The cause of the recent mass deaths of fish may be related to fertilizer contamination in the river in India’s water bodies.
Images of dead fish floating in the Banganga tank in Mumbai’s Malabar Hill area were widely shared on news sites and other media platforms in April 2022. Locals discovered the dead fish in the tank and alerted the Brihanmumbai Municipal Corporation, which then started the cleanup process. Four trucks of fish, according to the cleanup contractor, were hauled away from the scene. The depletion of oxygen, according to officials, was most likely what caused the large number of fish deaths.
This isn’t the first time that something similar has happened. In prior years, the Banganga tank’s widespread fish deaths were referred to be a “annual tragedy.” People putting a lot of food in the water as part of religious rituals has been one of the main causes of fish deaths.
In an another incident, which occurred more recently, a large number of dead fish were discovered in a five-kilometer section of the Najafgarh drain upstream of the Delhi-Haryana boundary. According to early accounts, these deaths may be related to fertilizer contamination in the river, which results in algal blooms that reduce the oxygen content of the water and kill aquatic life.
In many ponds, lakes, and other bodies of water throughout India, fish and other aquatic creatures have perished in large numbers. Water pollution, which most frequently results from anthropogenic activity, is the main source of this phenomenon.
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Even while mass fish deaths or polluted lakes, ponds, and other water bodies may not be instantly or directly felt by city people, it is important to understand one’s part in the issue and accept responsibility.
“Without our rivers, lakes, ponds and other water bodies, India’s geography, language and culture would be very different. People are intertwined with these water bodies in material and spiritual ways.” Priya Ranganathan, a PhD student at the Ashoka Trust for Research in Ecology and the Environment who has researched on subjects like wetland ecology, community-based conservation, and ecohydrological flows, argues that “water bodies are a crucial culture of any civilisation.
“When an aquatic ecosystem is adversely affected, local species are wiped out and this harms local livelihoods. Even if city dwellers do not interact with water bodies on a daily basis and may not immediately feel the effects of water pollution, it would be selfish not to care about and protect these important habitats,” she adds.
A wide variety of parameters can be used to measure water quality or pollution. Dissolved oxygen, temperature, electrical conductivity or salinity, pH, and turbidity are the five fundamental water quality markers.
The amount of oxygen that is dissolved in water—known as dissolved oxygen—is crucial for the survival and development of the majority of aquatic species. This is a crucial sign of the water’s quality and the ability of the body of water to sustain ecosystems and aquatic life.
The chemistry of the water and the activities of aquatic creatures, such as metabolic rates, timing of reproduction, migration, etc., are all influenced by the water’s temperature.
As a result of dissolved salts in the water splitting into positively and negatively charged ions, conductivity, or the capacity of the water to conduct electricity, is a result.
The quantity of salts in water is measured by salinity; as dissolved salts raise both salinity and conductivity, the two are connected. Aquatic biota are significantly impacted by salts and other dissolved chemicals. There is a typical salinity range that each type of creature can withstand.
The pH is a measure of the water’s acidity or alkalinity. A relatively small pH range is required for a number of chemical processes that aquatic organisms depend on to survive and grow. Physical harm to the creatures’ gills, exoskeletons, and fins can happen at the extreme ends of the pH range, which are severely acidic or excessively alkaline. The toxicity of a body of water is also impacted by pH changes.
The amount of suspended particles in the water is measured by turbidity. Turbidity is caused by suspended dirt, organic matter particles, and algae. Heat is absorbed and sunlight is diffused by suspended particles. As a result, the water body’s temperature rises, less light is available for algal photosynthesis, and fish gills become clogged. Additionally, as the material settles, it can foul gravel beds and smother fish eggs and benthic insects.
Nitrogen and total coliform are additional risk factors. Both fresh and salt water naturally contain the nutrient nitrogen. For plants to grow in an aquatic ecosystem, it is crucial. However, excessive algal development may result when significant amounts of nitrogen are delivered into an aquatic habitat, such as through fertilizer runoff.
The algae’s need of oxygen for photosynthesis causes a process known as “eutrophication,” which reduces the amount of oxygen accessible to aquatic creatures. The dissolved oxygen in the water body is decreased as a result, which might suffocate and kill the organisms there.
Total and faecal coliform bacteria, as well as E. coli, are indicators that a water body has been contaminated with feces, such as by untreated sewage discharge. Because they are simpler to detect than other pathogens and can consequently disclose the level of contamination in a water body, they are also known as “indicator bacteria.”
The Central Pollution Control Board of India assesses the quality of lakes and ponds using the aforementioned factors as well as a number of additional ones, including temperature, dissolved oxygen, pH, conductivity, biological oxygen demand, nitrates and nitrites, faecal coliform, and total coliform.
In the 2019 CPCB data (pdf below) on ponds and lakes, “dissolved oxygen” was the metric that was most thoroughly documented with the least gaps.
Dissolved oxygen, or DO, is a useful indicator of a body of water’s health and biological productivity. DO is a clear sign of how well an aquatic resource can support aquatic life.
When an excessive amount of organic matter or nutrients enter water bodies, it can lead to conditions like eutrophication, which can result in low oxygen levels (hypoxia) or no oxygen at all (anoxia). Each organism has a different range of DO tolerance, however concentrations below 3 mg/L are alarming and mostly lethal for fish populations. Hypoxic conditions are those with levels below 1 mg/L, which are often devoid of any life.
Using data from the Central Pollution Control Board from 2019, the dot chart below displays the average dissolved oxygen levels in water bodies throughout six Indian states. The CPCB data keeps track of the dissolved oxygen levels’ minimum and highest values. The values for states with 20 or more available data points have been averaged, and the resulting graphic is shown below.
The map shows that many of the water bodies located throughout the states are incapable of supporting any aquatic life. Most of the lakes and ponds in Karnataka and Telangana are between the DO range of 0–4 mg/L, where no fish can survive; the higher the DO range, the better the possibility that any fish can survive.
There are 215 water bodies that have been plotted, and of them, 76 are in the 0–4 mg/L DO range, 75 are in the 4-6.5 mg/L DO range, and 64 are in the 6.5–9.5 mg/L DO range. Assam and Madhya Pradesh are the two states that perform the best of the six states, with 28 and 18 respectively, of the 64 water bodies in the 6.5-9.5 mg/L range.
The most alarming finding is that, across all states, not a single body of water falls inside the 9.5+ mg/L DO range, where all fish can survive.
Urban water pollution
India’s rapid industrialization in recent years has rendered almost 70% of its surface water unsafe for consumption, and severe waterbody contamination has led to the mass extinction of aquatic life. For instance, numerous lakes in Bengaluru are now completely uninhabitable to aquatic life, while others routinely have dead fish, snails, or other aquatic life floating around in their waters as a result of untreated effluents, chemicals, and pesticides entering the area.
The livelihoods of fishermen are also negatively impacted by the contamination of water bodies. Several dead fish were discovered floating in a pond at Parwada in Visakhapatnam in September 2021. Local fish farmers protested for a week, claiming that nearby industrial facilities had contaminated the tank that supplied water to the pond. They urged that action be taken right away to resolve the situation.
The main causes of water pollution and low DO levels in India’s ponds and lakes are sewage and waste disposal. According to a Rajasthan Pollution Control Board report from 2017, infections and low oxygen levels in Jal Mahal Lake were primarily caused by indiscriminate sewage discharge.
The Banganga tank example demonstrates how religious events also contribute to the problem. Pushkar Lake in Rajasthan is another illustration. Due to its mythological significance, many pilgrims and tourists visit it every year, and anthropogenic activities cause water contamination.
The annual Pushkar Fair, which takes place in tandem with the Cattle Fair, places additional strain on the lake. Cows sometimes urinate close to the lake’s edge, which causes an accumulation of organic garbage, and people frequently try to feed the cows and other animals there. The aquatic life in the lake is put in danger and DO levels are decreased.
When dangerous elements like chemicals or microorganisms pollute a stream, river, lake, ocean, aquifer, or any other body of water, they cause water pollution. This lowers the water’s quality and makes it toxic for both humans and the environment.
Climate change, according to Ranganathan of ATREE, is a significant problem for water bodies. Numerous feedback reactions affect water bodies as temperatures rise. For instance, when the components holding carbon storage together disintegrate, carbon dioxide is released into the water.
Water pollution not only threatens human health but also has a variety of cascading effects on aquatic ecosystems. Ranganathan adds that in addition to agricultural and industrial sources, poorly designed infrastructure and excessively diverting water bodies, like rivers, from their intended flow can also drastically influence aquatic chemistry. She notes that untreated sewage and rubbish disposal are significant challenges in the Indian context.
Speaking of mass fish death events in particular, she says, “Heavy metal poisoning is often a key factor for such fish kill events. Even if a small amount of heavy metals enter a waterbody, their effect on the ecosystem gets amplified due to processes such as biomagnification and bioaccumulation. Heavy metals are often retained by aquatic plants and settle on waterbeds. The metals and toxins are first consumed by bottom feeding organisms, and the quantities magnify up the food chain. Industrial waste, pesticides, pest control chemicals can all drive such fish kill events due to the high concentrations of heavy metals in them.”
Recent years have seen the emergence of numerous lake and pond rehabilitation initiatives both abroad and in India. The best ways to carry out these projects are frequently through decentralized governance and localized efforts since they can address the problems unique to the water body in question.
One technique to successfully identify the local spread of water pollution is through data collecting, particularly using automated, geotagged, time-stamped real-time sensors to collect data on water quality in a non-stationary manner. In order to assist regulatory compliance decision-making, provide an early-warning indication system, and evaluate the efficacy of sanitary measures, reliable and accessible data is a crucial tool.
Furthermore, as Ranganathan points out, long-term research are crucial to determining the effectiveness and success of various approaches. These studies can demonstrate the types of solutions that can be maintained over time.
Water quality can change significantly and dramatically over time as a result of regulations, policies, and financing aimed at improving solid waste management, constructing infrastructure for wastewater treatment, and enacting strict legislation to reduce industry pollution.
It is also possible to promote and nurture innovations in the field of water pollution to bring about significant change. Building “floating islands,” where aquatic plants are positioned on buoyant mats and may absorb heavy metals like manganese, iron, aluminum, and other toxins through their roots and foliage to purify contaminated water, is an example of one such innovation.
A favourable climate for action that effectively tackles water pollution can be created by combining top-down government-led regulatory and legislative change with support for bottom-up localized initiatives. In the end, this can help aquatic systems regain their natural balance.
Read the study given below: