UGC NET JRF Environmental Science Full Material PDF

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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/375332181 UGC NET JRF Environmental Science full material Au Agri Organics Book · November 2023 CITATIONS READS 0 2,513 1 author: Senthamil Elasi University of Agricultural Sciences, Dharwad 43 PUBLICATIONS 3 CITATIONS SEE PROFILE All content following this page was uploaded by Senthamil Elasi on 04 November 2023. The user has requested enhancement of the downloaded file.  Environmental Science (For UGC NET & JRF) Study material (Covered topic wise based on syllabus with the latest data) Volume-1 (Unit I to V) (For private circulation only) Launching the softcopy of material for Reaching 30K Subscribers & Stepping into 8th year Au Agri Organics Follow us on youtube, telegram, intagram, linkedin, facebook… Compiled by E. Senthamil M.Sc. (Agri.) Agronomy (Qualified UGC NET & JRF and ICAR NET) Page | 1  I thank all my friends, juniors, seniors and team members for their support to publish this material. This material has been compiled with the materials that I used for my preparation. In our first hard copy we given print initially for 25 copies, but extended up to 75 copies due to the increased demand from various corners of the coumtry. Now, we are publishing this material as soft copy for the benefit of students. Our best wishes and success for your future. E. Senthamil Admin Au Agri Organics Follow us on youtube, telegram, intagram, linkedin, facebook… Page | 2 UGC JRF & NET SYLLABUS ENVIRONMENTALSCIENCE (89) Unit-I: Fundamentals of Environmental Sciences - 10 Unit-II: Environmental Chemistry - 46 Unit-III: Environmental Biology - 100 Unit-IV: Environmental Geosciences - 191 Unit-V: Energy and Environment - 259 Unit-VI: Environmental Pollution and Control Unit-VII: Solid and Hazardous Waste Management Unit-VIII: Environmental Assessment, Management and Legislation Unit-IX: Statistical Approaches and Modelling in Environmental Sciences Unit-X: Contemporary Environmental Issues Unit-I: Fundamentals of Environmental Sciences  Definition, Principles and Scope of Environmental Science.  Structure and composition of atmosphere, hydrosphere, lithosphere and biosphere.  Laws of thermodynamics, heat transfer processes, mass and energy transfer across various interfaces, material balance.  Meteorological parameters - pressure, temperature, precipitation, humidity, mixing ratio, saturation mixing ratio, radiation and wind velocity, adiabatic lapse rate, environmental lapse rate. Wind roses.  Interaction between Earth, Man and Environment. Biogeographic provinces of the world and agro-climatic zones of India. Concept of sustainable development.  Natural resources and their assessment.  Remote Sensing and GIS: Principles of remote sensing and GIS. Digital image processing and ground truthing. Application of remote sensing and GIS in land cover/land use planning and management (urban sprawling, vegetation study, forestry, natural resource), waste management and climate change.  Environmental education and awareness. Environmental ethics. Unit-II: Environmental Chemistry  Fundamentals of Environmental Chemistry: Classification of elements, Stoichiometry, Gibbs’ energy, chemical potential, chemical kinetics, chemical equilibria, solubility of gases in water, the carbonate system, unsaturated and saturated hydrocarbons, radioisotopes.  Composition of air. Particles, ions and radicals in the atmosphere.  Chemical speciation. Chemical processes in the formation of inorganic and organic particulate matters, thermochemical and photochemical reactions in the atmosphere, Oxygen and Ozone chemistry. Photochemical smog.  Hydrological cycle. Water as a universal solvent. Concept of DO, BOD and COD. Sedimentation, coagulation, flocculation, filtration, pH and Redox potential (Eh).  Inorganic and organic components of soils. Page | 3   Biogeochemical cycles – nitrogen, carbon, phosphorus and sulphur.  Toxic chemicals: Pesticides and their classification and effects. Biochemical aspects of heavy metals (Hg, Cd, Pb, Cr) and metalloids (As, Se). CO, O3, PAN, VOC and POP. Carcinogens in the air.  Principles of analytical methods: Titrimetry, Gravimetry, Bomb Calorimetry, Chromatography (Paper Chromatography, TLC, GC and HPLC), Flame photometry, Spectrophotometry (UV-VIS, AAS, ICP-AES, ICP-MS), Electrophoresis, XRF, XRD, NMR, FTIR, GC-MS, SEM, TEM. Unit-III: Environmental Biology  Ecology as an inter-disciplinary science. Origin of life and speciation. Human Ecology and Settlement.  Ecosystem Structure and functions: Structures - Biotic and Abiotic components. Functions - Energy flow in ecosystems, energy flow models, food chains and food webs. Biogeochemical cycles, Ecological succession. Species diversity, Concept of ecotone, edge effects, ecological habitats and niche. Ecosystem stability and factors affecting stability. Ecosystem services.  Basis of Ecosystem classification. Types of Ecosystem: Desert (hot and cold), forest, rangeland, wetlands, lotic, lentic, estuarine (mangrove), Oceanic.  Biomes: Concept, classification and distribution. Characteristics of different biomes: Tundra, Taiga, Grassland, Deciduous forest biome, Highland Icy Alpine Biome, Chapparal, Savanna, Tropical Rain forest.  Population ecology: Characteristics of population, concept of carrying capacity, population growth and regulations. Population fluctuations, dispersion and metapopulation. Concept of ‘r’ and ‘k’ species. Keystone species.  Community ecology: Definition, community concept, types and interaction - predation, herbivory, parasitism and allelopathy. Biological invasions.  Biodiversity and its conservation: Definition, types, importance of biodiversity and threats to biodiversity. Concept and basis of identification of ‘Hotspots’; hotspots in India. Measures of biodiversity. Strategies for biodiversity conservation: in situ, ex situ and in vitro conservation. National parks, Sanctuaries, Protected areas and Sacred groves in India.  Concepts of gene pool, biopiracy and bio-prospecting. Concept of restoration ecology. Extinct, Rare, Endangered and Threatened flora and fauna of India.  Concept of Industrial Ecology.  Toxicology and Microbiology: Absorption, distribution and excretion of toxic agents, acute and chronic toxicity, concept of bioassay, threshold limit value, margin of safety, therapeutic index, biotransformation. Major water borne diseases and air borne microbes.  Environmental Biotechnology: Bioremediation – definition, types and role of plants and microbes for in situ and ex situ remediation. Bioindicators, Biofertilizers, Biofuels and Biosensors. Page | 4 Unit-IV: Environmental Geosciences  Origin of earth. Primary geochemical differentiation and formation of core, mantle, crust, atmosphere and hydrosphere.  Concept of minerals and rocks. Formation of igneous and metamorphic rocks. Controls on formation of landforms - tectonic including plate tectonic and climatic.  Concept of steady state and equilibrium, Energy budget of the earth. Earth’s thermal environment and seasons. Coriolis force, pressure gradient force, frictional force, geo- strophic wind field, gradient wind.  Climates of India, western disturbances, Indian monsoon, droughts, El Nino, La Nina. Concept of residence time and rates of natural cycles.  Geophysical fields. Weathering including weathering reactions, erosion, transportation and deposition of sediments. Soil forming minerals and process of soil formation, Identification and characterization of clay minerals, Soil physical chemical properties, soil types and climate control on soil formation, Cation exchange capacity and mineralogical controls.  Geochemical classification of elements, abundance of elements in bulk earth, crust, hydrosphere and biosphere. Partitioning of elements during surficial geologic processes, Geochemical recycling of elements.  Paleoclimate.  Distribution of water in earth, hydrology and hydrogeology, major basins and groundwater provinces of India, Darcy’s law and its validity, groundwater fluctuations, hydraulic conductivity, groundwater tracers, land subsidence, effects of excessive use of groundwater, groundwater quality.  Pollution of groundwater resources, Ghyben-Herzberg relation between fresh-saline water.  Natural resource exploration and exploitation and related environmental concerns. Historical perspective and conservation of non-renewable resources.  Natural Hazards: Catastrophic geological hazards - floods, landslides, earthquakes, volcanism, avalanche, tsunami and cloud bursts. Prediction of hazards and mitigation of their impacts. Unit-V: Energy and Environment  Sun as source of energy; solar radiation and its spectral characteristics.  Fossil fuels: classification, composition, physico-chemical characteristics and energy content of coal, petroleum and natural gas. Shale oil, Coal bed Methane, Gas hydrates. Gross-calorific value and net-calorific value.  Principles of generation of hydro-power, tidal energy, ocean thermal energy conversion, wind power, geothermal energy, solar energy (solar collectors, photo- voltaic modules, solar ponds).  Nuclear energy - fission and fusion, Nuclear fuels, Nuclear reactor – principles and types.  Bioenergy: methods to produce energy from biomass. Page | 5   Environmental implications of energy use; energy use pattern in India and the world, emissions of CO2 in developed and developing countries including India, radiative forcing and global warming. Impacts of large scale exploitation of solar, wind, hydro and nuclear energy sources. Unit-VI: Environmental Pollution and Control  Air Pollution:  Sources and types of Pollutants - Natural and anthropogenic sources, primary and secondary pollutants.  Criteria air pollutants.  Sampling and monitoring of air pollutants (gaseous and particulates); period, frequency and duration of sampling.  Principles and instruments for measurements of (i) ambient air pollutants concentration and (ii) stack emissions.  Indian National Ambient Air Quality Standards. Impact of air pollutants on human health, plants and materials.  Acid rain.  Dispersion of air pollutants.  Mixing height/depth, lapse rates, Gaussian plume model, line source model and area source model.  Control devices for particulate matter: Principle and working of: settling chamber, centrifugal collectors, wet collectors, fabric filters and electrostatic precipitator.  Control of gaseous pollutants through adsorption, absorption, condensation and combustion including catalytic combustion. Indoor air pollution, Vehicular emissions and Urban air quality.  Noise Pollution:  Sources, weighting networks, measurement of noise indices (Leq, L10, L90, L50, LDN, TNI).  Noise dose and Noise Pollution standards. Noise control and abatement measures: Active and Passive methods.  Vibrations and their measurements.  Impact of noise and vibrations on human health.  Water Pollution:  Types and sources of water pollution. Impact on humans, plants and animals.  Measurement of water quality parameters: sampling and analysis for pH, EC, turbidity, TDS, hardness, chlorides, salinity, DO, BOD, COD, nitrates, phosphates, sulphates, heavy metals and organic contaminants.  Microbiological analysis – MPN. Indian standards for drinking water (IS:10500, 2012). Page | 6   Drinking water treatment: Coagulation and flocculation, Sedimentation and Filtration, Disinfection and Softening. Wastewater Treatment: Primary, Secondary and Advanced treatment methods. Common effluent treatment plant.  Soil Pollution  Physico-chemical and biological properties of soil (texture, structure, inorganic and organic components).  Analysis of soil quality.  Soil Pollution control.  Industrial effluents and their interactions with soil components.  Soil micro-organisms and their functions - degradation of pesticides and synthetic fertilizers.  Thermal, Marine Pollution and Radioactive:  Sources of Thermal Pollution, Heat Islands, causes and consequences. Sources and impact of Marine Pollution.  Methods of Abatement of Marine Pollution.  Coastal management.  Radioactive pollution – sources, biological effects of ionizing radiations, radiation exposure and radiation standards, radiation protection. Unit-VII: Solid and Hazardous Waste Management  Solid Waste - types and sources.  Solid waste characteristics, generation rates, solid waste components, proximate and ultimate analyses of solid wastes.  Solid waste collection and transportation: container systems - hauled and stationary, layout of collection routes, transfer stations and transportation.  Solid waste processing and recovery – Recycling, recovery of materials for recycling and direct manufacture of solid waste products.  Electrical energy generation from solid waste (Fuel pellets, Refuse derived fuels), composting and vermicomposting, biomethanation of solid waste.  Disposal of solid wastes – sanitary land filling and its management, incineration of solid waste.  Hazardous waste – Types, characteristics and health impacts.  Hazardous waste management: Treatment Methods – neutralization, oxidation reduction, precipitation, solidification, stabilization, incineration and final disposal.  e-waste: classification, methods of handling and disposal.  Fly ash: sources, composition and utilisation.  Plastic waste: sources, consequences and management. Unit-VIII: Environmental Assessment, Management and Legislation  Aims and objectives of Environmental Impact Assessment (EIA). Page | 7   Environmental Impact Statement (EIS) and Environmental Management Plan (EMP). EIA Guidelines.  Impact Assessment Methodologies.  Procedure for reviewing EIA of developmental projects. Life-cycle analysis, cost- benefit analysis.  Guidelines for Environmental Audit. Environmental Planning as a part of EIA and Environmental Audit.  Environmental Management System Standards (ISO14000 series).  EIA Notification, 2006 and amendments from time to time. Eco-labeling schemes.  Risk Assessment - Hazard identification, Hazard accounting, Scenarios of exposure, Risk characterization and Risk management.  Overview of Environmental Laws in India: Constitutional provisions in India (Article 48A and 51A). Wildlife Protection Act, 1972 amendments 1991, Forest Conservation Act, 1980, Indian Forest Act, Revised 1982, Biological Diversity Act, 2002, Water (Prevention and Control of Pollution) Act, 1974 amended 1988 and Rules 1975, Air (Prevention and Control of Pollution) Act, 1981 amended 1987 and Rules 1982, Environmental (Protection) Act, 1986 and Rules 1986, Motor Vehicle Act, 1988, The Hazardous and Other Waste (Management and Transboundary Movement) Rules, 2016, The Plastic Waste Management Rules, 2016, The Bio-Medical Waste Management Rules, 2016, The Solid Waste Management Rules, 2016, The e-waste (Management) Rules 2016, The Construction and Demolition Waste Management Rules, 2016, The Manufacture, Storage and Import of Hazardous Chemical (Amendment) Rules, 2000, The Batteries (Management and Handling) Rules, 2010 with Amendments, The Public Liability Insurance Act, 1991 and Rules 1991, Noise Pollution (Regulation and Control) Rules, 2000, Coastal Regulation Zones (CRZ) 1991 amended from time to time.  National Forest Policy, 1988, National Water Policy, 2002, National Environmental Policy, 2006.  Environmental Conventions and Agreements: Stockholm Conference on Human Environment 1972, Montreal Protocol, 1987, Conference of Parties (COPs), Basel Convention (1989, 1992), Ramsar Convention on Wetlands (1971), Earth Summit at Rio de Janeiro, 1992, Agenda-21, Global Environmental Facility (GEF), Convention on Biodiversity (1992), UNFCCC, Kyoto Protocol, 1997, Clean Development Mechanism (CDM), Earth Summit at Johannesburg, 2002, RIO+20, UN Summit on Millennium Development Goals, 2000, Copenhagen Summit, 2009. IPCC, UNEP, IGBP. Unit-IX: Statistical Approaches and Modelling in Environmental Sciences  Attributes and Variables: types of variables, scales of measurement, measurement of Central tendency and Dispersion, Standard error.  Moments – measure of Skewness and Kurtosis, Basic concept of probability theory, Sampling theory.  Distributions - Normal, log-normal, Binomial, Poisson, t, 2 and F-distribution. Page | 8   Correlation, Regression, tests of hypothesis (t-test, 2-test ANOVA: one-way and two- way); significance and confidence limits.  Approaches to development of environmental models; linear, simple and multiple regression models, validation and forecasting.  Models of population growth and interactions: Lotka-Voltera model, Leslie’s matrix model. Unit-X: Contemporary Environmental Issues  Global Environmental Issues – Biodiversity loss, Climate change, Ozone layer depletion. Sea level rise. International efforts for environmental protection.  National Action Plan on Climate Change (Eight National missions – National Solar Mission, National Mission for Enhanced Energy Efficiency, National Mission on Sustainable Habitat, National Water Mission, National Mission for Sustaining the Himalayan Ecosystem, National Mission for a ‘Green India’, National Mission for Sustainable Agriculture, National Mission on Strategic Knowledge for Climate Change). Current Environmental Issues in India:  Environmental issues related to water resource projects - Narmada dam, Tehri dam, Almatti dam, Cauvery and Mahanadi, Hydro-power projects in Jammu & Kashmir, Himachal and North-Eastern States.  Water conservation-development of watersheds, Rain water harvesting and ground water recharge.  National river conservation plan – Namami Gange and Yamuna Action Plan.  Eutrophication and restoration of lakes. Conservation of wetlands, Ramsar sites in India.  Soil erosion, reclamation of degraded land, desertification and its control.  Climate change - adaptability, energy security, food security and sustainability.  Forest Conservation – Chipko movement, Appiko movement, Silent Valley movement and Gandhamardhan movement. People Biodiversity register.  Wild life conservation projects: Project tiger, Project Elephant, Crocodile Conservation, GOI-UNDP Sea Turtle project, Indo-Rhino vision.  Carbon sequestration and carbon credits.  Waste Management – Swachha Bharat Abhiyan.  Sustainable Habitat: Green Building, GRIHA Rating Norms.  Vehicular emission norms in India.  Epidemiological Issues: Fluorosis, Arsenocosis, Goitre, Dengue.  Environmental Disasters: Minnamata Disaster, Love Canal Disaster, Bhopal Gas Disaster, 1984, Chernobyl Disaster, 1986, Fukusima Daiichi nuclear disaster, 2011. Page | 9  Unit-I: Fundamentals of Environmental Sciences The word environment is derived from the French verb “environner”, which means to “encircle” or “surround.” Thus, our environment can be defined as the physical, chemical and biological world that surrounds us, as well as the complex of social and cultural conditions affecting an individual or community. This broad definition includes the natural world and the technological environment, as well as the cultural and social contexts that shape human lives. The biologist Jacob Van Uerkal (1864-1944) introduced the term ‘environment’ in Ecology. The term Environment can be broadly defined as one’s surroundings. To be more specific we can say that it is the physical and biological habitat that surrounds us, which can be felt by our physical faculties (seen, heard, touched, smelled and tasted). Some important definitions of environment are as under:  According to Boring, ‘A person’s environment consists of the sum total of the stimulation which he receives from his conception until his death.’ Indicating that environment comprises various types of forces such as physical, intellectual, mental, economical, political, cultural, social, moral and emotional.  Douglas and Holland defined that ‘The term environment is used to describe, in aggregate, all the external forces, influences and conditions, which affect the life, nature, behaviour and the growth, development and maturity of living organisms’. Environmental science is essentially the application of scientific methods and principles to the study of environmental issues, so it has probably been around in some form as long as science itself. Environmental science is often confused with other fields of related interest, especially ecology, environmental studies, environmental education, and environmental engineering. Environmental science is not constrained within any one discipline and it is a comprehensive field. A considerable amount of environmental research is accomplished in specific department such as chemistry, physics, civil engineering, or the various biology disciplines. Importance of Environment studies The environment studies make us aware about the importance of protection and conservation of our mother earth and about the destruction due to the release of pollution into the environment. The increase in human and animal population, industries and other issues make the survival cumbersome. A great number of environment issues have grown in size and make the system more complex day by day, threatening the survival of mankind on earth. Environment studies have become significant for the following reasons: 1. Environment issues are being of global It has been well recognised that environment issues like global warming and ozone depletion, acid rain, marine pollution and biodiversity are not merely national issues but are global issues and hence require international efforts and cooperation to solve them. 2. Development and environment Development leads to Urbanization, Industrial Growth, Telecommunication and Transportation Systems, Hi-tech Agriculture and Housing etc. However, it has become phased out in the developed world. The North intentionally moves their dirty factories to South to cleanse their own environment. When the West developed, it did so perhaps in Page | 10 ignorance of the environmental impact of its activities. Development of the rich countries of the world has undesirable effects on the environment of the entire world. 3. Explosive increase in pollution World census reflects that one in every seven persons in this planet lives in India. Evidently with 16 per cent of the world's population and only 2.4 per cent of its land area, there is a heavy pressure on the natural resources including land. Agricultural experts have recognized soil health problems like deficiency of micronutrients and organic matter, soil salinity and damage of soil structure. 4. Need for an alternative solution It is essential, especially for developing countries to find alternative paths to an alternative goal. We need a goal as under 1. A true goal of development with an environmentally sound and sustainable development. 2. A goal common to all citizens of our planet earth. 3. A goal distant from the developing world in the manner it is from the over-consuming wasteful societies of the “developed” world. 4. It is utmost important for us to save the humanity from extinction because of our activities constricting the environment and depleting the biosphere, in the name of development. 5. Need for Wise Planning of Development Our survival and sustenance depend on resources availability. Hence Resources withdraw, processing and use of the products have all to be synchronised with the ecological cycle. In any plan of development our actions should be planned ecologically for the sustenance of the environment and development. The two major classifications of environment are: (A) Physical Environment: External physical factors like Air, Water, and Land etc. This is also called abiotic Environment. (B) Living Environment: All living organisms around us viz., plants, animals, and microorganisms. This is also called biotic Environment. Earth’s environment can be further subdivided into the following four segments: (1) Lithosphere (2) Hydrosphere (3) Atmosphere (4) Biosphere Lithosphere The earth’s crust consisting of the soil and rocks is the lithosphere. The soil is made up of inorganic and organic matter and water. The main mineral constituents are compounds or mixtures derived from the elements of Si, Ca, K, Al, Fe, Mn, Ti, O, etc. (Oxides, Silicates, Page | 11 and Carbonates). The organic constituents are mainly polysaccharides, organo compounds of N, P and S. The organic constituents even though form only around 4% – 6% of the lithosphere, they are responsible for the fertility of the soil and hence its productivity. Hydrosphere This comprises all water resources both surface and ground water. The world’s water is found in oceans and seas, lakes and reservoirs, rivers and streams, glaciers and snowcaps in the Polar Regions in addition to ground water below the land areas. The distribution of water among these resources is  Oceans and seas – 96-97%  Glaciers and polar icecaps – 2-3%  Fresh water - 0; the reaction is non-spontaneous and endergonic ΔG < 0; the reaction is spontaneous and exergonic ΔG = 0; reaction is at equilibrium Note: 1. According to the second law of thermodynamics entropy of the universe always increases for a spontaneous process. 2. ΔG determines the direction and extent of chemical change. 3. ∆G is meaningful only for reactions in which the temperature and pressure remain constant. The system is usually open to the atmosphere (constant pressure) and we begin and end the process at room temperature (after any heat we have added or which is liberated by the reaction has dissipated). 4. ∆G serves as the single master variable that determines whether a given chemical change is thermodynamically possible. Thus if the free energy of the reactants is greater than that of the products, the entropy of the world will increase when the reaction takes place as written, and so the reaction will tend to take place spontaneously. ΔS universe = ΔS system + ΔS surroundings 5. If ΔG is negative, the process will occur spontaneously and is referred to as exergonic. 6. Therefore spontaneity is dependent on the temperature of the system. Point To Remember Free energy change criteria for predicting spontaneity is better than entropy change criteria because the former requires free energy change of system only whereas the latter requires entropy change of system and surroundings. Chemical potential The chemical potential of a species is the energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. The chemical potential of a species in a mixture is defined as the rate of change of free energy of a thermodynamic system with respect to the change in the number of atoms or molecules of the species that are added to the system. Thus, it is the partial derivative of the free energy with respect to the amount of the species, all other species' concentrations in the mixture Page | 51 remaining constant. The molar chemical potential is also known as partial molar free energy. When both temperature and pressure are held constant, chemical potential is the partial molar Gibbs free energy. At chemical equilibrium or in phase equilibrium the total sum of the product of chemical potentials and stoichiometric coefficients is zero, as the free energy is at a minimum. In semiconductor physics, the chemical potential of a system of electrons at zero absolute temperature is known as the Fermi energy. Chemical kinetics Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with thermodynamics, which deals with the direction in which a process occurs but in itself tells nothing about its rate. Chemical kinetics includes investigations of how experimental conditions influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states, as well as the construction of mathematical models that also can describe the characteristics of a chemical reaction. A catalyst is a substance that alters the rate of a chemical reaction but it remains chemically unchanged afterwards. The catalyst increases the rate of the reaction by providing a new reaction mechanism to occur within a lower activation energy. In autocatalysis a reaction product is itself a catalyst for that reaction leading to positive feedback. Proteins that act as catalysts in biochemical reactions are called enzymes. Michaelis–Menten kinetics describe the rate of enzyme mediated reactions. A catalyst does not affect the position of the equilibrium, as the catalyst speeds up the backward and forward reactions equally. Chemical equilibrium In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system. This state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but they are equal. Thus, there are no net changes in the concentrations of the reactants and products. Such a state is known as dynamic equilibrium. Equilibrium can be broadly classified as heterogeneous and homogeneous equilibrium. Homogeneous equilibrium consists of reactants and products belonging in the same phase whereas heterogeneous equilibrium comes into play for reactants and products in different phases. The conditions that pertain to equilibrium may be given quantitative formulation. For example, for the reversible reaction A ⇋ B + C, the velocity of the reaction to the right, r1, is given by the mathematical expression (based on the law of mass action) r1 = k1(A), where k1 is the reaction-rate constant and the symbol in parentheses represents the concentration of A. The velocity of the reaction to the left, r2, is r2 = k2(B)(C) At equilibrium, r1 = r2. By methods of statistical mechanics and chemical thermodynamics, it can be shown that the equilibrium constant is related to the change in the thermodynamic quantity called the standard Gibbs free energy accompanying the reaction. The Page | 52 standard Gibbs free energy of the reaction, ΔG°, which is the difference between the sum of the standard free energies of the products and that of the reactants, is equal to the negative natural logarithm of the equilibrium constant multiplied by the so-called gas constant R and the absolute temperature T. The equation allows the calculation of the equilibrium constant, or the relative amounts of products and reactants present at equilibrium, from measured or derived values of standard free energies of substances Solubility of gas in water Solubility is a measure of how much of a solute can be dissolved in a specified amount of a solvent. Solubility is defined as the number of grams of a solute that can be dissolved in 100 g of a solvent to form its saturated solution at a given temperature and pressure. For example, 36 g of sodium chloride need to be dissolved in 100 g of water to form its saturated solution at 25°C. Thus the solubility of NaCl in water is 36 g at 25°C. The solubility is mathematically expressed as Solubility = (Mass of the solute/Mass of the solvent) × 100 The carbonate system The carbonate system involves the circulation of CO2 between the biosphere, lithosphere, atmosphere and the ocean. The ocean plays a vital role as it absorbs major quantities of atmospheric CO2 and without it, CO2 levels would rise rapidly in the atmosphere resulting in extreme changes such as exponential increase in temperature. The carbon system is an important process for marine ecosystems as it can not only influence the conditions of the oceans, such as pH levels, that can directly affect the survival of marine life, it also provides marine primary producers energy to start of the carbon pump and distribute energy throughout marine communities. The carbonate system incorporates 3 main species produced by an equilibrium: Firstly carbon dioxide enters the oceans though atmospheric CO2 as a form of an equilibrium: This aqueous CO2 can react with calcium carbonate to produce bicarbonate ions which can further dissolve calcium carbonate: Aqueous CO2 can also react to water to form carbonic acid (H2CO3): Impact to marine ecosystems As all main species for the carbonate system is all formed by an equilibrium, if one species is produced more, the other species will go through it’s process in order to create a Page | 53 stable equilibrium. This implies that a higher level of CO2 in either atmospheric or aqueous form will increase carbonic acid and bicarbonate within the water. Both species have their impacts to marine ecosystems. High levels of carbonic acid (H2CO3) disturbs the pH of the ocean, making the pH level lower and the oceans more acidic. This process is called ‘Ocean Acidification’. Although organisms do have a pH range in which they can sustain, the complication of ocean acidification is the additional difficulty for marine organisms to survive with the constant changes of acidity since the pH levels are increasing rapidly and not leaving sufficient time for organisms to adapt. High levels of bicarbonate ions within the water can lead to a decrease in calcification. Calcification is the process when marine organisms produce calcium carbonate (CaCO3) to form shells or skeletons. Increase in bicarbonate ions can destroy many marine life quickly as many organisms that live within the ocean use calcium carbonate as a source to protection and stability. Corals plays a vital role in the marine food web as they are the primary producers, however as CO2 and H2CO3 increases and since their skeletons are constructed from CaCO3, their chance to grow becomes more difficult and their rates of dissolving. This ultimately has a impact amongst all marine life as this interferes the with food web and energy flow that marine organisms need in order to live. Ocean Macroalgal Afforestation (OMA) Ocean afforestation is a method which has the potential to reduce atmospheric CO2 and therefore also the carbonate species within the ocean to prevent ocean acidification. This method is conducted by implementing natural populations of macroalgae to absorb CO2, then collected to produce renewable natural gas (e.g. biomethane and biocarbon) though anaerobic digestion and the plant nutrients remaining are recycled to expand agal forests and fish populations. Hydrocarbons The organic compounds that are composed of only carbon and hydrogen atoms are called hydrocarbons. The carbon atoms join together to form the framework of the compounds. These are regarded as the parent organic compounds and all other compounds are considered to be derived from hydrocarbons by replacing one or more hydrogen atoms with other atoms or group of atoms. Hydrocarbons are, further, sub divided into three classes such as: (a) Alkanes: These are hydrocarbons, which contain only single bonds. They are represented by the general formula CnH2n + 2 (where n = 1, 2, 3,.). The simplest alkane (for n=1) is methane (CH4). Since, all are single bonds in alkanes, they are saturated compounds. (b) Alkenes: The hydrocarbons, which contain one or more C=C bonds are called alkenes. These are unsaturated compounds. They are represented by the general formula CnH2n. The simplest alkene contains two carbon atoms (n=2) and is called ethylene (C2H4). (c) Alkynes: The hydrocarbons containing carbon to carbon triple bond are called alkynes. They are also unsaturated as they contain triple bond between carbon atoms. They have the general formula CnH2n–2. Acetylene (C2H2) is the simplest alkyne, which contains two carbon atoms. Saturated hydrocarbons: In this type of hydrocarbons, the carbon atoms are connected by a single covalent bond. These are called alkane and general formula CnH2n+2 where n=1, 2, 3….etc. These are less reactive as they contain strong sigma bond. They do not undergo hydrogenation reaction. For example: CH4. Page | 54 Unsaturated hydrocarbons: In this type of hydrocarbons, the carbon atoms are connected by multiple bonds like double or triple bonds. The double bonded compounds are called alkene and has general formula CnH2n and triple bonded compounds are called alkynes and has general formula CnH2n-2. These are more reactive as they contain one or more pi bonds which can be easily broken. They can undergo hydrogenation reaction. For example: CH2=CH2 is an alkene. Radioisotopes Different isotopes of the same element have the same number of protons in their atomic nuclei but differing numbers of neutrons. Radioisotopes are radioactive isotopes of an element. They can also be defined as atoms that contain an unstable combination of neutrons and protons, or excess energy in their nucleus. How do radioisotopes occur? The unstable nucleus of a radioisotope can occur naturally, or as a result of artificially altering the atom. In some cases a nuclear reactor is used to produce radioisotopes, in others, a cyclotron. Nuclear reactors are best-suited to producing neutron-rich radioisotopes, such as molybdenum-99, while cyclotrons are best-suited to producing proton-rich radioisotopes, such as fluorine-18. The best known example of a naturally-occurring radioisotope is uranium. All but 0.7 per cent of naturally-occurring uranium is uranium-238; the rest is the less stable, or more radioactive, uranium-235, which has three fewer neutrons in its nucleus. Radioactive decay Atoms with an unstable nucleus regain stability by shedding excess particles and energy in the form of radiation. The process of shedding the radiation is called radioactive decay. The radioactive decay process for each radioisotope is unique and is measured with a time period called a half-life. One half-life is the time it takes for half of the unstable atoms to undergo radioactive decay. Many radio isotopes can be obtained from radioactivity. These radio isotopes have found wide variety of applications in the fields of medicine, agriculture, industry and archeological research. Agriculture The radio isotope of phosphorous (P-32) helps to increase the productivity of crops. The radiations from the radio isotopes can be used to kill the insects and parasites and prevent the wastage of agricultural products. Certain perishable cereals exposed to radiations remain fresh beyond their normal life, enhancing the storage time. Very small doses of radiation prevent sprouting and spoilage of onions, potatoes and gram. Medicine Medical applications of radio isotopes can be divided into two parts: i) Diagnosis ii) Therapy Radio isotopes are used as tracers to diagnose the nature of circulatory disorders of blood, defects of bone metabolism, to locate tumors, etc. Some of the radio isotopes which are used as tracers are: hydrogen, carbon, nitrogen, sulphur, etc.  Radio sodium (Na24) is used for the effective functioning of heart.  Radio – Iodine (I131) is used to cure goiter.  Radio-iron is (Fe59) is used to diagnose anaemia and also to provide treatment for the same. Page | 55  Radio phosphorous (P32) is used in the treatment of skin diseases.  Radio cobalt (Co60) and radio-gold (Au198) are used in the treatment of skin cancer.  Radiations are used to sterilize the surgical devices as they can kill the germs and microbes. Industries In industries, radioactive isotopes are used as tracers to detect any manufacturing defects such as cracks and leaks. Packaging faults can also be identified through radio activity. Gauges, which have radioactive sources are used in many industries to check the level of gases, liquids and solids.  An isotope of californium (Cf 252) is used in the airlines to detect the explosives in the luggage.  An isotope of Americium (Am241) is used in many industries as a smoke detector. Archeological research Using the technique of radio carbon dating, the age of the Earth, fossils, old paintings and monuments can be determined. In radio carbon dating, the existing amount of radio carbon is determined and this gives an estimate about the age of these things. Half-life period Half-life, in radioactivity, the interval of time required for one-half of the atomic nuclei of a radioactive sample to decay (change spontaneously into other nuclear species by emitting particles and energy), or, equivalently, the time interval required for the number of disintegrations per second of a radioactive material to decrease by one-half. Half-lives are characteristic properties of the various unstable atomic nuclei and the particular way in which they decay. Alpha and beta decay are generally slower processes than gamma decay. Half-lives for beta decay range upward from one-hundredth of a second and, for alpha decay, upward from about one one-millionth of a second. Half-lives for gamma decay may be too short to measure (around 10-14 second), though a wide range of half-lives for gamma emission has been reported. Half-Life Formulas Here we consider the following,  N0 = the initial quantity of the substance  N(t) = the quantity that is left over  t1⁄2 = half-life  τ = mean lifetime of the decaying quantity  λ = decay constant Calculation The half life period of a radioactive substance is 32 h. how much time it would take for its 75% disintegration? Page | 56 Solution R/Ro = 25% R/Ro = (1/2)n 25/100 = (1/2)t/T1/2 ¼ = (1/2)t/T1/2 (1/2)2 = (1/2) t/T1/2 Compare power n= t/T1/2 2 = t/T1/2 t = 2 × T1/2 t = 2 × 32 t = 64 Ans: It takes 64 hours for the 75% disintegration of that radioactive substance. Decay constant Decay constant, proportionality between the size of a population of radioactive atoms and the rate at which the population decreases because of radioactive decay. Suppose N is the size of a population of radioactive atoms at a given time t, and dN is the amount by which the population decreases in time dt; then the rate of change is given by the equation dN/dt = −λN, where λ is the decay constant. Integration of this equation yields N = N0e−λt, where N0 is the size of an initial population of radioactive atoms at time t = 0. This shows that the population decays exponentially at a rate that depends on the decay constant. The time required for half of the original population of radioactive atoms to decay is called the half-life. The relationship between the half-life, T1/2, and the decay constant is given by T1/2 = 0.693/λ Calculation The half life of 91Sr38 is 9.7 hours. Find its decay constant. Solution The half life of 91Sr38 = T1/2 = 9.70 hours = 9.70 60 60 seconds = 34920 seconds λ = 0.693/T1/2 = 0.693/34920 = 1.9845 10-5 second-1 Composition of air The atmosphere is a mechanical mixture of many gases, not a chemical compound. In addition, it contains water vapour volume (4% of atmospheric composition) and huge number of solid particles, called aerosols. Some of the gases (N, O2, Ar, CO2) may be regarded as permanent atmospheric components that remain in fixed proportions to the total gas volume. Other constituents vary in quantity from place to place and from time to time. If the suspended particles, water vapour and other variable gases are excluded from the atmosphere, the dry air is very stable all over the earth up to an altitude of about 80 km. (Detailed explanation of composition of atmosphere is given unit I under the topic “composition of armosphere”) Page | 57 Atmospheric particles Atmospheric particles (aerosols) range in size from a few nanometers to tens of micrometers in diameter. (An aerosol is strictly defined as a suspension of fine liquid or solid particles in a gas. In common usage, however, the particles themselves are referred to as the aerosol.) Primary aerosols are those particles emitted directly into the atmosphere. Particles or particulate materials are also formed in the atmosphere by nucleation or condensation of vapor species; such gas-to-particle conversion processes are an important source of atmospheric particulate material. Particles are ubiquitous in the atmosphere; there is no region of it totally devoid of them. Particles are, in fact, the nuclei for the formation of clouds. Those particles that, in the presence of small amounts of water super saturation, grow spontaneously to form cloud droplets are called cloud condensation nuclei (CCN). The number of particles in a given ambient population that will form cloud droplets in a certain situation depends on the amount of ambient water supersaturation and the composition of the particles themselves. Particles containing water-soluble compounds preferentially act as CCN over those that contain largely insoluble compounds. Particulate matter Particles of wide range of sizes ranging from 0.1 μ to 10μ exist in the atmosphere. Highly polluted air may contain up to 105 particles per cc. Aerosols are particles with colloidal dimensions. Dust, fog, ash, mist, smoke, pollen, fumes and bacteria contribute to the presence of particulate matter. Particulate matter may be either organic or inorganic in nature. Inorganic particulates are volcanic ash, fine silica dust, iron oxide, and calcium oxide, Lead etc. Organic particulates are generated from automobile exacts, fuel combustion, and solid organic matter. Particulate matter may be generated either by natural means (Volcanic eruption, wild fires, dust storms etc.) or by anthropogenic means (Automobile exhaust, fossil fuel burning, mining and quarrying and various other industrial activities). Particulate matter is a health hazard since they enter the human beings and animals through the respiratory tract and are absorbed by them. Removal of particulate matter from the atmosphere is a very important function in air pollution control. However the particulate matter also lead to certain beneficial effects. They provide the nuclei for condensation of water vapor and cloud formation. They also contribute to maintaining a radiation and heat balance on earth. Ions At an altitude of 50 km to 100 kms considerable concentrations of electrons and positive ions such as O+, NO+ etc. exist for reasonably longer residence times. This zone of the atmosphere is called ionosphere. The UV radiations from the sun lead to the formation of ions in the ionosphere. Radicals The atmosphere also has free radicals that are highly reactive. These free radicals are generated by photochemical reactions and may be organic or inorganic. HO , HCO , NO2 , ROO , CH3 are some examples of the free radicals available in the atmosphere. These radicals interact with other chemical components of the atmosphere producing a series of chain reactions. Chemical speciation Chemical speciation refers to the distribution of an element amongst chemical species in a system. It is critical for understanding chemical toxicity, bioavailability, and environmental Page | 58 fate and transport. Despite the central importance of knowing the full speciation of a chemical in order to predict its behaviuor in a system, it is generally not possible to determine a speciation analysis using analytical chemistry methods alone. Most techniques are focused on detection of free metal ion concentrations or total metal concentrations. Direct speciation measurement using traditional analytical methods requires significant complexity and generally hyphenated techniques allows direct measure of chemical speciation of some metals. However, because environmental concentrations of most metals of interest are low, and because many relevant forms of metals cannot be measured directly, analytical techniques often are not effective for determining overall speciation. Thus chemical speciation determination generally relies on utilizing analytical methods in conjunction with chemical speciation models. Chemical reactions in the atmosphere The different chemical species available in the environment undergo chemical changes by reaction with other molecules. The chemical reactions are also assisted by the solar radiation. The chemical and photochemical reactions taking place in the atmosphere depend up on the temperature, nature and concentration of the chemical species available, humidity, and intensity of sun’s radiation. The oxides of nitrogen (Referred to as NOx) viz. N2O, NO and NO2 originate from burning of fossil fuels and other anthropogenic activities. In the stratosphere, N2O decomposes photo chemically to NO which intern depletes ozone layer. The oxidation of NO2 and subsequent absorption in water produces nitric acid forming acid rain. The oxides of sulphur (Referred to as SOx) viz. SO3 and SO2 originate from the burning of fossil fuels as well as from volcanic eruptions.). The sulphur dioxide absorbs solar radiation and produces electronically excited SO2, which is oxidized to SO3. In the presence of moisture SO3 is converted to H2SO4, contributing to acid rain. The overall photochemical reaction is as under. Organic compounds like hydrocarbons, aldehydes and ketones actively take part in chemical and photochemical reactions assisted by solar radiation and particulate matter The alkyl or aryl radicals R react with oxygen to form peroxyl radical, which subsequently reacts with NO2 to generate peroxyacyl nitrate (PAN), formaldehyde and a host of polymeric compounds. These compounds reduce visibility in the atmosphere and contribute to photochemical smog. Page | 59 Photochemical smog can also be initiated by the dissociation of NO2 and subsequent secondary reactions with hydrocarbons and other organic compounds. The stepwise chemistry of the formation of photochemical smog is illustrated below: (1) Nitrogen oxides generate oxygen atoms by photochemical reaction. (2) Oxygen atoms form hydroxyl (HO*) radicals catalyzed by particulate matter (PM). (3) Hydroxyl radicals generate hydrocarbon radicals (R*) from hydrocarbons (RH). (4) Hydrocarbon radicals form hydrocarbon peroxides (RO). (5) Hydrocarbon peroxides form aldehydes. (6) Aldehydes form aldehyde peroxides. (7) Aldehyde peroxides form peroxyacylnitrates (PAN). Photochemical smog result in very poor visibility leading to disruption/accidents in air and road traffic. It also causes irritation to the eyes and lungs and chronic respiratory problems. Damage to plants and rubber, polymer goods are also the adverse impacts of photochemical smog. Ozone is an important constituent in the atmosphere. At an altitude of 30 kms, its concentration is around 10 ppm. This stratospheric ozone layer absorbs UV radiation from the sun and hence protects the life on earth against radiation damages like skin cancer, mutation of DNA etc. The chemistry of ozone formation and depletion is as under: This reaction is catalyzed by a third body viz., N2 or O2. Thus ozone is continuously formed in the stratosphere by photochemical reaction. Ozone is also destroyed by chlorine released in to Page | 60 the atmosphere by natural (volcanic activity) or anthropogenic (Refrigerants containing Chloro Flouro Carbons) causes. Nitric Oxide and reactive hydroxyl radicals also contribute to ozone depletion. The overall ozone depletion reaction is Ozone layer depletion and Chlorofluoro Carbons Chlorofluro carbons are widely used as refrigerants owing to their properties, such as low viscosity, low surface tension, low boiling point, and chemical and biological inertness. The ozone depletion potential (ODP) of chlorofluorocarbons is defined as the ratio of the impact on ozone from a specific chemical to the impact from an equivalent mass of CFC-11. ODP value depends on the species’ reactivity, atmospheric residence time, and molecular mass. CFCs are unreactive in the troposphere but undergo photolytic decomposition in the stratosphere to produce chlorine radicles, which react with ozone molecules and break them apart. In the industrial-environmental perspective, hydrofluorocarbons (HCFCs) are generally considered as substitutes for chlorofluro carbons as they contain no chlorine atoms and have zero ODP value. Ozone layer depletion leads to an increase in UV-B radiation reaching the Earth’s surface. Exposure to this harmful radiation can cause skin cancer, eye cataracts, weakening of immune systems, damage to crops, and reductions in primary producers (plankton) in the ocean. Smog Smog is a type of critical air pollution, originally named for the mixture of smoke and fog in the air. Two distinct types of smog are recognized in the atmosphere: classical smog and photochemical smog. London smog or Classical smog Los Angeles smog or Photochemical smog  The main components are fog and  The word smog is a misnomer as it does not coal smoke (SO2). it is first involve any smoke or fog. It is first observed observed in London (1952) in Los Angeles (1943)  SO2 reacts with humidity in the air  In the presence of UV radiation, NOx and to form Sulphuric acid fog which hydrocarbons undergo photochemical deposits on the particulates. reactions to produce toxic secondary air pollutants, such as PAN (Peroxyacyl nitrates) aldehydes, ketones and ozone.  Early morning hours of winter  The secondary air pollutants are lachrymatory months are susceptible to the (eye irritants). formation of classical smog.  Chemically, it is reducing in nature  It is oxidizing in nature due to the high and causes bronchitis irritation. concentration of photochemical oxidants. Page | 61 Chemistry of Ozone Depletion The chemical reactions occur in the stratosphere are intimately connected with the presence of the ozone layer. The ultraviolet region covers the wavelength range between 100 and 400 nanometers, which is shorter than that of visible light but longer than X-rays. The ozone layer absorbs UV radiation at wavelengths below 300 nm. UVR is classified based on wavelength into three regions: UVA, UVB, and UVC Type Health consequences UVA Premature aging and wrinkling of the skin. Accounts for approximately 95 per cent of the UV (315nm – 400nm) radiation reaching the Earth's surface. UVB More dangerous than UVA and the prime cause of skin cancers and cataracts. (280nm- 315nm) UVC A lethal form of ultraviolet radiation but it fails to reach the earth’s surface due to absorption in the (100nm- 280nm) atmosphere by ozone. At higher altitudes, Chlorofluoro Carbons are exposed to an intense flux of ultraviolet radiation. As a consequence, the photolytic decomposition of CFC molecules takes place. CFCl3+ hѴ (ʎ< 290 nm) ---- > CFCl2+ Cl The released chlorine radical takes part in the following reactions causing ozone depletion Cl+ O3 --------- > ClO + O2 ClO+ O --- > Cl + O2 Net Reaction: O+ O3 --------- > 2O2 Heat Heat is the energy in transmission to or from a thermodynamic structure by mechanisms other than a transfer of matter or thermodynamic work. The SI unit of heat is the joule (J). Specific heat capacity It is the amount of heat needed for a unit mass of a given body in order to change its temperature by one degree. The SI unit of specific heat capacity is joule per kelvin per kilogram. Latent heat Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process – usually a first-order phase transition. Page | 62  Two examples of latent heat are: 1. The heat of freezing 2. The heat of vaporization The heat of freezing is the amount of thermal energy given off as a liquid freezes, and the heat of vaporization is the amount of thermal energy that must be added to change a liquid to a gas. Heat added or subtracted for a phase change = Latent heat × Mass Q = L heat M Where,  Q = heat (calories or joules)  L heat = latent heat (calories/gram or joules/gram)  M = mass (grams) Factors:  If liquid water at 100°C is changed into steam, the heat added (the latent heat of vaporization) is 540 calories for every gram of water.  If steam at 100°C is changed into the water at 100° C, 540 calories for every gram of steam must be subtracted. If ice at 0°C is changed into liquid water at 0°C, the heat added (the latent heat of melting) is 80 calories for every gram of ice.  If liquid water at 0°C changes into ice at 0°C, 80 calories for every gram of liquid water must be subtracted.  Latent heats can be very large. For example, the latent heat of vaporization of water is 540 cal/g and the latent heat of freezing of water is 80 cal/g. Therefore, changing a given quantity of water to steam requires 5.4 times as much heat as warming it from 0°C (+32°F) to 100°C (212°F), and melting ice requires as much heat as warming water from 20°C (68°F) to 100°C. Latent heat of sublimation definition The latent heat of sublimation is the heat required to change the state of a substance from solid to gas without any intermediate state at a constant temperature. Evaporation below 100 °C and sublimation require more energy per gram than 540 calories. At 20 °C (68 °F) about 585 calories are required to vaporize one gram of water. When water vapour condenses back to liquid water, the latent heat of vaporization is liberated. Page | 63 Hydrological cycle The natural circulation of water on earth is called the hydrologic cycle. Water cycle from bodies of water, via evaporation to the atmosphere, and eventually returns to the oceans as precipitation, runoff from streams and rivers, and groundwater flow. Water molecules are transformed from liquid to vapor and back to liquid within this cycle. On land, water evaporates from the soil or is taken up by plant roots and eventually transpired into the atmosphere through plant leaves. The sum of evaporation and transpiration is called evapotranspiration. Water is recycled continuously. The molecules of water in a glass is used to quench our thirst today, at some point in time may have dissolved minerals deep in the earth as groundwater flow, fallen as rain in a tropical typhoon, been transpired by a tropical plant, been temporarily stored in a mountain glacier, or quenched the thirst of people thousands of years ago. The hydrologic cycle has no real beginning or end but is a circulation of water that is sustained by solar energy and influenced by the force of gravity. Because the supply of water on earth is fixed, there is no net gain or loss of water over time. On an average annual basis, global evaporation must equal global precipitation. Likewise, for anybody of land or water, changes in storage must equal the total inflow minus the total outflow of water. This is the hydrologic or water balance. At any point in time, water on earth is either in active circulation or in storage. Water is stored in icecaps, soil, groundwater, the oceans, and other bodies of water. Much of this water is only temporarily stored. The residence time of water storage in the atmosphere is several days and is only about 0.04 per cent of the total freshwater on earth. For rivers and streams, residence time is weeks; for lakes and reservoirs, several years, for groundwater, hundreds to thousands of years; for oceans, thousands of years; and for icecaps, tens of thousands of years. As the driving force of the hydrologic cycle, solar radiation provides the energy necessary to evaporate water from the earth's surface, almost three-quarters of which is covered by water. Nearly 86 per cent of global precipitation originates from ocean evaporation. Energy consumed by the conversion of liquid water to vapor cools the temperature Page | 64 of the evaporating surface. This same energy, the latent heat of vaporization, is released when water vapor changes back to liquid. In this way, the hydrologic cycle globally redistributes heat energy as well as water. Understanding processes of the hydrologic cycle can help us develop solutions to water problems. The implications of global warming or greenhouse effects on the hydrologic cycle raise several questions. The possible changes in frequency and occurrence of droughts and floods are of major concern, particularly given projections of population growth. The hydrologic cycle influences nutrient cycling of ecosystem, processes of soil erosion and transport of sediment, and the transport of pollutants. Water is an excellent liquid solvent; minerals, salts, and nutrients become dissolved and transported by water flow. The hydrologic cycle is an important driving mechanism of nutrient cycling. As a transporting agent, water moves minerals and nutrients to plant roots. As plants die and decay, water leaches out nutrients and carries them downstream. The physical action of rainfall on soil surfaces and the forces of running water can seriously erode soils and transport sediments downstream. Any minerals, nutrients, and pollutants within the soil are likewise transported by water flow into groundwater, streams, lakes, or estuaries.  Riverine zone  Transitional zone  Lacustrine Zone  Dam  Source  Knick point  Potamon zone  Rhitron zone (High DO)  (Sandy, low DO)  Mouth Groundwater 1. Aquifer An aquifer is a saturated formation of earth material that not only stores water but also yields it in sufficient quantities. This layer of rocks transmits water easily due to its high-water permeability. Unconsolidated deposits of sand and gravel form good aquifers. 2. Aquitard The underground formation through which only seepage is possible due to its low permeability. Water may leak into the aquifer through the aquitards, such as sand, clay, etc. 3. Aquiclude Aquiclude is a geological formation that is porous but not permeable. Such rocks may bear water but do not yield the same as they are impermeable. 4. Aquifuge The underground formations, such as Granite and Quartzite belong to this category of rocks that are neither porous nor permeable. Water as universal solvent Water is called the "universal solvent" because it is capable of dissolving more substances than any other liquid. This is important to every living thing on earth. It means that Page | 65 wherever water goes, either through the air, the ground, or through our bodies, it takes along valuable chemicals, minerals, and nutrients. It is water's chemical composition and physical attributes that make it such an excellent solvent. Water molecules have a polar arrangement of oxygen and hydrogen atoms—one side (hydrogen) has a positive electrical charge and the other side (oxygen) had a negative charge. This allows the water molecule to become attracted to many other different types of molecules. Water can become so heavily attracted to a different compound, like salt (NaCl) that it can disrupt the attractive forces that hold the sodium and chloride in the salt compound together and, thus, dissolve it. Why salt dissolves in water? At the molecular level, salt dissolves in water due to electrical charges and due to the fact that both water and salt compounds are polar, with positive and negative charges on opposite sides in the molecule. The bonds in salt compounds are called ionic because they both have an electrical charge—the chloride ion is negatively charged and the sodium ion is positively charged. Likewise, a water molecule is ionic in nature, but the bond is called covalent, with two hydrogen atoms both situating themselves with their positive charge on one side of the oxygen atom, which has a negative charge. When salt is mixed with water, the salt dissolves because the covalent bonds of water are stronger than the ionic bonds in the salt molecules. The positively-charged side of the water molecules are attracted to the negatively- charged chloride ions and the negatively-charged side of the water molecules are attracted to the positively-charged sodium ions. Essentially, a tug-of-war ensues with the water molecules winning the match. Water molecules pull the sodium and chloride ions apart, breaking the ionic bond that held them together. After the salt compounds are pulled apart, the sodium and chloride atoms are surrounded by water molecules, as this diagram shows. Once this happens, the salt is dissolved, resulting in a homogeneous solution. Dissolved oxygen Dissolved oxygen (DO) is a measure of how much oxygen is dissolved in the water - the amount of oxygen available to living aquatic organisms. The amount of dissolved oxygen in a stream or lake can tell us a lot about its water quality. Although water molecules contain an oxygen atom, this oxygen is not what is needed by aquatic organisms living in natural waters. A small amount of oxygen, up to about ten molecules of oxygen per million of water, is actually dissolved in water. Oxygen enters a stream mainly from the atmosphere and, in areas where groundwater discharge into streams is a large portion of streamflow, from groundwater discharge. This dissolved oxygen is breathed by fish and zooplankton and is needed by them to survive. Oxygen demand Oxygen demand is a measure of the amount of oxidizable substances in a water sample that can lower DO concentrations. Biochemical Oxygen Demand BOD – Biochemical Oxygen Demand is applied to determine the aerobic destructibility of organic substances. It is the biological method used for the measurement of the total amount of dissolved oxygen (DO) used by microbes in the biological process of metabolizing organic molecules present in water. Page | 66  The total amount of oxygen gas present in the water is called dissolved oxygen (DO). The non-compound oxygen present in water may either be a by-product of the photosynthesis of the aquatic plants or the dissolved atmospheric oxygen gas. In some water bodies, organic matter is a great source of BOD. These organic matters include sewage and other pollutants present in the water bodies. The greater the BOD, the lower is the dissolved oxygen available for aerobic animals such as fishes and other aquatic organisms. The BOD is accordingly a reliable measure of the organic pollution of water bodies. The main reason for treating wastewater prior to its discharge into a water resource is to reduce its BOD level (the demand for oxygen). S.No BOD level Quality of water 1 1-2mg O2/Litre clean water 2 3-8 mg O2/Litre moderately clean 3 8-20 mg O2/Litre border line water 4 >20 mg O2/Litre polluted/unsafe BOD calculation Step 1: In order to calculate the BOD, the laboratory is sampling some waste water, then is diluting it in a BOD incubation bottle. The lab must measure the following data: D1 = oxygen diluted level in the diluted sample at t=0 (mg/l) D2 = oxygen diluted level in the diluted sample at t=5 days (mg/l) B1 = oxygen diluted level in the dilution water at t=0 (mg/l) B2 = oxygen diluted level in the dilution water at t=5 days (mg/l) V1 = volume of wastewater sampled for dilution (ml) V2 = volume of diluted sample (ml) Step 2: Calculate the BOD The BOD at 5 days can be calculated with the following formula: BOD5 = [(D1-D2)-(B1-B2)f]/P Where, f = (V2-V1)/V2 P = V1/V2 Example A factory has taken a sample of its effluents and sent it to the lab. The lab takes 10 ml of waterwater and dilute it in a BOD incubation bottle of 250 ml. The lab measures the oxygen level in the diluted water and gets 10 mg/l at t=0 and 2 mg/l at t=5 days, it takes also the same measures on the dilution water and gets 9.5 mg/l at t=0 and 8 mg/l at t=5 days. The lab wishes to calculate the BOD5 of the effluent. Step 1: collect the data D1 = oxygen diluted level in the diluted sample at t=0 = 10 mg/l D2 = oxygen diluted level in the diluted sample at t=5 days = 2 mg/l B1 = oxygen diluted level in the dilution water at t=0 = 9.5 mg/l B2 = oxygen diluted level in the dilution water at t=5 days = 8 mg/l V1 = volume of wastewater sampled for dilution = 10 ml V2 = volume of diluted sample = 250 ml Page | 67 Step 2: Calculate the BOD5 f = (V2-V1)/V2 = (250-10)/250 = 0.96 P = V1/V2 = 10/250 = 0.04 BOD5 = [(D1-D2)-(B1-B2)f]/P = [(10-2)-(9.5-8)*0.96]/0.04 = 164.4 mg/l Importance of BOD 1. BOD measures the amount of oxygen consumed by microorganisms for the process of decomposition of the organic matters in the water bodies. 2. It indicates the amount of organic pollution present in an aquatic ecosystem. 3. BOD is calculated in sewage treatment or wastewater treatment to find the destruction of organic wastes by aerobic microbes 4. It determines the amount of organic matter present in soils, sewages, sediment, garbage, sludge, etc. 5. The biochemical oxygen demand also determines the rate of respiration in living beings. 6. BOD is also used in the medicinal & pharmaceutical industries to test the oxygen consumption of cell cultures. Chemical Oxygen Demand (COD) Chemical Oxygen Demand (COD) is a test that measures the amount of oxygen required to chemically oxidize the organic material and inorganic nutrients, such as Ammonia or Nitrate, present in water. COD is measured via a laboratory assay in which a sample is incubated with a strong chemical oxidant for a specified time interval and at constant temperature (usually 2 h at 150°C). The most commonly used oxidant is potassium dichromate, which is used in combination with boiling sulphuric acid. It is important to note that the chemical oxidant is not specific to organic or inorganic compounds, hence both these sources of oxygen demand are measured in a COD assay. Furthermore, it does not measure the oxygen-consuming potential associated with certain dissolved organic compounds such as acetate. Thus, measurements are not directly comparable to Biochemical Oxygen Demand (BOD) but can be used to compliment (though is sometimes used as surrogate measure). Sedimentation Suspended solids present in the industrial wastewater can cause problems in the sewer system or in subsequent treatment units where they may settle out or cling to pipe or on reactor walls. Sedimentation is the process of removal of suspended solids from wastewater utilizing their ability to settle under the influence of gravity. The settling characteristics of suspended particles may be classified into one of the following types.  Discrete settling—Type 1  Flocculent—Type 2  Zone settling—Type 3  Compression Settling—Type 4 Discrete Settling The particle or pollutant while settling does not change in size, shape or density and also does not interact with other particles. It settles due to the competing forces of gravity and buoyancy. Page | 68 This type of settling is ideal and occurs in the following cases: 1. Stirrer 2. Granular inert materials that do not stick together. 3. Materials present in dilute suspension. 4. In flow system, for small liquid flow velocity. 5. For uniformly distributed particle sizes. Flocculent settling This occurs when particles do not settle in an independent manner. Most of the industrial water particles follow this type of settling. As the particles settle, (heavier) some particles move faster and collide with other settling particles. Thus the particles will stick together (flocculate) and becomes a larger particle with higher settling velocities. Zone Settling Zone settling occurs with flocculated chemical suspensions and biological flock particles adhere and the mass settles as blanket. Compression Settling This occurs when solids reach the bottom of a reactor, pile up, and continue compacting as water is squeezed from between the particles. Coagulation Coagulation is a process of aggregation or accumulation of colloidal particles to settle down as a precipitate. Substances like metals, their sulfides etc cannot be simply mixed with the dispersion medium to form a colloidal solution. Some special methods are used to make their colloidal solutions. Such kinds of sols are known as lyophobic sols. These kinds of colloidal solutions always carry some charge on them. All the particles of a given colloidal system have like charges because of which they don’t combine together and settle down. This is the main cause of the stability of colloids. If by any chance we can remove the charge present on the sol, the particles get closer to each other, and they accumulate to form aggregates and precipitate under the action of gravity. This process of accumulation and settling down of particles is further known as coagulation or precipitation. Coagulation Techniques The process of coagulation can be carried out in the following ways: 1. By electrophoresis: In this method, the colloidal particles are forced to move towards the oppositely charged electrodes, and then they are discharged and collected at the bottom. 2. By mixing two oppositely charged sols: In this type of coagulation equal amounts of oppositely colloids are mixed which mutually coagulates their charges resulting in the precipitation. 3. By boiling: Whenever we boil a sol, the molecules of the dispersion medium start colliding with each other and with the surface, this, in turn, disturbs the adsorption layer. This reduces the charge on the sol due to which the colloid particles come together, form aggregates and settle down. 4. By persistent dialysis: Under persistent dialysis parts of electrolytes are removed completely and the sol loses its stability and ultimately coagulates. Page | 69 Hardy Schulze Law of coagulation According to Hardy Schulze law, the quantity of electrolyte required to coagulate a definite amount of colloidal solution depends upon the valency of the coagulating ion.  The coagulating ions are the ions of electrolyte which carry the opposite charge of the colloidal particles.  The greater the valency of the coagulating ion, the greater the coagulation power.  The coagulation of a negatively charged sol (As2S3) is done by adding a positively charged colloid. Flocculation Flocculation is a process where a solute comes out of solution in the form of floc or "flakes." The term is also used in colloid chemistry to refer to the process by which fine particulates are caused to clump together into floc. The floc may then float to the top of the liquid, settle to the bottom of the liquid, or can be readily filtered from the liquid. According to the IUPAC definition, flocculation is a "process of contact and adhesion whereby the particles of a dispersion form larger-size clusters". Flocculation is synonymous with agglomeration and coagulation. For emulsions, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity. Flocculation is thus the initial step leading to further aging of the emulsion (droplet coalescence and the the ultimate separation of the phases). Flocculants, or flocculating agents, are chemicals that promote flocculation by causing colloids and other suspended particles in liquids to aggregate, forming a floc. Many flocculants are multivalent cations such as aluminium, iron, calcium or magnesium. These positively charged molecules interact with negatively charged particles and molecules to reduce the barriers to aggregation. In addition, many of these chemicals, under appropriate pH and other conditions such as temperature and salinity, react with water to form insoluble hydroxides which, upon precipitating, link together to form long chains or meshes, physically trapping small particles into the larger floc. Long-chain polymer flocculants, such as modified polyacrylamides, are manufactured and sold by the flocculant producing business. These can be supplied in dry or liquid form for use in the flocculation process. The most common liquid polyacrylamide is supplied as an emulsion with 10-40% actives and the rest is a carrier fluid, surfactants and latex. Emulsion polymers require activation to invert the emulsion and allow the electrolyte groups to be exposed. The following chemicals are used as flocculants:  Alum  Aluminium chlorohydrate  Calcium oxide  Iron(iii) chloride  Iron(ii) sulfate  Sodium aluminate  Sodium silicate The following natural products are used as flocculants:  Chitosan  Moringa oleifera seeds  Papain  A species of Strychnos (seeds) Page | 70   Isinglass Deflocculant A deflocculant is a chemical that is added to prevent a colloid from coming out of suspension. Filtration Filtration is technically defined as the process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of a membrane, called a filter. Filtration Process The mixtures are of two main types: homogeneous mixtures and heterogeneous mixtures. A homogeneous mixture is a mixture that is uniform throughout. A heterogeneous mixture is a mixture that is not uniform throughout, i.e., ingredients of the mixture are distributed unequally. Air is a homogeneous mixture of different gases, including oxygen, nitrogen, carbon dioxide, and water vapour. Homogeneous mixtures are sometimes also called solutions; especially when it is a mixture of a solid dissolved in a liquid. An example of a heterogeneous mixture is the mixture of sand in water. On shaking, sand will stay undissolved and are distributed unevenly. The sand particles floating around which will eventually settle to the bottom of the bottle makes it a heterogeneous mixture. Different types of filters are used to purify and for separation of mixtures from the contaminants. Based on the type of contaminant-large or small, filters of different pore sizes can be used, even at home. Water Filtration Methods 1. Activated Carbon Carbon removes contaminants by chemically bonding to the water that is poured into the system. Some are only effective at removing chlorine, which only improves taste and odor, while others remove more harmful contaminants, such as mercury and lead. It is important to note that carbon filters do not have the ability to remove inorganic pollutants such as nitrates, fluoride, and arsenic. Carbon filters are usually sold in block or granulated form to consumers. 2. Distillation Distillation is one of the oldest water purification methods. It vaporizes water by heating it to exceptionally high temperatures. The vapor is then condensed back into drinkable, liquid water. Distillation removes minerals, microorganisms, and chemicals that have a high boiling point. These filters cannot remove chlorine and many other volatile organic chemicals. 3. Deionization Deionization filters promote ion exchange in your water in order to remove salts and other electrically charged ions. If a contaminant lacks an electrical charge, it will be removed by these filters. Living organisms, such as viruses and bacteria will not be removed by these filters. 4. Ion Exchange Ion exchange technology uses a resin to replace harmful ions with ones that are less harmful. Ion exchange is often used to soften water since it has the ability to replace calcium and magnesium with sodium. In order for these filters to work for extended periods of time, the resin must be regularly “recharged” with harmless replacement ions. Page | 71 5. Reverse Osmosis Reverse osmosis works by moving water through a semi-permeable membrane in order to stop larger, more harmful molecules from entering. Since this process can only block molecules that are larger than water, contaminants with larger molecules, such as chlorine, cannot be removed. Reverse osmosis systems are able to remove more contaminants than carbon, making them a popular choice for many consumers. These filters consume far more water than they produce, so they are best suited for domestic use. 6. Mechanical Despite the fact that they cannot remove chemical contaminants, mechanical filters are an excellent option for consumers hoping to rid their water of sediments and cysts. Mechanical filters contain small holes that remove these contaminants, and they are sometimes used alongside other filtration technologies. If your water supply contains an undesirable amount of dirt and other particles, you may want to consider purchasing a mechanical filter. 7. Ozone Ozone is often employed alongside other technologies, and it is renowned for its ability to effectively kill large numbers of microorganisms. Ozone filters do not remove chemicals, but if you are worried about getting sick from your water, this may be your best option. 8. Carbon Block Carbon block filters are block-shaped filters that are composed of crushed carbon particles. These filters tend to be more effective than other types of carbon-based filters since they have a larger surface area. The rate at which water flows through these filters has a direct impact on their level of effectiveness. Fibredyne carbon block filters have a greater sediment- holding capacity than other types of block filters. 9. Granulated Carbon As the name suggests, these filters use small grains of carbon to filter your water. Due to their rather small surface area, granulated carbon filters tend to be slightly less effective than their block-shaped counterparts. Much like a carbon block filter, their level of effectiveness is strongly influenced by water speed. 10. Water Softeners Water softeners employ ion exchange technology in order to reduce the amount of magnesium and calcium in the water. This is especially useful if your plumbing fixtures are prone to accumulating mineral buildup. Since these harmful elements are replaced with sodium, water treated with this process tends to contain high levels of sodium. If you cannot consume large amounts of salt, it is best to avoid softened water. It is also unwise to water plants with softened water since it contains such high levels of sodium. Micro-filtration Micro-filtration (or MF for short) is one of the pressure-driven membrane processes in the series micro-filtration, ultra-filtration (UF), nano-filtration (NF) and reverse osmosis (RO). The micro-filtration process uses a membrane – a simple permeable material – which, in the case of micro-filtration, only allows particles smaller than 0.1 microns to pass through it. The micro- filtration membrane can consist of various materials like, for example, polysulfone, polyvinyldifluoride (PVDF), polyethersulfone (PES), ZrO2 and carbon. The pore size varies between 0.1 and 5 microns. Because the pores are large compared to other mentioned filtration Page | 72 techniques, pressure – needed to send the liquid through a micro-filter membrane – is limited to 0.1 to 3 bar. Ultrafiltration An ultrafiltration filter has a pore size around 0.01 micron. A microfiltration filter has a pore size around 0.1 micron, so when water undergoes microfiltration, many microorganisms are removed, but viruses remain in the water. Ultrafiltration would remove these larger particles, and may remove some viruses. Neither microfiltration nor ultrafiltration can remove dissolved substances unless they are first adsorbed (with activated carbon) or coagulated (with alum or iron salts). Nanofiltration A nanofiltration filter has a pore size around 0.001 micron. Nanofiltration removes most organic molecules, nearly all viruses, most of the natural organic matter and a range of salts. Nanofiltration removes divalent ions, which make water hard, so nanofiltration is often used to soften hard water. Reverse osmosis Reverse osmosis filters have a pore size around 0.0001 micron. After water passes through a reverse osmosis filter, it is essentially pure water. In addition to removing all organic molecules and viruses, reverse osmosis also removes most minerals that are present in the water. Reverse osmosis removes monovalent ions, which means that it desalinates the water. pH All the aqueous solutions may contain hydrogen and hydroxyl ions due to selfionisation of water. In addition to this ionisation, substances dissolved in water also may produce hydrogen ions or hydroxyl ions. The concentration of these ions decides whether the solution is acidic or basic. pH scale is a scale for measuring the hydrogen ion concentration in a solution. The 'p' in pH stands for ‘Potenz’ in German meaning 'power'. pH notation was devised by the Danish biochemist Sorensen in 1909. pH scale is a set of numbers from 0 to 14 which is used to indicate whether a solution is acidic, basic or neutral. Page | 73   Acids have pH less than 7  Bases have pH greater than 7  A neutral solution has pH equal to 7 The pH is the negative logarithm of the hydrogen ion concentration pH = –log10[H+] Common acids pH Common bases pH  HCl (4%) - 0  Blood plasma - 7.4  Stomach acid - 1  Egg white - 8  Lemon juice - 2  Sea water - 8  Vinegar - 3  Baking soda 9  Oranges - 3.5  Antacids 0 10  Soda, grapes - 4  Ammonia water - 11  Sour milk - 4.5  Lime water - 12  Fresh milk - 5  Caustic soda 4% (NaOH) - 14  Human saliva - 6-8  Pure water - 7  Coffee - 5.6  Tomato juice - 4.2  Blood - 7.35 to 7.45.  Rain water - approximately 7 Reduction Potential  Reduction involves gain of electrons, so the tendency of an electrode to gain electrons is called its reduction potential.  The equilibrium potential difference between the metal electrode and the solution surrounding it is called the electrode potential. It is also defined as the tendency of an electrode to lose or gain electrons. When a piece of metal is immersed in a solution of its own ions, a potential difference is created at the interface of the metal and the solution. The magnitude of the potential difference is a measure of the tendency of electrodes to undergo oxidation or reduction or the tendency to lose or gain electrons. The metal and ion represent the half cell and the reaction is half-reaction. The immersed metal is an electrode and the potential is due to reaction at the interface of the electrode and the solution is called the electrode potential. Thus electrode potential is the tendency of an electrode to lose or gain electrons. If the reduction takes place at the electrode, it is termed reduction potential. If the oxidation takes place at the electrode, it is called the oxidation potential M ⇢ M2+ + 2e– As metal ions start depositing on the metal surface this develops a positive charge on the metal rod. Since oxidation is just a reverse of reduction therefore reduction potential is obtained from the oxidation potential by simply changing the sign. In general for an electrode Oxidation potential = – Reduction potential Page | 74  The main distinction between the potential for oxidation and reduction is that the potential for oxidation shows a chemical element’s propensity to be oxidised. Conversely, the potential for reduction suggests the likelihood of a chemical element to be reduced. Soil consists of these major components Components of soil  Inorganic mineral matter about 40 to 45 per cent of the soil volume  Organic matter about 5 per cent of the soil volume  Water about 25 per cent of the soil volume  Air about 25 per cent of the soil volume The amount of each of the four major components of soil depends on the quantity of vegetation, soil compaction, and water present in the soil. A good, healthy soil has sufficient air, water, minerals, and organic material to promote and sustain plant life. The organic material of soil, called humus, is made up of microorganisms (dead and alive), and dead animals and plants in varying stages of decay. Humus improves soil structure, providing plants with water and minerals. The inorganic material of soil is composed of rock, slowly broken down into smaller particles that vary in size. Soil particles that are 0.1 to 2 mm in diameter are sand. Soil particles between 0.002 and 0.1 mm are called silt, and even smaller particles, less than 0.002 mm in diameter, are called clay. Some soils have no dominant particle size, containing a mixture of sand, silt, and humus; these soils are called loams. Composition of Soil and Atmospheric Air (%) Air O2 CO2 N2 Soil 20.05 0.25 79.20 Atmosphere 20.97 0.03 78.03 Soil Properties Optimal physical and chemical soil properties will lead to optimal soil biological properties and ideal soil health and productivity. Soil health indicators are used to assess physical, chemical and biological properties that lead to optimal soil functions such as efficient filtration, soil structure, nutrient and water cycling. Soil health indicators can be utilized Page | 75 for site specific management to recommend practices and management to improve soil properties in order to maximize soil health and productivity. Physical properties are the most visible and can be observed without using equipment like scanners or microscopes. They are reflective of the solid soil particles such as sand, silt and clay and the manner in which they are arranged. They can be used to define and classify soil types and horizons. In addition, they are very effective for field/lab demonstrations. They include:  Structure  Texture  Infiltration and Permeability  Aggregation and Aggregate Stability  Porosity  Bulk Density  Compaction  Crusting  Water Holding Capacity and Available Water  Moisture  Temperature Textural classification of soil USDA soil textural triangle Based on the proportion of sand, silt and clay particles, classification was made and standardized into twelve classes as shown in a triangular diagram. This triangle is known as USDA (United States Department of Agriculture) soil textural classification triangle. The twelve classes are as follows. 1. Sand, 2. Silt, 3. Clay, 4. Loam Sandy, 5. Clay silty, 6. Clay, 7. Clay-loam 8. Loamy sand, 9. Sandy loam, 10. Silty loam, 11. Sandy clay loam, and 12. Silty clay loam. For example, in a soil sample if the silt per centage is 20, sand per centage is 50 and clay per centage is 30, then these proportions are intersecting at sandy clay loam. (a) Sand - It contains < 50% clay and silt, and at least 70% of sand. Coarse, highly porous, large volume of non-capillary pore space, easy drainage, free air circulation, rapid decomposition of organic matter due to free air circulation, low water holding capacity, low nutrient content, low Page | 76 CEC, frequent irrigation requirement and easiness for workability of implements are the characteristic features of sandy soil. (b) Clay - I