Biology (0610) | Pollution

Welcome to Chapter 20.3: Pollution – Human Influences on Ecosystems!

Hi future Biologists! This chapter is super important because it connects what we learn about living things (like food chains and ecosystems) with the real-world impact that humans have every day.

Pollution refers to the introduction of contaminants into the natural environment, causing adverse change. Don't worry if some terms seem complicated; we will break down the three main types of pollution you need to master: Water, Plastic, and Air. Let's make sure you understand exactly how human actions affect our global ecosystems!

Part 1: Water Pollution and Eutrophication

Sources of Aquatic Pollution (Core)

The two main sources of nutrients entering aquatic ecosystems (rivers, lakes, ponds) that cause problems are:

• Untreated Sewage: This organic waste contains high levels of bacteria and dissolved nutrients, particularly nitrates and phosphates.
• Excess Fertiliser: When farmers use too much chemical fertiliser, the rain washes (leaches) the excess nitrates and other ions into nearby waterways.

The Process of Eutrophication (Supplement / Extended Content)

When too many nutrients enter a body of water, it causes a specific chain reaction called eutrophication. This is a crucial concept, so let's go step-by-step!

Imagine a small pond.

Step 1: Nutrient Overload

There is an increased availability of nitrate and other ions (from sewage or fertilizer). These ions are essential nutrients for producers (like aquatic plants and algae).

Step 2: Producer Bloom

These excess nutrients cause an increased growth of producers, especially tiny organisms like algae. This rapid growth is called an algal bloom.

Step 3: Light Blockage and Death

The thick layer of algae on the water surface blocks sunlight from reaching the plants deeper down, causing them to die. Eventually, the dense algae themselves start to die off because they use up all the available nutrients. This leads to increased decomposition after death of producers.

Step 4: Oxygen Depletion

When organic material (dead algae and plants) increases, decomposers (aerobic bacteria) multiply rapidly to break it down. These decomposers carry out increased aerobic respiration, which means they use up huge amounts of oxygen dissolved in the water.

Step 5: The Fatal Effect

The massive consumption of oxygen leads to a severe reduction in dissolved oxygen levels. This low oxygen level causes the death of organisms requiring dissolved oxygen in water, such as fish and aquatic insects.

Part 2: Plastic Pollution

Effects of Non-Biodegradable Plastics (Core)

Plastics cause long-lasting pollution because they are non-biodegradable. This means they cannot be broken down naturally by bacteria or other decomposers. They simply accumulate in the environment.

In Aquatic Ecosystems (Oceans, Rivers, Lakes)

The presence of plastics causes several major biological problems:

• Entanglement: Animals (like seals, turtles, and birds) get physically trapped in large plastic items, such as nets, plastic bags, or six-pack rings, leading to injury or drowning.
• Ingestion: Many marine animals (especially filter feeders or those that mistake plastic pieces for food like jellyfish) eat plastic. Since plastic cannot be digested, it fills their stomach, giving them a false sense of fullness.
• Blockage: Ingested plastic can cause digestive system blockage, leading to starvation and death, even if the animal's stomach is "full."

In Terrestrial Ecosystems (Land)

Although plastics are less immediately visible on land than in the ocean, they still cause harm:

• Habitat Disruption: Large amounts of waste plastic physically destroy habitats and spoil the environment.
• Soil Smothering: Plastic waste can cover the ground, blocking sunlight and preventing the growth of plants, disrupting food chains.

Did you know? Even when plastics break down physically (due to sunlight and waves), they turn into microplastics, which are still ingested by tiny organisms and move up the food chain!

Part 3: Air Pollution and Climate Change

Key Air Pollutants (Core)

The syllabus focuses on two gases responsible for the enhanced greenhouse effect:

• Carbon Dioxide (\(CO_2\)): The primary source is the combustion of fossil fuels (coal, oil, gas) for industry, power generation, and transport. It is also released through large-scale deforestation and decomposition.
• Methane (\(CH_4\)): A powerful greenhouse gas whose sources include large-scale livestock farming (released from digestion by cows) and decomposition in landfill sites and rice paddies.

The Greenhouse Effect (Core)

To understand the problem, you must first know that the natural greenhouse effect is essential for life on Earth!

The Earth absorbs solar radiation (light energy) and warms up. The Earth then radiates this energy back out as heat (infrared radiation). Certain gases in the atmosphere (like \(CO_2\) and methane) trap some of this heat, acting like a blanket and keeping the planet warm enough for life.

The Enhanced Greenhouse Effect

When humans release excessive amounts of \(CO_2\) and methane, the "blanket" becomes too thick.

The enhanced greenhouse effect is the increase in the natural effect due to increased concentrations of these gases, leading to more heat being trapped.

Analogy: Think of the Earth as a person sleeping under a blanket. The natural greenhouse effect is like one cozy blanket. The enhanced greenhouse effect is like adding five more thick blankets—you get way too hot!

Effects of Air Pollution: Climate Change (Core)

The enhanced greenhouse effect is the main driver of climate change. Climate change refers to long-term shifts in temperatures and weather patterns.

The effects are far-reaching and dangerous to ecosystems:

• Rising Global Temperatures: This alters habitats, forcing species to migrate or face extinction.
• Melting Glaciers and Ice Caps: This causes sea levels to rise.
• Changing Weather Patterns: Leading to more extreme weather events, like severe droughts or heavy flooding, which devastate crops and habitats.
• Ocean Acidification: Although not directly caused by the greenhouse effect, excess atmospheric \(CO_2\) dissolves into the oceans, lowering the pH, which harms marine life like corals and shell-forming organisms.