Environment, from the French word environment that means to encircle or surround, can be defined as the circumstances or conditions that surround an organism or group of organisms or the complex of social or cultural conditions that affect an individual or community.
‘Environment is the complete range of external conditions under which an organism lives-including physical, chemical and biological factors such as temperature, light and the availability of food and water.
The environment we live in represents the interplay of a number of segments involving the lithosphere, hydrosphere, atmosphere, and the biosphere. The interaction is promoted by energy input. The basic interaction in nature is the input of energy, supplied by the sun. The incidence of solar radiation on the surface of the earth varies from place to place due to latitude and longitude. In the tropical areas, sunlight is uniformly distributed throughout the year and, coupled with favourable rainfall, the landmass in such areas has good vegetation cover suggesting a strong interaction with water, soil and nutrient movements in the environment.
Water plays a major role in the environment. The hydrological cycle involves the movement of water in our environment. It acts as a carrier for essential materials such as nutrients, sediments and dissolved gases and can be viewed as consisting of a number of segments, be it rivers, oceans, atmosphere, groundwater or soil ice. Since water is constantly and efficiently transferred from one part to the other in the hydrological cycle, all dissolved materials are also proportionately transferred. Hence, water is the most common carrier of both wanted and unwanted materials in our environment.
Rocks also have a role to play in our environment. Rocks that are exposed on the surface of the earth, become weathered, eroded by wind and water and get deposited in oceans where they settle down completely. After a very long time, these get compacted into sedimentary rocks. Due to the pressure of overlying sediments and water, these rocks get buried deeper and deeper in the earth so that at some point in time, due to certain processes in the oceans-continent boundaries, they are sucked into the deep layers of the earth, thereby becoming a part of the continental earth once again. After uplifting of these masses of rocks over long periods, the weathering and erosion processes remove them once again. This entire process is called the rock cycle.
The geochemical cycle links the rock cycle with the hydrological cycle and basically refers to transport and transfer of dissolved solid substances through the environment on a certain time scale representing natural reactions involving rocks or soils, water, atmosphere and, to some extent, the biosphere. Thus, cyclic behaviour and rate of changes.
Human Impact on Ecology and Environment
Human beings have always exploited the resources available in their natural surroundings for their benefit. Air, water, land, atmosphere, living organisms-each of these elements is of importance in some form or other to human beings. However, in the last two hundred years or so, technological advancement has made human beings rapacious in their exploitation of natural resources. While it may be argued that the industrialized nations, having enjoyed the fruits of unthinking exploitation of nature, have now suddenly become environmentally conscious, and are obstructing the developing nations in their march towards material progress, in the long-term interests of the earth and the human species, environment management must be taken seriously by one and all.
Two factors, associated with the evolution of humans and which have had the most profound impact on the ecosystem, are rapid increase in human population over the centuries and an amazing development of science and technology as an integral part of culture. Increasingly, humans have become capable of altering their physical environment to suit themselves. Although the objective of these alterations was to improve living conditions, in some cases they have created major long-term problems and, in still others, they have been catastrophic, both for the natural environment and for humans themselves. Even extreme habitats such as tundra or hot deserts, only sparsely populated by humans, have not remained untouched, and they are often the most sensitive to the slightest interference. If we consider the food needs of the human population, it will be seen that humans are at the top of the ecological pyramid. The base of the pyramid, which consists of primary producers, is a fixed quantity, if the whole earth is considered. The top of the pyramid has got broadened without a corresponding widening of the base. Hence, the ecological pyramid or pyramid of numbers is tending to become unstable. The large human population can be supported only by replacing the natural ecosystem over large areas and by increasing productivity by huge inputs of energy by use of tractors and other implements, irrigation and manufacture of fertilisers and pesticides.
Environmental degradation refers to the deterioration in the physical component of the environment, mainly due to biological processes, but more specially due to human activity, to such a great extent that it cannot be easily restored by the self-regulatory mechanism or homeostatic mechanism of the environment.
Environmental degradation may be due to extreme events and hazards or due to pollution. Extreme events and hazards are unexpected threats of large impact. They may be classified on the basis of causative factors.
Natural hazards are caused by natural factors. These may be terrestrial natural hazards which occur on the earth’s land surface, e.g., the continents, and are caused by endogenetic forces, e.g., volcanic eruptions, earthquakes, etc.; atmospheric natural hazards which occur by atmospheric processes affecting the living and non-living (abiotic) components of the natural environmental system, e.g., cyclones, forest fires, etc.; and cumulative atmospheric hazards, caused by atmospheric processes which accumulate for several years in continuation, e.g., flood, drought, etc.
Human-induced hazards are the result of cumulative and even sudden effects of human activities. These could be physical man-induced hazards, caused by large-scale landslides, deliberate forest fires, etc.; chemical and nuclear hazards, caused by the release of toxic elements in the atmosphere by human activities, accidental outbursts of poisonous gases from chemical factories, nuclear explosions; and biological hazards induced by humans, such as sudden increase or decrease in the population of a species in a region due to increased nutrients or increase in toxic elements
Biological hazards (not caused by humans include dangers posed by epidemics, natura extinction of any particular species, locust swarms etc.
Modification of Landforms
Mining and quarrying, deforestation, the introduction of exotic plants and animals, the use of agricultural machinery, the building and use o tracks and roads, and the overgrazing of pastures have all, singly or in combination, profoundly
deposition. These activities have greatly increased since the Industrial Revolution with the development of enormous machine power and explosives for moving material. Railway and motorway construction provides many familiar examples of man-made slopes, embankments and cuttings. 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 some of the forms of scarification.
Land Degradation Implies temporary on permanent long-term decline in ecosystem function and productive capacity. It may refer to the destruction or deterioration in health of terrestria ecosystems, thus affecting the associated biodiversity, natural ecological processes and ecosystem resilience. It also considers the reduction or loss of biological/economic productivity and complexity of croplands, pasture, woodland, forest etc. While natural causes may be behind land degradation, serious effects are due to humar activities. Degradation includes deforestation and desertification of drylands.
Causes of or contributors to land degradation include: natural conditions, e.g. soil type topography (steep gradient), weather/climatic conditions (high intensity rainfall, natural hazards) invasive species, pollution; drought; clearance o vegetative cover; soil erosion by wind or water unsustainable agricultural practices; habita alteration, such as through urban expansion.
The effects of land degradation include decline in the chemical, physical and/or biologica properties of soil, e.g. lower organic content an nutrient levels; salinisation; pH changes in soi (acidification or alkalinisation); reduced availabilit of potable water; reduced volumes of surfac water; depletion of aquifers due to lack of recharge biodiversity loss; general reduction in the abilit of the community to depend on the natura environment for livelihood; decline in economi productivity and national development; conflic over access to resources; and ultimately even mas migration
Impact of Agriculture
Impact of Agriculture Agriculture alter earth’s land cover, primarily by clearing forests This alteration in land cover can change the abilit of earth to absorb or reflect heat and light, thus
down of forests for agricultural purposes causes habitat change for living organisms, and even extinction of species. Land use change such as deforestation and desertification, and the use of fossil fuels are the major anthropogenic sources of carbon dioxide; agriculture itself is the major contributor to increasing greenhouse gases such as methane and carbon dioxide, as well as nitrous oxide concentrations in earth’s atmosphere. Largescale and intensive farming involves the use of chemical fertiliser and pesticides which cause pollution and thus disturb the ecology.
Monoculture cropping practices are narrowing the base of biodiversity. As a result, new diseases and deficiencies have crept in. The nutrient cycle of the soil gets disturbed and the soil becomes impoverished.
Reckless deforestation, especially on slopes, exposes the soil to erosive forces which further lead to siltation of streams.
The over exploitation of water resources for irrigation brings about ground water depletion and increase in toxic elements in groundwater. Soil degradation can also result from careless use of land and water.
Impact of Industrial Activity Industrial
activity needs land, and much land has been diverted from forests, pasture and agriculture to accommodate growing industrialisation. The effects on the environment connected with industrial activities are mainly related to the production of industrial wastes: solid waste, such as dust particles or slag from coal; liquid wastes from various processes, including radioactive coolants from power stations, and gas wastes, largely produced by the chemical industry. Each of these has its own impact on the environment and can cause changes to the ecological system.
Degradation of Slopes
There is a close relationship between the amount of vegetation cover and erosion rates on hill slopes, and, hence, with the amount of sediment in streams. A stable vegetation cover acts as an effective regulator of natural erosion, protecting the ground from direct raindrop effect, absorbing some of the run-off, and making the slope more cohesive. With the removal of the vegetation, the surface loses its plant litter, causing a loss of soil structure, cohesion, and porosity.
flow are a natural state in some locations, creating badlands as in the Chambal region of central India and in South Dakota in the USA. The alteration of infiltration and run-off on slopes by modifying the vegetation inevitably has a profound effect on the adjacent rivers in at least two respects-it increases both the discharge and the sediment supply. There seems little doubt that many of the floods in mid-latitude rivers would not occur if the vegetation in the drainage basin were in its natural state.specific operations of humans leading to local cases of river silting and aggradation include mining operations, urbanisation and highway construction all of which are sources of excessive sediment.
Wind Erosion caused by Huamn Activity
The phenomenon of the dustbowl in the Great Plains region of America in the 1930s is a wellknown example of human-induced land erosion. The area was formerly a grassland, underlain by rich brown and chestnut soils, but both overgrazing and ploughing contributed to the catastrophe which caused widespread abandonment of farms. A great expansion in wheat cultivation in the early years of the decade was followed by a series of droughts; the soil, largely exhausted of its natural fertility, was subject to deflation and particle drifting of disastrous proportions.
Modification of Hydrological Processes
The impact of the hydrological cycle varies from the local to the regional levels. Such modifications have both positive and negative effects. The input of precipitation may be modified by humans through cloud seeding. Surface storage is modified by various processes like land clearance, agricultural practices, urbanisation, drainage systems, mining, etc., whereas surface runoff is enhanced by deforestation and cultivation. Infiltration of water is modified by deforestation, urbanisation and irrigation. Such an impact on a massive scale may lead to falling groundwater, deterioration in water quality, massive eutrophication of water bodies and river systems.
Coastal Erosion and Deposition
Humans may not have an impact on the forces that govern waves, tides and currents, but they have had some effect on coastal erosion and
structures and by removing beach material for ballast or construction.
Specifically, modification of coastal areas can come about in the following ways.
(i) Disrupting wave motion and reducing the energy of coast-bound waves by injecting air bubble curtains.
(i) Construction of sea walls, groynes, breakwaters to resist sea waves.
(iii) Trapping or import of soil for replenishment of sea beaches.
(iv) Tree plantation to stabilise sea beaches and dunes.
(v) De-vegetation and agriculture in the hinterlands of the catchment of rivers draining the coast, leading to progradation of the coast.
(vi) Construction of dams and reservoirs on major rivers adversely affecting the process of growth of beaches, as the supply of sediments is stopped, leading to rapid erosion of coastal areas.
(vii) Reclamation of tidal marshes and mudflats for the construction of human settlements and industries in coastal areas causing damage.
(viii) Overgrazing, removal of vegetation from stable dunes, etc., destabilising dunes. (ix) Practices like aquaculture.
(x) Human activities like fishing which cause immense damage to the ecosystem leading to the death of endangered species, e.g., death of Olive Ridley turtles on the Gahirmatha coast of Odisha due to reckless trawling
Modification of River Processes
Human-induced modifications of river processes can come about by two processes: (i) direct intervention for some useful purposes, and (ii) indirect intervention which has adverse effects on human society. Direct modifications may include flood control methods, channel improvements, construction of dams and reservoirs, channelisation of streams, canal diversion etc. Construction of dams and reservoirs as part of multipurpose projects is called ‘point modification’. Indirect modification refers to changes that take place in the general surface characteristics of the.
Such indirect modification modifies the river course itself. For example, deforestation at an accelerated rate in the catchment basin of a river induces soil erosion. This leads to deposition of sediments on the riverbed; ultimately, the river loses its water retention capacity and causes floods. Gradually, the river divides itself into many channels.
Modification of Subsurface Environment
The modification of subsurface environment considered to be the most hazardous of all types of human activities. Anthropogenic activities such as the construction of dams, canals, bridges, drilling for petroleum and natural gas, etc., exert tremendous pressure on the underlying structures. Several instances of earthquakes are found in such places of heavy construction, such as the 1931 earthquake in Greece due to the Marathon Dam; regular earthquakes around the Hoover Dam (the USA) since 1936, and tremors felt around Kariba (Zambia), Manic (Canada), Monteynard and Grandvale (France)
Subsurface equilibrium is also disturbed due to disbalances in the hydrostatic pressure caused by pumping of water. The supply of water through irrigation channels, particularly in arid regions, causes hydrocompaction as dry soils are compacted after getting into contact with water. As a result, the general surface subsides up to 1-2 m leading to widespread damage to construction structures. Wrong mineral extraction methods cause inundation of mines and roof collapse, leading to the death of labourers. Subsurface extraction of minerals also causes diversion of underground flow, release of poisonous gases, rockbursts and so on.
Modification of Periglacial Environment
The destabilisation of thermal conditions of permafrost regions occurs in the following manner: . removal of surface vegetation;
• melting of ice lenses, leading to subsidence of ground surface, because of excavation for construction of roads, airports, oil refineries, etc.;
• pollution caused by vehicles leading to the melting of permafrost;
•forest fires which remove natural vegetation.
thermokarst process begins.
Environmental degradation in the periglacial areas causes severe bottlenecks for engineering constructions and hydrological regime.
Modification of the Atmosphere
Atmospheric circulation systems operate on such a large scale that one is inclined to doubt that man’s activities could have any appreciable effect on them. However, it is known that the global heat balance has changed over the last few decades. Atmospheric changes induced by humans may be grouped into three categories
(i) introduction of solids and gases not normally found in the atmosphere (pollutants).
(ii) changes in proportions of the natural component gases of the atmosphere.
(iii) alterations of the earth’s surface in such a way as to affect the atmosphere.
The atmospheric pollutants include particulate matter, both solid and liquid particles, and gaseous substances such as sulphur dioxide, oxides of nitrogen, carbon monoxide, and hydrocarbon compounds. Once in the atmosphere, the primary pollutants undergo a number of chemical reactions, generating a second group of pollutants.
Precipitation, containing acidic substances, also called the acid rain, renders agricultural fields and crops useless. It also adds to soil degradation and contamination of groundwater resources. Photochemical reactions are brought about by the action of sunlight: for instance, sunlight acting on nitrogen oxides and organic compounds produces ozone. Another toxic chemical produced by photochemical actions is ethylene.
Increase in the proportion of greenhouse gases, and depletion of the ozone layer in the stratosphere are two of the most serious problems associated with atmospheric pollution today.
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 possibility of a lowering of the oxygen content of the atmosphere to levels which might have a detrimental effect on animal life.
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