Chapter 15: Biodiversity, Conservation and Environmental Issues
In the early 1960s, an American biologist named Rachel Carson began collecting reports that troubled her deeply. Farmers were spraying the pesticide DDT over fields to kill insects, and it worked remarkably well. But bird watchers in several regions were noticing something strange: fewer songbirds each spring, and fish-eating birds of prey such as eagles laying eggs with shells so thin that they cracked under the weight of the parent bird.
Carson pieced the reports together. The DDT was not staying in the field. Rain washed it into ponds and rivers, where it entered the bodies of tiny floating organisms. Small fish ate those organisms, larger fish ate the small fish, and birds ate the larger fish. At every step the chemical was passed on, but almost none of it was broken down or thrown out of the body. A poison that was almost undetectable in the water was ending up concentrated inside the birds at the top of the food chain.
In 1962 she published her findings in a book called Silent Spring — a title imagining a spring morning with no bird calls left in it. The book caused an uproar, and it changed how the world thought about pollution. It showed that harming one part of nature quietly harms everything connected to it.
Diagram
Fig. 15.0 – Opening illustration: a spray plane over farmland with a stream running from the field into a lake, and along the lake a rising series of organisms (plankton → small fish → large fish → fish-eating bird), the bird shown beside a cracked, thin-shelled egg
This chapter will answer each of these questions — read on, and check your answers as you go.
15.1 Levels of Biodiversity
What Biodiversity Means
Diversity simply means variety. When we speak of the variety of life on Earth, we call it biodiversity. It covers an enormous range of living forms — viruses, bacteria and other microorganisms, algae, fungi, plants and animals — living either on land (terrestrial habitats) or in water (aquatic habitats), together with the ecological complexes of which they are a part.
Notice that biodiversity is not only a list of organisms. It also includes the living systems these organisms build together — a mangrove swamp, a coral reef, a grassland — because a species cannot be understood apart from the surroundings and the other species it interacts with.
This variety shows itself in almost every feature you can think of. Organisms differ in size (from microscopic to macroscopic), in shape, colour and form, in their mode of nutrition, in the type of habitat they occupy, in how they reproduce, in whether they can move about (motility), and in the duration of their life cycle.
Why should life be so varied? The answer lies in survival. Different regions of the Earth offer very different conditions — climatic (temperature, rainfall), edaphic (soil-related), topographic (the lie of the land) and geographic. To survive and to continue their kind (perpetuation), living organisms must fit themselves to these conditions. In doing so they develop distinct features, and these features are passed on and become fixed in the life cycle. In short, adaptation to different environments is the basis of diversity.
A Formal Definition
Bodies such as the IUCN (International Union for Conservation of Nature), UNEP (United Nations Environment Programme) and WRI (World Resources Institute) define biodiversity in a way that covers three different scales at once: the differences in the genes among the individuals of a species; the variety and richness of all plant and animal species at different scales in space — a local region, a country, the whole world; and the types of ecosystem, both terrestrial and aquatic, within a defined area.
The word itself is fairly new. The term biodiversity was coined by Walter Rosen (1982), and it was popularised by Edward Wilson to describe the combined diversity at all levels of biological organisation. The idea it names, however, is very old — it is the whole record of life’s branching.
In this chapter we shall study the basic concepts of biodiversity: its levels and patterns, its expanse, its importance, how it is being lost, and the methods and efforts undertaken to conserve it.
The Three Levels
Diversity in the living world can be observed at many levels, ranging all the way from the molecular level up to the ecosystem level. Three of these levels are treated as the major ones. They are hierarchical — each is built out of the level below it — and they are interrelated, so a change at one level affects the others. These are genetic diversity, species diversity (the community level) and ecosystem or ecological diversity. The relationship between them is shown in FC 15.1.
Flowchart
FC 15.1 – Levels of biodiversity, from lowest to highest: genes and alleles → individuals of a species → populations → species (species diversity within a community) → community → ecosystem (ecosystem diversity) → landscape/region
a. Genetic diversity
Genetic diversity is intraspecific diversity — diversity within a single species. It is the diversity in the number and types of genes as well as chromosomes present in different species, and also the variation in the genes and their alleles within the same species. (Recall that a gene is a unit of heredity, and that alleles are the alternative forms of the same gene.)
Genetic diversity includes both the variation found within a single population and the differences between separate populations of the same species — differences that arise because each population becomes adapted to its own local conditions.
Genetic variations, such as those caused by allelic genes, lead to individual differences within a species. These differences matter enormously. They pave the way to evolution, because natural selection can only act on variation that already exists. They improve the chances of a species continuing under changing environmental conditions, since some individuals will be better suited to the new conditions and will survive. The existence of subspecies and races within a species is an example of genetic diversity.
The rule that follows from this is simple: the greater the genetic diversity, the better the sustenance of a species. Genetic diversity or variability is essential for a healthy breeding population of a species.
India is unusually rich at this level. There are about 1000 varieties of mangoes and 50,000 varieties of rice or wheat in India — all belonging to the same species, but differing in their genes, and therefore in taste, yield, grain size, disease resistance and tolerance of drought.
b. Species diversity
Species diversity is interspecific diversity — diversity between species. The number of species of plants and animals present in a region constitutes its species diversity. Some areas or regions are clearly richer in species than others.
Species diversity has two components, and both must be counted. It deals with the variety of species present, which is called species richness, and also with the number of individuals of each of those different species, which is called species evenness, in the area under study.
Diagram
Fig. 15.1.1 – Two square plots A and B, each with the same total number of trees but different mixes of tree types, for comparing species richness and species evenness
A few examples make the idea concrete. Amphibian species diversity is greater in the Western Ghats than in the Eastern Ghats. Natural, undisturbed tropical forests have much greater species richness than a monoculture plantation of a single timber species raised by forest plantation — because a monoculture, by design, contains one species where nature would have placed hundreds. India is one among the 15 nations that are rich in species diversity.
c. Ecological (ecosystem) diversity
Ecosystem diversity is related to the different types of ecosystems or habitats present within a given geographical area. There is a large variety of ecosystems on Earth, and each one has its own complement of distinctive, interlinked species — the species are interlinked because they depend on one another for food, shelter, pollination and much else. These differences between ecosystems arise from differences in the habitat itself.
Ecosystem diversity is always described for a specific geographical region. Generally, a region may contain one type of ecosystem or many. This is exactly why ecosystem diversity is very high in India while it is quite low in Norway — India spans many climatic and topographic zones, whereas Norway spans far fewer.
In India we can find a great variety of ecosystems — deserts, rain forests, deciduous forests, estuaries, wetlands, grasslands, and more. Even within the country the contrast is sharp. The Western Ghats show great ecosystem diversity, while regions such as Ladakh and the Rann of Kutch do not show the variance we observe in the Western Ghats.
These three levels are not independent shelves in a cupboard; they are stacked. Genetic diversity supplies the raw material from which new species arise; species diversity fills up each ecosystem; and the range of ecosystems decides how many kinds of species can exist at all. Damage one level and the others feel it.
That is the concern with which this chapter proceeds. The diversity of life at all the three levels is now rapidly being modified by modern man.
15.2 Patterns of Biodiversity
Biodiversity is not scattered randomly over the Earth. If you plot where species are found, clear patterns appear — patterns regular enough that ecologists can describe them in words and even in equations. Two such patterns are studied here: the latitudinal and altitudinal gradients, and the species–area relationship.
a. Latitudinal and altitudinal gradients
A gradient means a steady change in one direction. Biodiversity — barring arid and semi-arid habitats and aquatic habitats, which behave differently — shows both a latitudinal gradient and an altitudinal gradient.
Latitudinal gradient
Ecological studies have revealed that the distribution of diversity is not uniform around the globe. Species richness exhibits a latitudinal gradient for many plants and animals, if not for all. The observation is consistent: species richness is high at lower latitudes, that is, near the equator, and there is a steady decline towards the poles.
Why should a line on a map make such a difference? Several factors, working together over very long periods, have been suggested.
The first is stability. Tropical regions have remained more or less stable for millions of years. There is less climatic change through the year, and plenty of sunlight is available. Tropical areas have far less often experienced drastic disturbances such as the periodic glaciations seen at the poles. Such stability over millions of years might have favoured speciation — the formation of new species — simply because populations were given the long, undisturbed stretches of time that speciation requires.
The second is isolation. Lesser migrations in the tropics might have reduced gene flow between geographically isolated regions. When two populations exchange fewer genes, they drift apart genetically, and over time they may become separate species. So reduced gene flow also favoured speciation.
The third is abundance. Scientists have considered the availability of more intense sunlight, warmer temperatures and higher annual rainfall in the tropics as factors responsible for the bountifulness of these regions. More sunlight and water mean more plant growth, and more plant growth means more food for everything above it in the food chain.
Abundance also allows specialisation. In more or less constant climatic conditions, and with resources available in plenty, some animals can afford to be fussy — they enjoy food preferences. For example, since fruits are available throughout the year in rain forests, the variety of frugivorous (fruit-eating) organisms is obviously more there than in temperate regions, where a fruit-only diet would leave an animal starving for half the year.
In short, species richness or diversity for plants and animals decreases as we move away from the equator towards the poles. It is maximum in tropical rain forests — for example, the Amazon rain forest (40,000 plants, 1300 birds, 427 mammals, 3000 species).
Altitudinal gradient
The altitudinal gradient speaks for height from mean sea level (MSL) upwards. Species diversity is more at lower altitudes than at the higher altitudes.
The reason is much the same as before, only stacked vertically instead of spread horizontally. At higher altitudes, the climatic conditions change and the seasonal variations become drastic — the air is thinner, the temperature swings sharply between day and night, and the growing season is short. These harsh and unstable conditions lead to a decrease in species diversity.
b. Species–area relationships
Scientists have also tried to establish a relationship between species diversity and the size of the habitat. The starting assumption is a reasonable one: the number of species present is directly proportional to the area. It is understood that larger areas may have more resources, and these resources can be distributed amongst the inhabitant species. But does this always hold true?
The German naturalist Alexander von Humboldt gave the first careful answer. Humboldt observed that species richness does increase with an increase in area, but only up to a certain limit. Beyond that, adding more area adds fewer and fewer new species — for the simple reason that after a point you are only sampling more of the same habitat, not new kinds of habitat. Observe the graph for the species–area relationship in Fig. 15.1.
Diagram
Fig. 15.1 – Graph showing species–area relationship: species richness on the Y-axis against area on the X-axis, drawn as a rectangular hyperbola labelled S = CA^Z, with the same relationship shown as a straight line on a log–log scale labelled log S = log C + Z log A
For many species this relationship takes the form of a rectangular hyperbola — a curve that rises steeply at first and then flattens out. If we let \(S\) be the species richness, \(A\) the area under study, \(C\) the Y-intercept, and \(Z\) the slope of the line, the relationship can be described by the equation:
\[S = CA^{Z}\]
Taking logarithms on both sides converts this curve into something far easier to handle:
\[\log S = \log C + Z \log A\]
Here \(S\) is species richness (the number of species), \(A\) is the area (for example, in \(\text{km}^2\)), \(C\) is the Y-intercept of the straight line, and \(Z\) is its slope, called the regression coefficient. Both \(C\) and \(Z\) are constants for a given data set; they have no units in the usual sense, since they simply fix the position and steepness of the line.
On a logarithmic scale, therefore, this relationship is a straight line, as observed in the figure above.
The value of \(Z\) turns out to behave in an interesting way. For smaller areas, the value of \(Z\) ranges between 0.1 and 0.2, regardless of the species or the region under study — a surprisingly constant figure, which is what makes the relationship worth calling a general pattern at all.
But for larger areas, like entire continents, the slopes are closer to the vertical axis, that is, they are steeper. This observation indicates that in very large areas, the number of species found increases faster than the area explored. This makes sense: as you expand from a patch of forest to a whole continent, you are no longer adding more of the same forest — you are adding deserts, mountains, rivers and coasts, each with an entirely new set of species.
In NEET and board examinations, this pattern is most often tested through the graph itself — you may be shown two lines on the same axes and asked which one represents \(S = CA^{Z}\) and which represents \(\log S = \log C + Z \log A\), or asked what the value of \(Z\) tells you about the region. Learn to read the graph, not merely to recite the equation.
Importance of Species Diversity to the Ecosystem
We have now seen how much diversity exists and where it is concentrated. But a fair question remains: do we really need all the diversity around us? What would actually happen if a few species were lost permanently?
To answer this, ecologists first had to define what a healthy ecosystem looks like. A community is said to be stable if its average biomass production remains fairly constant over a period of time. Beyond that, a stable community should be strong enough to withstand disturbances — a drought, a flood, a fire — and to recover quickly afterwards. It must also be resistant to invasive species, which is to say that an outsider species should not be able to walk in and take over.
David Tillman carried out various field experiments and proved that species richness does help the stability of an ecological community. His plots showed that rich diversity leads to lesser variation in biomass production over a period of time. In other words, a diverse community does not swing wildly between good years and bad years — if one species does badly in a particular year, another takes up the slack. This is called the Productivity–Stability Hypothesis.
Paul Ehrlich, an ecologist from Stanford, gave a memorable analogy to explain the significance of diversity. It is called the Rivet Popper Hypothesis. He compared an aeroplane to an ecosystem, and the species to the rivets that hold all the parts of the aeroplane together. Of course, thousands of rivets are needed to hold the whole aeroplane together.
Now suppose each passenger decides to pop out even one rivet — in other words, suppose one species after another goes extinct. Initially, not much turbulence will be experienced. But slowly, as the number of popped rivets increases, there will be a serious threat to the safety of the aeroplane. Also — and this is the crucial point — which rivets are removed will matter.
Suppose the rivets at key positions, such as the ones that bind the wings to the body of the aeroplane, are removed. The situation will become serious at once, however few rivets have gone. Species work the same way: some are ordinary members of the community, while others are keystone species on which many others depend.
Putting both ideas together, we can say that the relationship between diversity and the well-being of an ecosystem is not linear. It is certain that the loss of species may not pose a threat to the ecosystem only initially. But the loss of key species will certainly cause a threat in a very short span of time. It will affect food chains, food webs, energy flow and natural cycles — in short, it will affect the balance of the ecosystem. The chain of consequences is summarised in FC 15.2.
Flowchart
FC 15.2 – Consequence of species loss: key species lost → food chains and food webs broken → energy flow through trophic levels altered → natural cycles (nutrient recycling) disturbed → biomass production becomes unstable → ecosystem balance destroyed
15.3 Biodiversity Current Scenario
How many species really exist on Earth, and how many of them are found in India? These sound like questions with a simple answer waiting in some book. They are not. It is difficult to come to a consensus about the exact number of species that are present on Earth today.
What We Have Counted, and What We Have Missed
Over 1.5 million species have been documented so far, as per IUCN data (2004). Documented means named, described and formally placed in a classification. But we are yet to study far more than these. We are also unaware of the speciation process that might have continued all this while — new species do not wait for taxonomists to catch up.
There is a further bias in what we know. Most of the studies that have been carried out are in temperate regions. Yet the tropical rain forests, which are the major diversity hubs, are yet to be explored completely. In other words, we have searched hardest exactly where there is least to find, and least where there is most to find.
Because of this uncertainty, estimates vary wildly. Some exorbitant numbers, such as the existence of 20 to 50 million varieties, have been proposed. But Robert May has given a convincing estimate of about 7 million species around the globe. This is the figure most often used when we want to ask what fraction of life we have actually catalogued.
Reading the Pie Charts
Observe the pie charts given in Fig. 15.2 and find out the relative share of the various plant and animal groups in our existing knowledge of biodiversity.
Diagram
Fig. 15.2 – Graphic representation of known animal and plant groups: (A) Known species of organisms, total roughly 1,800,000 species, divided into Eubacteria, Protists, Fungi, Plants and Animals; (B) Known species of animals, total roughly 1,315,378 species, split into Vertebrates 58,498 species (fish, amphibians, reptiles, birds, mammals) and Invertebrates 1,256,880 species (crustaceans, echinoderms, sponges, cnidarians, rotifers, flatworms, mollusks, annelid worms, nematode worms, arachnids, insects); (C) Known species of plants, total 287,655 species, divided into mosses, ferns, conifers, flowering plants (monocots) and flowering plants (dicots)
The Missing Prokaryotes
Look carefully at the diagrams and you will notice an odd absence: we do not find any data on prokaryotes. This is not carelessness. Several moneran species are not cultivable under laboratory conditions, so they cannot be grown, isolated and studied in the usual way. Moreover, conventional taxonomic methods — which rely largely on visible structural features — are not suitable for the identification of prokaryotic species, since one bacterial rod looks much like another under a microscope.
The result is that an entire kingdom of life, and possibly an enormous number of species, is missing from our charts altogether.
15.4 Loss of Biodiversity
Loss of biodiversity leads to an overall imbalance in the ecosystem. The chief and most serious aspect of this loss is the extinction of species — the permanent disappearance of a kind of organism that took millions of years to appear and can never be recovered.
Three Types of Extinction
There are three types of extinction: natural extinction, mass extinction and man-made (anthropogenic) extinction. Natural extinction is the slow, background disappearance of species as environments change and better-adapted forms replace them. Mass extinction is the wiping out of a very large fraction of the world’s species within a geologically short period. Man-made or anthropogenic extinction is the loss of species caused directly by human activity.
Damage to biodiversity takes place due to both natural and man-made reasons. Natural reasons include forest fires, earthquakes and volcanic eruptions. Man-made reasons are habitat destruction, hunting, settlement, over-exploitation and reclamation — for example, the reclamation of mangrove lands, where a coastal wetland is filled in and built over.
The Seventh Extinction
We are aware of six mass extinctions during various stages of the history of the Earth — the ice age being one familiar example. The current loss of biodiversity is considered to be the 7th extinction, and it is progressing at an alarming rate, estimated to be 100 to 1000 times faster than in prehuman times.
That comparison is the heart of the matter. Extinction is not new; the speed is new. Ecologists blame this on human intervention in natural habitats, and they do not forget to warn that if the current trend continues, we might lose about 50% of diversity.
The consequences are practical, not merely sentimental. Loss of biodiversity in any area can lead to a decline in plant production and to lower resilience to environmental disturbances such as floods — a mixed forest holds the soil and slows the water in a way a bare or single-species slope cannot. It may also lead to alteration in environmental processes such as disease cycles and plant productivity.
Causes of Biodiversity Losses
There are four major causes of biodiversity loss, popularly known together as ‘The Evil Quartet’. They are summarised in FC 15.3.
Flowchart
FC 15.3 – The Evil Quartet — four causes of biodiversity loss: (i) Habitat loss and fragmentation → (ii) Over-exploitation → (iii) Alien species invasion → (iv) Co-extinctions; all four converge on → decline of species → extinction
i. Habitat loss and fragmentation
This is the prime cause of destruction. Two things are happening at once, and the difference between them is worth holding on to. Habitat loss is the outright reduction of vast natural habitats. Habitat fragmentation is the breaking up of what remains into small, disconnected patches, along with local degradation by pollution. Both create a crisis situation for living beings.
Fragmentation is particularly cruel to two kinds of animals. Loss of local habitat due to human activities creates a threat to migratory birds, which depend on a whole chain of stopover sites and are defeated if even one link is destroyed. It also threatens those animals that need larger territories — a tiger or an elephant cannot survive in a patch of forest smaller than its natural range, however well that patch is protected.
Tropical rain forests, the very hubs of diversity we spoke of earlier, are being lost at an alarming rate. Tropical rain forest cover has reduced from 14% to 6% over the years.
ii. Over-exploitation
The basic difference between human beings and other animals is that humans have the tendency to accumulate beyond their needs. A predator kills when it is hungry; we harvest to store, to sell and to export. This has resulted in the over-exploitation of resources, which in turn causes threats to various organisms. Can you correlate this with the dearth of fish that we observe nowadays?
The Dodo bird, the Steller’s sea cow and the passenger pigeon are a few examples of extinction due to over-exploitation. Notice, in Fig. 15.3, that all three were once abundant — abundance is no protection when the killing is fast enough.
Diagram
Fig. 15.3 – Examples of extinction due to over-exploitation: (a) Dodo bird, (b) Steller’s sea cow, (c) Passenger pigeon
iii. Alien species invasion
When a new species gets introduced into any ecosystem — accidentally or intentionally — there are chances that it proves harmful to the existing species. Sometimes it can even lead to the extinction of local species. In such a case, it is called an invasive species.
Examples include carrot grass (Parthenium), Lantana, and water hyacinth (Eichhornia). Animals can be invasive too. The introduction of the predator fish Nile perch into Lake Victoria proved deleterious for 200 local species of Cichlid fish — a single introduced predator eating its way through an entire community of native fishes.
One of the major reasons for such a harmful effect of alien species is the lack of a local predator. In its own homeland, a species is held in check by predators, parasites and competitors that evolved alongside it. Transported to a new region, it arrives without these controls, and its population can explode.
iv. Co-extinctions
Many a time, organisms are associated with each other in an obligatory way — that is, one simply cannot live without the other. In such cases, the extinction of one variety leads to the loss of its associated variety from the ecosystem.
For example, the extinction of a host fish causes the extinction of the unique parasites that live only on it. A co-evolved plant–pollinator pair faces the same threat: if the plant has evolved a flower that only one insect can pollinate, and that insect disappears, the plant cannot set seed.
Co-extinction is the clearest proof that species are not independent items on a list. They are knots in a web, and pulling out one knot loosens the others.
Extinct, Endangered and the Red List
We are aware of the threat to diversity and the loss of species from the Earth. Some vocabulary is needed to speak about it precisely.
The International Union for Conservation of Nature and Natural Resources (IUCN) maintains a Red Data Book, also known as the Red List, in which the conservation status of plant and animal species is recorded. The Red List is not merely a catalogue of the doomed; it is a working tool that tells governments and conservationists where to spend their limited effort first.
IUCN Categories
After a given species has been thoroughly evaluated, it is placed into one of the following categories. The path a species takes through this system is shown in FC 15.4.
Flowchart
FC 15.4 – IUCN Red List assessment: All species → if not assessed → Not Evaluated (NE); if evaluated → data checked → if data lacking → Data Deficient (DD); if adequate data → assessed against criteria → Least Concern (LC) → Near Threatened (NT) → threatened categories: Vulnerable (VU) → Endangered (EN) → Critically Endangered (CR) → Extinct in the Wild (EW) → Extinct (EX), in order of increasing risk of extinction
- Extinct (EX) — a designation applied to species in which the last individual has died or is not recorded.
- Extinct in the Wild (EW) — a category containing those species whose members survive only in captivity.
- Critically Endangered (CR) — a category containing those species that possess an extremely high risk of extinction, with very few surviving members (50).
- Endangered (EN) — a designation applied to species that possess a very high risk of extinction as a result of rapid population decline of 50 to more than 70 percent over the previous 10 years (or three generations).
- Vulnerable (VU) — a category containing those species that possess a very high risk of extinction as a result of rapid population decline of 30 to more than 50 percent over the previous 10 years (or three generations).
- Near Threatened (NT) — a designation applied to species that are close to becoming threatened, or may meet the criteria for threatened status in the near future.
- Least Concern (LC) — a category containing species that are pervasive and abundant after careful assessment.
- Data Deficient (DD) — a condition applied to species in which the amount of available data related to its risk of extinction is lacking in some way.
- Not Evaluated (NE) — a category used to include any of the nearly 1.9 million species described by scientists but not assessed by the IUCN.
Notice how the categories are built. Two of them (DD and NE) are statements about our knowledge, not about the species. The rest are ranked along a single axis — increasing risk of extinction — running from Least Concern, through Near Threatened, into the three threatened categories (Vulnerable, Endangered, Critically Endangered), and finally to Extinct in the Wild and Extinct. In examinations, the order of this ladder and the exact percentage decline figures for EN and VU are frequently tested, often as sequence-ordering or match-the-following questions.
15.5 Conservation of Biodiversity
Having seen how fast biodiversity is being lost, the obvious question is what can be done about it. Conservation of biodiversity means the protection, upliftment and scientific management of biodiversity, so as to maintain it at its optimum level and also to derive sustainable benefits from it for present and future strategies.
Read that definition carefully. Conservation is not the same as locking nature away and never touching it. It includes use — but use of a kind that does not reduce what is left for tomorrow.
Why to Conserve Diversity?
The reasons for the conservation of biodiversity can be classified into three categories. The first two ask what nature does for us; the third asks what we owe to nature.
a. Narrowly utilitarian reasons
Since time immemorial, humans have been reaping direct material benefits from biodiversity. These may be resources for basic needs such as food, clothes and shelter, or industrial products such as resins, tannins and perfume bases. There is aesthetic use as well, as in ornaments and artefacts.
The medicinal use of plants and animals is another major factor, and its scale surprises most students. It shares 25% of the global medicine market. Around 25,000 species are put to use by tribals worldwide as traditional medicines, and several more are yet to be explored for their potential as medicinal plants. Every species lost before it is studied is a medicine that will now never be discovered.
Nowadays, bioprospecting of economically important species is carried out on a large scale. It is essentially organised searching — combing forests, soils and seas for a molecule or a gene worth developing.
b. Broadly utilitarian reasons
Narrowly utilitarian reasons cover things we take out of nature. Broadly utilitarian reasons cover the services nature performs for us, quietly and free of charge, which we would otherwise have to pay for.
If we find out the cost of an oxygen cylinder and try to calculate the value of the oxygen we breathe with such ease, we will begin to understand what nature is giving us for free. Animals, too, play a crucial role in pollination and seed dispersal — services on which a very large fraction of our crops depends.
The Amazon forest alone is estimated to produce 20% of the total oxygen of the Earth’s atmosphere. We also need to consider the recreational use of diversity — the value of a forest walk, a bird sanctuary or a coral reef to human well-being.
c. Ethical reasons
We have no right to destroy diversity simply because we share the Earth with other species. All living beings have an equal right to survive, irrespective of their known or prospective economic use.
This is a different kind of argument altogether. The first two reasons say we should conserve species because they are useful to us. The ethical reason says we should conserve them even if they are never useful to us — a species need not justify its existence by serving humans.
How Do We Conserve Biodiversity?
Conservation means the sustainable use of natural resources. There are two main types of conservation strategies, and the difference between them is simply where the species is protected. The full picture is given in FC 15.5.
Flowchart
FC 15.5 – Conservation strategies: Conservation → branch 1: in situ (in the natural habitat) → biodiversity hotspots, biosphere reserves, national parks, wildlife sanctuaries, tiger reserves, sacred groves, traditional farm varieties; branch 2: ex situ (away from the natural habitat) → zoological parks, wildlife safari parks, botanical gardens, seed banks, tissue culture, in vitro fertilization, cryopreservation
a. In situ conservation
Protection of an organism will automatically take place if its natural habitat is protected — for example, by announcing Kanha forest as a tiger reserve. This is called in situ conservation. It is the most appropriate method of conservation. It is nothing but conservation ‘at home’.
The logic behind calling it the most appropriate method is worth spelling out. Protecting the habitat protects not one species but everything living in it, including the countless species we have never identified. It also keeps the species in the environment to which it is adapted, so that natural selection continues to act and the population keeps its genetic diversity — something no cage can provide.
Around 34 Biodiversity hotspots have been identified by conservationists. These are the regions with high species richness as well as high density. Such areas need to be protected strategically, by setting legislative measures apart from awareness and conservation work.
India has four of the world’s biodiversity hotspots — the areas with a high density of biodiversity: the Western Ghats, the Indo-Burma region, Sundaland and the Eastern Himalayas. It has been estimated that protection of these diversity-rich hotspots could reduce the extinction rate by almost 30%. That is a remarkable return: a small fraction of the Earth’s surface, protected well, saves nearly a third of the species that would otherwise be lost.
In situ conservation also includes the introduction of traditionally used varieties into farming and horticulture. For example, in Maharashtra, the Pawra tribals in Satpuda have protected varieties of corn with differently coloured kernels. A farm can therefore be a site of conservation, not only a forest — the field where an old variety keeps being sown is the safest place for that variety’s genes.
India at present has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries. In Maharashtra, there are 5 national parks and 11 sanctuaries.
Sacred Groves
Indian culture and traditions have always been connected with nature, and rituals were laid down that protect biodiversity. In many cultures, stretches of forest were set aside and protected in the name of the Almighty. These are called sacred groves.
Such sacred groves are found in the Khasi and Jaintia hills in Meghalaya, in the Western Ghat regions of Maharashtra and Karnataka, in the Aravali hills of Rajasthan, and in Bastar as well as the Chanda and Sarguja areas of Madhya Pradesh.
Sacred groves serve as the only chance of survival for some endangered varieties of animal and plant species. Tribals do not allow even a single branch of a tree to be cut from a sacred grove. But with increasing lust and greed, are sacred groves still safe? We must think about it.
b. Ex situ conservation
Sometimes, when a species is critically endangered, special measures have to be undertaken to protect it. It might be protected in captivity, as one of the measures of protection. This is called Ex situ conservation.
Wildlife safari parks, zoological parks and botanical gardens serve this purpose. Animals whose numbers have decreased are allowed to breed in captivity in order to protect them — for example, at the crocodile bank of Chennai.
Seed banks are established to conserve wild varieties of food grains and vegetables. Wild varieties matter because they carry genes for disease resistance and drought tolerance that our high-yielding crop varieties have lost, and a seed bank keeps those genes available for future breeding.
Nowadays, modern techniques such as tissue culture, in vitro fertilization of eggs, and cryopreservation — preservation at the very low temperature of \(-196\ ^\circ\text{C}\) — of gametes are used to protect endangered species. At that temperature all biochemical activity effectively stops, so gametes can be stored for years and used long after the donor animal has died.
By now we have, thus, understood the immense importance of biodiversity and the dire need to protect it. What remains is to see how this need is written into law — which is the subject of the next section.
15.6 Biological Diversity Act 2002
Awareness and good intentions alone cannot protect biodiversity. A country as rich in living wealth as India also needs law — rules about who may take a biological resource, for what purpose, and with whose permission. That is what this section is about.
From Rio to India
India participated in the Earth Summit at Rio de Janeiro and is a party to the Convention on Biological Diversity (CBD-1992). The CBD was the first international agreement to treat a nation’s biodiversity as its own sovereign wealth, rather than as a free resource open to anyone who wished to collect it.
In order to provide a framework for the sustainable management and conservation of our country’s natural resources, the Government of India passed the Biological Diversity Act (BD Act) in the year 2002, in compliance with the CBD.
What the Act Covers
The law broadly defines biodiversity as plants, animals and microorganisms, together with their parts, their genetic materials and their by-products. Notice how wide this is — a leaf, a seed, a strain of bacteria and an extracted gene all fall within it.
The Act, however, excludes value-added products and human genetic material. Value-added products are excluded because once a raw biological resource has been processed into a manufactured commodity, it is dealt with by other laws; human genetic material is deliberately kept out of a law meant to govern the use of the country’s biological resources.
Two objectives were the main reasons for proposing this Act: the regulation of access to Indian biological resources, and the scientific cataloguing of traditional knowledge about ethnobiological materials — that is, putting on record what our communities already know about the plants and animals they have used for generations.
The Three-Tier System
To put the law into practice, a three-tier system has been established, working at three levels of government. The structure is shown in FC 15.6.
Flowchart
FC 15.6 – Three-tier system under the BD Act 2002: National level → National Biodiversity Authority (NBA) → State level → State Biodiversity Boards (SBBs) → Local level → Biodiversity Management Committees (BMCs); any request to use a biological resource for commercial or research purpose passes through this system for approval
At the national level there is the National Biodiversity Authority (NBA); at the state level, the State Biodiversity Boards (SBBs); and at the local level, the Biodiversity Management Committees (BMCs). Together they handle the approval of the utilisation of any biological resource for commercial or research purposes.
The rules are strict. It is mandatory for foreigners, NRIs, as well as Indian citizens and institutions, to seek permission from the NBA before exploiting a local resource. The NBA has the powers of a civil court. Not seeking the approval of the NBA can incur jail as well as a fine of up to 10 lakh rupees.
15.7 Environmental Issues
The exponential growth of the human population, coupled with industrial development, has resulted in the rampant loss of natural resources over the last ten decades. Growth by itself is not the whole story; it is growth combined with the sheer quantity each person now consumes.
This uncontrolled exploitation of nature has disturbed the delicate balance between the living and non-living components of the biosphere. The utilisation and production of synthetic materials, along with construction activities, have pumped several undesired substances into the ecosphere. This has resulted in severe pollution. The main types of pollution are shown in Fig. 15.7.1.
Diagram
Fig. 15.7.1 – Types of pollution: a central circle labelled ‘Types of pollution’ with five branching circles — air pollution, water pollution, soil pollution, noise pollution and radioactive pollution
Note the phrase “or a form of energy”. A pollutant need not be a chemical at all: heat and sound are also pollutants, which is why thermal pollution and noise pollution appear in this chapter. In order to protect and improve the quality of our environment, the Government of India has passed the Environment Protection Act, 1986.
a. Air Pollution
Effect of air pollution
The respiratory surfaces of living beings are constantly interacting with air. This is precisely why air pollution is so dangerous — the lung has evolved to be thin, moist and richly supplied with blood so that gases cross it easily, and a pollutant crosses just as easily as oxygen does. Any unfavourable alteration in air quality therefore affects the respiratory system.
The severity of damage depends on three things: the concentration of the pollutant, the duration of exposure, and the organism itself — a child, an asthmatic patient and a healthy adult do not suffer equally from the same air.
Plants suffer too. Even in the case of plants, air pollution results in poor yield of crops and premature death of plants. Nowadays automobiles are omnipresent, and they are a major cause of atmospheric (air) pollution. Regular maintenance of vehicles and the use of lead-free petrol or diesel can reduce the pollutants coming from exhausts.
Types of air pollutants
Air pollutants are of two types — particulate pollutants and gaseous pollutants.
Particulate air pollutants are solids, and also fine liquid droplets called aerosols. What matters most about a particle is not what it is made of but how big it is, because size decides where it ends up.
Particles with a diameter of 10 μm may settle in the soil, but particles of 1 μm or less remain suspended in the air. According to the Central Pollution Control Board (CPCB), particulate matter of size 2.5 μm or less in diameter (PM2.5) is responsible for causing the greatest harm to humans.
These fine particulates can be inhaled deep into the lungs — they are small enough to slip past the nose, throat and airways, which trap larger particles — and they are responsible for irritation, inflammation and damage to the lungs. In addition to this, they cause breathing and respiratory disorders and premature deaths.
Smoke, smog, pesticides, heavy metals, dust and radioactive elements are examples of particulate pollutants.
Gaseous pollutants include \(CO_2\), \(CO\), \(SO_2\), \(NO\) and \(NO_2\), among others.
Carbon dioxide
Carbon dioxide is a greenhouse gas. In the past, the levels of \(CO_2\) in the atmosphere remained low. Due to the burning of fossil fuels, as well as increasing deforestation, the levels of \(CO_2\) are now rising at an alarming rate.
Nature has two ways of pulling \(CO_2\) back out of the air. The process of photosynthesis balances the \(CO_2 : O_2\) ratio of the air to a great extent — green plants take in carbon dioxide and release oxygen. Carbon dioxide is also removed from the air by the weathering of silicate rocks, forming limestone; this is a slow, purely chemical route.
Both of these removal processes are being outpaced. One figure makes the imbalance vivid: a jet plane, in a single trip across the Atlantic, uses 35 tonnes of oxygen and releases 70 tonnes of \(CO_2\). We shall discuss the role of \(CO_2\) in global warming later in this chapter.
Carbon monoxide (CO)
Carbon monoxide is a poisonous gas produced by the incomplete combustion of fuel such as coal or wood. Vehicular exhausts are the largest source of CO.
Why is it so poisonous? Because haemoglobin, the respiratory pigment of our blood, binds carbon monoxide far more strongly than it binds oxygen. The CO occupies the very sites meant for oxygen, forming carboxyhaemoglobin, and that blood can no longer carry oxygen to the tissues. The person is starved of oxygen even though the lungs are working normally.
Nitrogen dioxide (\(NO_2\)) and nitrogen monoxide (\(NO\))
These are released by automobiles and chemical industries as waste gases. \(NO_2\), when it combines with water vapour, forms nitric acid — which is why these gases are linked with acid rain, and why they attack any moist surface they meet.
It causes irritation to the eyes and lungs. At high concentration, it causes injury to the lungs, liver and kidneys.
Control measures
Various ingenious mechanisms have been developed to control the emission of gaseous and particulate pollutants from vehicles and industries. A few examples are explained below.
Electrostatic precipitator
The electrostatic precipitator is the most widely used device for removing particulate matter such as soot and dust present in industrial exhaust. It can remove almost 99% of the particulate matter present in the exhaust from a thermal power plant. Its working is shown in Fig. 15.4.
Diagram
Fig. 15.4 – Electrostatic precipitator: gas stream containing particles entering, negatively charged metal grid giving particles a negative charge, positively charged collector plates attracting the smoke particles, particles removed into a reservoir, and clean gas stream leaving
In this method, a high voltage is applied and an electric discharge takes place, which causes ionisation of the air in the smokestack. Free electrons in the ionised air get attached to the gaseous and dust particles moving up the stack, giving those particles a negative charge.
These negatively charged particles then move towards the positive electrode — the collector plates — and settle down there, because unlike charges attract. The collected particles are removed by vibrating the electrodes, and are gathered in a reservoir. The gas that finally leaves the stack is largely free of particulate matter.
Exhaust gas scrubbers
Exhaust gas scrubbers are used to clean air of both dust and gases, by passing the exhaust through dry or wet packing material. A scrubber can remove gases such as \(SO_2\). In the scrubber, the exhaust is passed through a spray of water or lime, as shown in Fig. 15.5. The gas dissolves or reacts chemically with the spray instead of escaping into the atmosphere.
Diagram
Fig. 15.5 – Exhaust gas scrubber: boiler producing flue gas with SO2 → sprayers spraying water/lime → SO2 scrubber where CaSO3·2H2O forms in the collection tank → treated flue gas leaving through the smokestack
Catalytic converters
Motor vehicles equipped with a catalytic converter should use unleaded petrol, because the lead in leaded petrol inactivates the catalyst — it coats the metal surface and the converter stops working permanently.
Inside the converter, the exhaust passes through two stages, as shown in Fig. 15.6. First, the exhaust gases enter the reduction block of the catalyst, where the oxides of nitrogen react and form nitrogen and oxygen. Then the exhaust gases enter the oxidation block, where the hydrocarbons and the newly formed oxygen react to form carbon dioxide. The exhaust that finally exits the converter is much less harmful.
Diagram
Fig. 15.6 – Catalytic converter: harmful exhaust (hydrocarbons HC, carbon monoxide CO, oxides of nitrogen NOx) entering → reduction block converting NOx into N2 and O2 → oxidation block converting HC and CO with O2 into CO2 and H2O → less harmful exhaust (N2, CO2, H2O) leaving
Flowchart
FC 15.7 – Working of a catalytic converter: exhaust gases (HC, CO, NOx) → reduction block → oxides of nitrogen split into N2 + O2 → oxidation block → hydrocarbons and CO react with the newly formed O2 → CO2 + H2O → less harmful exhaust released
Controlling Vehicular Air Pollution: A Case Study of Delhi
In the year 1990, Delhi ranked fourth among the 41 most polluted cities of the world. In response to a PIL (Public Interest Litigation), the Supreme Court of India sent orders to the Delhi government to take appropriate actions.
In response, several measures were taken by the Delhi Government. By 2002, all the city buses were converted to run on CNG (compressed natural gas). CNG is advantageous over other fuels because it is economical, it burns efficiently — leaving very little unburnt residue — and it is an adulteration-proof fuel, since it cannot easily be diluted with cheaper substances the way petrol or diesel can.
According to the new fuel policy, norms were set to reduce the sulphur and aromatic content of petrol and diesel. Another provision is the upgradation of engines. For this, Bharat Stage emission standards (BS) are set. These standards are equivalent to the Euro norms, and have evolved on similar lines, from Bharat Stage II (BS II) to BS VI, over the period 2001 to 2017. Let us observe how the norms have changed, in Table 15.7.
Table 15.7: Bharat stage emission standards in cities of India
| Vehicle | Norms | Cities of Implementation |
|---|---|---|
| 4 wheelers | Bharat Stage II | All metro cities |
| 4 wheelers | Bharat Stage III | Throughout the country since October 2010 |
| 4 wheelers | Bharat Stage IV | 13 mega cities (Delhi and NCR, Mumbai, Kolkata, Chennai, Bengaluru, Surat, Kanpur, Agra, Lucknow, Solapur) since April 2010 |
| 2 wheelers | Bharat Stage III | Throughout the country since October 2010 |
| 3 wheelers | Bharat Stage III | Throughout the country since October 2010 |
Have you noticed that BS V is missing from the above table? There is a reason for it, and the story is instructive.
In 2001, Bharat Stage II emission norms were set for CNG and LPG vehicles. These stipulate that the emission of sulphur be controlled at 50 ppm in diesel and 150 ppm in petrol, and that aromatic hydrocarbons should be just 42% in the concerned fuel. The aim is to reduce sulphur emission to 50 ppm in petrol as well as diesel, along with bringing aromatic hydrocarbons down to 35%.
The Government of India directly adopted BS VI in the year 2018, skipping BS V altogether — a deliberate jump, made because the air quality crisis would not wait for a gradual transition. These efforts decreased the levels of \(CO_2\) and \(SO_2\) in Delhi.
Why does smog settle in winter in particular? Colder weather and stagnant winds trap smoke from various sources such as firecrackers, burning crop stubble, lit garbage and road dust — the cold air simply does not rise and carry the pollutants away.
During that episode, citizens suffered breathlessness, chest muscle contraction, irritation in the eyes, asthma and allergy. The administration took certain measures, such as closing educational institutions, suspending construction or demolition work, and undertaking vacuum cleaning of roads. Even the Badarpur thermal power plant was temporarily closed down.
Do you think that merely setting standards is not enough? We must also encourage means such as car pooling and the use of public transport — because the standards govern each vehicle, while the pollution depends on how many vehicles there are.
b. Noise pollution
In India, the Air (Prevention and Control of Pollution) Act 1981, amendment 1987, includes noise as an air pollutant. This may seem strange at first — noise is not a substance. But recall the definition of a pollutant: it includes any form of energy that adversely affects health, and sound is energy travelling through air.
There is a dire need to create awareness about the noise pollution caused during festivals and processions in our society.
Exposure to an extremely high sound level (150 decibels or more), such as that generated during the take-off of a jet plane or a rocket, may damage the ear drums and cause permanent hearing loss.
Noise can also cause sleeplessness, increased heartbeat, altered breathing pattern and psychological stress. Noise may negatively interfere with a child’s learning and behaviour pattern. The common sources of noise pollution are machines, transportation, construction sites, industries, public functions, festivals and family functions.
Control of noise pollution
Reduction of noise in our industries can be brought about by the use of sound-absorbent materials or by muffling the noise at its source. Laws that prohibit the blowing of horns in the areas of schools and hospitals need to be implemented strictly, to curb decibel levels.
The Government of India has rules and regulations against firecrackers and loudspeakers. The Supreme Court of India has banned loudspeakers at public gatherings after 10 pm.
c. Water Pollution and its Control
Water has always been a controlling factor in the distribution and density of living beings in an area. Human water consumption increased many-fold with increased industrialisation. The increased utilisation and discharge of harmful waste water into water bodies has caused severe pollution.
Most water pollution is man-made. Polluted water may be turbid, foul smelling, and may contain a number of pathogens, heavy metals, oils and other harmful substances.
Realising the importance of maintaining the cleanliness of water bodies, the Government of India has passed the Water (Prevention and Control of Pollution) Act 1974 to safeguard our water resources.
Domestic sewage and industrial effluents
Water is unforgiving of impurity. Even a small quantity of about 0.1% impurities in water can make it unfit for human consumption, and can also affect aquatic plants and animals.
Not all impurities are equally troublesome. Solids are relatively easy to separate — they can be filtered or allowed to settle. But dissolved salts such as nitrates and phosphates, other nutrients and toxic metal ions, as well as organic compounds, are difficult to remove, because they are no longer separate particles but part of the water itself.
Domestic sewage is one of the most common sources of water pollution. It contains biodegradable organic matter. This readily gets decomposed by bacteria and other microorganisms, which use the organic matter as a substrate and utilise some amount of the sewage.
This decomposition sounds helpful — and up to a point it is. The problem is what the decomposers consume while doing it.
Biochemical Oxygen Demand (BOD)
It is possible to estimate the biodegradable organic matter in sewage water by measuring the Biochemical Oxygen Demand (BOD).
A high BOD indicates an intense level of microbial pollution. The reasoning is direct: more organic matter means more microorganisms, and more microorganisms means more oxygen consumed. BOD is therefore not a measure of the organic matter directly — it is a measure of the oxygen the water will lose because of that organic matter.
The microorganisms involved in the biodegradation of organic matter in a water body consume a lot of dissolved oxygen. This results in a sharp decline in the oxygen level of the water, which leads to the mortality of fish and other aquatic creatures.
Algal bloom
The presence of a large amount of nutrients in water causes the excessive growth of planktonic free-floating algae, especially blue green algae. This is called an algal bloom, and it gives colour to the water body — the green, blue-green or reddish tinge you may have seen on a stagnant pond.
An algal bloom often releases toxins into the water. Fish therefore die not only from lack of oxygen but also from toxicity. The quality of the water deteriorates and it becomes toxic for human beings and other animals.
Eutrophication
Natural Eutrophication is the ageing of a lake due to nutrient enrichment of the water. Depending on the size of the lake, the climatic conditions and other factors, the natural ageing of lakes requires thousands of years. Every lake, left alone, slowly fills with sediment and nutrients and eventually becomes a marsh — but over geological, not human, timescales.
However, pollutants from human activities — such as effluents from agricultural lands, industries and homes (households) — have accelerated this ageing process. This phenomenon is called Cultural or Accelerated Eutrophication. Fertiliser washed off a field is, from a lake’s point of view, a thousand years of nutrient enrichment delivered in a single monsoon.
Study the sequence of events in FC 15.8 and understand the process of eutrophication.
Flowchart
FC 15.8 – Eutrophication: Nutrient enrichment of water → biological enrichment of water (algal bloom, planktonic algae and higher plants) → death of submerged plants due to reduced light → increase in organic loading of the lake → reduced contents of dissolved oxygen → death of aquatic animals including fish → loss of species diversity → stinking eutrophic lake with coloured and turbid water
The final result is the non-availability of dissolved oxygen for aquatic organisms. This leads to the death of fish and other aquatic organisms. Their decomposition further depletes the dissolved oxygen — the dead bodies themselves become organic matter for the decomposers, deepening the shortage. So a lake can literally get choked to death.
Biological magnification
A few substances usually present in industrial waste waters can undergo biological magnification.
Many pesticides are non-degradable. So they get accumulated in the tissues of organisms. They neither get metabolised nor are they excreted — the body has no enzyme that can break them down, and being fat-soluble, they are not flushed out in urine either. They simply stay.
Because they stay, they are passed on to the next trophic level. A fish that eats a thousand contaminated zooplankton takes in the pesticide of all thousand and keeps almost all of it. This is commonly seen in the case of DDT and mercury. Observe the food chain in Fig. 15.9, which shows how the biomagnification of DDT takes place.
Diagram
Fig. 15.9 – Biomagnification of DDT along a food chain: water 0.000003 ppm → zooplankton 0.04 ppm → small fish 0.5 ppm → large fish 2 ppm → fish-eating birds of prey 25 ppm, with arrows showing each level being eaten by the one above
Thermal pollution
Thermal pollution of water is caused due to a rise in the temperature of the water. The main sources of thermal pollution are thermal and nuclear power plants. These power plants use water as a coolant and release hot water back into the water body.
Why should warm water be a pollutant? For two reasons. Many aquatic organisms are sensitive to temperature — fish and their eggs can survive only within a narrow range. Warm water also holds less dissolved oxygen than cold water, so a warmed river is a suffocating river. A sudden rise in temperature therefore leads to the loss of flora and fauna.
Measures to reduce sewage water
In order to conserve water and prevent the creation of sewage in the first place, ecosan offers a sustainable system for handling human excreta using dry composting toilets. This is a practical, efficient and cost-effective solution for human waste disposal.
An ecosan toilet is a closed system that does not need water. It is an alternative to leach-pit toilets in places where water is scarce, or where there is a risk of ground water contamination — a leach pit lets liquid seep into the soil, and where the water table is high, that seepage reaches the very wells people drink from.
It is based on the principle of the recovery and recycling of nutrients from excreta, to create a valuable resource for agriculture. Waste, in other words, is treated as a misplaced resource rather than as a nuisance.
When the pit of an ecosan toilet fills up, it is closed and sealed. After about 8–9 months, the faeces are completely composted into organic manure. There are working EcoSan toilets in many areas of Gujarat, Kerala, Tamil Nadu and Sri Lanka.
Recycling water
The recycling of sewage water by reverse osmosis will help to solve the problem not only of the scarcity of water, but also of the disposal of sewage water — one process answering two problems at once.
At Tirumala hills, millions of pilgrims visit every year. Every building here has an R.O. system, which solves the problem of the huge water demand. The recycling of sewage water is also seen in many townships in Mumbai. Rain water harvesting is encouraged, and has been made mandatory for new constructions by the Municipal Corporation.
Solid Waste Management
You have already studied solid waste management in the ninth standard.
Solid waste is everything that goes into the trash. It includes wastes from homes, offices, stores, schools, hospitals and so on. These wastes are collected and disposed of by the municipality. Municipal solid waste generally consists of paper, food, plastic, glass, metals, rubber, leather, textiles and similar materials.
Burning reduces the volume of the waste. But generally it is not burnt to completion, and so open dumps become breeding grounds for rats and flies — and the incomplete burning itself releases smoke and toxic gases into the air.
Sanitary landfills are a substitute for open burning dumps. Here, wastes are dumped in a depression or a trench, and everyday wastes are added to this pit.
Landfills, however, are not a permanent answer. They get filled very soon, especially in metro cities, because the amount of garbage generated is far too high. In addition to this, there is the danger of chemicals percolating downwards, reaching the ground water and contaminating this water source.
All wastes can be categorised into three types:
- Biodegradable
- Recyclable
- Non-biodegradable
Our rag pickers and kabadiwallahs do a great job of separating materials for recycling. But the primary goal of all citizens should be to reduce the generation of waste in the first place — because waste that is never created needs neither burning nor burial.
The biodegradable materials can be put into deep pits in the ground and left for natural degradation, where decomposers will break them down. Non-biodegradable wastes have to be disposed of by other means.
Biomedical waste
Hospitals generate harmful waste that contains disinfectants, harmful chemicals and also pathogenic microorganisms. Such wastes require careful treatment and disposal — a discarded syringe or dressing carries live pathogens straight from a patient into the environment. You are aware of the colour code used for the disposal of biomedical waste.
E-waste
Irreparable computers and other electronic goods, as well as electrical waste, are known as e-wastes. They are buried in landfills or are completely burnt.
A major part of the e-waste generated by developed countries is exported to developing countries such as China, India and Pakistan. During the recycling process of this waste, metals such as copper, iron, silicon, nickel and gold are recovered — which is why it is worth exporting at all.
But here the difference between countries becomes a difference in human cost. Developed countries have facilities for the mechanised recycling of e-waste. In developing countries, manual participation is involved, and so workers are directly exposed to toxic substances from the e-waste — lead, mercury and acid fumes among them. The treatment of e-waste should be carried out in an environment-friendly manner.
You have already studied radioactive pollution in an earlier class.
15.8 Greenhouse Effect and Global Warming
Greenhouse Effect
The greenhouse effect is responsible for the heating of the Earth’s surface and its atmosphere. It is important to begin by saying something that surprises many students: this effect is not, in itself, a problem. It is the reason the Earth is habitable at all.
Without the greenhouse effect, the average temperature of the Earth would have been \(-18\ ^\circ\text{C}\), rather than the average of \(15\ ^\circ\text{C}\) that we actually enjoy. At \(-18\ ^\circ\text{C}\) the oceans would be frozen and life as we know it could not exist. The greenhouse effect gives us a planet warmer by some \(33\ ^\circ\text{C}\) than it would otherwise be.
How the Warming Happens
Of the solar radiation that reaches the Earth, clouds and gases reflect about \(\frac{1}{4}\) of it and absorb some of it. But half of the total incoming radiation reaches the Earth’s surface and heats it, and only a small portion of that is reflected back.
The Earth’s surface then re-emits this heat in the form of infrared radiation. Here is the crucial step: part of this infrared radiation does not escape into space, because atmospheric gases such as \(CO_2\) and \(CH_4\) absorb a major portion of it.
The molecules of these gases then radiate heat energy in all directions, and a major part of it comes back to the Earth’s surface — thus reheating the Earth. This cycle is repeated many times, and each repetition adds a little more warmth. Study the sequence in FC 15.9.
Flowchart
FC 15.9 – Greenhouse effect: solar radiation reaches Earth → about 1/4 reflected and some absorbed by clouds and gases → half of the incoming radiation reaches Earth’s surface and heats it → surface re-emits heat as infrared radiation → greenhouse gases (CO2, CH4) absorb a major portion of this infrared radiation → gas molecules radiate heat energy in all directions → a major part returns to Earth’s surface → Earth is reheated → cycle repeats many times
A similar phenomenon prevails inside a greenhouse or a glass house — the glass lets sunlight in but does not let the heat out again — and hence this warming of the Earth is called the greenhouse effect. The gases \(CO_2\) and \(CH_4\) that are involved in this process are called greenhouse gases.
The atmosphere around the Earth thus acts as the glass wall of a greenhouse. It absorbs solar radiation from the Sun and radiates it to the Earth, and it prevents the infrared radiation emitted by the Earth from escaping into space.
Diagram
Fig. 15.10 – Greenhouse effect: two panels side by side — (left) Natural greenhouse effect, with solar radiation entering, a normal layer of greenhouse gases (CO2, CH4, N2O), re-radiated heat from the Earth, and more heat escaping into space; (right) Human-enhanced greenhouse effect, with more greenhouse gases in the atmosphere, more re-emitted heat returning to Earth and less heat escaping into space
The Greenhouse Gases
The gases responsible for this effect are carbon dioxide (\(CO_2\)), methane (\(CH_4\)), chlorofluorocarbons (CFC), nitrous oxide (\(N_2O\)) and water vapour.
Each has its own human sources. Because of the burning of fossil fuels in industries and by automobiles, and the burning of agricultural wastes, the levels of \(CO_2\) are increasing. Biogas plants, paddy fields and cattle sheds add methane to the atmosphere — methane is produced wherever organic matter decomposes without oxygen, which is exactly the condition inside a flooded paddy field or the gut of a cow. Chlorofluorocarbons are emitted by fire extinguishers and air conditioners.
Global Warming
An increase in the atmospheric concentration of greenhouse gases has resulted in the heating of the Earth, that is, a rise in its temperature. This is global warming.
During the past century, the temperature of the Earth has increased by \(0.6\ ^\circ\text{C}\), most of it during the last three decades.
Consequences
This rise in temperature leads to unfavourable changes in the environment, resulting in odd climatic changes — the El Niño effect being one example. The El Niño effect results in the melting of the polar ice caps and of the Himalayan snow caps, which may be the cause of the submerging of coastal areas.
The link is straightforward: ice that has been locked up on land for thousands of years melts and runs into the sea, and the sea rises. For a country with a coastline as long as India’s, this is not a distant problem.
Control of Global Warming
Global warming can be controlled by reducing the use of fossil fuel, improving the efficiency of energy usage, reducing deforestation, planting trees, and checking human population growth.
Notice that these measures attack the problem from both ends. Reducing fossil fuel use, improving efficiency and checking population growth all reduce how much \(CO_2\) we add. Reducing deforestation and planting trees increase how much \(CO_2\) is removed, since growing trees lock carbon away in their biomass. Both halves are needed, because the atmosphere responds only to the balance between the two.
15.9 Ozone Depletion
Ozone is a form of oxygen. Ordinary atmospheric oxygen exists as \(O_2\), a molecule of two atoms; ozone is \(O_3\), a molecule of three. That one extra atom changes everything about how the molecule interacts with radiation — and on it depends the survival of life on land.
Where Ozone Comes From
In the stratosphere, ozone is continuously photo-dissociated (broken apart by light) and is also continuously generated by the absorption of short-wavelength UV radiation. The two reactions are:
\[O_3 \rightarrow O_2 + [O]\]
\[O_2 + [O] \xrightarrow{\text{UV rays}} O_3\]
In the first reaction, an ozone molecule absorbs UV radiation and splits into an oxygen molecule and a free oxygen atom, written as \([O]\). In the second, that free oxygen atom recombines with an oxygen molecule, under the action of UV rays, to form ozone again.
The generation and dissociation of ozone are in equilibrium, which leads to a steady concentration of ozone in the stratosphere (12 to 15 kilometres from the Earth’s surface in the atmosphere).
The Ozone Shield
This ozone layer acts as a shield that absorbs UV radiation from the Sun and protects all types of life on Earth. The absorption of UV radiation by the ozone blanket is proportional to its thickness — a thicker layer absorbs more. Interestingly, the thickness is greater above the poles than at the equator.
Why are UV rays so dangerous? UV rays are highly injurious to living organisms because DNA and proteins — the two molecules on which all life depends — absorb UV rays, and the high energy of this radiation breaks the chemical bonds within these molecules. A broken bond in a protein destroys its shape and function; a broken bond in DNA is a mutation.
The thickness of the ozone in a column of air, from the ground to the top of the atmosphere, is measured in Dobson units (DU).
How the Shield Is Being Damaged
The ozone shield has been disturbed due to an increased rate of ozone degradation by chlorofluorocarbons (CFCs).
CFCs are stable, unreactive gases used in refrigerants, fire extinguishers and air conditioners. Their very stability is the problem: nothing in the lower atmosphere destroys them, so they persist and slowly move upwards until they reach the stratosphere.
There, UV rays act on them and release chlorine (Cl) atoms. Chlorine degrades ozone, releasing molecular oxygen. And here is the sting in the tail — the Cl atoms act as a catalyst. Being a catalyst, chlorine is not consumed in the reaction. It therefore remains in the stratosphere and continues the effect of ozone degradation, destroying ozone molecule after ozone molecule. A single chlorine atom can go on doing this for years. The full sequence is shown in FC 15.10.
Flowchart
FC 15.10 – Ozone depletion by CFCs: CFCs released from refrigerants, air conditioners and fire extinguishers → being stable, they persist and move upwards → reach the stratosphere → UV rays act on CFCs → free Cl atoms released → Cl degrades ozone (O3), releasing molecular oxygen (O2) → Cl acts as a catalyst and is not used up → remains in the stratosphere → continues to degrade more ozone → ozone depletion → ozone hole
This results in ozone depletion. Although it occurs widely in the stratosphere, the depletion is particularly marked over the Antarctic region. This has resulted in the formation of a large area of thinned ozone layer, commonly called the ozone hole.
What Increased UV-B Does
UV radiation of wavelength shorter than UV-B, that is, 100–280 nm, is almost completely absorbed by the Earth’s atmosphere — given that the ozone layer is intact. That last condition is the whole point of this section.
UV-B (wavelength 280–322 nm) damages DNA, and mutation may occur. It causes ageing of the skin, damage to skin cells, and various types of skin cancers.
In the human eye, the cornea absorbs UV-B radiation. A high dose of UV-B causes inflammation of the cornea, called snow blindness, and also cataract. Such exposure may permanently damage the cornea.
The Montreal Protocol
Recognising the harmful effects of ozone depletion, an international treaty known as the Montreal Protocol was signed at Montreal (Canada) in 1987, to control the emission of ozone-depleting substances.
Later, many more efforts have been made, and protocols have laid down definite roadmaps — separately for developing and for developed countries — for reducing the emission of CFCs and other ozone-depleting chemicals. The separate roadmaps recognise a simple fairness: developed countries released most of these chemicals in the first place, and can afford substitutes more easily, so they were asked to phase them out sooner.
15.10 Deforestation
Deforestation is the conversion of a forest area into a non-forest area. Notice that the definition says conversion, not merely the cutting of trees. A forest that is cut and allowed to grow back has not been deforested; a forest that is cut and turned into a field, a road or a settlement has.
The Scale of the Loss
According to an estimate, almost 40% of forests are lost in the tropics, and only 1% in the temperate region. Recall the latitudinal gradient from earlier in this chapter, and the seriousness of this figure becomes clear at once: the forests being destroyed fastest are precisely the ones that hold the most species.
The scenario of deforestation is grim in India as well. At the beginning of the 20th century, the forest cover was about 30% in India. By the end of the century, it had got reduced to 19.4%. The National Forest Policy 1988 of India has recommended 33% forest cover for the plains and 67% for the hills. Compare these numbers in Fig. 15.10.1.
Diagram
Fig. 15.10.1 – Bar chart of India’s forest cover: 30% at the beginning of the 20th century, 19.4% at the end of the 20th century, with two horizontal target lines marking the National Forest Policy 1988 recommendations of 33% for the plains and 67% for the hills
Why Forests Are Cut
Deforestation takes place mainly by the conversion of forest to agricultural land, so as to feed the growing human population. Trees are also cut for timber, for firewood, for keeping cattle in farms, and for other purposes.
Slash and burn agriculture, commonly called Jhum Cultivation, is practised in the north-eastern parts of India. Here, farmers cut down the trees of the forest and burn the plant remains. The ash is used as a fertilizer, and the land is used for farming and cattle grazing. After cultivation, the area is left for several years so as to allow its recovery. The cycle is shown in FC 15.11.
Flowchart
FC 15.11 – Jhum (slash and burn) cultivation: forest patch selected → trees cut down → plant remains burnt → ash acts as fertilizer → land used for farming and cattle grazing → soil fertility falls → patch abandoned and left fallow for several years → forest slowly recovers → farmer returns to the patch → cycle repeats
Effects of Deforestation
The major effect of deforestation is the increased concentration of \(CO_2\) in the atmosphere. The reason is that trees hold a great deal of carbon in their biomass, and that carbon is lost with deforestation — released back into the air when the wood is burnt or decays. A forest, in other words, is a carbon store, and cutting it converts a store into an emission.
Deforestation also leads to the loss of biodiversity due to habitat destruction — which, as we have seen, is the prime member of the Evil Quartet. It disturbs the hydrologic (hydrological) cycle, because trees draw water up from the soil and return it to the air by transpiration; remove them and both rainfall patterns and groundwater recharge are affected. It causes soil erosion, since there are no roots to bind the soil and no canopy to break the fall of the rain, and in extreme cases it leads to desertification.
Flowchart
FC 15.12 – Effects of deforestation: forest cleared → branch 1: carbon stored in tree biomass released → increased atmospheric CO2 → global warming; branch 2: habitat destroyed → loss of biodiversity; branch 3: transpiration and infiltration reduced → hydrological cycle disturbed; branch 4: roots and canopy gone → soil erosion → in extreme cases, desertification
Reforestation
Reforestation is the process of restoring a forest that once existed but was destroyed or removed at some time in the past.
Reforestation occurs naturally in a deforested area — nature will, given time, reclaim bare land. We can speed up this process by the plantation of trees, with due consideration to the biodiversity that existed there before. That last condition matters greatly: planting a single fast-growing species is a plantation, not a forest, and, as we saw in the section on species diversity, a monoculture supports only a fraction of the species that a natural forest does.
People Who Rebuilt Forests
The best example of people’s participation in reforestation is Saalumarada Thimmakka, an Indian environmentalist from the state of Karnataka, noted for her work in planting and tending 385 banyan trees along a 4 km stretch of highway between Hulikal and Kudur. She has also planted nearly 8000 other trees. Her work has been honoured with the National Citizens Award of India, and she was conferred with the Padma Shri in 2019.
Moirangthem Loiya from Manipur dedicated 17 years of his life to restoring the Punshilok forest. He left his job and took over the task of bringing back the lost glory of 300 acres of forest land. He planted a variety of trees such as bamboo, oak, ficus, teak, jackfruit and magnolia. Today the forest has over 250 varieties of plants, including 25 varieties of bamboo. It has now been selected as home by a great diversity of animals too.
Notice what happened in Punshilok, because it is the whole argument of this chapter in miniature: once the plants were restored — and restored as a variety of native species, not a single crop of timber — the animals returned on their own. Restore the habitat, and the biodiversity follows.
Case Study of People’s Participation in Conservation of Forests
The history of people’s participation in India can be traced back to 1731.
The Government of India has recently instituted the Amrita Devi Bishnoi Wildlife Protection Award for individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife.
Joint Forest Management
In the 1980s, realising the significance of the participation of local communities, the Government of India introduced the concept of Joint Forest Management (JFM), so as to work closely with local communities for protecting and managing forests.
In return for their services to the forest, the communities get the benefit of various forest products — fruits, gum, rubber, medicine and so on — and thus the forest can be conserved in a sustainable manner.
The logic of JFM deserves a moment’s thought. Guards and fences protect a forest against the people living around it. JFM protects the forest through them — by making the standing forest more valuable to the community than the felled forest would be. This is the same principle that made sacred groves last for centuries, now written into policy.
15.11 Mission Harit Maharashtra
Everything discussed so far — the causes of biodiversity loss, the reasons for conserving it, the laws, the pollution, the deforestation — comes together in what a State actually does on the ground. Mission Harit Maharashtra is one such effort, and it is worth studying closely because it is happening in our own districts.
The Project
An ambitious project of planting 50 crore trees in four years was taken up by the Government of Maharashtra in the year 2016. Under this project, yearly targets were given to each district.
The plantation drive is in line with the National Forest Policy (NFP), which aims at maintaining 33% forest cover in the country — the same figure recommended for the plains that we met in the previous section. Mission Harit Maharashtra, in other words, is not a stand-alone tree-planting event; it is the State’s contribution towards a national target that the country has fallen well short of.
A 24-hour toll-free helpline number, 1926, called ‘Hello Forest’, has been set up to provide information regarding plantation and protection, and for mass awareness.
Recording and Caring for the Saplings
Planting a sapling is easy; keeping it alive is not. The Forest Department has therefore created a mobile application called ‘My Plants’, to record the details of the plantation — such as the numbers, the species and the location of the saplings planted. Authorities are expected to take care of the saplings in the first year, which is the period when a young plant is most likely to die.
The progress of the mission can be read from its yearly counts. In the first year, 2016, 2.87 crore saplings were planted. In 2017, the count was 5.17 crore, and in 2018, a plantation count of 15.17 crore was achieved. In the year 2019, the government aimed at a phenomenal 33 crore sapling plantation, which was launched at Anandwan, Warora.
The Method Chosen
The Government has decided to adopt the Japanese Miyawaki method of plantation for this project. You have already read how this method works — dense, layered planting of native species on soil enriched with local biomass, producing a self-sustaining forest about ten times faster than natural growth.
Its suitability here is easy to see. A mission of this size needs green cover quickly and on land that is often degraded, and it must produce something more than a row of identical trees along a road. The State Forest Department and the Social Forestry Department have run successful pilot plantation programmes using the Miyawaki pattern in various districts such as Beed, Hingoli, Pune, Jalgaon and Aurangabad.
15.12 Summary
Biodiversity and its levels
- Biodiversity is the variety of all life — microorganisms, algae, fungi, plants and animals — in terrestrial and aquatic habitats, together with the ecological complexes of which they are a part. In short, it is the totality of genes, species and ecosystems in a region.
- The term was coined by Walter Rosen (1982) and popularised by Edward Wilson. Today’s biodiversity is the outcome of over 3.5 billion years of evolutionary history.
- Adaptation to different environmental conditions — climatic, edaphic, topographic and geographic — is the basis of diversity.
- There are three major, interrelated levels of biodiversity: genetic (intraspecific), species (interspecific) and ecosystem (ecological).
- Genetic diversity is variation in genes, alleles and chromosomes within a species — for example, about 1000 varieties of mangoes and 50,000 varieties of rice or wheat in India, and the varying reserpine content of Rauwolfia serpentina across Himalayan ranges. It is essential for a healthy breeding population and is the raw material of evolution.
- Species diversity covers both species richness (how many species) and species evenness (how the individuals are shared among them). India is one of 15 nations rich in species diversity.
- Ecosystem diversity is the variety of ecosystems in a region — deserts, rain forests, deciduous forests, estuaries, wetlands and grasslands in India. It is high in India, low in Norway.
Patterns of biodiversity
- Species richness is high at lower latitudes and declines steadily towards the poles, because tropical regions have been climatically stable for millions of years, escaped glaciations, had less gene flow between isolated regions, and receive more sunlight, warmth and rainfall — all of which favoured speciation. Diversity is maximum in tropical rain forests, such as the Amazon (40,000 plants, 1300 birds, 427 mammals, 3000 species).
- Species diversity is also greater at lower altitudes than at higher altitudes, where climatic conditions and seasonal variations are drastic.
- Alexander von Humboldt showed that species richness increases with area, but only up to a limit. For many species the relationship is a rectangular hyperbola, \(S = CA^{Z}\), which on a logarithmic scale becomes the straight line \(\log S = \log C + Z \log A\), where S is species richness, A is area, C is the Y-intercept and Z is the slope.
- For smaller areas, Z ranges between 0.1 and 0.2 regardless of the species or region. For very large areas such as continents, the slopes are steeper, showing that species numbers rise faster than the area explored.
- A community is stable if biomass production stays fairly constant, if it withstands and recovers from disturbances, and if it resists invasive species.
- David Tillman’s field experiments showed that species richness reduces year-to-year variation in biomass production — the Productivity–Stability Hypothesis.
- Paul Ehrlich’s Rivet Popper Hypothesis compares species to rivets in an aeroplane: losing a few may cause little immediate harm, but losses accumulate, and the loss of a key species is immediately dangerous.
Current scenario
- Over 1.5 million species have been documented (IUCN, 2004), but Robert May estimates about 7 million species on the globe. Most surveys are from temperate regions; tropical rain forests remain incompletely explored.
- Prokaryotes are missing from the known-species charts, because many monerans cannot be cultured in the laboratory and conventional taxonomic methods do not suit them.
- India has 8.1% of the world’s biodiversity wealth on 2.4% of its land area, and is one of 12 megadiversity countries. About 45,000 plant species and nearly double that number of animal varieties have been identified — only 22% of our natural wealth by May’s estimate.
Loss of biodiversity
- Extinction is of three types: natural, mass and man-made (anthropogenic). Six mass extinctions are known; the current loss is the 7th, running 100 to 1000 times faster than in prehuman times, and could cost us about 50% of diversity.
- The four major causes — the Evil Quartet — are habitat loss and fragmentation (the prime cause; tropical rain forest cover has fallen from 14% to 6%), over-exploitation (Dodo, Steller’s sea cow, passenger pigeon), alien species invasion (Parthenium, Lantana, Eichhornia; Nile perch destroying 200 Cichlid species in Lake Victoria; Clarias gariepinus in India), and co-extinctions.
- A species totally eliminated from Earth is extinct; one whose numbers are dwindling is endangered. The IUCN maintains the Red Data Book (Red List).
- The IUCN categories, in order of increasing risk, are: Least Concern (LC), Near Threatened (NT), Vulnerable (VU), Endangered (EN), Critically Endangered (CR), Extinct in the Wild (EW) and Extinct (EX); Data Deficient (DD) and Not Evaluated (NE) describe the state of our knowledge rather than the species’ risk.
Conservation of biodiversity
- Conservation is the protection, upliftment and scientific management of biodiversity to maintain it at an optimum level and derive sustainable benefits.
- Reasons to conserve are narrowly utilitarian (food, shelter, resins, tannins, medicines — 25% of the global medicine market; bioprospecting), broadly utilitarian (oxygen, pollination, seed dispersal, recreation; the Amazon produces 20% of atmospheric oxygen) and ethical (every species has an equal right to survive).
- In situ conservation protects the species in its natural habitat — 34 biodiversity hotspots worldwide, of which India has four (Western Ghats, Indo-Burma region, Sundaland, Eastern Himalayas); protecting them could reduce extinction rates by almost 30%. India has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries; Maharashtra has 5 national parks and 11 sanctuaries. Sacred groves are a traditional form of in situ conservation.
- Ex situ conservation protects species away from their habitat — zoological parks, safari parks, botanical gardens, seed banks, and modern techniques such as tissue culture, in vitro fertilization and cryopreservation of gametes at \(-196\ ^\circ\text{C}\).
Biological Diversity Act 2002
- India is a party to the Convention on Biological Diversity (CBD-1992) and passed the BD Act in 2002 to regulate access to Indian biological resources and to catalogue traditional knowledge.
- A three-tier system operates: the National Biodiversity Authority (NBA), the State Biodiversity Boards (SBBs) and local Biodiversity Management Committees (BMCs). The NBA has the powers of a civil court; violation can bring jail and a fine of up to 10 lakh rupees.
Environmental issues
- A pollutant is any substance — chemical or form of energy — that adversely affects the health of living organisms. The Environment Protection Act was passed in 1986.
- Air pollutants are particulate (aerosols, smoke, smog, dust, heavy metals; PM2.5 causes the greatest harm) or gaseous (\(CO_2\), \(CO\), \(SO_2\), \(NO\), \(NO_2\)). CO binds haemoglobin and is poisonous; \(NO_2\) forms nitric acid with water vapour and injures the lungs, liver and kidneys.
- Control devices: the electrostatic precipitator (removes almost 99% of particulate matter), exhaust gas scrubbers (remove gases such as \(SO_2\) using water or lime) and catalytic converters (reduction block converts \(NO_x\) to \(N_2\) and \(O_2\); oxidation block converts hydrocarbons and \(CO\) to \(CO_2\)).
- Delhi’s measures — CNG buses by 2002, and Bharat Stage norms evolving from BS II to BS VI (BS V was skipped, BS VI adopted in 2018) — reduced \(CO_2\) and \(SO_2\) levels.
- Noise is included as an air pollutant under the Air (Prevention and Control of Pollution) Act 1981, amendment 1987. Sound of 150 decibels or more can rupture ear drums; noise also causes sleeplessness, raised heartbeat and stress.
- Water pollution is largely man-made. The Water (Prevention and Control of Pollution) Act was passed in 1974. Even 0.1% impurities can make water unfit for use.
- BOD is the dissolved oxygen (in mg/L) needed by microorganisms to decompose organic matter; a high BOD means intense microbial pollution and falling oxygen for fish.
- Nutrient enrichment causes algal blooms of planktonic algae, which release toxins. Water hyacinth (Eichhornia crassipes), the ‘Terror of Bengal’, chokes water bodies.
- Natural eutrophication takes thousands of years; cultural (accelerated) eutrophication, driven by human effluents, does the same far faster and can choke a lake to death.
- Biomagnification is the increasing concentration of non-degradable pollutants at successive trophic levels — DDT rises from 0.000003 ppm in water to 25 ppm in fish-eating birds of prey; mercury behaves similarly.
- Thermal pollution, mainly from thermal and nuclear power plants using water as coolant, kills temperature-sensitive flora and fauna.
- Ecosan (ecological sanitation) uses dry composting toilets, converting excreta into manure in 8–9 months and reducing the need for chemical fertilizers. Reverse osmosis recycling and rainwater harvesting reduce water demand.
- Solid waste is biodegradable, recyclable or non-biodegradable. Sanitary landfills replace open burning dumps but fill quickly and risk contaminating ground water. Biomedical waste and e-waste need special, environment-friendly treatment.
Greenhouse effect, global warming and ozone depletion
- The greenhouse effect is natural and necessary — without it the Earth’s average temperature would be \(-18\ ^\circ\text{C}\) instead of \(15\ ^\circ\text{C}\). Greenhouse gases (\(CO_2\), \(CH_4\), CFCs, \(N_2O\), water vapour) absorb the infrared radiation re-emitted by the Earth and send much of it back.
- Global warming is the excess heating caused by rising greenhouse gas concentrations; the Earth warmed by \(0.6\ ^\circ\text{C}\) in the past century, mostly in the last three decades, bringing odd climatic changes such as the El Niño effect and melting ice caps. It can be controlled by using less fossil fuel, improving energy efficiency, reducing deforestation, planting trees and checking population growth.
- Ozone (\(O_3\)) in the stratosphere (12 to 15 km up) is continuously formed and destroyed in equilibrium: \(O_3 \rightarrow O_2 + [O]\) and \(O_2 + [O] \xrightarrow{\text{UV rays}} O_3\). Its thickness is measured in Dobson units (DU).
- CFCs reaching the stratosphere release Cl atoms, which act as catalysts and destroy ozone repeatedly, causing the ozone hole, most marked over Antarctica.
- Increased UV-B (280–322 nm) damages DNA, causing mutation, skin ageing and skin cancers, and in the eye causes snow blindness and cataract. The Montreal Protocol (1987) was signed to control ozone-depleting substances.
Deforestation and green missions
- Deforestation is the conversion of forest area into non-forest area. Almost 40% of tropical forests and 1% of temperate forests have been lost. India’s forest cover fell from about 30% at the start of the 20th century to 19.4% by its end; the National Forest Policy 1988 recommends 33% for the plains and 67% for the hills.
- Slash and burn (Jhum) cultivation, timber, firewood and conversion to farmland drive deforestation. Its effects are rising \(CO_2\), loss of biodiversity, a disturbed hydrological cycle, soil erosion and desertification.
- Reforestation restores lost forests. Saalumarada Thimmakka (385 banyan trees, Padma Shri 2019) and Moirangthem Loiya (Punshilok forest, 300 acres, 250 plant varieties) are outstanding examples.
- People’s participation dates back to 1731, when Amrita Devi and hundreds of Bishnois died protecting trees at Jodhpur; the Amrita Devi Bishnoi Wildlife Protection Award honours this tradition. Joint Forest Management (JFM), introduced in the 1980s, lets communities protect forests in return for forest products.
- Mission Harit Maharashtra (2016) aimed to plant 50 crore trees in four years, using the Miyawaki method, the ‘Hello Forest’ helpline (1926) and the ‘My Plants’ app.
Flowchart
FC 15.13 – The chapter at a glance: Biodiversity (genetic → species → ecosystem levels) → patterns (latitudinal and altitudinal gradients; species–area relationship) → importance (stability, productivity, ecosystem services) → loss (Evil Quartet → extinction → IUCN Red List) → conservation (in situ / ex situ; BD Act 2002) → environmental issues (air, noise, water, solid waste pollution) → global effects (greenhouse effect → global warming; CFCs → ozone depletion) → deforestation → reforestation and people’s participation (JFM, Mission Harit Maharashtra) → back to protecting biodiversity
15.13 Points to Ponder
Tribals do not allow even a single branch to be cut from a sacred grove, and these groves have survived for centuries without fences or guards. With increasing greed and pressure on land, are sacred groves still safe today — and can belief alone go on protecting a forest?
The Rivet Popper Hypothesis says that the relationship between diversity and the well-being of an ecosystem is not linear. If we cannot tell in advance which species is a “key rivet”, what does that imply about how carefully we should treat even the species that seem unimportant?
Delhi set emission standards, converted its buses to CNG and skipped straight to BS VI — and still suffered the great smog of November 2016. Is merely setting standards enough? What must change in the way we travel, and not only in the way our vehicles are built?
Is the greenhouse effect a boon or a bane? Remember that without it the Earth would average \(-18\ ^\circ\text{C}\). Where exactly does a necessary natural process turn into a global problem?
India holds 8.1% of the Earth’s biodiversity wealth on 2.4% of its land, and yet only about 22% of that wealth has been recorded. What is lost, permanently and silently, when a species disappears before anyone has even named it?
The narrowly and broadly utilitarian arguments say we should conserve species because they are useful to us. The ethical argument says we should conserve them even if they never are. Which of these reasons do you find most convincing — and which one do you think actually persuades governments?
Jhum cultivation once worked sustainably, because the land was left long enough to recover. Many traditional practices are like this — sustainable at one population density and destructive at another. How should a society decide when to keep such a practice and when to change it?
An alien species becomes invasive largely because it arrives without its natural predators. Before any species is introduced for aquaculture, agriculture or ornament, what questions should we insist on answering first?
A large part of the world’s e-waste is generated in developed countries and dismantled by hand in developing ones. Is it fair for the profit of using an electronic device to lie in one country and the toxic cost of disposing of it in another?
Amrita Devi and hundreds of Bishnois died in 1731 protecting trees, and Joint Forest Management now offers communities a share of forest products in return for protection. Which do you think conserves a forest more durably in the long run — reverence, or benefit?
15.14 Objective Questions
- Observe the graph and select the correct option.
Diagram
Fig. 15.E1 – Graph for the species–area relationship with species richness on the Y-axis and area on the X-axis, showing two lines labelled A (a curve) and B (a straight line)
- Line A represents, \(S = CA^{2}\)
- Line B represents, \(\log C = \log A + Z \log S\)
- Line A represents, \(S = CA^{Z}\)
- Line B represents, \(\log S = \log Z + C \log A\)
- Select the odd one out on the basis of Ex situ conservation.
- Zoological park
- Tissue culture
- Sacred groves
- Cryopreservation
- Which of the following factors will favour species diversity?
- Invasive species
- Glaciation
- Forest canopy
- Co-extinction
- The term ‘terror of Bengal’ is used for ___________.
- algal bloom
- water hyacinth
- increased BOD
- eutrophication
- CFCs are air polluting agents which are produced by ___________.
- Diesel trucks
- Jet planes
- Rice fields
- Industries
15.15 Check Your Concepts
Assertion: Genetic diversity is essential for a healthy breeding population of a species. Reason: Genetic variation allows at least some individuals to survive when environmental conditions change. State whether both statements are correct and whether the reason correctly explains the assertion.
Two forest plots each contain 200 trees belonging to 10 species. In plot A, one species accounts for 180 of the trees; in plot B, all ten species are almost equally represented. Which plot has greater species evenness, and why is species richness alone not enough to describe their diversity?
Why is in situ conservation described as the most appropriate method of conservation, even though ex situ techniques such as cryopreservation and tissue culture are far more advanced?
What would happen to an ecosystem if a keystone species were removed, as compared with the removal of an equally numerous but non-key species? Answer using the Rivet Popper Hypothesis.
Arrange the following steps of eutrophication in the correct order: death of aquatic animals including fish; nutrient enrichment of water; loss of species diversity; algal bloom and biological enrichment; reduced dissolved oxygen; death of submerged plants due to reduced light; increase in organic loading of the lake; stinking eutrophic lake.
Arrange the IUCN categories in order of increasing risk of extinction: Critically Endangered, Least Concern, Extinct, Vulnerable, Near Threatened, Extinct in the Wild, Endangered.
Why does the pie chart of known species contain no data on prokaryotes? Give two reasons.
What happens if an alien species is introduced into an ecosystem in which it has no natural predator? Illustrate your answer with the example of Lake Victoria.
Distinguish between an alien species and an invasive species. Is every alien species invasive?
Match the following:
| Column A | Column B |
|---|---|
| a. Rivet Popper Hypothesis | i. Robert May |
| b. Productivity–Stability Hypothesis | ii. Walter Rosen |
| c. Species–area relationship | iii. Paul Ehrlich |
| d. Estimate of about 7 million species | iv. David Tillman |
| e. Coined the term biodiversity | v. Alexander von Humboldt |
- Match the following:
| Column A | Column B |
|---|---|
| a. Electrostatic precipitator | i. Removes SO2 using water or lime |
| b. Exhaust gas scrubber | ii. Converts NOx to N2 and O2 |
| c. Catalytic converter | iii. Removes almost 99% particulate matter |
| d. CNG | iv. Adulteration-proof fuel |
Why is PM2.5 considered more harmful to human health than a particle of 10 μm diameter, even though the larger particle carries more material?
Assertion: A high BOD value indicates heavy microbial pollution of water. Reason: Microorganisms decomposing organic matter consume large amounts of dissolved oxygen. Comment on both statements.
Why is DDT found in the highest concentration in fish-eating birds of prey and in the lowest concentration in water, even though the DDT entered the ecosystem through the water?
Why can a warmed river support less life than a cool one, even if no chemical pollutant has been added to it?
Draw a labelled diagram of an electrostatic precipitator and mark: the negatively charged metal grid, the positively charged collector plates, the incoming gas stream containing particles, and the clean gas stream.
Draw the food chain showing the biomagnification of DDT and label each trophic level along with its DDT concentration in ppm.
Why is the greenhouse effect necessary for life on Earth, and at what point does it become a problem? Distinguish clearly between the greenhouse effect and global warming.
Assertion: A single chlorine atom in the stratosphere can destroy a very large number of ozone molecules. Reason: Chlorine acts as a catalyst in the degradation of ozone. Explain.
Ozone depletion and the greenhouse effect are two distinct problems, yet CFCs contribute to both. Explain how.
Why are people working on snowfields advised to wear protective goggles? Name the condition caused by high doses of UV-B on the cornea.
Jhum cultivation traditionally included a fallow period that allowed the forest to recover. Why, then, has it become a cause of deforestation in recent years?
What happens to the hydrological cycle and to the soil of a hill slope when its forest cover is removed? Connect your answer to the flooding of low-lying areas downstream.
Why does the National Forest Policy 1988 recommend a much higher forest cover for the hills (67%) than for the plains (33%)?
Explain why the BD Act 2002 places a Biodiversity Management Committee at the local level, when a National Biodiversity Authority already exists.
Sacred groves have protected forests for centuries without any legal machinery, while Joint Forest Management protects them by sharing forest products with local communities. Compare the two approaches as methods of conservation.
What would happen to the species richness of a region if a natural tropical forest were replaced by a monoculture timber plantation of the same total area? Explain your reasoning.
Why is co-extinction considered proof that species do not exist independently of one another? Give two examples.
Give two examples of biodegradable materials released from the sugar industry. (30–40 words)
Name any 2 modern techniques of protection of endangered species. (30–40 words)
Where was the ozone hole discovered? (30–40 words)
Give one example of a natural pollutant. (30–40 words)
What do you understand by the EW category of a living being? (30–40 words)
Dandiya raas is not allowed after 10.00 pm. Why? (80–100 words)
Tropical regions exhibit greater species richness as compared to polar regions. Justify. (80–100 words)
How does genetic diversity affect the sustenance of a species? (80–100 words)
Is the greenhouse effect a boon or a bane? Give your opinion. (80–100 words)
How does CO cause giddiness and exhaustion? (80–100 words)
Name two types of particulate pollutants found in air. Add a note on the ill effects of the same on human health. (80–100 words)
The Montreal Protocol is an essential step. Why is it so? (150–200 words)
Name any 2 personalities who have contributed to controlling deforestation in our country. Elaborate on the importance of their work. (150–200 words)
How have BS emission standards changed over time? Why is it essential? (150–200 words)
During large public gatherings like the Pandharpur vari, mobile toilets are deployed by the government. Explain how this organic waste is disposed of. (150–200 words)
How have Indian culture and traditions helped in biodiversity conservation? Give the importance of conservation in terms of utilitarian reasons. (150–200 words)
15.16 Practice With Numericals
For a species–area study, the relationship \(\log S = \log C + Z \log A\) holds, with \(\log C = 1.0\) and \(Z = 0.2\). Calculate the species richness \(S\) expected for an area of \(A = 1000\ \text{km}^2\).
In two separate studies, the slope \(Z\) of the species–area line is found to be 0.15 for a set of small forest patches and 0.9 for an entire continent. Using these values, explain quantitatively which study shows species numbers rising faster with area, and state what this indicates.
Over 1.5 million species have been documented as per IUCN data (2004), while Robert May estimates about 7 million species globally. Calculate the percentage of the world’s estimated species that has been documented, and the number still undescribed.
India occupies 2.4% of the world’s land area but holds 8.1% of the Earth’s biodiversity wealth. Calculate how many times richer India is in biodiversity per unit land area than the world average.
Using Fig. 15.9, calculate the factor by which the DDT concentration increases (i) from water (0.000003 ppm) to zooplankton (0.04 ppm), and (ii) from small fish (0.5 ppm) to fish-eating birds of prey (25 ppm).
A jet plane, on a single trip across the Atlantic, uses 35 tonnes of oxygen and releases 70 tonnes of \(CO_2\). Calculate the mass of \(CO_2\) released per tonne of oxygen consumed, and the total \(CO_2\) released if 20 such flights are made in a day.
Without the greenhouse effect the average temperature of Earth would be \(-18\ ^\circ\text{C}\); the actual average is \(15\ ^\circ\text{C}\). The Earth has warmed by a further \(0.6\ ^\circ\text{C}\) over the past century. Calculate the natural greenhouse warming, and express the additional warming as a percentage of it.
Tropical rain forest cover has reduced from 14% to 6% over the years. Calculate the percentage of the original tropical rain forest cover that has been lost.
India’s forest cover fell from about 30% at the beginning of the 20th century to 19.4% by its end. Calculate the loss in percentage points, and the additional forest cover (in percentage points) still required to meet the National Forest Policy 1988 target of 33% for the plains.
Under Mission Harit Maharashtra, 2.87 crore saplings were planted in 2016, 5.17 crore in 2017 and 15.17 crore in 2018, against a four-year target of 50 crore trees. Calculate the total planted in the three years and the number required in the fourth year to meet the target.
An electrostatic precipitator removes almost 99% of the particulate matter in the exhaust of a thermal power plant. If the untreated exhaust carries 500 kg of particulate matter per hour, calculate the mass of particulate matter still released into the air in one hour, and in 24 hours.
Bharat Stage norms aim to reduce sulphur emission to 50 ppm in petrol, from the earlier level of 150 ppm in petrol permitted under the BS II norms of 2001. Calculate the percentage reduction in permitted sulphur content in petrol.