Quality of water in waterbodies

Description

Context:

Microbes from human, animal excreta found above desirable limits in Yamuna
The report submitted to the Union Ministry of Jal Sakti also stated that in the absence of a “minimum environmental flow” (flow of water) of the Yamuna in Delhi.
“Minimum environmental flow for the dilution of the polluted water in the Yamuna in Delhi is required to meet the desired water quality levels in the river for bathing purpose i.e. BOD<3 mg/l and DO>5 mg/l,” the report read.
The 22 km stretch of Yamuna from Wazirabad to Okhla in Delhi, accounts for about 80% of the pollution load in the river.

Assessment of water quality

The Central Pollution Control Board (CPCB) in 2018 identified 351 polluted river stretches in India.
The assessment of water quality for identification of polluted river stretches found that 31 states and Union territories (UT) had rivers and streams that did not meet the water quality criteria.
These states / UTs have to submit their action plans for the same.

The key water-quality indicators:

Dissolved oxygen (DO): The DO test measures the amount of oxygen dissolved in the water. Oxygen is essential for both plants and animals, but high levels in water can be harmful to fish and other aquatic organisms.
Water temperature: Aquatic organisms are dependent on certain temperature ranges for optimal health. Temperature affects many other parameters in water, including dissolved oxygen, types of plants and animals present and the susceptibility of organisms to parasites, pollution and disease.
pH: A pH test measures the alkalinity or acidity of water. A pH of 7 is neutral, below 7 is acidic and above 7 is basic or alkaline. Acid rain, from auto exhaust or other pollutants, causes a drop in the pH.
Escherichia coli (E. coli): coli is a fecal coliform bacteria that comes from human and animal waste. The Environmental Protection Agency uses E. coli measurements to determine whether fresh water is safe for recreation. Disease-causing bacteria, viruses and protozoans may be present in water that has elevated levels of E. coli. Levels of E. coli can increase during flooding. E. coli is measured in number of colony forming units.
Specific conductance: The specific conductance test measures the ability of water to pass an electrical current. Conductivity in water is affected by inorganic dissolved solids such as chloride, sulfate, sodium, calcium and others. High conductance readings also can come from industrial pollution or urban runoff, such as water flowing from streets, buildings and parking lots.
Nitrates: Nitrogen is a nutrient necessary for growth of all living organisms. The CRWN nitrogen tests measure nitrate (NO3-N). Excessive amounts of nitrates increase algae growth. Algae can rob the water of dissolved oxygen and eventually kill fish and other aquatic life.
Transparency: Transparency measures how far light can penetrate a body of water. Sunlight provides the energy for photosynthesis and determines the depth at which algae and other plants can grow, defining the ecological make-up of a water body. A change in water clarity may be noticed after heavy rains, as silt and debris can run off, causing the visibility to decrease.