GS Notes

5. New Environment Notes 06

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Elaborate Notes

WETLANDS

  • Distinction between Lakes and Wetlands: The differentiation between lakes and wetlands is crucial for ecological management and is based on a range of limnological (study of inland aquatic ecosystems) characteristics.

    • Origin: Lakes are often formed by large-scale geomorphic processes. Tectonic lakes, for instance, are formed by crustal movements like faulting and warping; a prime example is Wular Lake in Jammu and Kashmir, which is a result of tectonic activity. Glacial lakes like Pangong Tso in Ladakh are also common. In contrast, wetlands are frequently of fluvial origin (formed by rivers), such as oxbow lakes in river floodplains (e.g., Kanwar Lake in Bihar), or are residual water bodies left over from larger, ancient lakes.
    • Hydrology: The permanence of water is a key differentiator. While lakes are generally permanent water bodies, wetlands can range from permanently flooded (like marshes) to seasonally or intermittently flooded (like vernal pools). This variability in the water regime is a defining feature of wetlands. Consequently, water level fluctuations in wetlands are often significant, driven by seasonal rainfall and river flows, whereas in deep lakes, they are relatively minor.
    • Physical Characteristics: Vertical mixing of water in deep lakes is governed by thermal stratification, where distinct layers of water at different temperatures (epilimnion, metalimnion, hypolimnion) form, especially in summer. In shallow wetlands, the water column is generally not deep enough to stratify and is constantly mixed by wind action, leading to a more uniform temperature profile.
    • Ecological Characteristics: The dominant primary producers differ significantly. In lakes, sunlight penetrates deep into the water column, supporting a community of free-floating microscopic algae known as phytoplankton. This forms the base of a grazing food chain (phytoplankton → zooplankton → small fish → large fish). In wetlands, the shallow water allows sunlight to reach the bottom, promoting the growth of rooted emergent and submerged plants called macrophytes (e.g., cattails, water lilies). When these macrophytes die, they contribute large amounts of organic matter, forming the base of a detritus food chain, where decomposers (bacteria, fungi) and detritivores (invertebrates) are dominant.
    • Productivity and Trophic Status: Due to the abundance of nutrients and macrophytes, wetlands are among the most productive ecosystems in the world, often exhibiting a eutrophic state (rich in nutrients). Deep lakes, particularly those in high altitudes with low nutrient inflow, are often oligotrophic (poor in nutrients), leading to lower productivity.
    • Ecosystem Services: Wetlands are highly significant for flood control, acting as natural sponges that absorb and slowly release floodwaters. Lakes have a lesser capacity for this. Furthermore, the complex biological and chemical processes within wetlands, involving microbes and plants, enable them to act as natural water purifiers, treating waste by filtering sediments and breaking down pollutants. This service is largely absent in lakes.

  • Significance of Wetlands: Wetlands are often termed “biological supermarkets” for the extensive food webs and rich biodiversity they support. Their ecological and economic importance is immense.

    • Kidneys of the Landscape: This metaphor highlights their crucial role in water purification. Wetland plants and anaerobic soil microbes absorb and break down pesticides, heavy metals, and other pollutants from water. This function was formally recognized by the Ramsar Convention on Wetlands (1971).
    • Nutrient Recycling: Wetlands are hotspots for biogeochemical cycling. They sequester carbon and play a key role in the nitrogen cycle through processes like denitrification, which converts nitrates in runoff back into atmospheric nitrogen gas, mitigating the effects of eutrophication.
    • Hydrological Regulation: By holding excess water during floods and releasing it slowly during dry periods, wetlands help in maintaining stream flows, recharging groundwater aquifers, and mitigating the impacts of both floods and droughts. The degradation of the Pallikaranai marshland in Chennai has been cited by ecologists as a major factor in the severity of the 2015 Chennai floods.
    • Biodiversity Hotspots: They provide critical habitats for a vast array of species, including migratory birds (e.g., Siberian cranes at Keoladeo National Park, Rajasthan), fish, amphibians, and insects.
    • Climate Mitigation and Regulation: Wetlands, particularly peatlands, are significant carbon sinks, storing vast amounts of carbon in their soil. They also exert a local cooling effect through evapotranspiration.
    • Livelihood and Culture: They are a source of food (fish, rice), fodder, fuel, and fibre for local communities. Many wetlands also hold deep cultural and spiritual significance, as seen in the reverence for Loktak Lake in Manipur.

  • Issues and Threats to Wetlands: Despite their importance, wetlands are among the world’s most threatened ecosystems.

    • Urbanisation and Encroachment: This is the most significant threat in India. Cities like Bengaluru, once known as the ‘City of Lakes’, have lost a large percentage of their water bodies to construction and urban sprawl. The Bellandur Lake in Bengaluru is a classic example of urban wetland degradation.
    • Pollution and Eutrophication: The inflow of untreated domestic sewage and industrial effluents introduces excess nutrients (nitrogen and phosphorus) and toxins. Agricultural runoff containing fertilizers exacerbates this, leading to cultural eutrophication. This causes explosive growth of algae (algal blooms), which upon decomposition deplete dissolved oxygen, leading to fish kills and creating ‘dead zones’.
    • Methane Emissions: The anaerobic decomposition of organic matter in wetlands naturally produces methane (CH₄), a potent greenhouse gas. While a natural process, increased nutrient loading from pollution can accelerate methane production. The infamous fires on the surface of Bellandur Lake were attributed to the ignition of methane bubbles amidst a layer of industrial pollutants and sewage.
    • Invasive Alien Species: Introduction of non-native species like Water Hyacinth (Eichhornia crassipes) can outcompete native vegetation, choke water bodies, and drastically alter the ecosystem structure and function.
    • Other Threats: Deforestation in catchment areas leads to increased soil erosion and siltation of wetlands. Overgrazing, over-fishing, and unsustainable aquaculture practices (including the use of antibiotics that disrupt microbial communities) also degrade wetland health.

BIODIVERSITY

  • Definition and Origin: The term biodiversity gained prominence following the United Nations Conference on Environment and Development (UNCED), or the Rio Earth Summit, in 1992. The resulting Convention on Biological Diversity (CBD) provided the widely accepted definition: “the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.” This definition holistically covers all levels of biological organisation.

  • Levels of Biodiversity:

    • Genetic Diversity: This refers to the total number of genetic characteristics in the genetic makeup of a species. It is the variation in genes and alleles within a species. High genetic diversity is crucial for a population’s ability to adapt to changing environments, resist diseases, and evolve. For example, India has over 50,000 genetically different strains of rice and 1,000 varieties of mango. The historic Irish Potato Famine (1845-1849) was a tragic consequence of extremely low genetic diversity in the potato crop, which made it susceptible to a single pathogen, Phytophthora infestans.
    • Species Diversity: This refers to the variety of different species (species richness) and their relative abundance (species evenness) within a given region. For instance, the tropical rainforests of the Western Ghats have far greater species diversity compared to the coniferous forests of the Himalayas due to factors like higher solar energy input and stable climatic conditions.
    • Ecosystem Diversity: This is the variety of different habitats, biotic communities, and ecological processes in the biosphere. It encompasses the diversity of ecosystems like deserts, rainforests, mangroves, coral reefs, grasslands, etc., within a geographical area. India exhibits high ecosystem diversity, from the alpine meadows of the Himalayas to the coral reefs of the Andaman Islands.

  • Measurement of Species Diversity:

    • Richness and Evenness: These are two fundamental components.
      • Species Richness: A simple count of the number of different species in an area. For example, a forest with 10 species of trees is richer than a forest with 5 species.
      • Species Evenness: A measure of the relative abundance of the different species. A community is considered more even if all species have similar numbers of individuals. An ecosystem with 10 species each represented by 10 individuals is more even (and thus considered more diverse) than an ecosystem with 10 species where one species has 91 individuals and the other nine have 1 individual each.
    • Scales of Diversity (Whittaker, 1960): Ecologist Robert H. Whittaker proposed three terms to describe species diversity on different spatial scales:
      • Alpha (α) diversity: Refers to the species diversity within a single, localized, homogeneous habitat or community. It is essentially the species richness of that specific habitat.
      • Beta (β) diversity: Measures the change or turnover in species composition between different habitats. A high beta diversity implies that the species composition varies significantly as one moves from one habitat to another. It is calculated as the ratio between regional and local species diversity.
      • Gamma (γ) diversity: This is the total species diversity over a large geographic area or region, encompassing several different habitats. It is a product of both alpha diversity of the habitats and beta diversity between them.

  • Biodiversity and Ecosystem Stability: The relationship between diversity and stability is a central theme in ecology. Ecologist David Tilman’s long-term experiments at Cedar Creek, Minnesota (1990s), demonstrated that plots with higher species diversity showed less year-to-year variation in biomass (productivity) and were more resilient to disturbances like drought. A stable ecosystem exhibits:

    • Resistance: The ability to withstand disturbances without significant change.
    • Resilience: The ability to recover quickly after a disturbance.
    • The Shannon-Wiener Index, mentioned in the India State of Forest Report (ISFR), is a mathematical measure that quantifies diversity by incorporating both species richness and evenness, providing a more robust metric for ecological assessment.

ENDEMISM

  • Definition and Significance: Endemism refers to the ecological state where a species is unique to a defined geographic location, such as an island, a specific mountain range, or a particular nation. These species are not found naturally anywhere else in the world.

    • Indicator of Biodiversity: Regions with a high concentration of endemic species are considered biodiversity hotspots and are often prioritized for conservation. The Western Ghats in India, for example, is a global biodiversity hotspot with numerous endemic species like the Lion-tailed Macaque and the Nilgiri Tahr.
    • Indicator Species: The health and population of an endemic species can serve as a powerful indicator of the health of its specific ecosystem. A decline in an endemic species often signals a broader environmental problem.
    • Evolutionary Insights: Endemic species, especially those on isolated islands like the finches of the Galapagos Islands studied by Charles Darwin, provide invaluable insights into processes of evolution, speciation, and adaptation.
    • Conservation Imperative: The extinction of an endemic species represents a global loss of unique genetic material and evolutionary history. Protecting them is critical for preserving global biodiversity.

  • Classification of Species by Origin and Impact:

    • Native Species (Indigenous): A species that historically originated and evolved in a particular ecosystem or region without any human involvement.

      • Endemic: A native species that is restricted exclusively to that specific region. (e.g., Sangai Deer in Loktak Lake, Manipur).
      • Non-Endemic: A native species that occurs naturally in a region but also has a wider natural distribution. (e.g., The Asiatic Lion, native to India, historically had a range extending to the Middle East).

    • Alien Species (Exotic, Non-native, Introduced): A species that has been introduced into an ecosystem outside its natural past or present distribution, either intentionally or accidentally by human activity.

      • Non-Invasive Alien Species: An introduced species that coexists with native species without causing significant ecological or economic harm. Many agricultural crops like tomatoes and potatoes are non-native to India but are not invasive.
      • Invasive Alien Species: An introduced species that spreads aggressively, outcompetes native species for resources, and causes significant harm to the environment, economy, or human health. Lantana camara and Prosopis juliflora (Vilayati Babul) are prominent invasive plants in India that have degraded vast tracts of land.

DISTRIBUTION OF BIODIVERSITY

  • Biogeographic Realms: This is a large-scale classification of the Earth’s land surface based on the historical and evolutionary distribution patterns of plants and animals. The concept was pioneered by naturalist Alfred Russel Wallace in his 1876 work “The Geographical Distribution of Animals”. There are eight recognized terrestrial realms:

    1. Nearctic: North America.
    2. Neotropic: South and Central America.
    3. Palearctic: Europe, North Asia, and North Africa.
    4. Afrotropic: Sub-Saharan Africa.
    5. Indo-Malayan: Indian subcontinent and Southeast Asia.
    6. Australasian: Australia, New Guinea, and surrounding islands.
    7. Oceanic: Polynesia, Fiji, and Micronesia.
    8. Antarctic: Antarctica.
    • India’s unique geographic position places it at the confluence of two major realms: the Palearctic realm covering the Himalayan region and the Indo-Malayan realm covering the peninsular and northeastern parts. This intersection of faunal and floral elements from two distinct realms is a major reason for India’s exceptionally high biodiversity.

  • Megadiverse Countries: This is a term used to refer to a group of nations that harbour the majority of Earth’s species and are therefore considered extremely rich in biodiversity. The concept was first proposed by ecologist Russell Mittermeier in 1988 and is now used by Conservation International (CI) to identify priority countries for conservation efforts.

    • There are 17 megadiverse countries: Australia, Brazil, China, Colombia, Democratic Republic of Congo, Ecuador, India, Indonesia, Madagascar, Malaysia, Mexico, Papua New Guinea, Peru, Philippines, South Africa, United States, and Venezuela.
    • Together, these countries account for over 70% of the planet’s terrestrial biodiversity while covering only about 10% of the Earth’s surface.
    • Criteria for identification: A country must satisfy two primary conditions to be classified as megadiverse:
      1. It must possess at least 5,000 species of endemic plants.
      2. It must have a marine ecosystem within its borders.

Prelims Pointers

  • Wetlands: Often called the “kidneys of the Environment” for their water purification function.
  • Lakes vs. Wetlands: Lakes are often deep, thermally stratified, and dominated by phytoplankton (grazing food chain). Wetlands are shallow, wind-mixed, and dominated by macrophytes (detritus food chain).
  • Tectonic Lake Example: Wular Lake in Jammu and Kashmir.
  • Fluvial Wetland Example: Kanwar Lake (an oxbow lake) in Bihar.
  • Bellandur Lake: Located in Bengaluru, known for pollution, foam, and fires caused by methane and industrial pollutants.
  • Biodiversity Definition: Formalized by the Convention on Biological Diversity (CBD) at the Rio Earth Summit (1992).
  • Levels of Biodiversity: Genetic, Species, and Ecosystem diversity.
  • Irish Potato Famine (1845-49): A historical example of the dangers of low genetic diversity.
  • Species Diversity Measurement: Based on Species Richness (number of species) and Species Evenness (relative abundance of species).
  • Alpha, Beta, Gamma Diversity: Concepts developed by ecologist R.H. Whittaker (1960) to measure diversity at different spatial scales.
  • Shannon-Wiener Index: A quantitative measure of species diversity, used in reports like the India State of Forest Report (ISFR).
  • Biodiversity and Stability: Experiments by David Tilman showed that higher diversity leads to greater ecosystem stability and resilience.
  • Endemic Species: Species unique to a specific geographic location.
  • Indian Endemic Species Examples: Lion-tailed Macaque (Western Ghats), Nilgiri Tahr (Western Ghats), Sangai Deer (Loktak Lake).
  • Invasive Alien Species Examples: Water Hyacinth (Eichhornia crassipes), Lantana camara, Prosopis juliflora.
  • Biogeographic Realms: A concept developed by Alfred Russel Wallace. India is at the junction of the Palearctic and Indo-Malayan realms.
  • Megadiverse Countries: A concept by Russell Mittermeier, list maintained by Conservation International. There are 17 such countries, including India.
  • Criteria for Megadiverse Country:
    1. At least 5,000 endemic plant species.
    2. Presence of marine ecosystems.

Mains Insights

Wetlands: The Urban-Conservation Conflict

  • Cause-Effect Relationship (GS-III, Environment):
    • Cause: Rapid, unplanned urbanization leads to the encroachment and conversion of wetlands into real estate, infrastructure projects, and waste dumpsites. This is driven by high land value and weak enforcement of environmental laws like the Wetland (Conservation and Management) Rules.
    • Effect: The degradation of urban wetlands (natural sponges) directly correlates with an increased frequency and intensity of urban floods. Cities like Chennai (2015), Mumbai (2005), and Hyderabad (2020) serve as stark case studies. This loss also leads to groundwater depletion, local climate change (loss of cooling effect), and a decline in urban biodiversity.
  • Policy and Governance Perspective (GS-II, Governance):
    • The dichotomy between development goals and conservation imperatives presents a major governance challenge. There is a need for an integrated urban planning approach that incorporates “blue-green infrastructure” (a network of water bodies and green spaces). The failure to effectively implement the Wetland Rules, 2017 and the lack of coordination between urban local bodies and environmental agencies exacerbate the problem.
  • Economic Dimension (GS-III, Economy):
    • Wetlands provide invaluable ecosystem services (flood control, water purification) that are often not accounted for in economic planning. The economic cost of disasters like urban floods far outweighs the short-term gains from converting wetlands. There is a growing need for the economic valuation of ecosystem services (EVES) to be integrated into cost-benefit analyses for urban projects.

Biodiversity: A Foundation for Resilience

  • Ecological and Economic Significance (GS-III, Environment & Economy):
    • The principle that “diversity begets stability” (as shown by Tilman’s work) is fundamental. For India, a biodiverse agricultural landscape with multiple native crop varieties offers greater resilience against climate change and pest attacks than monoculture-based systems. Loss of biodiversity, therefore, is not just an environmental issue but a direct threat to food security and economic stability.
    • The debate on “development vs. conservation” is often a false dichotomy. Sustainable development models must integrate biodiversity conservation as a core principle. The economic potential of biodiversity through bioprospecting (discovery of new drugs, products from nature) is immense, but this must be governed by equitable benefit-sharing principles as laid out in the Nagoya Protocol under the CBD.
  • Ethical Perspective (GS-IV, Ethics):
    • The conservation of biodiversity raises fundamental ethical questions. Does nature have an intrinsic value, independent of its utility to humans (ecocentrism), or is its value purely instrumental/utilitarian (anthropocentrism)? The principle of inter-generational equity demands that the present generation acts as a steward of biodiversity, preserving it for the future.

Endemism and Invasive Species: The Silent Crisis

  • Threat Analysis (GS-III, Environment):
    • Invasive Alien Species (IAS) are recognized as the second-biggest threat to biodiversity globally, after habitat destruction. They disrupt food webs, outcompete native (especially endemic) species, and can alter entire ecosystem processes. The silent invasion of Prosopis juliflora in arid and semi-arid regions of India has displaced native vegetation and impacted groundwater levels.
    • Protecting endemic species hotspots like the Western Ghats, the Himalayas, and the Andaman & Nicobar Islands is a national priority. These areas are cradles of evolution but are also extremely fragile. Conservation strategies must be habitat-focused and community-inclusive.
  • Biosecurity and Policy Framework (GS-III, Science & Tech/Environment):
    • Managing the threat of IAS requires a robust biosecurity framework with strict quarantine measures at borders to prevent their entry, along with early detection and rapid response mechanisms. This involves international cooperation and adherence to frameworks like the WTO’s Agreement on the Application of Sanitary and Phytosanitary Measures (SPS Agreement). Addressing this issue is critical for protecting both ecological integrity and agricultural productivity.

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