VCE Environmental Science (Year 11) · Unit 2 — Pollution, Food and Water Security · 16m read

Pollution and Human Impacts on Ecosystems

Ever wondered why a single dam can transform an entire river ecosystem? Human activities like farming, urbanisation, and pollution fundamentally reshape how ecosystems function—disrupting food chains, changing water cycles, and threatening biodiversity. By analysing these impacts, you'll understand the tipping points where ecosystems collapse and discover how human choices can either degrade or restore the natural systems we depend on.

Learning objective: Explain how pollutants move through the environment and analyse the effects of human activities on ecosystem function and integrity.

By the end of this lesson you can:

• I can trace a pollutant from its source to a receptor and explain biomagnification.
• I can explain eutrophication and its causes and effects.
• I can describe the effects of land clearing on ecosystems.
• I can evaluate the environmental impact of an industry using life cycle assessment.

Human impact is a footprint. Farming, mining and cities press heavy footprints into ecosystems.

Key human impacts on ecosystems

### Eutrophication

Definition: Excessive enrichment of a water body with nutrients (mainly nitrogen and phosphorus), causing algal blooms and ecosystem damage.

Process:
1. Agricultural fertilisers or sewage runoff → N and P into waterways.
2. Rapid algal and plant growth (algal bloom).
3. When algae die and decompose, bacteria consume massive amounts of oxygen.
4. Hypoxia (oxygen depletion) — fish and invertebrates die.
5. Dead zone created.

Example: Murray-Darling Basin blue-green algae blooms. Gulf of Mexico dead zone (from Mississippi agricultural runoff).

### Land clearing effects

Salinity: Tree roots draw up groundwater, limiting water table rise. When trees are cleared, water tables rise, bringing salt to the surface — salinisation makes soil infertile.

Erosion: Vegetation holds soil. Clearing → wind and water erosion → sediment in waterways → turbidity → reduced photosynthesis → ecosystem damage.

Habitat fragmentation: Patches of remnant habitat isolated by cleared land. Species cannot move between patches → reduced genetic diversity → local extinctions.

Carbon release: Trees store carbon. Burning or decomposition releases stored carbon as CO₂.

### Climate change impacts on ecosystems

• Range shifts: Species moving poleward or to higher altitudes as temperatures rise.
• Phenological mismatch: Seasonal timing changes — flowers bloom before pollinators emerge.
• Coral bleaching: Warm ocean temperatures cause corals to expel symbiotic algae → whitening → starvation.
• Ocean acidification: CO₂ absorbed by oceans lowers pH → dissolves calcium carbonate → threatens shellfish and coral.

### Ecological footprint and environmental impact

Ecological footprint: The amount of biologically productive land and sea area required to support a population.

• Australia: ~7.7 global hectares per person (among world's highest).
• Global average: ~2.7 gha/person.
• Earth's biocapacity per person: ~1.6 gha/person.

We are currently using 1.7 Earths — ecological overshoot.

AARI TIP: Ask Aari to explain how to calculate your personal ecological footprint.

Pollution — sources, pathways and management

### What counts as pollution

A pollutant is a substance (or a form of energy such as heat, noise or light) added to the environment at a level that harms living things or the systems they depend on.

• Point sources come from one identifiable outlet, such as a factory pipe or a sewage outfall. They are easier to measure and regulate.
• Diffuse (non-point) sources come from many scattered places, such as fertiliser runoff from farms, urban stormwater and vehicle exhaust. They are much harder to control.

### Source → pathway → receptor

Every pollution problem can be traced along the same chain:
1. Source — where the pollutant is released.
2. Pathway — how it moves: through air, water, soil or a food chain.
3. Receptor — what it harms: organisms, people or a whole ecosystem.

Management can break the chain at any point: stop the release at the source, block the pathway (for example, a wetland that filters stormwater), or protect the receptor.

### Persistence, bioaccumulation and biomagnification

Persistent pollutants break down very slowly. Examples include heavy metals such as mercury and lead, some older pesticides such as DDT, and PFAS chemicals.

• Bioaccumulation: a persistent pollutant builds up inside one organism faster than the body can remove it.
• Biomagnification: its concentration increases at each step up a food chain, because every predator eats many contaminated prey. Top predators carry the highest concentrations.

### Measuring pollution

Concentrations are reported in units such as mg/L or ppm (parts per million; 1 ppm is 1 mg per kg, about 1 mg per L in dilute water). Results are compared with guideline values, such as Australia's drinking water and water quality guidelines.

### Managing pollution

• Prevent first: avoid or reduce the pollutant at its source (cleaner processes, less fertiliser, better waste handling). This is usually cheaper and more effective than cleaning up later.
• Treat: sewage treatment, filters and scrubbers, constructed wetlands.
• Remediate: clean up contaminated land and water after the damage.
• Regulate and monitor: environment protection authorities (EPA Victoria in Victoria) license polluters, set limits and monitor air and water quality.

Check with your teacher which pollution case studies your course uses.

Worked example (Medium)

A persistent pesticide is measured along a lake food chain: plankton 0.04 ppm, small fish 0.5 ppm, fish-eating bird 25 ppm. Calculate the biomagnification factor from plankton to bird, and explain why the bird has the highest concentration.

1. Biomagnification factor. Factor = concentration in the bird ÷ concentration in plankton = 25 ÷ 0.04 = 625.
2. Explain. The pesticide is persistent and stored in fatty tissue, so it is not broken down or excreted. Each small fish eats many plankton and keeps the pesticide from all of them; each bird eats many fish. The amount builds up at every step, so the top predator has the highest concentration.

Answer: The concentration in the bird is 625 times that in the plankton. Because the pesticide persists in the body and each consumer eats many contaminated prey, it biomagnifies up the food chain.

Quick reference

| Impact | Example |
|---|---|
| Land clearing | Habitat loss |
| Pollution | Runoff, plastics |
| Overexploitation | Overfishing |
| Invasive species | Cane toads |
| Climate change | Bleaching |

Key ideas at a glance

• Direct vs indirect: Impacts.
• Cumulative effects: Add up.
• Management: Restoration.
• Evidence: Data-based.

Worked example (Medium)

Explain the process of eutrophication in a lake receiving agricultural runoff.

1. Nutrient input. Fertiliser containing nitrogen and phosphorus washes off farmland into the lake during rainfall events.
2. Algal bloom. Elevated N and P stimulate rapid growth of algae and cyanobacteria (blue-green algae). The bloom covers the water surface, blocking light to submerged plants.
3. Die-off and decomposition. When algae die (either naturally or from depletion of nutrients in deeper water), decomposing bacteria consume oxygen rapidly during breakdown.
4. Hypoxia. Dissolved oxygen falls below levels fish and invertebrates need to survive. Mass mortality of aquatic organisms occurs — a "dead zone."
5. Long-term effects. Cyanobacterial toxins may accumulate (harmful to humans and livestock). Benthic communities (bottom-dwelling organisms) are eliminated. Recovery is slow — sediment stores nutrients that continue feeding future blooms.

Answer: Eutrophication: nutrient input → algal bloom → oxygen depletion → aquatic death. Prevention requires reducing agricultural runoff through buffer strips, nutrient management plans, and wetland restoration.

Worked example (Medium)

Use the IPAT equation to discuss why total CO₂ emissions from a country can fall even as population rises.

1. Equation. I = P × A × T — Impact = Population × Affluence × Technology.
2. Population effect. Population rising drives I up.
3. Technology effect. Cleaner energy lowers T (carbon intensity).
4. Net result. If T falls faster than P × A rises, I falls overall.

Answer: IPAT shows that decarbonising technology can decouple emissions from population growth, but only if the technology factor falls faster than the population × affluence product rises.

Common mistakes

• Skipping steps in the eutrophication sequence Students jump from "fertiliser runoff" directly to "fish die" without tracing the intermediate stages. Fix: Trace the full chain: nutrient input → algal bloom → algae die and decompose → bacterial oxygen consumption → hypoxia → aquatic organism death. Each step has a distinct mechanism.
• Confusing salinity and erosion mechanisms Both result from land clearing, but the processes are entirely different. Fix: Salinity: clearing reduces transpiration → water table rises → salt reaches surface. Erosion: clearing removes root systems → topsoil lost to wind/water. Explain each mechanism separately.
• Treating ecological footprint as a precise measurement Students present footprint figures as exact when they are estimates dependent on methodology and assumptions. Fix: Acknowledge that ecological footprint is an estimate useful for comparison, not a precise measurement. Note the methodology limitations while using the concept to illustrate overshoot.

Ecosystem services — nature's invisible economy

Ecosystem services are the benefits that healthy ecosystems provide to human societies, often without any market price attached. Understanding their value helps explain why environmental degradation has economic consequences far beyond what traditional accounting captures.

Ecosystem services are categorised into four types:

Provisioning services: Direct products — food, fresh water, timber, fibre, genetic resources, medicines.

Regulating services: Benefits from ecosystem processes — climate regulation (carbon sequestration), flood control (wetlands absorb floodwater), water purification (soil and vegetation filter contaminants), pollination (insects pollinate ~75% of food crops).

Cultural services: Non-material benefits — recreation, tourism, spiritual significance, aesthetic value, education, sense of place.

Supporting services: Underlying processes that enable all others — nutrient cycling, soil formation, primary production, water cycling.

The Millennium Ecosystem Assessment (2005) found that 60% of global ecosystem services are being degraded or used unsustainably. Attempts to value these services economically estimate that global ecosystem services are worth $125-145 trillion per year — more than global GDP.

For Unit 1 Environmental Science, the ecosystem services framework helps evaluate human impacts: when we clear a forest, we lose not just trees but carbon storage, water filtration, flood regulation, habitat, pollination, and cultural value. Understanding this full cost is essential for informed environmental decision-making.

Practice questions

1. Eutrophication in aquatic systems is primarily caused by excess:

   1. Carbon dioxide
   2. Nitrogen and phosphorus from agricultural runoff
   3. Pesticides
   4. Heavy metals

   (1 marks)

2. Explain how land clearing for agriculture contributes to dryland salinity.

   (3 marks)

Summary

• Eutrophication: nutrient (N/P) runoff → algal bloom → O₂ depletion → hypoxia → dead zone.
• Land clearing: salinity (water table rise), erosion, fragmentation, carbon release.
• Climate change: range shifts, phenological mismatch, coral bleaching, ocean acidification.
• Ecological footprint: Australia = 7.7 gha/person vs Earth's 1.6 gha biocapacity = overshoot.