Our Environment – Comprehensive Study Notes

Environment & Ecosystem Basics

• Environment = sum of physical + biological factors and their chemical interactions that affect an organism.

  • Physical = abiotic (land, air, water, sunlight, temperature, rainfall, light availability).

  • Biological = biotic (flora & fauna).

• Biosphere: All components interact in an organized manner → balance + gradual evolution.

• Habitat: Place where an organism lives.

• Organisms cannot violate environmental balance without risking their own survival.

Food Chains & Food Webs

• Food chain: Linear sequence showing “who eats whom.”
  • Arrows point from food → feeder (energy direction).
  • Usually short (≤ 4 steps) because energy diminishes each level.

• Typical examples (producer → … → top carnivore):
  • Grass → Grasshopper → Frog → Snake → Hawk
  • Grass → Rabbit → Fox/Wolf
  • Grass → Goat → Man

• Energy loss per transfer: $80{-}90\%$ dissipated as heat; only $10{-}20\%$ passed on.

• Food web: Network of interconnected food chains; reflects complexity and alternative feeding links.

  • Demonstrates niche concept: each species’ role, diet, mode of life (e.g., aphids vs. caterpillars vs. deer on leaves).

Trophic Levels & Energy Flow

• Trophic level (TL): Position in food chain/web.
  • TL1 – Producers
  • TL2 – Primary consumers (herbivores)
  • TL3 – Secondary consumers
  • TL4 – Tertiary consumers / top carnivores

• Energy flow model:
  $\text{Sun (solar)} \rightarrow \text{Producers (chemical)} \rightarrow \text{Consumers (chemical)} \rightarrow \text{Heat}$

• After three transfers very little energy remains for top carnivores → explains short chains & decreasing organism numbers.

Ecological Pyramids

• Graphic representation of trophic structure (Charles Elton, $1927$). 3 Types:

  1. Pyramid of Numbers

  • Base = producers; bars represent individual counts per TL.

  • Typical upright form: many small producers → few large predators.

  • Can be inverted (e.g., single banyan tree → many insects → few woodpeckers)

  1. Pyramid of Biomass

  • Bars = total dry mass (kg/$m^2$) at each TL.

  • Terrestrial systems: upright.

  • Aquatic systems: often inverted (tiny phytoplankton biomass < zooplankton < fish).

  1. Pyramid of Energy

  • Always upright because energy diminishes irreversibly (heat loss).

  • Illustrates $\approx10\%$ rule.

Biomass & Biofuels

• Biomass: Organic material of biological origin (trees, crops, residues, wastes).
  • Ultimate source = $CO_2$ fixation via photosynthesis.
  • Only $10{-}20\%$ of biomass moves to next TL.
  • Undigested parts excreted; some lost in respiration.

• Biofuels: Biomass converted to energy ↓ dependence on fossil fuels; releases same $CO_2$ previously fixed.

Human Impacts on Ecosystems

• Activities: deforestation, agriculture, aquaculture, industry, dams, urbanization, pesticide use.

• Effects: habitat loss, altered food webs, pollution, eutrophication, species endangerment, bioaccumulation.

Case Study: Kolleru Lake (AP, India)

• One of India’s largest freshwater lakes; catchment $6121\,km^2$; discharges via 65-km Upputeru to Bay of Bengal.

• Biodiversity: $193$ bird species; $20\,00\,000$ migratory birds/yr; important for $\sim20$ million residents.

• Changes 1967→2004 (satellite data):

  • Lake-water spread ↓ from $70.70\,km^2$ → $62.65\,km^2$.

  • Sparse weed area ↑ $0$ → $47.45\,km^2$; dense weed $15.20\,km^2$ (eutrophication).

  • Aquaculture ponds $0$ → $99.74\,km^2$; flood-liable zone vanished.

• Pollution Sources: agricultural runoff (fertilizers, agro-chemicals), fish-tank discharges, industrial effluents, sewage.

• Consequences: alkaline, turbid water; low DO, high BOD; weed explosion (Eichhornia, Pistia); loss of $15$ fish species; vector-borne & water-borne diseases.

• Govt. response: Operation Kolleru by MoEF to restore ecological balance.

Pollution, Bioaccumulation & Biomagnification

• Pesticides & Herbicides: Many non-degradable (mercury, arsenic, lead).
  • Ideal pesticide (target-specific + harmless) does not exist.

• Bioaccumulation: Pollutant entry + storage in organism tissues.

• Biomagnification: Progressive ↑ in pollutant concentration up trophic levels (top predators most affected).

• Classic example: Minamata disease (Japan, $1932{-}1968$) – methyl-mercury → shellfish → humans.

Case Study: Edulabad Water Reservoir (Telangana)

• Polluted by industrial effluents; compared with cleaner Bibinagar reservoir.

• Heavy metals in water: sequence $Fe > Pb > Cr > Ni > Cd$ (all above standards).

• Bioaccumulation in common carp tissues: $Cd > Cr > Fe > Ni > Pb$; highest in liver, gill, kidney.

• Seasonal trend: lower accumulation during monsoon (dilution effect).

• Human health risks: hypertension, renal damage, nausea; aquatic life stress (↓ glycogen, lipids in fish).

Historical Example: China’s Sparrow Campaign (1958)

• Goal: eliminate sparrows (believed to eat $\approx4$ lb grain/sparrow/yr) to raise crop yields.

• Methods: shooting, drumming, nest destruction; millions killed.

• Outcome: loss of natural pest predators → locust swarms → crop failure + Great Chinese Famine; pesticide use worsened land degradation.

• Lesson: Eradicating a species disrupts food chains, causes ecological & human disasters.

Pest Management & Alternatives

• Problems with blanket pesticide bans: pests still threaten food security.

• Integrated, eco-friendly strategies:

  1. Crop rotation – alternate crops yearly to break pest life cycles.

  2. Life-history timing – adjust sowing to vulnerable pest stage.

  3. Biological control – introduce natural predators/parasites.

  4. Sterile-male technique – render males infertile to suppress population.

  5. Genetically resistant strains – GM or bred varieties resistant to pests.

• Environmental ethics: Moral responsibility to distinguish right vs. wrong actions impacting nature; public awareness essential (“Protect nature, protect yourself”).

Key Terms

• Food chain, Food web, Niche, Trophic level, Ecological pyramid, Biomass, Pyramid of numbers/biomass/energy, Bioaccumulation, Biomagnification, Eutrophication, BOD (Biological Oxygen Demand), DO (Dissolved Oxygen), Environmental ethics.

Review / Self-Check Questions

1. Why are most food chains limited to 4 trophic levels? (Hint: $80{-}90\%$ energy loss at each step.)

2. Explain how pyramids depict energy, biomass, and numbers differences in an ecosystem.

3. Show an inverted pyramid of biomass for a pond (phytoplankton → zooplankton → small fish → large fish).

4. Describe bioaccumulation vs. biomagnification with a real example.

5. List three eco-friendly pest-control methods and their biological basis.

6. How did aquaculture expansion contribute to Kolleru Lake eutrophication?

7. Connect dissolved oxygen, BOD, and fish mortality in polluted water.