Environmental Management (0680) | Water pollution and its sources

🌊 Chapter 4.7: Water Pollution and Its Sources 💧

Hello future Environmental Manager! This is a really crucial chapter. We rely on fresh water for almost everything—drinking, farming, and industry. But sadly, much of our water is getting contaminated.

In this section, we will break down exactly what water pollution is and, more importantly, track down the main sources of contamination based on human activities. Understanding where the pollution comes from is the first step toward managing and stopping it!

What is Water Pollution?

Put simply, Water pollution occurs when substances are introduced into water bodies (like rivers, lakes, or groundwater) that change the water quality, making it harmful to living organisms or unusable for humans.

Key Concept: Point Source vs. Non-Point Source Pollution

When classifying pollution sources, we usually divide them into two categories. This helps us decide how to regulate and clean up the waste.

1. Point Source Pollution

• Definition: Pollution that comes from a single, identifiable location.
• Analogy: Imagine a specific pipe (a 'point') dumping waste directly into a river.
• Examples: A sewage treatment plant outlet pipe, a factory drainage ditch.
• Management: Easier to monitor and regulate because you know exactly who is responsible.

2. Non-Point Source Pollution

• Definition: Pollution that comes from a wide, spread-out area, making the source hard to pinpoint. It usually happens when rainfall or snowmelt runs over land.
• Analogy: Imagine rain washing fertiliser off an entire farm field. You can't point to one specific pipe.
• Examples: Agricultural runoff (fertiliser and pesticides), oil and grit washed off city roads.
• Management: Much harder to control because it involves managing large areas and many different land users.

The Three Main Sources of Water Pollution (Syllabus Focus 4.7)

Human activity generates three major types of waste that pollute water: domestic, industrial, and agricultural.

1. Domestic Waste (Sewage)

This comes from our homes and settlements, both urban (cities) and rural (villages).

What is it?

• Sewage: Water containing human waste, laundry water, bathing water (often called grey water).
• Solid Waste: Household garbage that leaks contaminants (leachate) when dumped near water sources.

The Impact on Water Quality:

The two main problems caused by untreated sewage are Pathogens and Organic Matter.

• Pathogens: Sewage contains high levels of harmful microorganisms (bacteria, viruses, parasites) that cause severe water-borne diseases.
  Did you know? Diseases like Cholera, Typhoid, and Dysentery are often spread through water contaminated by human sewage.
• High Organic Matter: This includes human faeces, food scraps, and soap residue. When this matter enters water, bacteria start decomposing it.
  This decomposition process uses up huge amounts of dissolved oxygen in the water. If the oxygen levels drop too low, fish and other aquatic life will die (a process called deoxygenation).

2. Industrial Processes

Industry uses vast amounts of water for cooling, washing, and as a solvent in chemical reactions. The waste products are often the most dangerous forms of pollution.

What is it?

• Toxic Chemicals: By-products from manufacturing (like textiles, plastics, and electronics) can include corrosive acids, powerful alkalis, and complex organic chemicals.
• Heavy Metals: These include mercury, lead, and cadmium. They are highly poisonous, even in small concentrations, and do not break down naturally.
• Thermal Pollution: Factories (especially power plants) often use water to cool machinery. They then release the hot water back into rivers or lakes.

The Impact on Water Quality:

• Toxicity: Direct poisoning of aquatic organisms and humans who drink the water.
• Bioaccumulation: Heavy metals are particularly dangerous because they build up in the tissues of organisms as they move up the food chain. This is called bioaccumulation or biomagnification (we will cover this more later, but remember: the longer the food chain, the higher the concentration of the toxin in the top predator, like us!).
• Thermal Shock: Hot water reduces the dissolved oxygen capacity of the water (less oxygen can dissolve in warm water) and stresses aquatic organisms, changing their migration patterns or killing sensitive species.

3. Agricultural Practices

Pollution from farms is typically a Non-Point Source, washed off the land by rain (runoff). The main culprits are fertilisers and pesticides.

What is it?

• Fertilisers: Excess nitrogen and phosphorus applied to crops to boost growth.
• Pesticides/Herbicides: Chemicals used to kill unwanted insects (pests) or weeds (herbs).
• Sediment: Soil eroded from fields, which increases the cloudiness (turbidity) of the water, blocking sunlight.
• Animal Waste: Manure from livestock farming, which acts similarly to human sewage (high organic matter and pathogens).

The Impact: Eutrophication

This is the most important concept linked to fertiliser pollution. Eutrophication is the process of nutrient enrichment in a body of water, leading to excessive plant growth and subsequent oxygen depletion.

Here is the step-by-step process of eutrophication:

1. Nutrient Runoff: Excess nitrates and phosphates from fertilisers wash into a lake or river.
2. Algal Bloom: These nutrients act as super-food for tiny water plants (algae), causing them to multiply rapidly and cover the surface of the water—this is the 'algal bloom.'
3. Sunlight Blocked: The dense layer of algae blocks sunlight from reaching plants deeper underwater, killing them.
4. Algae Die: Eventually, the algae run out of nutrients or light and die, sinking to the bottom.
5. Oxygen Depletion: Decomposer bacteria use up huge amounts of dissolved oxygen while breaking down the dead algae and deeper plants.
6. Dead Zone: The resulting lack of oxygen kills fish and other aquatic life, creating a "dead zone" (or anaerobic environment).