| dc.description.abstract | Anthropogenic factors such as climate change, land use land cover change and industrial and population growth can influence river water quality. Climate change affects water quality due to changes in stream temperature and streamflow due to increased air temperature and varied precipitation patterns associated with warming. Land use land cover influences water quality mainly from the agricultural runoff, which carries the pollutants from fertilizers and pesticides and reaches the nearby water body. Population growth can increase the water demand and sewage generated hence aggravating pollution. Industrial growth has the potential to affect water quality through increased effluent loads. The work presented in this thesis contributes to quantifying such anthropogenic influences on river water quality using a coupled hydrological-water quality simulation model. The study area considered is a 238km stretch of Ganga river in India from Ankinghat to Shahzadpur, passing through Kanpur, which is identified as the most polluted stretch of Ganga river by the Central Pollution Control Board of India.
Sensitivity studies with forcings such as climate change and land use are extremely important for any management decision on water quality. In the initial part of the thesis, the sensitivity of nine water quality parameters to climate change and land use change is assessed using idealized scenarios and a standalone water quality simulation model, QUAL2K. The key input model parameters contributing to model uncertainty and key locations are identified using first order reliability analysis. The water quality parameters considered are DO, BOD, ammonia, nitrate, total nitrogen, organic-, inorganic-, and total phosphorous and faecal coliform. The non-point source pollution is quantified using the export coefficient method, in which pollutants from all land use classes are considered. Eight climate change and six land use land cover scenarios are framed based on historical data analysis to assess their sensitivity to water quality parameters. DO is the most sensitive indicator to the climate change scenarios considered, while nutrients and faecal coliform are more sensitive to the land use scenarios. In general, the water quality parameters are found to improve with a rise in air temperature and deteriorate with a reduction in streamflow. An increase in the agricultural land area leads to higher nutrient concentration, while an increase in the built-up area causes an increase in faecal coliform concentration. An increase in forest land shows better water quality in terms of all water quality parameters. The key input variables contributing to the uncertainty of water quality simulation are the head water discharge, point and non-point pollution loadings, water temperature, and corresponding reaction rates. The key locations identified using first order reliability analysis are Kanpur downstream and Jajmau downstream.
Risk assessment studies on water quality for future scenarios are limited in the literature. In the next part of the thesis, the effect of climate change on water quality, the risk of eutrophication and fish kill for the mid-and end of the 21st century for this river stretch are assessed. The risk of eutrophication and fish kill are quantified using simulated concentrations of nutrients and DO, respectively. Downscaled climate change projections for two climate change scenarios (RCP4.5 and RCP8.5) are used to drive a hydrological model coupled with a water quality simulation model. The simulations indicate a potential deterioration of water quality in this stretch in the mid-21st century, with a potential increase in pollutant concentration by more than 50% due to climate change alone. The risk of reduced dissolved oxygen and increased organic and nutrient pollution, and the risk of eutrophication and fish kills increase with warming due to the rise in the frequency of low-flow events and a reduction in streamflow during low-flow events. However, the risk of nitrate and microbial pollution is reduced due to increased denitrification and pathogen decay rates with warming. The risk of eutrophication and fish kill is found to increase by 43.5% and 15% due to climate change alone by the mid-21st century. The risk of eutrophication is found to increase by 6% due to land use change which can be attributed to an increase in nutrient loading with land use change.
In the final part of the thesis, the individual effects of climate change, land use land cover change, population and industrial growth on river water quality are assessed with a coupled hydrological-water quality simulation model and the predominant factor contributing to pollution is identified. Also, the future water quality is projected for mid 21st century considering climate change, land use projections, population and industrial growth, and the proposed treatment for the stretch considered using socio-environmental scenarios. The effectiveness of the proposed treatment to offset the reduction in water quality from anthropogenic forcings is also assessed. The climate change effect is found to have a larger effect on water quality than other drivers, with a percentage contribution of above 70% because of the considerable sensitivity of water quality parameters to the amount of streamflow. Climate change projections combined with socio-environmental scenarios imply that the large increase in pollution due to climate change, land use land cover, industry, and population growth cannot be controlled by the current treatment proposals for 2050 by the authorities. However, providing adequate STPs to meet the population of 2050, and allowing only domestic sewage to reach STPs can help in achieving the objective of the Ganga Action Plan in the mid-21st century.
The thesis comprises of five chapters. An introduction to the problem addressed, and the objectives of the work presented in the thesis are provided in Chapter 1. Details of the case study and analysis of the sensitivity of water quality parameters to climate change and land use with idealized future scenarios are discussed in Chapter 2. In Chapter 3, the risk assessment of low water quality, eutrophication and fish kill under changing climate and land use land cover is presented. Chapter 4 presents the analysis of the individual effects of all external forcings, including climate change, land use change, population and industrial growth. Conclusions drawn from the study are presented in Chapter 5. | en_US |
