Contents
Environmental biology is one of the critical Biology Topics that involves understanding how humans impact the environment and how to address environmental issues.
Why is Water an Important Natural Resource? and what is water Pollution?
Oceans, rivers, streams, lakes, ponds, pools, polar ice caps, water vapour, etc., collectively form the hydrosphere. Flydrosphere comprises water which is an inexhaustible natural resource. Water persists as a liquid above 0°C and below 100°C. 71% of Earth is covered by oceans which contain 97.5% of the total water. The land contains 2.5% of the total water. A major part (1.9% of the total) of water occurs as ice caps and glaciers. The remaining (0.6% of the total) supports total life. It is called fresh water (water with a salt content of less than 0.5%).
More than 90% of this freshwater is found underground as groundwater. The remaining 10% fresh wafer occurs as surface water (rivers, dams, lakes, ponds), soil water, or water vapours present in the atmosphere. Terrestrial life cannot consume seawater because their bodies can neither tolerate the high salt content of seawater nor eliminate the excess salts from the body. The source of freshwater is rainfall.
Water is one of the most unusual natural compounds found on Earth and it is also one of the most important. Water exists in solid (snow), liquid (water), and gaseous (water vapour) forms. Life on Earth began, in the seas and water in some form or the other is essential for the maintenance of all life. Water is one of the key agents in soil formation and serves as the living medium for several different ecosystems. Humans use water for drinking, washing utensils and clothes, sewage disposal, irrigation, and for various other purposes.
All reactions that take place within our body and within our cells occur among water-soluble substances. Substances get transported from one part of the body to the other in dissolved form. Hence, organisms need to maintain a minimum level of water within their bodies in order to stay alive. Terrestrial-life forms require fresh water for this purpose because their bodies cannot tolerate or get rid of the high amounts of dissolved salts in saline water. Thus, water sources need to be easily accessible to animals and plants to survive on land.
To study the number and variety of plants and animals in an area in the dry summer season and after the rainy season
Select a small area in some unused land near your school. Count the number and variety of individuals of each species of plant and animal and record the data in your notebook. Report this exercise in the same place at least twice a year, once during the dry summer season and once after the rainy season.
You will observe that the number and variety of plants and animals are not similar at both times. In dry summer months, the number and variety of plants and animals are less as compared to the period after the rainy season. It is because of the dry condition in the summer season when water availability is less in the soil and environmental temperature becomes relatively high. On the contrary, after the rainy season, environmental temperature becomes favourable, having high moisture content and the soil also has a sufficiently high content of water.
To study the relationship between the quantity of available water and the number and variety of plants and animals in an area
Select a small area near a water body (e.g., a pond, lake, stream, or river). Count the number and variety of plant and animal species present in this area and record the data in your notebook. Now, select another small area in a dry, rocky region and again count the number and variety of plants and animals present in this area. Record this data also in your notebook. Repeat this activity in two regions in different seasons (;.e., summer, winter, and rainy seasons).
You will observe that the number and variety of plants and animals are more in areas near a water body than in an area in a dry, rocky region. It is due to more availability of water and fertile soil near the water body. You will also observe that the number and variety of living organisms (plants and animals) are less in the dry summer, and winter seasons and more in the rainy seasons. It is again due to the availability of water and other favourable environmental factors in the rainy season as compared to summer and winter months which have less favourable parameters.
Thus, the availability of water decides not only the number of individuals of each species that are able to survive in a particular area but also decides the diversity of life there. Besides the water, there are some other environmental factors that determine the biodiversity of a region. These factors are temperature and the nature of the soil.
What is Groundwater?
When rain falls, some water is lost as it runs off into trains This water reaches the rivers and seas and some of it gets lost through evaporation. The remaining water percolates into the ground through the pores between the soil particles and is termed groundwater. Tiny pore spaces in soil act as capillaries which allow water to move against the pull of gravity resulting in capillary water. Some water forms an extremely thin, tightly held film around the soil particles. It is termed as hygroscopic water.
A small portion of soil water is chemically bound with soil materials and is known as combined water. The downward-moving water, called gravitational water, reaches the underground water table, if enough rain falls. Plants can draw only capillary water from the soil. This water is known as available water.
Water Conservation: Rainwater Harvesting
This technique is used to capture, store, and reutilize rainwater, by making special water-harvesting structures such as dug-out wells, percolation pits, check dams, and lagoons. Rainwater harvesting can be beneficial for all, particularly in the region of scanty rainfall.
Explanation of Water Harvesting Technique
The water which rains down cannot percolate through the hardened soil and flows away quickly to streams, rivers, and sea without replenishing the underground water tables. As the withdrawal of huge quantities of freshwater continues, the underground water table is receding deeper and deeper around the world. The failure of a centralized distribution system and the depletion of the underground water table has forced Indian people to adopt rainwater harvesting and groundwater recharge projects.
1. Rainwater Harvesting:
Rainwater harvesting involves the collection, storage, and subsequent use of water deposited by rains. In water-stressed, dry regions of the world, rainwater harvesting is an ancient practice. In parts of Rajasthan and Gujarat, people collect whatever they can, the meager quantity of water that is deposited by rain, in large storage tanks and vessels. This water serves them for most of the year.
In another technique of rainwater harvesting, rooftops properly cleaned are used to collect rainwater which is directed through pipes to large underground pucca storage tanks which are sealed off from all sides except for a small opening used for cleaning and Withdrawal purpose. In cities such as Dwarika, and Gujarat, people use this collected water for drinking and cooking purposes for most of the year.
2. Ground Water Recharging:
We can improve the groundwater storage capacity of Earth’s crust by adopting the following methods.
- Collection of water deposited over rooftops, open fields, and slopes by erecting impediments to check the flow.
- Directing this water to the underground water table through wells, bore wells and deep shafts drilled in the soil for the purpose so that collected water goes to underground deposits quickly.
Advantages of Rainwater Harvesting
The technique of rain-water harvesting has the following advantages:
- It reduces the run-off loss of rainwater.
- It is helpful in controlling floods.
- It maintains a supply of water during the dry months of the year.
- It helps to raise the water table.
- It checks soil erosion.
Traditional Rain-water Harvesting in India
In India, there has been an age-old tradition in villages to have a pond or tank to collect rainwater during the rainy season. This pond is used to be a necessary part of village life. Throughout the year, the stored water of the ponds is used for animals and for small irrigation projects. Even the village washerman wash the clothes on these ponds.
Likewise, in the foothills, the water from the springs is collected by small embankments. The spring water is diverted and transported by hollow bamboo sticks. In Rajasthan, underground tanks (tankas) are well known and khadins were used for harvesting rainwater. Almost every town in Rajasthan has a number of tanks, baolis and johads, and hauzes. All these structures provide a supply of water during water shortage periods.
Rajendra Singh, fondly known as “Water Man”, was awarded Magsaysay Award in 2001 for his ingenious technique of harvesting rainwater. He has revived the age-old Indian technique of collecting of rainwater in earth check dams (Johads) to increase the level of the water table, recharge the wells and restore greenery in Sirska forest hills in Rajasthan.
Conservation and Management of Water Resources
Some of our natural resources such as air, water, and soil, require proper attention and management. In India, we often face water scarcity. The ground water level goes down in the summer seasons. As a result, during summers the municipal/corporation water supply is restricted, and our wells and hand pumps become dry. Such frequent situations of water crises have forced environmental biologists to seek various means of water conservation. They have suggested the following measures for avoiding misuse and wastage of potable water:
- Development of an integrated watershed plan for drinking, irrigation, and industrial uses.
- Adoption of various flood control methods.
- Transfer of surplus water to water deficit basins by interlinking of Indian rivers.
- To identify the over-exploited areas of fresh water, extensive hydrogeological surveys are done.
- The groundwater is recharged by artificial means.
- To avoid wastage and misuse of water, there is an urgent need for mass awareness programmes through public and private agencies.
- Usually, water is wasted by leaking taps and excessive irrigation of crop fields.
Collect the water samples from different sources such as a pond, lake; river, tap, well, and even drain. First, observe the presence of biotic components (algae, aquatic plants, zooplankton, etc.) with the help of a magnifying glass. Then perform certain chemical tests (e.g., soap test, EDTA test) for dissolved salts such as sulphates and chlorides (these salts tend to give hardness to water).
Test the pH value (i.e., hydrogen ion concentration or alkalinity and acidity) of water with the help of pH paper strips or pH universal indicator. This process of observation can be repeated by collecting water samples from other localities and during different periods of the year.
Water Pollution
An undesirable change in the physical, biological, or chemical qualities of water (due to the addition of foreign organic, inorganic, biological, or radioactive substances) that adversely affects aquatic life and makes the water unfit for use, is called water pollution. Pollution of water is one of the most serious environmental problems in the world.
Water pollution may be of the following three types:
- Surface water pollution (or Inland water pollution)
- Underground water pollution
- Marine water pollution.
Human beings are the main cause of water pollution. However, some pollution also occurs naturally. Soil particles enter the water through soil erosion; minerals dissolve in water from rocks and soil; animal wastes and dead fallen leaves (litter) pollute the water sources.
Water Pollution & its Control – Causes, Effects
Agents or substances that pollute water are called water pollutants. Water pollutants can be classified into the following three categories: physical, chemical, and biological water pollutants.
1. Physical Water Pollutants:
These include heat and oil spills. Specific industries and thermal/nuclear power plants use water for cooling in various operations and later return this hot water to water bodies. This results in thermal pollution. Another manner in which the temperature of the water in a river can be affected is when water is released from dams. The water inside the deep reservoir would be colder than the water at the surface which gets heated by the sun. The high temperature of water reduces its dissolved oxygen content.
2. Chemical Water Pollutants:
These include organic wastes (e.g. sewage), detergents, fertilizers, pesticides (e.g., dieldrin, DDT, DDE, BHC, etc.), polychlorinated biphenyls [PCBs], inorganic chemicals (e.g., arsenic, cadmium, mercury, lead, nickel, phosphates, nitrates, fluorides, etc.) and radioactive wastes. Common inorganic impurities in water are compounds of calcium and magnesium.
3. Biological Water Pollutants:
These include pathogens such as viruses, bacteria, protozoa, fungi, helminths, nematodes, etc.
Sources or Causes of Water Pollution
The water is polluted by pollutants released by the following sources:
1. Sewage:
Organic wastes are contributed as domestic and commercial sewage by food processing plants, dairy farms, piggeries, poultry farms, slaughterhouses, breweries, tanneries, etc. Animal excreta discharged into fields or dumped into pits reaches water bodies through runoff and leaching, particularly during the rainy season.
2. Industrial Wastes:
Effluents of mills and industries such as paper mills, petroleum refineries, etc., contain large quantities of harmful chemicals including acids, alkalies, and heavy metals (e.g., mercury salts from paper industries) that are discharged into water bodies (rivers and lakes). These include both inorganic and organic chemicals.
3. Synthetic Soaps and Detergents:
Water containing soaps and detergents is discharged from houses and certain factories.
4. Fertilizers and Pesticides:
Fertilizers and pesticides are being used excessively in the fields to increase crop production. These are washed by rainwater into water bodies and pollute them.
5. Petroleum Oil:
Drilling and shipping operations are common in the oceans. Leakage of petroleum oil during such operations or due to accidents results in water pollution.
6. Solid Particles:
Rain erodes soil and carries silt to water. Tiny suspended particles of clay and dust also settle in water from the air. These soil particles cause turbidity.
7. Thermal Pollution:
The discharge of hot water from industries and thermal plants into the water body changes the normal temperature of the water. The content of oxygen decreases. Reduced oxygen content kills aquatic animals and reduces the rate of decomposition of organic matter which, therefore, accumulates.
Point and Non-point Sources of Water Pollution
1. Point Sources:
These sources have a specific location for the discharge of water pollutants directly into water bodies. Therefore, these sources are located near the water bodies, i.e., factories, power plants, breweries, underground coal mines, and oil wells. It is always easy to treat the pollution coming out of point sources before their discharge into the nearby water bodies.
2. Non-point Sources:
These pollution sources are scattered and do not have any specific location to discharge pollutants into the water bodies. Examples of non-point sources are run-off from fields, lawns and gardens, roads and streets, construction sites, logging areas, etc. Unlike point sources, these sources are difficult to monitor and treat to remove the pollutants.
Harmful Effects of Water Pollution
1. Human Diseases:
Pathogens are biological pollutants in the water. They include viruses, bacteria, fungi, protozoans, helminths, nematodes, etc. They cause following diseases in humans such as typhoid, cholera, dysentery, jaundice, and hepatitis.
2. Disturbance in Ecological Balance:
All types of water pollutants affect the life forms living in the water. The pollutants can encourage the growth of some life forms and can harm some other life forms. This affects the balance between various organisms that persists in that system.
3. Removal of Desirable Substances from Water Bodies:
With the increase in the amount of organic waste in water, bacteria multiply rapidly and use up the available oxygen. Lack of oxygen kills the fish and other animals. Biological oxygen demand (BOD) indicates the quality of wastewater. BOD refers to the amount of dissolved oxygen needed by bacteria in decomposing the organic waste present in water. It is expressed in milligrams of oxygen (O2) per liter of water. A weak organic waste has a BOD of less than 1500 mg/litre; a strong one has higher than this.
4. Effect of Thermal Pollution or Change in Temperature:
Aquatic organisms are used to a certain range of temperature in the water body where they live; a sudden marked change in this temperature can be dangerous for them, e.g., it affects the breeding of aquatic animals. The eggs and larvae of various animals are particularly susceptible to temperature changes.
5. Destruction of Useful Microorganisms:
When untreated industrial wastes get mixed with water in rivers and lakes, etc., the acids, alkalies, and heavy metals present in the industrial wastes kill the useful organisms present in water bodies. As these microorganisms are the natural cleansing agents of water, the self-purification process is hindered in these water bodies.
6. Eutrophication:
Eutrophication is the process in which dissolved oxygen in water gets reduced due to excessive growth of algae as a result of extra loading of nutrients in the water body. The presence of sewage and fertilizers (nitrates and phosphates) in polluted water provides a lot of nutrients to the algae (phytoplankton) present in a water body, resulting in excessive growth of algae, termed algal bloom. The algae subsequently die and aerobic decomposers become active. They rapidly consume the dissolved oxygen of the water during the decomposition of the dead algae. In the absence of dissolved oxygen, all the aquatic life (including fish) in the water body dies.
7. Biomagnification (Food Chain Magnification) of Chemical:
Pesticides such as DDT, DDE, dieldrin, etc., are harmful chemicals that are regularly being used in agriculture to protect crops from pests (fungi, insects, etc.). Also, heavy metals (e.g., mercury, cadmium, tin, lead, arsenic, etc.) are regularly poured from industries into the water bodies. These chemicals are non-biodegradable, i.e., unlike organic sewage wastes they are not broken down by the activity of microorganisms. These pesticides/heavy metals enter the soil or are washed away by runoff water to surface water bodies such as lakes, streams, and rivers.
From soil or water, these pesticides/heavy metals then enter the food chain via the producers. At each trophic level, their concentration goes on increasing. This phenomenon of an increase in the concentration of harmful non-biodegradable chemical substances in the body of living organisms at each trophic level of the food chain is called biomagnification. Due to biomagnification fish-eating predatory birds such as kingfishers, osprey, and loon become poisoned.
For example, biomagnification of mercury in the fishes through a food chain results in Minamata disease in fish-eating human populations of the region. Likewise, DDT can accumulate through a series of plankton, small fish, large fish, and birds, and this ultimately results in a magnification of the DDT concentration amounting to several hundredfolds in humans.
Cadmium (Cd), another heavy metal, bioaccumulates in the liver and kidney, and the amount of Cd stored in the kidney increase with age. Kidney damage is the most prevalent chronic effect of Cd exposure. The Cd poisoning in Japan has once resulted in itai itai disease, which was due to the eating of rice produced from soil containing high levels of cadmium.
Bioaccumulation:
This term refers to the storage of a pollutant in the body tissues of animals and humans (fats, bone, kidney, etc.) at levels higher than found in the environment. Cadmium, dioxins, PAHs ( = polycyclic aromatic hydrocarbons), PCBs (polychlorinated biphenyls), etc., are some examples.
Biomagnification:
This term is used for the food chain magnification so that the organisms at the top of the food chain contain harmful chemicals such as DDT, methylmercury, etc.
8. Decomposition of Organic Matter:
Microorganisms bring about the decomposition of organic matter brought about by sewage and other organic remains. The process requires oxygen. If organic matter is large or oxygen content is low, anaerobic breakdown of organic matter occurs. This produces various pollutants such as hydrogen sulphide, ammonia, methyl sulphides, organic sulphides, and methane. Scum and sludge are formed. The water of such a water body becomes, odorous and turbid.