Variation in Physicochemical Water Quality of Mansagar Lake, Jaipur, Rajasthan, India

Freshwater lakes are more than just scenic backdrops; they are living systems that balance the needs of nature and people. They provide drinking water, support fish populations, and help regulate local climates. However, when cities grow around them, these water bodies face a constant struggle. Human activities like dumping sewage, running off stormwater from streets, and building on the surrounding land can overwhelm a lake's ability to clean itself. The health of a lake is often measured by a few key indicators: how much oxygen is dissolved in the water for fish to breathe, how much organic waste is present that bacteria must break down, and the concentration of dissolved minerals and salts. When these factors shift too far, the water can become toxic or unable to support life. Understanding how these conditions change with the seasons is critical, because a lake that looks healthy in the rain might be in crisis during the dry heat.

In the heart of Jaipur, Rajasthan, lies Mansagar Lake, a historic reservoir famous for the Jal Mahal, a palace that sits in its center. While it is a major tourist attraction, the lake is also a vital part of the local ecosystem. Researchers Manish Kumar and Dr. Swati Gupta from Vivekananda Global University set out to understand how the water quality here changes throughout the year. They focused on three distinct seasons: the hot summer, the rainy monsoon, and the cool winter. By collecting water samples from four different spots around the lake—including the entry points where city drains flow in, the central area near the palace, and the outlet—they tracked how the water's physical and chemical makeup shifted over time. Their goal was to see if the changing weather and the pressure from the surrounding city were making the water better or worse at different times of the year.

The team followed strict, standard procedures to test the water, measuring everything from temperature and clarity to the amount of oxygen and organic pollution. What they found was a clear pattern of seasonal stress. During the summer, the lake was in its worst state. The water levels dropped, and the heat seemed to concentrate the pollutants. The most alarming finding was the level of biological oxygen demand, a measure of how much oxygen bacteria need to break down organic waste. In the summer, this value soared to an average of 164.75 milligrams per liter, a sign that the water was choked with sewage and runoff. At the same time, the amount of dissolved oxygen available for fish and other life plummeted to just 2.02 milligrams per liter. This combination suggests that the lake is receiving a continuous, heavy load of untreated waste, which consumes the oxygen that aquatic life needs to survive.

The situation improved slightly during the monsoon season, but not in the way one might hope. The heavy rains brought a massive influx of water, which diluted the concentration of some pollutants like salts and minerals. However, the rain also washed a large amount of dirt and sediment into the lake, making the water cloudy and turbid. While the oxygen levels rose slightly compared to the summer, the overall organic pollution remained high. The winter season offered the best conditions, with higher oxygen levels and lower pollution readings, yet the water still showed signs of significant human impact. The data revealed that the lake is not just suffering from one bad event, but from a persistent cycle of pollution driven by the city's sewage and runoff, which the lake cannot fully clean on its own.

Statistical analysis confirmed that these changes were not random. The differences in oxygen, pollution, and mineral content between the seasons were significant enough to rule out chance. The researchers found a strong link between the amount of organic waste and the drop in oxygen, confirming that as pollution increases, the water becomes less able to support life. They also noted that the water in the lake remained alkaline throughout the study, with pH values ranging from 8.15 in the summer to 9.20 in the monsoon season, a condition influenced by minerals washed in from the surrounding hills and the city. The study highlights that while the monsoon rains provide a temporary relief by flushing out some contaminants, they also bring new problems in the form of sediment and runoff.

The findings paint a picture of a lake under constant pressure. The high levels of pollution, particularly during the hot summer months, indicate that the current management of the surrounding area is insufficient. The researchers suggest that to save the lake, specific actions are needed right where the pollution enters. This includes better treatment of the sewage that flows into the lake, managing the runoff from the city streets, and protecting the land around the lake from erosion. Without these targeted efforts, the lake will likely continue to struggle, facing ongoing threats to its fish and its ability to serve the community. The study serves as a clear warning that for urban lakes in dry regions like Rajasthan, seasonal changes do not fix the problem; they only change how the problem appears. Sustainable recovery requires a consistent, year-round approach to cleaning the water and managing the land that feeds into it.