Dr Debapriya Mukherjee
River that plays a vital role in the water cycle, both in terms of their socioeconomic beneûts and as channels for nutrient cycling and energy ûow between diverse ecosystems is crying for her despair. Our society is practically responsible for this because we are only concerned to rapid development of industrialization and urbanization, conventional agriculture practice and our comfort using advanced technology but without any concern to ecology.
The rivers around the world are suûering dramatically and unrecognizably from increasing interference and destruction. Many human activities, such as dam construction, channel modification, flow regulation, overexploitation of water, river cut-oû, riverbank solidiûcation and unreasonable uses of riverbed vegetation not only upset the normal ûow of rivers but also jeopardize the key processes such as sediment transport, nutrient cycling and energy exchange. Moreover, the wastewater originating from point and non-point pollution sources and the excessive use of aquatic organisms is leading to the deterioration of river water quality, biological habitat fragility, biodiversity reduction and a lack of ecological ûow as well as damage river structure. These activities have adverse impact on natural ecosystem and societal system. Fish mortality and spreading of water borne diseases are reportedly the clear evident of deterioration of water quality.
Natural river water quality, better to say river health is crucial to the survival of humanity, as they not only provide water for domestic, industrial and agricultural uses but are also essential for ecological services to commerce, transportation, recreation and other activities.
As rivers are an important component of the terrestrial environment, they are vulnerable to human impacts, leading to changes in water quality and biological diversity. Globally, climate change and disruptive human activities have altered water cycles and river environments, such as hydrological conditions, pollutant loads, and habitat attributes. Human activities that affect river ecosystem continue to increase and its impact on the river ecosystem is becoming more and more serious, and causing a continuous degradation of the health of rivers and has become a major crisis for human survival and sustainable development.
Thereby rivers must be protected through ecological restoration for the benefit of the people. The restoration of river ecosystems and the sustainable management of rivers have become a common concern of the international community.
In India, water quality of the rivers is assessed based on chemical parameters namely, Biological Oxygen Demand, Dissolved Oxygen, Total Coliform, pH, Free Ammonia and Electrical Conductivity with reference to its designated “best use” (a. drinking water sources with chlorination; b. Outdoor bathing; c Drinking water source after conventional treatment and disinfection, d. Propagation of wildlife and fisheries and; e. Irrigation, industrial cooling and controlled waste disposal), assuming the wastewater being discharged to river contains mainly biodegradable organic substances. This practice was invented and implemented in 1978 considering the level of pollution potential and limitations in water quality monitoring particularly sampling and analytical techniques and lack of understanding of water ecosystem during that period.
In the last two decades, with the advancement of science and technology and contamination of river water by a series of chemical substances due to industrialization, agricultural practice using chemical fertilizers and pesticides, and change of human lifestyle, this practice has serious drawbacks in assessing river health because ecological integrity with reference to strong human activities remain well hidden. Another major drawback is lack of accuracy of the water quality data. Nowadays, the study of river health assessment method has made a great progress, and many methods are available and widely used but the practices adopted in 1978 are being still followed.
The river ecosystem is a dynamic process with constant changes, especially when the disturbance of human activities reach to a certain level, making the originally natural rivers moved toward socialization. The evolution of river ecosystem will then gradually shift toward the direction of human service demands. Now emergent need is to expand the connotation of river health from the perspective of harmony and dynamic evolution to lay the foundation for river health assessment as the basis of scientiûc management of rivers. Evaluation should be done from the aspects of ecosystem integrity and human service demands.
Therefore assessment of a river ecosystem needs to integrate physical, chemical and biological variables to characterize the threats to its health in a sufficiently robust way. Among these variables, water quality , aquatic species, riparian condition and sediment health considering large geographical diûerences, catchment characteristics and habitat-speciûc species attributes present in river systems determines the structure of river ecosystem communities. My experience from the study of different rivers ( 8 nos) based on the measurements of physical and chemical parameters and biotic communities of the rivers and basin characteristics including human activities helps to understand the necessity of balancing ecological integrity and human demand services and to provide status of river health.
The rivers flowing through mountain areas (Meghalaya, Sikkim and others) particularly at the upstream of mountainous cities face the weak intensity of human activity and its impact on the river ecosystem is negligible. The river ecosystem has evolved entirely under natural forces, and maintains its dynamic balance through the natural attributes of river. With the enhancement of human activity even in hilly area with small human settlement and farming, the river has a larger social attribute but the natural attributes of the river still dominate the evolution of the river ecosystem and thereby its adverse effect due to human activities is restored through its self assimilation process. Human activities like construction, sprawling of towns, development of small and medium industries and agriculture is moderately stronger and its impact on the river ecosystem exceeds the threshold of critical damage. In this situation, the temporary equilibrium established by both natural and social attributes continues to change with the continuous change of human activities and cause an upward evolutionary trend. If the human activities are controlled, the river ecosystem may reach to an equilibrium state through self-regulation. Human activities in the metropolitan cities, large industrial areas and mining areas is so strong that the social attribute of the river gradually increases and the river ecosystem cannot restore through self-regulation to meets the river health requirements. The problem is further aggravated due to insufficient ecological ûow quantity that is required to dilute the pollutants. The climate change and human activities are the two main reasons for the ûow variation.
As a result of human activities, the reduction in forest cover due to industrial and housing complex development has changed the corresponding regional evapotranspiration so that the forest water balance and water cycle of the basin have been destroyed, resulting in the tendency of the variation of the ûow of the many rivers. In these rivers, the water quality and even sediment quality with reference to physical and chemical parameters including metals are above the healthy level and it is practically in a morbid status and thereby the aquatic environment has been seriously destroyed. The habitat complexity due to discharge of pollutants and riparian vegetation due to non-eco-friendly developmental activities are poor. In terms of river structure, the water system has poor connectivity. The sustainable utilization of rainwater resources in almost all the river basins is low. The wastewater treatment and management strategy are not satisfactory as observed in the cities in India. It is true that many rivers systems all over India are either moderately influenced or strongly influenced by the social attribute. If the intensity of human activity is going to reach the extreme level, the river ecosystem will continue to deteriorate to the brink of collapse.
This is the high time to avoid this devastation of river ecosystem. Now human must take some active measures to repair the river ecosystem systematically, comprehensively and accurately considering the harmony between human development and river ecosystem health. For this purpose, appropriate methodology must be defined to assess the river health and to provide a scientiûc decision-making basis for river health management in actual watershed management. Based on this assessment, some harmonious measure is to be taken to improve the relationship between human and rivers. In addition to these, regulatory measure must be strengthened.
The writer is Former Senior Scientist, Central Pollution Control Board, and is based in Kolkata and can be reached at 919432370163 & 916290099509 or [email protected]