eChapters

11.1 Introduction

Salinity is the saltiness or dissolved salt content of a body of water. The technical term for saltiness in the ocean is halinity, from the fact that halides, chloride specifically are the most abundant anions in the mix of dissolved elements. In oceanography, it has been traditional to express halinity not as percent, but as parts per thousand (ppt ), which is approximately grams of salt per liter of solution. In other disciplines chemical analyses of solutions, and thus salinity is frequently reported in mg/L or ppm (parts per million). Prior to 1978, salinity or halinity was expressed as % usually based on the electrical conductivity ratio of the sample to “Copenhagen water”, an artificial sea water manufactured to serve as a world “standard”(Lewis, E.L 1980). In 1978, oceanographers redefined salinity in Practical Salinity Units (psu): the conductivity ratio of a sea water sample to a standard KCl solution (UNESCO, 1981a) (UNESCO, 1981b). Ratios have no units, so it is not the case that 35 psu exactly equals 35 grams of salt per litre of solution (UNESCO, 1985).

These seemingly esoteric approaches to measuring and reporting salt concentrations may appear to obscure their practical use; but it must be remembered that salinity is the sum weight of many different elements within a given volume of water. It has always been the case that to get a precise salinity as a concentration and convert this to an amount of substance required knowing much more about the sample and the measurement than just the weight of the solids upon evaporation. For example, volume is influenced by water temperature; and the composition of the salts is not a constant. Saline waters from inland seas can have a composition that differs from that of the ocean. For the latter reason, these waters are termed saline as differentiated from ocean waters, where the term haline applies.

10.1 Introduction

Biochemical Oxygen Demand (BOD) is a chemical procedure for determining how fast biological organisms use up oxygen in a body of water. It is usually performed over a 5 day period at 20 C. It is used in water quality management and assessment, ecology and environmental science. BOD is not an accurate quantitative test, although it could be considered as an indication of the quality of a water source.

10.2 Typical BOD values

Most pristine rivers will have a 5-day BOD of less than 1 mg/l. Moderately polluted rivers may have a BOD value in the range of 2 to 8 mg/l. Municipal sewage that is efficiently treated by a three stage process would have a value of about 20 mg/l. Untreated sewage varies, but averages around 600 mg/l in India and as low as 200 mg/l in the U.S., or where there is severe groundwater or surface water infiltration. Slurry from dairy farms is around 8000 mg/l and silage liquor around 60000 mg/l.

9.1. Introduction

Oceans (from Okeanos in Greek) are saline waters that cover almost three quarters (71%) of the surface of the Earth. The area of the oceans is 361 million sq. km., and nearly half of the world’s marine waters are over 3,000 meters deep.

Though somewhat arbitrarily divided into several “separate” oceans, these oceans are in fact one global, interconnected body of salt water, often called the World Ocean. The major divisions are defined in part by the continents and a variety of archipelagos, and are labeled the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean, and the Arctic Ocean. Smaller regions of the oceans are called seas, gulfs and straits.

There are a some smaller bodies of salt water that are not interconnected with the World Ocean. These are not considered to be oceans or parts of oceans, though some of them have been given the name, sea.

Geologically, an ocean is an area of oceanic crust covered by water. Oceanic crust is the thin layer of solidified volcanic basalt that covers the Earth’s mantle where there are no continents. From this point of view, there are three “oceans” today: the World Ocean, and the Black and Caspian Seas that were formed by the collision of Cimmeria with Laurasia. The Mediterranean Sea is very nearly its own “ocean”, being connected to the World Ocean through the Strait of Gibraltar, and indeed several times over the last few million years movement of the African Continent has closed the strait off entirely, making the Mediterranean a fourth “ocean”.

8.1 Introduction

A lake is a body of water or other liquid of considerable size surrounded entirely by land (Fig. 8.1). A vast majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes. In ecology, the environment of a lake is referred to as lacustrine.

Fig 8.1 A Typical Lakes

Large lakes are occasionally referred to as “inland seas” and small seas are occasionally referred to as lakes. Smaller lakes tend to put the word “lake” after the name, as in Green Lake, while larger lakes often invert the word order, as in Lake Ontario, at least in North America. The term lake is also used to describe a feature such as Lake Dal, which is a wet basin most of the time but may become filled under seasonal conditions of heavy rainfall and snowfall. Many lakes are artificial and are constructed for hydro electric power supply, recreational purposes, industrial use, agricultural use, or domestic water supply.

7.1 Introduction

The coast is one of the most important boundaries in the world. It separates the marine part of the world from the continents. It separates the salt-water communities from fresh water communities; it separates land life from water borne life but amphibians living both environments (Fig. 7.1).

Some of the marine organisms move towards estuary for reproduction with less water salinity. The coastline as such is not a stable. It fluctuates in place over considerable distances due to erosion and sedimentation, but also due to the relative change of sea level with respect to land. The coastal zone is thus a very mobile part of the earth from a geographical point of view. Due to its specific geophysical properties, the coast is also a very important area for the development of flora and fauna. There is hardly any other part of the world that houses such a variety of species, both in flora and fauna.

The abundance of opportunities along the coast has also attracted a lot of human activities. The coastal zone has become an indispensable resource for mankind. It provides excellent opportunities for fisheries, housing, recreation, transport, defense purpose, industrial activities and many others. The influx of man with their social and economic activities, their needs for safe housing, food, drinking water, and with the tremendous quantities of waste they are producing poses at the same time a serious threat to the unique features of the coastal zone. It is therefore necessary to study this valuable region so as to prevent that competing activities are gradually causing depletion of the resources in the coastline. The following figures (Fig. 7.1and 7.2) show the typical coastal area of rocky coast and sandy coast.

6.1. Introduction

A river is a large natural waterway. The source of a river may be a lake, a spring, or a collection of small streams, known as headwaters. From their source, all rivers flow downhill, typically terminating in the ocean. The mouth, or lower end, of a river is known as its base level.

A river water is confined to a channel, made up of a stream bed between banks. Most rainfall on land passes through a river on its way to the ocean. Smaller side streams that join a river are tributaries. The scientific term for any flowing natural waterway is a stream; so in technical language, the term river is just a shorthand way to refer to a large stream. Rivers throughout history have been the source and support for civilization, and many major cities today are near a river of some sort (Fig. 6.1).

6.1.1 Topography

A river conducts water by constantly flowing from a higher to a lower elevation, thereby converting the potential energy of the water into kinetic energy. It starts to form loops and snakes through the plain by eroding the river banks. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake from the cut off section. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths, if conditions permit. Rivers, whose mouths are in saline tidal waters, may form estuaries. River mouths may also be rias.

5.1 Introduction

The water quality modeling methodologies are started from conceptual models such as defining the problem in a particular region of interest like fresh water ecosystem, coastal ecosystems, ocean ecosystems, the following methodology can be studied carefully for water quality modeling.

Identification of problems in the region of interest

Monitoring of field data using standard methods like APHA, USGS, BIS etc.

Evaluation of primary data for the toxins, higher amount of concentration from the ambient conditions

Processing of primary data to secondary data

Based on the primary data and secondary data, suitable modeling software can be used. If the temperature of the region is higher than the ambient, it should be used Qual2E, MIKE21 etc.

Modeling results can be compared with field data for calibration and validation.

4.1 Introduction

The developed or commercially available models can be applied for any water bodies such as fresh water lakes, ponds, rivers, estuaries and marine ecosystems. The predicted results can be compared with proved with field data and existing approved models and applies to the other such ecosystems. In this chapter, we can discuss about modeling of water bodies, water quality model, spatial discretizafion, modeling pollutants and toxicants, concentration modeling, hydrodynamic mixing zone analysis.

4.2 Modeling of Water bodies

The need for predictive water quality modeling has arisen largely as a result of increased eutrophication of lakes throughout the world (Forsberg, 1987; Canfield and Hoyer, 1988). The most common modelling approach is exemplified by the development and application of steady state, input-output models. Generally, nutrient concentrations are calculated from net inputs and chlorophyll a concentration is predicted by correlation with the limiting nutrient, most often phosphorus (Dillon and Rigler, 1975; Canfield and Bachmann, 1981; OECD, 1982).

Factors that can also influence phytoplankton biomass, such as light, climate, biological interactions and internal loading of nutrients, are not considered. Further more, the assumption that a lake is a continuously mixed system is very restrictive and only applicable at discrete times of the year. As a result, the shortcomings of such approaches include an inability to make predictions in the face of varying physical and biological conditions, and a failure to offer insights into the determinants of changing water quality.

3.1 Introduction

By the end of the twentieth century one of our most important scientific accomplishments has been the explicit realization that the human population is changing the earth system. Some of these changes are occurring at a remarkable rate. We know, with certainty, that human activities are changing land use, habitats, the chemistry of the Earth’s atmosphere and water, rates and balance of biogeochemical processes, and diversity of life on the planet (Vitousek et al. 1997). One prominent mode of human disturbance has resulted from activities that mobilize the nutrient elements nitrogen and phosphorus through land clearing, production and applications of fertilizer, discharge of human waste, animal production, and combustion of fossil fuels (Nixon 1995).

As a result of these activities, surface waters and ground waters throughout the world now have elevated concentrations of N and P compared to concentrations even in the middle of the 20th century. Our mobilization of N and P has accelerated the fluxes of these elements to coastal waters, and fertilization of coastal ecosystems is now a serious environmental problem because it stimulates plant growth and disrupts the balance between the production and metabolism of organic matter in the coastal zone. Coastal eutrophication is a recently recognized phenomenon (Nixon 1995), and scientific investigation of this human disturbance has progressed for only a few decades, so our conceptual model of the problem is evolving rapidly. Here, I describe 2 phases in the evolution of our conceptual model of how nutrient enrichment disrupts coastal ecosystems, and then finish with a view to the future, suggesting critical questions that must be answered as we work to advance and broaden our understanding of this complex environmental problem. This examination of conceptual models is designed as a complement to the excellent general reviews of coastal eutrophication (Vollenweider 1992, Heip 1995, Nixon 1995, Jørgensen & Richardson 1996, National Research Council 2000).

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.

A model is something that mimics the behavior of some real system of interest. Our interest here will be in water quality models, which are usually equations, and which predict some result based on factors that influence that result. A water quality model is a representation of a real system. The essence of a good water quality model is that it is simple in design and exhibits the basic properties of the real system that we are attempting to understand. The model should be testable against empirical data. The comparisons of the model to the real system should ideally lead to improved mathematical models. The model may suggest improved experiments to highlight a particular aspect of the problem, which in turn may improve the collection of data. Thus, modeling itself is an evolutionary process, which continues toward learning more about certain processes rather than finding an absolute reality.

Water pollution is a large set of adverse effects upon water bodies such as lakes, rivers, oceans, groundwater caused by human activities. Although natural phenomena such as volcanoes, storms, earthquakes etc. also cause major changes in water quality and the ecological status of water while these are not deemed to be pollution. Water pollution has many causes and characteristics. Increases in nutrient loading may lead to eutrophication. Organic wastes such as domestic sewage and farm waste impose high oxygen demands on the receiving water leading to oxygen depletion with potentially severe impacts on the whole ecosystem. Industrial discharge a variety of pollutants in their wastewater including heavy metals, organic toxins, oils, nutrients, and solids. Discharges can also have thermal effects, especially those from thermal and nuclear power stations, and these too reduce the available oxygen. Siltbearing runoff from many activities including construction sites, forestry and farms can inhibit the penetration of sunlight through the water column restricting photosynthesis and causing blanketing of the lake or river bed which in turns damages the ecosystems the process is called as eutrophication.

Pollutants in water include a wide spectrum of chemicals, pathogens, and physical chemistry or sensory changes. Many of the chemical substances are toxic or even carcinogenic. Pathogens can obviously produce waterborne diseases in either human or animal hosts. Alteration of water’s physical chemistry include acidity, conductivity, temperature, and excessive nutrient loading. Even many of the municipal water supplies in developing countries can present health risks leads to many diseases.

Introduction

The resource conservation technologies (RCTs) is primarily focussed on resource savings through minimal tillage, ensuring soil nutrients and moisture conservation through crop residues and growth of cover crops, and adoption of spatial and temporal crop sequencing. These practices have long been practised by the farmers in the Indo Gangetic Plains (IGP) but it got eroded in recent times due to various geo-socio economic- political reasons. This region (10.5 million ha) comprises of Punjab, Haryana, Uttar Pradesh, Himachal Pradesh, Bihar and West Bengal and have major share in production of rice and wheat due to adoption of green revolution technologies followed by area expansion. It has been reported that rice-wheat system has strained the natural resources of this region (Swarup and Singh, 1989; Kumar and Yadav, 1993; Lal et al., 2004). In present scenario there is little scope to meet future target by earlier approaches like area expansion and intensive use of natural resources. Therefore, RCTs can be regarded as energy, water and labour efficient system to sustain soil health and production environment and produce more at less cost (Jat et al., 2012; Gathala et al., 2011b).

Major emphasis is given upon the RCTs components like zero/reduced tillage, direct seeded rice, crop residue management and crop diversification. However, other RCTs like site specific nutrient management, leaf colour chart, laser land leveller, nutrient use efficient genotypes, integrated crop and pest management provide options to the farmers as per their resource endowment.

Introduction

Persistent income from agriculture is most important for sustaining the farming sector. Conservation agriculture (CA) is a resource-saving agricultural production system that aims to achieve production intensification and high yields while enhancing the natural resource base through compliance with three interrelated principles, along with other good production practices of plant nutrition and pest management (Abrol and Sangar, 2006). Conservation agriculture is largely promoted as one of the few win–win technologies affordable to farmers, in the sense that potentially it improves farmers’ yields (in the long term) at the same time conserving the environment. CA is described by FAO (http://www.fao.org.ag/ca) as a concept for resource saving agricultural crop production which is based on enhancing the natural and biological processes above and below the ground. As per FAO definition CA is to a.) Achieve acceptable profits, b.) High and sustained production levels, and c.) Conserve the environment. It aims at reversing the process of degradation inherent to the conventional agricultural practices like intensive agriculture, burning/removal of crop residues. Shifting from tillage-based agriculture to no-tillage CA systems removes unsustainable elements in the current tillage based systems and replaces them with CA elements that make the production systems profitable and ecologically sustainable. Conservation agriculture offers an opportunity for arresting and reversing the downward spiral of resource degradation, decreasing cultivation costs and making agriculture more resource – use-efficient, competitive and sustainable.

Introduction

Precise and continuous measurement the greenhouse gases (GHGs) fluxes/ emissions in agricultural systems are required for accounting and budgeting of carbon. Further, the long-term measurements of GHGs fluxes are equally important as precise measurement. Therefore, high frequency and long-term measurement of GHGs across the cropping systems are essential for chalking out the GHGs emissions mitigation strategies. Various technologies with definite working principles are used for estimation of GHGs emissions in agriculture.

Greenhouse Gases Estimation Techniques

Two basic principles are followed to estimate greenhouse gases in agriculture. One is the collection of GHGs from the field and subsequent analysis of the concentration of gases through gas chromatography (GC). Another principle is based on sensors measurement with the help of infrared gas analyze (IRGA). The two techniques used for the measurement are (i) ‘closed chamber method’ (manual/automatic), and (ii) ‘sensor-based method’. Generally, the GHGs fluxes in agricultural crop field are estimated by ‘closed chamber method’ for methane (CH₄) and nitrous oxide (N₂O). And for carbon dioxide (CO₂) measurement either soil respiratory chamber or canopy chamber is used that measures CO₂ with the help of infrared gas analyzer (IRGA).

Introduction

Intensive soil tillage, burning of crop residues and over use of fertilizer and irrigation water under current agricultural practices has accelerated the pace of degradation in Indian agriculture. Intensive soil tillage increases soil erosion and nutrient runoff into nearby waterways. Crop residue burning resulting in loss of plant nutrients and release of greenhouse gases (GHGs) in the atmosphere. Imbalanced use of chemical fertilizer leads to soil compaction, slows down the fertilizer utilization rate and contaminates the local environment. Increasing demand of irrigation water causes water shortage and harms the environment in several ways including increased salinity, nutrient pollution, and the degradation of flood plains and wetlands. In the face of these management and environmental challenges, there is a need to formulate such agricultural practices which improve the productivity of natural resources as well as of external inputs and help to prevent soil degradation. Conservation agriculture (CA) practices such as reduced tillage, residue retention and proper crop rotations offer such solutions. CA also helps in making agricultural systems more resilient to climate change and safeguard ecosystem services.

Introduction

Conservation of biodiversity and mitigation of global warming are two major environmental challenges today. In the context of climate change and the global carbon cycle, the relationship between plant biodiversity and soil organic carbon (SOC) sequestration has become a subject of considerable scientific interest. The Earth’s terrestrial vegetation plays a pivotal role in the global carbon cycle. Not only are tremendous amounts of carbon stored in the terrestrial vegetation, but large amounts are also actively exchanged between vegetation and the atmosphere. Anthropogenic perturbations exacerbate the emission of CO₂ from soil caused by decomposition of soil organic matter (SOM) or soil respiration (Schlesinger, 2000). The emissions are accentuated by agricultural activities including tropical deforestation and biomass burning, plowing, drainage of wetlands and low-input farming or shifting cultivation. In addition to its impact on decomposition of SOM, macroclimate has a large impact on a fraction of the SOC pool which is active. Conversion of natural to agricultural ecosystems increases maximum soil temperature and decreases soil moisture storage in the root zone, especially in drained agricultural soils (Lal, 1996). Thus, land use history has a strong impact on the SOC pool (Pulleman et al., 2000). The dynamic relationship between plant biodiversity and SOC depicts that any land use practices that increase vegetative cover, or reduce its removal, could have an influence on the global carbon budget by increasing the terrestrial carbon sink.

Introduction

The inevitability of detrimental effects of climate change is looming large not only on the sustenance of agriculture, but also on the survival and progress of mankind. Estimates by the Organization for Economic Cooperation and Development (OECD) reveal that the atmospheric concentration of GHG would exceed 680 parts per million (ppm) CO₂-equivalents by 2050, which is about 50% higher than baseline year 2010 (OECD, 2012). Additionally, global temperature is predicted to increase by 2°C within this period, resulting in meansea level rise and erraticweather conditions. Consequently, the catastrophic effects on food consumption pattern by the end of 2050 will create malnutrition in at least 290 million people. Agricultural crops provide 63% of the human protein, and additionally supply almost 100% protein to the livestock, which are the second major sources of protein in human diet. Altogether, the detrimental effect of climate change on agriculture would make about 300 million additional people malnourished. Add to that a 2.7 billion increase in human population by 2050, coupled with shortage of water availability that would affect 3.9 billion people by 2050, and one can easily perceive the grim scenario for our kind in not so distant future.

Introduction

The basic needs of life are food, clothing and shelter. In the 21^st century a fourth need added to mankind is energy. According to the laws of physics, energy is defined as capacity to do work. Energy, economics and the environment are mutually dependent. Also, there is very close relationship between agriculture and energy. The level and pattern of energy use in agricultural production system depends on variety of agronomic and socio-economic factors. Energy use in agriculture encouraged maximization of yields from limited available arable land, minimization of labour intensive operations and improving standard of living. Efficient and effective energy use in agriculture is one of the conditions for sustainable agricultural production, since it provides financial savings.

Introduction

India agriculture is now at turning point as we have travelled a long way after the advent of green revolution. Over the past four to five decades our strategies, policies and actions were guided by goals of ‘self-sufficiency’ in foodgrains production via green revolution. Indian agriculture has been successful in achieving increased food grains production albeit at a low level of satisfaction. While the mission of increasing foodgrains production stands somehow achieved, these gains were accompanied by widespread problems of resource degradation and high factor productivity, which now pose a serious challenge to the continued ability to meet the demand of an increasing population and lifting our people above the poverty line (Tan et al., 2010). Indian agriculture has reached a point where it must seek new directions – those by way of strategies, policies and actions which must be adopted to move forward addressing sustainable intensifications. The past strategies to increase food grains production, however, have resulted in massive exploitation of natural resources, contributing to unsustainable growth; there is need to change this approach in the future. This will call for strategies, which are different than the ones we adopted in the ‘green revolution’ era. High levels of fertilizer use and decreasing resource use-efficiency are increasingly contributing to groundwater pollution and increased emissions of green-house gases (GHGs) (Gupta, 2004). High level uses of pesticides in many areas have become a major health hazard. Thus, with continuously deteriorating resources, widespread problem of soil and water contamination and eroding ecological foundation, sustainability of agriculture is becoming highly questionable (Conway and Barbier, 1990). There is need to seriously debate on the strategies required to ensure that agriculture continues to play a critical role in the overall development.

Introduction

Conservation tillage is a model of sustainable agriculture as it leads to profitable food production while protecting and even restoring natural resources. Conservation agriculture benefits farmers because it reduces production costs and increases yields, but it also has positive impacts on the whole society: enhancement of food security thanks to a better soil fertility, improvement of water quality, reduction of erosion and mitigation of climate change by increasing carbon sequestration. Conservation agriculture (CA) systems are also less sensitive to extreme climatic events and therefore contribute to the adaption of climate change and the resilience of agricultural systems. Hence, CA becomes a fundamental element of sustainable production intensification, combining high production with the provision of environmental security.

CA is based on healthy functioning of the whole agro-ecosystem with a maximum attention and focus on the soil. The soil is the entry point and it has to be considered not only as simple physical support to roots and plants, but as a living entity with its physical, chemical and biological characteristics. The focus of CA embraces not only the nutrient contents of the soil but also its biological and structural status, which are determinants of sustained productivity.

The paradigm of CA is that an undisturbed soil has the opportunity to develop and produce healthier plants. Soil life can develop in a stable habitat in quantity and quality better than on tilled soils, the structural integrity of soil is maintained, so continuous vertical macro-pores are not destroyed and remain as drainage channels for rainwater into the soils. Seeding under conditions of minimum soil disturbance is achieved by direct seeding through the mulch cover without tillage.