Environment, Ecology & Biodiversity

Each step in a food chain is a trophic level. Producers are the first trophic level, herbivores the second, and so on. Energy enters at level one from the sun and moves upward only — it never comes back down. This one-way movement is called unidirectional energy flow.

At every transfer, only about 10% of the energy reaches the next level; the remaining ~90% is lost as heat in respiration and movement. This is Lindeman's Ten Per Cent Law. It is why food chains are short — usually only 4 or 5 links. After five steps there is simply not enough energy left to support another predator.

Nutrients, unlike energy, are recycled through biogeochemical cycles. Where the main store is the atmosphere, the cycle is gaseous (carbon, nitrogen, oxygen); where it is rock and soil, the cycle is sedimentary and much slower (phosphorus, sulphur).

• Carbon cycle: plants take CO₂ from air by photosynthesis; respiration, decomposition, forest fires and burning of fossil fuels return it. Oceans are the largest active sink of carbon; fossil fuels and carbonate rocks are the long-term store.
• Nitrogen cycle: the air is 78% nitrogen, but plants cannot use it directly. Nitrogen fixation (by Rhizobium in legume roots, free-living Azotobacter, and lightning) → nitrification (Nitrosomonas makes nitrite, Nitrobacter makes nitrate) → plants absorb nitrate → ammonification on death → denitrification (Pseudomonas) returns free nitrogen to the air.

Ecological succession is the orderly change of communities at a place over time. The first settlers are the pioneer community (lichens on bare rock, algae in bare water) and the final stable stage is the climax community. Succession on a brand-new surface such as cooled lava is primary; on land cleared by fire or flood, where soil already exists, it is secondary — and therefore much faster. Succession starting in water is hydrarch, on dry rock it is xerarch; both tend towards a mesic (moderately moist) climax.

Biodiversity — a term popularised by Edward O. Wilson — is the variety of life at three levels. Learn them from small to large: genetic (variation within a species, like hundreds of rice varieties), species (number of different species in an area), and ecosystem (variety of habitats — forest, wetland, desert, mangrove).

India is one of the world's 17 megadiverse countries. With only about 2.4% of the world's land area, it holds roughly 8% of all recorded species — a remarkable concentration, produced by the meeting of the Himalayan, Peninsular, desert and island worlds in one landmass. Species found only in one region and nowhere else are endemic — like the lion-tailed macaque and Nilgiri tahr of the Western Ghats, or the Asiatic lion of Gir.

A biodiversity hotspot (concept of Norman Myers) must satisfy two conditions: it must have a large number of endemic plant species, and it must have already lost most of its original vegetation — that is, it is both rich and threatened. Four hotspots extend into India.

There are only two ways to save a species. Protect it where it lives — that is in-situ conservation. Or take it out and protect it elsewhere — that is ex-situ conservation. In-situ is always preferred, because it saves the whole ecosystem and lets natural evolution continue; ex-situ is the emergency backup.

• Project Tiger, 1973 — launched with 9 tiger reserves; today run by the National Tiger Conservation Authority (NTCA), created by the 2006 amendment to the Wildlife Act. Tiger numbers are estimated by the All India Tiger Estimation exercise every four years.
• Project Elephant, 1992 — protects elephants, their habitat and migration corridors, and addresses human-elephant conflict. The elephant is India's National Heritage Animal.
• Ramsar Convention, 1971 (signed at Ramsar, Iran; in force 1975) — the treaty for wetlands of international importance. World Wetlands Day is 2 February. India's first Ramsar sites included Chilika Lake (Odisha) and Keoladeo (Bharatpur, Rajasthan).

Bihar is a plains state, densely populated and intensively farmed — so its forest cover is low, roughly 7–8% of its geographical area (India State of Forest Report, 2021: about 7.8%), far below the national average of around 21%. Almost all of it sits in two pockets: the Himalayan foothill (Terai) belt of West Champaran in the north, and the Kaimur–Rohtas plateau in the south.

• Jal-Jeevan-Hariyali Abhiyan — Bihar's flagship state mission (launched 2019) linking water conservation, water-body revival and tree plantation, with the declared aim of raising the state's green cover substantially. It also covers well and ahar-pyne restoration and rooftop rainwater harvesting.
• Floods: north Bihar is India's most flood-prone region, because Nepal-origin rivers — the Kosi ("Sorrow of Bihar"), Gandak, Bagmati, Burhi Gandak and Kamla Balan — drop suddenly from steep hills onto a flat plain, shed their silt, raise their beds and change course.
• Groundwater contamination: arsenic is the serious problem in the Gangetic belt districts along the river (such as Bhojpur, Buxar, Samastipur, Bhagalpur); fluoride affects parts of south Bihar (Gaya, Nawada, Jamui, Banka); and iron affects the north-eastern districts (Kishanganj, Araria, Katihar). Arsenic causes skin lesions and cancers, fluoride causes fluorosis of teeth and bones.

Pollution is the addition of any substance or energy to the environment at a rate faster than it can be dispersed or absorbed. Classify it by the medium affected — then the pollutants and their diseases follow logically.

The Air Quality Index (AQI) turns eight pollutants into one number from 0 to 500 so that an ordinary citizen can understand the day's air. PM10 means particles of diameter 10 micrometres or less; PM2.5 means 2.5 micrometres or less — these are the dangerous ones, because they slip past the nose and lungs' defences and enter the bloodstream.

Eutrophication is worth understanding as a chain, not a definition. Fertiliser and sewage add nitrates and phosphates to a lake → algae multiply into an algal bloom → the bloom blocks sunlight and then dies → decomposers consume it, and their respiration raises the Biochemical Oxygen Demand (BOD) → dissolved oxygen crashes → fish suffocate and the lake "dies". High BOD therefore means dirty water. This is a live threat to Bihar's chaurs and oxbow lakes.

The greenhouse effect is natural and necessary: certain gases let short-wave sunlight in but trap the long-wave heat radiated back by the earth, keeping the planet about 33 °C warmer than it would otherwise be. Without it, earth would be frozen. The problem is not the effect — it is the enhanced greenhouse effect caused by our extra emissions.

• Main greenhouse gases: water vapour, carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), ozone and the synthetic CFCs/HFCs. CO₂ contributes the most overall, but methane is many times more powerful per molecule — that is its higher Global Warming Potential (GWP).
• Global warming vs climate change: global warming is only the rise in average temperature. Climate change is the wider set of consequences — shifting monsoon patterns, more extreme rainfall and drought, glacier retreat, sea-level rise, cyclone intensification. Warming is the cause; climate change is the whole story.
• Ozone depletion is a different problem. In the stratosphere, the ozone layer shields us from ultraviolet (UV-B) radiation. Chlorofluorocarbons (CFCs) release chlorine that destroys ozone, thinning it most over Antarctica (the "ozone hole"). Do not confuse it with global warming — stratospheric ozone is a shield, while ground-level (tropospheric) ozone is a pollutant. World Ozone Day: 16 September.

India's position rests on equity: our historical and per-capita emissions are low, so the burden of cutting must be differentiated. In its updated NDC (2022) India committed to reduce the emission intensity of its GDP by 45% by 2030 from the 2005 level, and to reach about 50% of installed electric power capacity from non-fossil-fuel sources by 2030. At COP-26 (Glasgow, 2021) India announced the "Panchamrit" targets including net-zero emissions by 2070, and launched the LiFE (Lifestyle for Environment) idea of individual behaviour change.

• The National Action Plan on Climate Change (NAPCC, 2008) runs through eight National Missions: Solar; Enhanced Energy Efficiency; Sustainable Habitat; Water; Sustaining the Himalayan Ecosystem; Green India; Sustainable Agriculture; and Strategic Knowledge for Climate Change.
• States prepare their own State Action Plans on Climate Change; for Bihar the priorities are flood management, drought-proofing agriculture, groundwater quality and expanding green cover.