eChapters

4.1 Introduction

Water pollution is the contamination of water by an excess amount of a substance that can cause harm to human beings and/or the ecosystem. The level of water pollution depends on the abundance of the pollutant, the ecological impact of the pollutant, and the use of the water. Pollutants are derived from biological, chemical, or physical processes. Although natural processes such as volcanic eruptions or evaporation sometimes can cause water pollution, most pollution is derived from human, land-based activities (Figure 4.2). Water pollutants can move through different water reservoirs, as the water carrying them progresses through stages of the water cycle (Figure 4.1). Water residence time (the average time that a water molecule spends in a water reservoir) is very important to pollution problems because it affects pollution potential. Water in rivers has a relatively short residence time, so pollution usually is there only briefly. Of course, pollution in rivers may simply move to another reservoir, such as the ocean, where it can cause further problems. Groundwater is typically characterized by slow flow and longer residence time, which can make groundwater pollution particularly problematic. Finally, pollution residence time can be much greater than the water residence time because a pollutant may be taken up for a long time within the ecosystem or absorbed onto sediment.

Ours is a Living Planet because ours is a Water Planet. The health of the Living Planet depends on the health of its water resources. Ironically, the health of its water resources is at stake. And so of its life! The waters of the Earth are in the grips of pollution. Much of the water is already polluted and the rest is increasingly becoming polluted. Water pollution, indeed, is one of the worst problems life on Earth is faced with. Water pollution is halting human progress and is phenomenally affecting all walks of human civilization. Water pollution is even putting a question mark on our sustainable future. This chapter presents the causes, magnitude, and consequences of water pollution and also suggests ways and means to prevent and control water pollution and also attempts to manage water resources.

Introduction
In the global perspective, water contamination is a significant issue. Every day, it is the cause of almost 14,000 deaths. The most valuable natural resource on Earth is water, which makes up more than 70% of its surface.
Definitions
• The term “water pollution” refers to the contamination of water bodies by human activity, which can be detrimental to the plants and organisms that call thesem bodies of water home. It can be characterized as any alteration in the quality of water brought about by human activity that makes it less suitable for any of its positive uses, actual or potential. Excess of any substance or heat that could endanger people, animals, or aquatic lifeMan’s actions alter the quality or composition of water, either directly or indirectly, making it unfit for any purpose.
Sources of Water Pollution
• Point source pollution, which is defined as pollution having a distinct source and point of entry into the water, making it easy to identify. It describes impurities that find their way into a waterway by a covert channel, like a ditch or pipe. For instance, contaminants include metals and organics in municipal and industrial discharge pipelines.

5.1 Introduction

The source of pollution are many and varied. The most critical are domestic sewage and industrial effluent discharging into rivers, lakes, ponds etc. Treatment facilities for domestic sewage in class 1 cities having population of more than 1,00,0000 and class 2 cities having population between 50,000 and 99,999 can process hardly 10% of the wastewater generated. Wastewater treatment facilities are difficult to quantify due to lack of continuous data. On an average, the treatment capacity in class 1 cities can handle only 60% of the wastewater collected and less than 15% of the total volume of wastewater generated.

The Indian industry has grown annually at an average rate of 5.5% during the last 50 years. Among different industrial sectors, water pollution is concentrated with in a few industrial sub-sectors mainly in the form of toxic wastes and organic pollutants. Out of the total pollution contributed by the industrial sub-sectors, 40% to 45% of the total pollutants can be traced to the processing of industrial chemicals and nearly 40% of the total organic pollution to the food products industry alone. Food products and agro-based industries together contribute 65% to 70% of the total industrial wastewater in terms of organic load. Blair T Bower, consultant, the Urban Institute, USA, remarks: "… If substantial further growth of Asia’s cities cannot be avoided and if the environmental disasters that could be associated with that growth are to be prevented, there is only one alternative: urban environmental quality management must be substantially improved throughout the region".

The total quantity of water used by the domestic and industrial sectors is much less than that consumed for irrigation. However, the wastewater released from the above sectors has a great concentration of pollutants, and is discharged at specific disposal points. Thus, the wastewater generated from domestic and industrial projects causes much more water pollution as compared to any other source.

Water is indispensable for our life. About 2/3 of earth is covered with water. No organism can survive without water. So keeping water free from any pollutant is very important. Water is said to be  “polluted” when it is hanged in its quality and composition directly or indirectly by man’s activity so that it becomes less suitable for drinking, domestic, agricultural or any other purpose. Polluted water transmits a large number of diseases in man. They are cholera, typhoid, dysentery, jaundice and other bacterial or viral diseases.  Water becomes polluted by the presence or addition on inorganic or organic substances or biological agents. Soil erosion, leaching of minerals from rocks, decaying of organic matter are natural sources of water pollution. There has been an alarming increase in the degradation of water quality in the recent past in the large cities and industrial areas.

Water pollution can be studied under the following heads—  (i) medium in which it occurs (surface water, ground water); (ii) habitat (lakes, estuaries and open seas); and (iii) type of pollutants (bacterial, metallic, thermal and radioactive).

It is estimated that the world requires nearly 70 per cent increase in agriculture production to meet the demand for food by the year 2050 based on current trends in population growth it can be achieved either by increasing land under cultivation (which is not possible), increasing the availability of more water for agriculture and efficient utilisation of available land and water resources. The best available option is to increase in productivity of unit of land for unit water. However, the availability of water for agriculture production cannot be presumed to be same year after year as the major source of water is precipitation more known for its uncertainty due to change in weather patterns from season to season and year to year all over the world. The element of uncertainty is increasing since the beginning of the present century due to climate change under the present circumstance, the crop production is practiced -
• In Irrigated Areas
• In Rainfed Areas
• Under Conserved Moisture Condition Without Any Source Of Irrigation
For increasing crop production under irrigated condition, it is necessary to identify crops and varieties that can produce more yield per unit of water even when there is some decrease in availability of water through irrigation. Therefore, the concept of water production function is used for evaluation of water use efficiency of the crops.

16.1 Introduction

Producing more crops, livestock, fish and forest products per unit of water use is an essence of water productivity and is highly essential for both food and environmental security. A variety of options exist for improving the productivity of water in agriculture through breeding, better management practices and supporting policies and institutions. It is imperative to identify a range of means to enhance water productivity in agriculture, assess their potential and the consequences of their adoption. The production systems to be considered can vary from purely rainfed to irrigated, and from dry zones to semi-humid monsoonal areas.

The productivity of water used in agriculture has almost doubled during 1961 to 2001, It is mainly due to increases in crop yields. Irrigated rice yields doubled and rain-fed wheat yields rose by 160% in that period, with little variation in water consumption per kilo of output. Globally, FAO estimates that water needs for food per capita halved from about 6 m³/day to less than 3 m³/day during 1961 to 2001 which is a significant saving and an equally significant gain for other water users.

According to an estimate, a 1% increase in water productivity in food production enables to save about 24 lit/day of water per head of population, while a 10% increase would equal current domestic water consumption. Importance of saving water in agriculture can be realised from the above observation.

The quality of irrigation water is a crucial factor for long-term soil productivity. Poor quality water if used for a long time can make the soil less productive or even barren, depending on the amount and type of constituents present in it and the texture of the soil in question. Low or marginally saline waters sometimes appear to stimulate crop growth because of the higher amounts of nutrient ions present.

Irrigation water always contains some soluble salts irrespective of its source. The suitability of waters for a specific purpose depends on the types and amounts of dissolved salts. Some of the dissolved salts or other constituents may be useful for crops. However, the quality or suitability of waters for irrigation purposes is assessed in terms of the presence of undesirable constituents, and only in limited situations is irrigation water assessed as a source of plant nutrients. Some of the dissolved ions, such as NO₃^- are useful for crops.

Collection of water samples

A representative water sample (500 ml) is collected in a glass or polyethylene bottle, which should be properly washed/rinsed with the same water that is being sampled. Floating debris or any other contaminant should be avoided while collecting the sample. After proper labelling (e.g. source of water, date of collection, and type of analysis required), the sample should be sent to the laboratory without undue delay.
Some of the anions such as SO₄ and NO₃ may be quite low in irrigation waters. Hence, the large volume of the sample has to be first concentrated by evaporating it to about 100 ml in order to obtain their detectable amounts.

Water is a critical and essential nutrient in poultry production, necessary in greater amounts than any other nutrient. It plays a vital role in various physiological processes such as digestion, metabolism, nutrient transportation, enzymatic and chemical reactions, regulating body temperature, and lubricating joints and organs. Water deprivation can have severe consequences on poultry health, impacting growth, egg production, and even leading to increased mortality if prolonged. Therefore, providing cool, clean water that is free from contaminants is crucial for maintaining poultry health and optimizing farm profitability.

Water Consumption in Poultry

Water consumption in poultry varies under different conditions. Generally, under thermo-neutral conditions, birds will consume approximately twice the amount of water as the amount of feed. However, water intake is influenced by several factors, including environmental temperature, relative humidity, dietary salt and protein levels, the productivity of the birds (growth rate or egg production), and the bird’s ability to reabsorb water in the kidneys. In poultry houses, water consumption tends to be higher in areas with more birds and higher ambient temperatures. Studies indicate that birds prefer water at about 10°C; when water temperatures exceed 27°C, both water intake and daily weight gain are significantly reduced.

Introduction

In the 21st century aquaculture has become one of the most important booming industries in the world. With just a mere contribution to the worlds fish production in 1960’s, and able to contribute to about nearly 50% in 2021, production from aquaculture has increased manifolds. Successful aquaculture relies on creating a suitable environment for growth of aquatic animals. Water quality has to be the most important component for successful aquaculture production. Throughout the farming period, it is necessary to maintain good water quality to ensure high survival and fast growth of cultured species. There are numerous water quality parameters that can impact the well-being of fish and crustaceans, most of which are discussed in this chapter.

Factors like salinity and water temperature play a critical role in assessing the suitability of a location for the cultivation of specific species. Additionally, factors such as alkalinity, turbidity, phosphorus, and nitrogen hold significance due to their impact on plant productivity, which, in turn, affects aquaculture production. As the cultivation progresses, factors like dissolved oxygen, carbon dioxide, ammonia, and others gain importance, as they have the potential to create stress for the cultured animals. This chapter offers an overview of the presence and behavior of each of these variables in both natural water environments and aquaculture ponds.

Water is the most important and abundantly required nutrient for poultry. A continuous supply of clean, fresh and wholesome potable water is essential for poultry. Poultry rearing is becoming more and more intensive with which the chances of the infectious diseases being sustained in the different flocks also increase. Consequently, the need for effective disease control measures to be adopted also gains further importance.

Most often, poultry farmers get alarmed only when the mortality level or death rate in a farm is high. However, even the existence of disease at a sub-clinical level may hinder the performance of the birds, in terms of body weight or egg number; such economic losses, sometimes relatively less and unnoticed, may mean the difference between success or failure in the poultry business. Treatment of a sick flock after the onset of any disease becomes costlier and more frequently impracticable. The recovered birds may not regain their production to original levels and may also continue as source of infection to other healthy birds. Hence, the adage ‘prevention is better than cure’ applies more to poultry industry than any other field.

Fish culture is an age old tradition modified and improved by several scientific inventions. Farmers can easily take up fish culture in village ponds, tanks or any water body and can improve their financial position substantially. Pond aquaculture is the most common method of fish culture throughout the world. For successful aquaculture of fish, molluscs, crustacean and even aquatic plants, the water and soil in which fish are grown should have favourable conditions for their growth which, in turn, is intimately linked with several physical, chemical, biological characteristics of water and management practices adopted. Physical and chemical characters of the soil and water will affect the primary and secondary production of water bodies.

The survival and production of fish in a pond is dependent on the primary and secondary production. Primary production depends on the water quality parameters. Phytoplankton make carbohydrate using sunlight and releases oxygen. This is the major source of energy and oxygen in the ecosystem. Zooplankton which feed on the phytoplankton form major source of food for the fishes.

In Indian aquaculture hatcheries, water quality management is crucial for successful fish seed production. It involves maintaining key parameters like pH, dissolved oxygen, alkalinity, and temperature within the optimal range for the specific fish species being bred. Proper management techniques include monitoring water quality, ensuring adequate water flow, maintaining appropriate feeding practices, implementing aeration and oxygenation systems, and implementing effective waste management.
PARAMETERS
Fish health is closely linked to a delicate equilibrium between the host, potential pathogens, and their aquatic environment. Any disturbance—particularly in water quality—can induce stress in fish, making them more vulnerable to diseases. Therefore, understanding and managing key water quality parameters is essential for optimizing fish growth and survival.
Dissolved Oxygen
The optimal range for dissolved oxygen (DO) in pond water is between 5 mg/ litre and saturation, ensuring healthy fish growth. Aeration is an effective method to improve DO levels. Common aerators include paddle-wheel and aspirator types. In high-aeration ponds, improper placement of aerators along pond edges can generate strong currents that erode the pond bottom. Hence, strategic placement is crucial.
Temperature
Temperature governs fish metabolism by affecting molecular properties and biochemical reaction rates. Ideal temperature ranges vary: 14–18°C for coldwater species and 24–30°C for warmwater species. In controlled environments like hatcheries, water temperature can be regulated. In large ponds, aerator operation during calm, warm afternoons helps disrupt thermal stratification. Tree planting for shade may help regulate temperature but can reduce sunlight penetration, thus lowering pond productivity.

Aquaculture is the cultivation of fish, molluscs, crustaceans (shell fish) and aquatic plants in controlled conditions, provides an increasingly significant proportion of food production globally. The sector has represented the greatest growth of all food production systems in the last two decades and an estimated 10% yearly increase in output is likely to bring productivity to a predicted 47 million tonnes in the year 2010 (Pedini and Shehadeh, 1997). Significantly, the greatest contribution to total production and the greatest rate of uptake of aquaculture activity is in the developing world. More than 82% of the total global yield in 1999 was produced by developing countries (GESAMP, 2000) and growth rates between 1984 and 1995 were six times higher than that from developed countries (Rana, 1997; Tacon, 1996).

Learning about water chemistry is often neglected by most of the aquarium owners. By understanding the concepts of water chemistry, they can considerably improve success rate in rearing healthy fishes. It is well known that the quality of water has a direct impact on the health of the fish. But many aquarium owners do not understand the basic internal chemistry of the water, nor do they understand how to correct it or safely adjust it. Until the basics of water chemistry is understood and some common water maintenance techniques are learnt, it will be difficult to maintain a healthy and safe environment for the fish in tank. The water quality is by far the single most important factor for the healthy fish, and the more is known, the better management is expected.

Fish depends for their basic necessities on the water in which they live. The most characteristic feature of an aquarium system is, therefore, the quality of the water available in tanks/aquarium. This water must be obtained from some source, pre-treated to make it suitable for the fish, delivered to the fish in sufficient quantities and maintained in good condition. The water supplied to an aquarium is not pure, but it contains dissolved and particulate materials, some are necessary for up keep of the fish and rests are harmful. Contamination may occur not only at source or from the animals, but often takes place within the aquarium from the materials used for its construction. The number of fish that can be maintained within the aquarium is said to be according to the quality and quantity of the water supplied to an aquarium. However, it is rarely the quantity of water per unit which limits the carrying capacity. The capacity is usually set by the requirement of dissolved oxygen and the accumulation of toxic metabolic products in the aquarium.

2.1 Historical Development

We have seen in Chapter 1 that modeling is about establishing cause effect relationship. Perhaps one of the earliest attempts in this direction is made as early as 1848 in Germany where it was tried to establish a relation between purity and pollution to the occurrence of certain biological organism. But as far as water quality modeling is concerned the first major breakthrough in this direction is the effort of Streetor and Phelps (1925) in oxygen sag curve. They developed model for estimating DO and BOD in Ohio River. The work of O’Conner (1962) for bacteria models are major milestone in pre-computer era modeling.

With the advent of computer during 1960s complicated kinetics and time variable simulation came into being. Most of the workers presented their efforts in terms of linear programming based water management models concerning waste discharge. Thomann(1963) has formulated linear programming based models for dissolved oxygen in an estuary. So a stage is set for study of eutrophication through modeling, but the problem is determination of values of various parameters in these equations.

During 1970s models expanded in terms of complexities mainly because of enhanced computational facilities. Two dimensional and dynamic framework has started replacing one dimensional steady state configurations. In the same year, Di Toro presented an analysis of the steady state two dimensional concentration distribution that results in the horizontal plane from the continuous discharge of a non-conservative substances (DO and BOD) into an infinite body of water.

Water quality standards (Classification)

Some countries have established national standards and criteria for evaluation and classification of water quality. The classification of irrigation waters has been made according to one or more of the following criteria.

1.    Salinity or total concentration of soluble salts (EC)
2.    Sodicity hazards (SAR)
3.    Alkalinity hazards (RSC)
4.    Combined evaluation on the basis of EC and SAR by USSL diagram
5.    Combined evaluation on the basis of EC and Adj. SAR
6.    Combined evaluation on the basis of EC, SAR and RSC

1. Relative Water Content

Relative water content (RWC) is an important parameter to measure the water status of plant tissue. High RWC, under moisture stress, denotes ability of plants to tolerate drought. (Ritchi et al. 1990). RWC and water potential have often been reported as indicators of drought tolerance (Schonfeld et al. 1988).

Leaf water status may be estimated by measuring the RWC following Barrs and Weatherlay’s (1962) method as given below:

4.1 Introduction

A reservoir that collects and harvests in-situ rainfall as well as runoff from the catchment area can be used for many purposes: the most important of which is the supply of water to crops as supplemental irrigation. The water of the reservoir can be used for domestic and industrial uses. It is also a good source for recreational use. Total water demand of the reservoir including irrigation to different crops in different seasons, domestic and other non-agricultural uses are to be assessed. While estimating the crop water requirement and irrigation requirement, various crops to be grown in the service area of the reservoir, their water requirements, crop duration, extent of coverage and water management practices followed are to be taken into consideration. Multiplying the irrigation requirement with crop coverage area, volumetric irrigation water requirement of crop can be found out. Summation of irrigation requirement of all crops grown in service area of the reservoir gives total irrigation demand of the reservoir.

4.2 Water and Irrigation Demand of Crops

Of the various demand of water from the reservoir, irrigation demand of crops grown in the command area of the reservoir is very important. Most of the crop water demand is met from rainfall. However, when the rainfall is deficient to meet the crop water demand, then the deficit is met from the stored water of the reservoir in the form of irrigation, more commonly called as supplemental irrigation. The irrigation to the crops is required mostly to meet the evapotranspiration requirement of the crop. Before discussing the water and irrigation demand/requirement of crops, it is essential to know some commonly used terms frequently used.