Influence of Man on Ecology and Environment

Influence of Man on Ecology and Environment: Introduction

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Man’s relation with his natural environment is a complex one. While he is subject to certain natural controls and events, he also acts as the dominant force in many of the Earth’s physical and biological systems. This relationship has changed profoundly with time — increasingly, man has become capable of altering his physical environment to suit himself.

Although the scale of man’s impact on the environment has accelerated rapidly since the Industrial Revolution, man has been a factor in environmental change for at least 40,000 years — since the late stages of the Pleistocene ice age. Although the object of these alterations was to improve living conditions, in some cases they have created major long-term problems, and in others they have been catastrophic — both for the natural environment and for humanity itself.

Man is simultaneously subject to natural controls and an active agent transforming those very systems — a paradox that defines the human-environment relationship across all scales of geography and time.

Scale and Scope of Human Impact

• Overpopulation
  • Rising human numbers drive disproportionate resource extraction, habitat loss, and waste generation — the root pressure behind most environmental changes.
• Pollution
  • Introduction of chemical, biological, and physical contaminants into air, water, and soil — with cascading effects across ecosystems.
• Burning Fossil Fuels
  • Releases stored carbon, raises atmospheric CO₂, drives climate change, acid rain, and urban smog.
• Deforestation
  • Removes vegetation cover, triggers soil erosion, disrupts water cycles, reduces biodiversity, and releases stored carbon.

Consequences at Global Scale

These human-driven changes have triggered climate change, soil erosion, poor air quality, and undrinkable water. These negative impacts can affect human behaviour itself — prompting mass migrations and conflicts over clean water and arable land.

Three Major Domains of Human Influence

Man’s Impact covers three interlocking domains

1. Modification of Landforms
2. Modification of the Atmosphere
3. Modification of Ecosystems

Modification of Landforms:

• Mining and quarrying, deforestation, the introduction of exotic plants and animals, the use of agricultural machinery, the building and use of tracks and roads, and the overgrazing of pastures — all of these, singly and in combination, have profoundly altered landforms and caused accelerated erosion and deposition to occur.
• Man’s role in landform modification can be understood through two modes of action:
  • Direct Agent of Change
    • Where man himself excavates or piles up material — open-pit mining, quarrying, land reclamation from sea, waste heaps. The effect is immediate and spatially concentrated.
  • Indirect Agent of Change
    • Where man causes natural processes — wind action, water erosion — to accelerate or diminish. By far the most widespread. Much of this influence occurs accidentally or as a secondary consequence of another purpose.

Key Principle

Indirect effects are by far the most widespread form of landform modification. Conscious attempts to influence landform processes — for example, building coastal groynes or re-afforestation — are inevitably expensive and limited in spatial extent.

Activities Causing Landform Modification

• Mining and quarrying:Excavation of the Earth’s surface for mineral resources — creates craters, tunnels, and waste heaps
• Deforestation:Removal of forest cover accelerates sheet wash, rill formation, and gully erosion on slopes
• Introduction of exotic species:Invasive plants and animals alter soil stability and vegetation structure
• Agricultural machinery:Heavy machinery compacts soils, destroys structure, and increases runoff
• Road and track construction:Cuts through slopes, disrupts drainage, and creates new erosion pathways
• Overgrazing:Destroys protective vegetation, exposes bare soil to rain splash and wind deflation

Direct Alteration of Landforms

• Man has a direct effect on the shape of landforms by excavating and piling up earth, reclaiming land from the sea, and causing subsidence through mining. These activities have greatly increased since the Industrial Revolution, with the development of enormous machine power and explosives for moving material.
• Land scarification is sometimes used as a general term for disturbances created by the extraction of mineral resources. Open-pit mines, quarries, sand and gravel pits are among the forms of scarification. Strip-mining is one of the most devastating examples of landform alteration of this kind.

⚠ Strip-Mining — Most Devastating Form

Strip-mining involves removing entire layers of the Earth’s surface to access underlying minerals. It destroys topsoil permanently, alters drainage patterns, and creates vast areas of barren, unstable land that is almost impossible to restore to its original ecological state.

• Equally obvious as man-created landforms are coal tips and other waste heaps from mining and quarrying. Many of these features are geomorphologically unstable, allowing various forms of mass movement to occur. When saturated by heavy rain, spoil tips are frequently subject to sliding and flowage, supplying sediment that clogs stream channels.

Indirect Effects: Slopes and Rivers

• By far the most important of all man’s effects on landforms are those connected with his interference with natural vegetation — in particular, the clearing of forests for agricultural purposes. There is a close relationship between the amount of vegetation cover and erosion rates on hillslopes, and hence with the amount of sediment in streams.

Role of Vegetation Cover

A stable vegetation cover acts as an effective regulator of natural erosion, protecting the ground from direct raindrop impact, absorbing some of the runoff, and making the slope more cohesive.

What Happens When Vegetation is Removed

Impact on Rivers

• The alteration of infiltration and runoff on slopes by modifying vegetation inevitably has a profound effect on adjacent rivers in at least two respects: by increasing both the discharge and also the sediment supply. The result is rivers that flood more frequently, carry more suspended load, and deposit more material in their lower reaches — filling reservoirs, damaging agriculture, and destroying aquatic habitats.

Wind Deflation and Coastal Erosion

Wind Deflation — The Dustbowl

• The phenomenon of the Dustbowl in the Great Plains region of America in the 1930s is a well-known example of man-induced land erosion. The area was formerly grassland underlain by rich brown and chestnut soils, but both overgrazing and ploughing contributed to the catastrophe which caused the widespread abandonment of farms.

• The dustbowl situation is by no means unique. In the marginal areas around today’s hot deserts — such as the Thar desert of Pakistan and India, and the Egyptian desert — a great deal of deflation is initiated by grazing animals. Overgrazing in semi-arid margins is the single most consistent trigger of desertification worldwide.

Coastal Erosion and Deposition

• Man can have relatively little impact on the forces that govern waves, tides, and currents, but he has had some effect on coastal erosion and deposition at the shoreline by building various structures and by removing beach material for ballast or construction.
• Various engineering structures such as groynes, breakwaters, and seawallshave been built to check marine erosion. However, these are not only extremely expensive to build and maintain, but often defeat the object of the exercise — by checking erosion in one place they may lead to its increase elsewhere. This is the classic problem of coastal sediment budget disruption.

Modification of the Atmosphere:

• The global heat balance has changed over the last few decades, and a significant portion of this change is attributable to man polluting the atmosphere. Pollution has marked local effects on the atmosphere, and increasingly, cumulative global effects.
• Three Categories of Atmospheric Changes Induced by Man
  1. Introduction of pollutants (solids & gases not normally found)
  2. Changes in proportions of natural constituent gases
  3. Alterations of Earth’s surface affecting the atmosphere

Pollutants in the Atmosphere

• To city-dwellers the most obvious way in which man has affected the atmosphere is through pollution. Pollutants include particulate matter — both solid and liquid particles — and gaseous substances such as sulphur dioxide (SO₂), oxides of nitrogen (NO, NO₂, NO₃), carbon monoxide (CO), and hydrocarbon compounds.
• But not all man-made pollution comes from cities. Isolated industrial activities frequently create a footprint of atmospheric pollution in countryside areas downwind from the industrial site. Mining and quarrying activities send large amounts of mineral dust into the air. Even man-induced forest and grass fires, as well as bonfires, can greatly add to particulate pollution at certain times of year.

Primary and Secondary Pollutants

Changes in Atmospheric Gas Levels

• Of the main natural constituent gases in the atmosphere, carbon dioxide (CO₂) and oxygen (O₂) are the most critical from an environmental viewpoint, for both are inextricably involved in the biochemical cycles between the atmosphere and the surface of the Earth. Nitrogen comprises four-fifths of the atmosphere but its inert chemical nature relegates it to a minor role in this respect.
• Oxygen and carbon dioxide are naturally added to the atmosphere by ‘out-gassing’ from the Earth’s interior. The work of plants has been essential in removing carbon dioxide from the atmosphere and storing it as coal and other fossil organic substances.

The CO₂ Crisis

• It has been suggested that, in contrast to the effect of solid particles, an increased level of carbon dioxide will increase the temperature of the atmosphere, since the gas is an absorber of long-wave radiation — the greenhouse effect. This represents one of the most serious long-term threats from human activity to global climate stability.
• Man’s large-scale combustion of hydrocarbon fuels requires a large quantity of oxygen to be withdrawn from the atmosphere and converted into carbon dioxide and water vapour. There is therefore the theoretical possibility of a lowering of the oxygen content of the atmosphere to levels which might have a detrimental effect on animal life.

The Greenhouse Mechanism

Alterations to the Earth’s Surface and Microclimates

• Meteorological processes close to the ground are extremely sensitive to the character of the Earth’s surface. Man’s alteration of this surface through deforestation, agricultural practice, and urbanization has had several important atmospheric effects.
  • Altered Evapotranspiration
    • Complete removal of a forest cover will sharply reduce transpiration and thus the amount of water returning to the atmosphere in vapour form — reducing local rainfall and changing regional water cycles.
  • Urban Heat Islands
    • Closely built urban areas develop their own heat island on calm nights in summer. Concrete and asphalt absorb more solar radiation than vegetation. Cities can be 3–7°C warmer than surrounding rural areas.
  • Wind Modification
    • Trees and hedges effectively break the wind, causing a simultaneous diminution in evaporation and in the carbon dioxide exchange close to the ground. Removal of windbreaks increases wind erosion and crop desiccation.

Modification of Ecosystems

• With the beginnings of agriculture, far-reaching effects — both obvious and subtle — were introduced into ecosystems. Man gradually became more sophisticated in knowing how much to modify an ecosystem in order to harvest the crop he wanted. In achieving this end, he has inevitably:
  • Simplified ecosystems— reducing species diversity to serve crop production
  • Disrupted nutrient cycling— removing biomass continuously without returning nutrients
  • Introduced alien species— which may outcompete native flora and fauna
  • Eliminated native species— through habitat destruction, hunting, and pesticides
  • Caused pollution— chemical inputs to soil and water bodies

Ecosystem Simplification — The Most General Effect

• The most general effect of man on ecosystems is that he tends to simplify them. This comes about because man’s prime concern is to direct energy and material cycling in the system towards himself so that he can easily crop them. Species other than the ones he wants to crop are regarded as weeds or pests, and he attempts to eliminate them. Hence, reduction in species diversity — often to a single species population — is a notable characteristic of man’s impact on ecosystems.

The Monoculture Trap

A single species population — such as a field of wheat or a herd of cows — offers great opportunity for the development and spread of disease, pests and parasites. The Irish Potato Famine (1845–52), caused by the Phytophthora infestans pathogen attacking a monoculture potato crop, killed over one million people and forced another million to emigrate — a stark demonstration of ecosystem simplification’s catastrophic potential.

Eutrophication and Effects on Individual Species

Eutrophication

• When chemical fertilizers are applied to the land, many of the elements contained in them are retained by the soil, adding to the clay-humus complex. However, certain ions are not retained — and among them is nitrate, an important constituent of most fertilizers.
• Nitrate is being added to the soil from fertilizers and nitrogen-fixing plants at a much faster rate than it can be broken down by denitrifying agents in the soil. Being soluble, it is rapidly leached out into rivers and lakes. Here, the increased nitrogen input permits the accelerated growth of plants, algae, and other phytoplankton. This chemical enrichment resulting in increased productivity is called eutrophication.

Effect on Individual Species

• The extinction or reduction in numbers of plant and animal populations is a well-known consequence of man’s impact on the environment. Often the species become endangered not so much by hunting or conscious elimination, but by the disruption and fragmentation of habitats.
• Some species — particularly large predators — require an extensive area of specialised habitat in which to breed and hunt. Fragmentation of this habitat by man’s interference has frequently had disastrous effects. The marsh harrier (Circus aeruginosus) — a large raptorial bird of reed beds and fens — is a prime example: drainage of wetlands for agriculture eliminated much of its specialist habitat.
• A contrary but equally far-reaching effect has been the accidental or purposeful introduction of alien species into ecosystems. Some animals and plants, because of their greater genetic adaptability and high reproductive rates, have made places for themselves at the expense of native species.

Signs of Ecosystem Imbalance

• Under natural conditions, ecosystems have been in a state of ecological equilibrium. With the increasing impact of man, their essential characteristics are altered, so that now signs of severe imbalance or declining efficiency are beginning to be observed in many of them:
  • Progressive devastation of formerly good fertile agricultural or grazing land through over-intensive use
  • Reduction of species when secondary forest replaces primary forest
  • General loss of biological productivity in many ecosystems
  • An increasing amount and geographic spread of pollution

Positive Effects of Human Activities

• Not all the ways that humans affect the ecosystem are negative. Conservation action, technological innovation, and policy-driven restoration have begun to reverse some environmental damage.
• Recycling & Waste Reduction
  • Every time used paper, plastic, or metal is recycled, or trash is removed from public spaces, there is a direct positive impact on reducing pollution and resource consumption.
• Ocean Plastic Cleanup
  • In 2011, 16-year-old inventor Boyan Slat created a device to sweep plastic from the ocean. He later founded The Ocean Cleanup project — estimated to clean half the plastic in the Great Pacific Garbage Patch in five years.
• Afforestation & Re-greening
  • India’s National Afforestation Programme; China’s Great Green Wall; India’s pledge to restore 26 million hectares of degraded land by 2030 under the Bonn Challenge.
• Protected Areas
  • Tiger Reserves (54 in India), Biosphere Reserves, Wildlife Sanctuaries — systematic protection of habitat has allowed populations of tigers (3,682 in 2022) and other species to recover.
• Renewable Energy Transition
  • India’s target of 500 GW renewable energy by 2030; Solar and wind replacing fossil fuels — reducing CO₂ emissions and air pollution simultaneously.
• International Conservation Policy
  • Montreal Protocol (1987) — most ratified environmental treaty — has begun healing the ozone layer. Paris Agreement (2015) — 195 nations committed to limiting warming to 1.5°C.