite the many constraints, effective international institutions will provide a channel for scientific advice and help support and enable the capability capacity of local, national, and transnational river-management organisations. Further, river governance must include local stakeholders. Creative financial instruments are also essential to delivering the investment necessary to fund restoration, protection, and management.
The writer is a former Senior Scientist, Central Pollution Control Board. Views expressed are personal