Environment & Ecology

Ecology basics

• Ecology (a term coined by Ernst Haeckel, 1866) is the study of the relationship between organisms and their environment. Environment = biotic (living) + abiotic (non-living) factors.
• Ecosystem (the term is by A. G. Tansley, 1935): a functional unit of nature with the living community and its physical environment. Types: natural (forest, grassland, desert, pond, ocean) and artificial (crop field, aquarium).
• Levels of organisation: organism → population → community → ecosystem → biome → biosphere. A habitat is where an organism lives; a niche is its role.
• Components: producers (autotrophs) — green plants, phytoplankton; consumers (heterotrophs) — primary (herbivores), secondary and tertiary (carnivores), omnivores; decomposers — bacteria and fungi; detritivores — earthworms.

Food chain, web and energy flow

• Food chain: a linear sequence of who eats whom: grass → grasshopper → frog → snake → eagle. Grazing food chain (starts with green plants) and detritus food chain (starts with dead matter).
• Food web: a network of interconnected food chains.
• Trophic levels: T1 producers; T2 primary consumers; T3 secondary; T4 tertiary.
• 10 per cent law (Lindeman, 1942): only about 10 % of the energy passes from one trophic level to the next; the rest is lost as heat. Hence food chains have 4–5 levels at most.
• Ecological pyramids (Charles Elton): of numbers, biomass and energy. The pyramid of energy is always upright; the pyramid of biomass in a pond is inverted; the number pyramid of a tree is inverted.
• Gross primary productivity (GPP) and net primary productivity (NPP) = GPP − respiration.
• Biomagnification (bioaccumulation): the increasing concentration of a persistent substance (DDT, mercury) at higher trophic levels. Eutrophication: enrichment of water with nutrients (nitrates, phosphates) causing algal blooms, oxygen depletion and the death of fish; BOD (biochemical oxygen demand) measures organic pollution (a high BOD = polluted water).

Biogeochemical cycles

• Carbon cycle: photosynthesis, respiration, decomposition, combustion; the largest carbon store is the oceans (and rocks).
• Nitrogen cycle: nitrogen fixation (by Rhizobium, Azotobacter, cyanobacteria, and lightning), nitrification (Nitrosomonas, Nitrobacter), denitrification (Pseudomonas).
• Water (hydrological) cycle, phosphorus cycle (sedimentary; no gaseous phase), sulphur cycle.
• Ecological succession: the gradual change of the community; primary (on bare rock — lichens are the pioneer) and secondary; the final stable stage is the climax community. Xerarch (dry), hydrarch (water). Ecotone — a transition zone between two ecosystems; the edge effect.

Biomes and ecosystems

Tropical rainforest, savanna, desert, temperate grassland, taiga, tundra; aquatic: freshwater, estuaries, marine, coral reefs, mangroves, wetlands (the "kidneys of the landscape").

Biodiversity

• Biodiversity (the term by Walter G. Rosen, 1985) — the variety of life at three levels: genetic, species and ecosystem diversity. Alpha, beta, gamma diversity. The tropics have the highest biodiversity; diversity decreases from the equator to the poles.
• Hotspots (Norman Myers, 1988): 36 globally; India has four — the Himalaya, Indo-Burma, Western Ghats and Sri Lanka, and Sundaland (Nicobar).
• Threats: habitat loss, poaching, invasive alien species, pollution, climate change (the "Evil Quartet" — habitat loss, over-exploitation, alien species, co-extinction).
• Conservation: in-situ (national parks, sanctuaries, biosphere reserves, sacred groves) and ex-situ (zoos, botanical gardens, seed banks, cryopreservation — the Svalbard Global Seed Vault in Norway). IUCN Red List categories; CITES; the details of Indian protected areas are in the National Parks note.
• Keystone species (an outsized effect — the tiger, the sea otter), flagship species (the giant panda, the tiger), indicator species (lichens for air pollution), invasive species (water hyacinth, Lantana, parthenium/congress grass, Eichhornia).
• Extinction: the "sixth mass extinction"; the dodo and passenger pigeon are extinct.

Pollution

Air pollution

• Pollutants: particulate matter (PM10, PM2.5), sulphur dioxide (SO₂), nitrogen oxides (NOx), carbon monoxide (CO) (binds with haemoglobin, reducing oxygen transport), ozone (O₃) at ground level, lead, volatile organic compounds, ammonia.
• Sources: vehicles, industry, thermal power plants, biomass and stubble burning, construction, dust.
• Effects: respiratory diseases, acid rain (pH below 5.6; SO₂ and NOx → sulphuric and nitric acids; damages the Taj Mahal ("marble cancer"), forests, and lakes), smog (photochemical smog — Los Angeles-type, NOx and hydrocarbons in sunlight; classical smog — London-type), the Bhopal gas tragedy (2–3 December 1984; methyl isocyanate (MIC) from the Union Carbide plant).
• Measurement: Air Quality Index (AQI) (launched in India in 2014; six categories — Good, Satisfactory, Moderate, Poor, Very Poor, Severe). National Clean Air Programme (NCAP, 2019). BS-VI emission norms (from April 2020). Graded Response Action Plan (GRAP) in Delhi–NCR. Catalytic converters convert CO, hydrocarbons and NOx into less harmful gases.
• Indoor air pollution from biomass fuels; the Ujjwala LPG scheme.

Water pollution

• Sources: sewage, industrial effluents, agricultural run-off (fertilisers and pesticides), oil spills, thermal pollution. Minamata disease (mercury), Itai-itai disease (cadmium), blue baby syndrome (nitrates), fluorosis (excess fluoride), arsenic contamination (West Bengal, Bangladesh).
• Water quality: dissolved oxygen (DO); BOD, COD; coliform bacteria show faecal contamination. Namami Gange (2014) and the National Mission for Clean Ganga to clean the Ganga; the Ganga Action Plan (1985). Jal Jeevan Mission (tap water).
• Water treatment: primary (physical), secondary (biological), tertiary; STP (sewage treatment plant), ETP.

Soil, noise and other pollution

• Soil: pesticides, fertilisers, plastics, salinisation, e-waste. Noise: measured in decibels (dB); WHO limits; India's Noise Pollution (Regulation and Control) Rules 2000; thermal, radioactive and light pollution.
• Solid waste and plastic: Solid Waste Management Rules 2016, Plastic Waste Management Rules (single-use plastics banned from 1 July 2022), Extended Producer Responsibility (EPR), e-waste rules, bio-medical waste rules, Swachh Bharat Mission. The "3 Rs" — reduce, reuse, recycle. Biodegradable vs non-biodegradable waste.
• Nuclear accidents: Chernobyl (1986), Fukushima (2011), Three Mile Island (1979).