The inflow of pollutants and solid wastes from the urban areas carried by the river Nambul has been cited as the main cause for increasing the pollution level in the lake and also influencing eutrophication leading to the aging of the Loktak lake
By Salam Rajesh
The conservation and wellbeing of freshwater ecosystems are closely linked to the preservation of the natural hydrological regime, writes Andrzej Wałega and Alban Kuriqi (editors) in a recent publication, ‘Advances in Sustainable River Management: Reconciling Conflicting Interests under Climate Extremes’ (2022).
On the other hand, Walega and Kuriqi writes, human activities often alter the natural hydrologic regime and habitat conditions for aquatic ecosystems by substantially affecting several essential life-stages of aquatic organisms, such as migration and spawning of fish, macro invertebrates and other aquatic species.
Many river basins and their sub-basins in different pockets of the globe are subjected to various forms of degradation and degeneration primarily through anthropogenic influences, such as constructions of barricades (dams, barrages, weirs) that obstruct their natural environmental flow and reducing their capability to render ecosystem services in the natural system.
Citing a case study of the river Thames in England, Martin Richardson and Mikhail Soloviev in their academic paper “The Thames: Arresting Ecosystem Decline and Building Back Better”, writes that ‘Prior to 1800, the river was clean enough to support large populations of many species’.
‘Diadromous species which use the ocean and freshwater at different stages of their lifecycle including smelt, salmon, eels, sprat and flounder, were caught for food along the river for centuries. Fishing and fisheries have been an integral part of the Thames community for several hundred years. Fishing communities lived for generations at several locations along the river including Kew and Chiswick’.
The problem with the river in modern times, as the writers says, is that ‘combined sewer network deposits domestic and industrial waste as well as urban drainage release raw sewage, with added hydrogen peroxide to the river, particularly during periods of heavy rain or flooding. Historical levels of 150 million tonnes a year were discharged in the 1850s. Around 40 million tonnes were still being released to the river in 2011 but recent improvements have reduced this to 18 million tonnes’.
The problem is accentuated today as the river Thames, as well as other rivers, ‘now contain large quantities of nano-plastics, micro-fibres and other micro-plastics which cannot feasibly be removed but aggregate with biogenic particles and eventually settle into the sediment. These are continually replenished by others through aerial deposition as well as run-off from the land and roads’.
The other dimension of the problem, the authors say, is that ‘Many native species of all taxa are in decline and local extinction may be inevitable for populations of native mussels, salmonids (smelt, trout and salmon), several plants, gastropods and some types of river flies. Continuing occurrence does not necessarily mean that there is potential to recover species. Population decline beyond a certain minimum level of genetic diversity might take decades to reverse’.
The interesting aspect of the study is that the river Thames has been ‘invaded’ by several non-native species of fish, of which surprisingly is the Grass carp (Ctenopharyngodon idella) as similarly as it was introduced in Manipur in the recent past and which is today a dominant cultured fish in the wetlands and fish culture ponds.
The introduction of exotic fishes is intrinsically linked to the degeneration of the native species due to several factors of which human induced disturbances in the natural ecosystem, over-harvesting and dominance by the non-native species is common.
Another case study by Naresh Suwal et al in their academic paper ‘Environmental Flows Assessment in Nepal: The Case of Kaligandaki River’ looks at the reduction in e-flows of rivers due to artificial obstructions, wherein the authors say that, ‘adverse effects, such as reducing total flow discharge left to the river, changing the seasonal flow regime, altering the magnitude and frequency of floods, and modifying the groundwater table are a severe threat to the aquatic ecosystem existence’.
Reflecting on the negative impacts of artificial barriers (dams, barrages) the authors opine that, “Most rivers with dams and diversion projects are at the ecological tipping point, which means act now or face the projects’ worst effects soon. The escalating hydrological alterations of the rivers flow regime, and its resulting severe impacts on the riverine ecosystem’s health is recognized globally”.
“With the advent of growing public consciousness in the river health and its hydrological alteration causing adverse impacts, river scientists developed the science of environmental flows (e-flows) assessments, which aid in determining the quality and quantity of water required for the protection of the riverine ecosystem and its inhabitants”.
The case studies on the river Thames in England and the Kaligandaki in Nepal are fairly similar to the processes that have since been observed on ground with the rivers Nambul and Manipur in relation to their impacts on the freshwater Loktak Lake and other wetlands in the Manipur River Basin.
The reduction in the e-flow of both the rivers Nambul and Manipur, due to obstruction by the barrier Ithai Barrage, had evidently impacted the natural ecosystem of Loktak, wherewith increase in silt load deposition had caused the lake to become shallow with each consequent year. The inflow of pollutants and solid wastes from the urban areas carried by the river Nambul has been cited as the main cause for increasing the pollution level in the lake and also influencing eutrophication leading to the aging of the lake.
Where Martin Richardson and Mikhail Soloviev says that the high pollution level and obstruction in the e-flow of the river Thames had caused the decline in population of native fish species, quite importantly the trout and salmon, it is arguably the similar case with decline in original species of fish along the Manipur River and other water bodies in the Manipur River Basin.
The obstruction by Ithai Barrage had halted the free passage of the migratory fish species coming upstream along the Manipur River from the Chindwin-Irrawaddy river system in western Myanmar. The decline in the original population of highly relished fish like the Khabag (Cirrhinus reba) and Ngaton (Labeo bata) had largely impacted the rural economy and food supplement of local people living along the river course and specifically alongside Loktak Lake and the adjoining wetlands.
For Loktak, Nambul and Manipur rivers, it is high time that the relevant authorities roll up their sleeves and dip their hands in the water to feel and see for themselves the processes that are said to be influencing conditions which accentuates aging of the water bodies while reducing the ecosystems services of these water bodies to a level almost equal to zero. For Loktak, the return of the Khabags and the Ngatons is essentially important in reviving both ecosystem of the lake and the livelihoods of the local populace.
(The writer is member, IUCN Commission on Environmental, Economic and Social Policy CEESP. He can be reached at [email protected])