River Water Temperature (RWT), and Dissolved Oxygen (DO) are crucial indicators of the water quality of rivers and determine the health of the river and its ecosystem.
Water temperature is one of the most important factors affecting water bodies and can impact dissolved oxygen levels, chemical and biological processes, species compositions, water density and stratification, and life-stages in different organisms living in the water.
Aquatic organisms need optimal temperatures for their survival and high and low temperatures can have detrimental effects on aquatic life increasing stress levels and can lead to death. The reproductive stage (spawning & embryo development) in fish is the most temperature-sensitive period. Temperature also affects ammonia levels in the water, the rate of photosynthesis, metabolic rates in aquatic organisms, and increase pollution levels thus threatening the survival of aquatic organisms.
Water temperatures can fluctuate throughout the day, and between seasons. While water temperatures in freshwater systems are heated by the sun, a number of factors such as precipitation, groundwater, and surface runoff can influence the water temperatures leading to loss or gain in heat depending on condensation and evaporation.
A recently published study titled 'Impact of climate change on river water temperature and dissolved oxygen: Indian riverine thermal regimes' published in Nature Scientific Reports informs that global warming has been found to have an adverse impact on River Water Temperatures (RWT), which in turn are known to adversely impact Dissolved oxygen (DO) levels in rivers, which are important indicators of river water quality.
The influence of climate change on DO in relation to RWT can lead to water quality degradation and ecological disturbances in the river habitats and affect the river’s ability to self-purify by lowering the amount of oxygen that can be dissolved and utilised for biodegradation. Hence, understanding climate change impacts on RWT and DO are important in understanding the projected river water quality and possible alterations in quality standards.
While recent studies have looked at how climate change affects RWTs, the question of how climate change affects DO has yet to be answered.
Tropical rivers receive more solar radiation and have higher RWTs. For example, Indian tropical river systems experience the highest RWTs during low flow periods of non-monsoon and summer months. Seasonality plays a vital role in the Indian river systems as maintaining flows in the summer season is a challenge leading to water quality deterioration.
The assessment of DO saturation rates with respect to RWT is crucial for Indian river systems due to minimum flows and higher temperatures during non-monsoon seasons.
This study aimed at predicting the impacts of climate change on riverine thermal processes in India and assessing the possible variability in DO saturation levels with respect to RWT in seven majorly polluted catchments of India namely Ganga, Narmada, Cauvery, Sabarmati, Tungabhadra, Musi and Godavari in the time period of 2071-2100.
The study provides an assessment of the impacts of rise in river water temperatures (RWTs) on dissolved oxygen content in the river waters indicative of the health of rivers and its ecology under climate change scenarios, which will be greatly helpful for the policymakers and pollution control authorities to design sustainable river water quality management strategies for the future, argues the paper.