Ecosystem

**Environment** = total planetary inheritance and the totality of all resources; includes all biotic and abiotic factors that influence each other. **Four vital functions of the environment:** 1. **Supplies resources** — both renewable and non-renewable 2. **Assimilates waste** 3. **Sustains life** by providing genetic and bio diversity 4. **Provides aesthetic services** like scenery **Carrying capacity** = the environment can perform these functions without interruption as long as demand is within its carrying capacity. Carrying capacity means the resource extraction is not above the rate of regeneration AND wastes generated are within the assimilating capacity. **Absorptive capacity** = ability of the environment to absorb degradation. When demand on the environment exceeds its carrying capacity → **environmental crisis**. --- ### Sustainable Development **UNCED definition (United Nations Conference on Environment and Development):** "Development that meets the need of the present generation without compromising the ability of the future generation to meet their own needs." **Our Common Future (Brundtland Commission report):** "Meeting the basic needs of all and extending to all the opportunity to satisfy their aspirations for a better life." **Brundtland Commission** emphasises protecting the future generation — the present generation should bequeath a better environment to future generation; at least leave next generation a stock of 'quality of life' assets no less than what we have inherited. **Edward Barbier's definition:** Sustainable development is one which is directly concerned with increasing the material standard of living of the poor at the grass root level — quantitatively measured in terms of increased income, real income, educational services, health care, sanitation, water supply etc. **Herman Daly's conditions for sustainable development:** 1. Limiting the human population to a level within the carrying capacity of the environment 2. Technological progress should be input efficient and not input consuming 3. Renewable resources should be extracted on a sustainable basis (rate of extraction should not exceed rate of regeneration) 4. For non-renewable resources: rate of depletion should not exceed rate of creation of renewable substitutes 5. Inefficiencies arising from pollution should be corrected **SDGs:** In 2015, the UN formulated **17 Sustainable Development Goals (SDGs)** intended to be achieved by the year **2030**. --- ### India's Environmental Challenges **Five priority environmental issues identified for India:** 1. Land degradation 2. Biodiversity loss 3. Air pollution (with special reference to vehicular pollution in urban areas) 4. Management of fresh water 5. Solid waste management **Causes of land degradation (10 factors listed in NCERT):** (i) Loss of vegetation due to deforestation (ii) unsustainable fuel wood and fodder extraction (iii) shifting cultivation (iv) encroachment into forest lands (v) forest fires and overgrazing (vi) non-adoption of adequate soil conservation measures (vii) improper crop rotation (viii) indiscriminate use of agro-chemicals (fertilisers and pesticides) (ix) improper planning and management of irrigation systems (x) extraction of ground water in excess of recharge capacity **Per capita forest land:** Only **0.06 hectare** against requirement of **0.47 hectare** to meet basic needs — resulting in excess felling of about 15 million cubic metre forests over the permissible limit. **Soil erosion data:** Soil being eroded at a rate of **5.3 billion tonnes a year** for the entire country; country loses 0.8 million tonnes of nitrogen, 1.8 million tonnes of phosphorus and 26.3 million tonnes of potassium every year. Quantity of nutrients lost from 5.8 to 8.4 million tonnes per year. **India's population-resource pressure:** India supports approximately **17 per cent** of the world's human and **20 per cent of livestock population** on mere **2.5 per cent** of the world's geographical area. **Air pollution:** About **70 per cent** of water in India is polluted. Motor vehicles: increased from about 3 lakh in 1951 to 35 crores in 2022. Two-wheeled vehicles and cars constituted about **85 per cent** of registered vehicles and thus contribute significantly to air pollution. **CPCB (Central Pollution Control Board):** Set up in **1974** to address water and air pollution. States established their own state-level boards. CPCB has identified **17 categories of industries** (large and medium scale) as significantly polluting. *(For full CPCB/SPCB legislative framework, see [[environment/acts-and-policies/environmental-acts-india.md]])* **Global Warming (Box 7.1):** Gradual increase in average temperature of lower atmosphere since Industrial Revolution. CO₂ has increased by 31% and CH₄ by 149% above pre-industrial levels since 1750. Atmospheric temperature has risen by 1.1 F (0.6 C); sea level has risen several inches. Kyoto Protocol (1997): international agreement to reduce greenhouse gas emissions by industrialised nations. **Ozone Depletion (Box 7.2):** Ozone depletion in the **stratosphere** caused by CFCs (chlorofluorocarbons) used in air-conditioners, refrigerators, aerosol propellants; and halons (bromofluorocarbons) in fire extinguishers. 5% reduction in ozone layer detected from 1979-1990. **Montreal Protocol**: banned use of CFC compounds and other ozone-depleting chemicals (carbon tetrachloride, trichloroethane/methyl chloroform, bromine compounds/halons). --- ### Strategies for Sustainable Development **Use of Non-conventional Sources of Energy:** - Wind power: wind mills in areas of high wind speed; no adverse environmental impact; initial cost high but benefits outweigh - **Solar power (photovoltaic cells):** India is naturally endowed with solar energy; cells capture solar energy and convert to electricity; useful for remote areas; totally free from pollution. India is leading the **International Solar Alliance (ISA)**. - **Mini-hydel plants:** Use energy of perennial streams in mountainous regions; do not change land use patterns; generate enough power for local demands; avoid large transmission towers and cables - **Gobar gas / biogas in rural areas:** Cattle dung fed to plant → gas used as fuel, slurry left over is excellent organic fertiliser. LPG is a clean fuel — reduces household pollution. Subsidised LPG and gobar gas plants provided through easy loans and subsidy. - **CNG in urban areas:** Delhi's use of CNG in public transport has significantly lowered air pollution. **Biocomposting:** Switched back from chemical fertilisers to compost made from organic wastes; earthworms convert organic matter into compost faster than normal composting process. **Biopest control:** Neem-based pesticides; mixed cropping; growing different crops in consecutive years on same land. **Traditional Knowledge and Practices:** India has about 15,000 species of plants with medicinal properties; about 8,000 used in various systems of treatment including folk tradition. Ayurveda, Unani, Tibetan, folk systems — environment friendly, no large-scale industrial processing. ---

Energy flow in an ecosystem is unidirectional — from the sun to producers, and then to consumers. No energy trapped into an organism remains in it forever; it is either passed on to a consumer or released when the organism dies. **Food chains:** A food chain shows the linear transfer of food energy from one trophic level to the next. Two main types exist: 1. **Grazing Food Chain (GFC):** Begins with living green plants. Example: Grass → Goat → Man. This is the major energy conduit in aquatic ecosystems. 2. **Detritus Food Chain (DFC):** Begins with dead organic matter. Decomposers (saprotrophs — mainly fungi and bacteria) degrade this material. In terrestrial ecosystems, a much larger fraction of energy flows through the DFC than through the GFC. Food chains are interconnected into **food webs** because many organisms like cockroaches and crows are omnivores that feed from multiple chains. **Trophic levels:** Based on their source of nutrition, organisms occupy specific trophic levels: - First trophic level: Producers (green plants/phytoplankton) - Second trophic level: Primary consumers (herbivores — insects, molluscs) - Third trophic level: Secondary consumers (primary carnivores) - Fourth trophic level: Tertiary consumers A given species may occupy more than one trophic level simultaneously. A sparrow is a primary consumer when eating seeds, and a secondary consumer when eating insects. **10 per cent law:** Only 10 per cent of the energy is transferred to each successive trophic level from the lower trophic level. This limits the number of trophic levels in a grazing food chain — typically not more than 3-4 levels in nature. **Standing crop** is the mass of living organisms (biomass) at a particular trophic level at any given time. **Ecological pyramids** represent the relationship between trophic levels in terms of number, biomass, or energy. Three types: 1. **Pyramid of numbers** — upright in most ecosystems (grassland); inverted in a tree ecosystem (one tree supports many insects) 2. **Pyramid of biomass** — upright in terrestrial ecosystems; inverted in aquatic ecosystems (small standing crop of phytoplankton supports large zooplankton biomass) 3. **Pyramid of energy** — ALWAYS upright; can never be inverted because energy is always lost as heat at each trophic level Limitations of ecological pyramids: they do not account for the same species belonging to multiple trophic levels; they assume a simple food chain and cannot accommodate food webs; saprophytes are not given any place.

An ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment. Ecosystems vary greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth. Ecosystems are broadly classified as terrestrial (forests, grasslands, deserts) and aquatic (ponds, lakes, wetlands, rivers, estuaries). Crop fields and aquariums are examples of man-made ecosystems. **Structural features:** The biotic and abiotic components interact to produce a physical structure characteristic for each ecosystem type. Species composition and vertical stratification are the two main structural features. In a forest, trees occupy the top layer, shrubs the second, and herbs and grasses the bottom. **Functional components:** Every ecosystem functions through four key processes: 1. **Productivity** — the rate at which producers synthesise organic matter 2. **Decomposition** — breakdown of dead organic matter by decomposers 3. **Energy flow** — unidirectional flow of energy from sun through producers to consumers 4. **Nutrient cycling** — repeated recycling of mineral elements through biotic and abiotic components **Productivity:** Primary productivity is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. Gross Primary Productivity (GPP) is the rate of total organic matter production during photosynthesis. Net Primary Productivity (NPP) = GPP - Respiration losses. Secondary productivity is the rate of formation of new organic matter by consumers. The annual net primary productivity of the whole biosphere is approximately 170 billion tonnes (dry weight). Despite occupying about 70 per cent of the surface, oceans produce only 55 billion tonnes — the rest comes from land. **Decomposition:** Dead plant remains (leaves, bark, flowers) and dead animal remains, including faecal matter, constitute detritus — the raw material for decomposition. Key steps are fragmentation (by detritivores like earthworms), leaching (water-soluble nutrients move into soil), catabolism (bacterial/fungal enzyme action), humification (formation of humus), and mineralisation (release of inorganic nutrients). Decomposition is largely an oxygen-requiring process; warm and moist environments favour it, while low temperature and anaerobiosis inhibit it, causing build-up of organic materials. **Ecosystem services:** Healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, maintain biodiversity, pollinate crops, and provide carbon storage. Robert Costanza and colleagues estimated the average value of ecosystem services at US $33 trillion per year — nearly twice the global GNP of US $18 trillion. Soil formation accounts for about 60 per cent of total ecosystem service costs.

Nutrients are never lost from ecosystems — they are recycled repeatedly. The movement of nutrient elements through the various components of an ecosystem is called **nutrient cycling**, also known as **biogeochemical cycles** (bio: living organism, geo: rocks, air, water). Nutrient cycles are of two types: 1. **Gaseous cycles:** Reservoir is in the atmosphere or hydrosphere. Examples: Carbon cycle, Nitrogen cycle. 2. **Sedimentary cycles:** Reservoir is in Earth's crust. Examples: Sulphur cycle, Phosphorus cycle. Environmental factors (soil moisture, pH, temperature) regulate the rate of release of nutrients into the atmosphere. The reservoir's function is to meet the deficit that occurs due to imbalance in the rate of influx and efflux. **Carbon Cycle:** Carbon constitutes 49 per cent of dry weight of organisms — next only to water. Of total global carbon, 71 per cent is found dissolved in oceans, which regulate the amount of CO₂ in the atmosphere. The atmosphere contains only about 1 per cent of total global carbon. Fossil fuels also represent a carbon reservoir. Carbon cycling occurs through atmosphere, ocean, and through living and dead organisms. According to one estimate, 4 × 10¹³ kg of carbon is fixed in the biosphere through photosynthesis annually. A considerable amount returns to the atmosphere as CO₂ through respiratory activities of producers and consumers. Decomposers also contribute substantially by processing dead organic matter. Some amount of fixed carbon is lost to sediments and removed from circulation. Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuels for energy and transport have significantly increased the rate of release of CO₂ into the atmosphere (contributing to the greenhouse effect). **Phosphorus Cycle:** Phosphorus is a major constituent of biological membranes, nucleic acids, and cellular energy transfer systems (ATP). Many animals also need large quantities to make shells, bones, and teeth. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates. When rocks are weathered, minute amounts of phosphates dissolve in soil solution and are absorbed by plant roots. Herbivores and other animals obtain this from plants. Waste products and dead organisms are decomposed by phosphate-solubilising bacteria, which release phosphorus. Unlike carbon cycle: - There is **no respiratory release** of phosphorus into the atmosphere - Atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs - Gaseous exchanges of phosphorus between organisms and environment are negligible The standing state refers to the amount of nutrients (carbon, nitrogen, phosphorus, calcium, etc.) present in the soil at any given time. It varies in different kinds of ecosystems and on a seasonal basis.

An important characteristic of all communities is that their composition and structure constantly change in response to changing environmental conditions. These changes are orderly and sequential, running parallel with changes in the physical environment. The gradual and fairly predictable change in the species composition of a given area is called **ecological succession**. During succession, some species colonise an area and their populations become more numerous, while other species decline and disappear. The final stable community, which is in near-equilibrium with the environment, is called the **climax community**. The entire sequence of communities that successively change in a given area are called **sere(s)**; individual transitional communities are termed serial stages or seral communities. With each successive seral stage, there is a change in species diversity, an increase in the number of species and organisms, and an increase in total biomass. **Types of succession:** 1. **Primary succession:** Occurs in areas where no living organisms have ever existed, or where all living organisms have been removed — e.g., bare rock, newly cooled lava, newly created ponds. Establishment of a new biotic community is generally slow. Depending mostly on climate, natural processes take several hundred to several thousand years to produce fertile soil on bare rock. 2. **Secondary succession:** Begins in areas where natural biotic communities have been destroyed — abandoned farm lands, burned or cut forests, flooded lands. Since some soil or sediment is already present, succession is faster than primary succession. The climax is also reached more quickly. **Succession of plants:** - **Hydrarch succession:** Takes place in wetter areas; succession progresses from hydric to mesic conditions. Sequence: phytoplankton → free-floating angiosperms → rooted hydrophytes → sedges → grasses → trees (forest). The water body is converted into land over time. - **Xerarch succession:** Takes place in dry areas; succession progresses from xeric to mesic conditions. Pioneer species on rocks are usually lichens, which secrete acids to dissolve rock, aiding weathering and soil formation. These give way to bryophytes, then bigger plants, and ultimately a stable climax forest community. Both hydrarch and xerarch succession lead to a **mesic** (medium water) condition — neither too dry (xeric) nor too wet (hydric). All succession, whether taking place in water or on land, proceeds to a similar climax community — the mesic. **Pioneer species** are the species that first invade a bare area. In primary succession on rocks, these are usually lichens. Natural or human-induced disturbances (fire, reforestation) can convert a particular seral stage to an earlier stage, or create new conditions that encourage some species and discourage others.

Aquatic ecosystems are classified by salt content: - **Fresh water:** salt content < 5 ppt (lakes, ponds, springs, streams, rivers) - **Marine:** salt ≥ 35 ppt (shallow seas, open ocean) - **Brackish water:** 5–35 ppt (estuaries, salt marshes, mangrove swamps) Key limiting factors: **sunlight and oxygen** (unlike terrestrial: moisture and temperature)

Terrestrial ecosystems are characterised by the interrelations between organisms and their land environment. The most important limiting factors are moisture and temperature (contrast with aquatic: sunlight and oxygen). Due to altitudinal and latitudinal variations in climate, terrestrial ecosystems show great diversity — from tundra to tropical rainforests. **Champion and Seth Classification** divides India's forests into 16 types.