Water quality monitoring: a practical guide to the design and implementation of freshwater quality studies and monitoring programmes

Full text

Water Quality Monitoring. A practical guide to the design and
implementation of freshwater quality studies and monitoring programmes
ISBN 0-419-21730-4
Edited by
Jamie Bartram and Richard Ballance
Published on behalf of
United Nations Environment Programme

World Health Organization
E & FN SPON
An Imprint of Chapman & Hall
London
· Weinheim · New York · Tokyo · Melbourne · Madras
Published by E&FN Spon, an imprint of Chapman & Hall,
2-6 Boundary Row, London SE1 8HN, UK
Chapman & Hall, 2-6 Boundary Row, London SE1 8HN, UK
Chapman & Hall GmbH, Pappelallee 3, 69469 Weinheim, Germany
Chapman & Hall USA, 115 Fifth Avenue, New York, NY 10003, USA
Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 2-2-1 Hirakawacho, Chiyoda-
ku, Tokyo 102, Japan
Chapman & Hall Australia, 102 Dodds Street, South Melbourne, Victoria 3205, Australia
Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East, Madras 600 035,
India
Distributed in the USA and Canada by Van Nostrand Reinhold,
115 Fifth Avenue, New York, NY 10003, USA
First edition 1996
© 1996 UNEP/WHO
Printed in Great Britain by TJ Press (Padstow) Ltd, Padstow, Cornwall
ISBN 0 419 22320 7 (Hbk) 0 419 21730 4 (Pbk)
Apart from any fair dealing for the purposes of research or private study, or criticism
or review, as permitted under the UK. Copyright Designs and Patents Act, 1988, this
publication may not be reproduced, stored or transmitted, in any form or by any
means, without the prior permission in writing of the publishers, or in the case of
reprographic reproduction only in accordance with the terms of the licences issued by
the Copyright Licensing Agency in the UK, or in accordance with the terms of licenses
issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries
concerning reproduction outside the terms stated here should be sent to the publishers
at the London address printed on this page.

The publisher makes no representation, express or implied, with regard to the
accuracy of the information contained in this book and cannot accept any legal
responsibility or liability for any errors or omissions that may be made.
A catalogue record for this book is available from the British Library
Publisher’s note
This book has been produced from camera ready copy supplied on behalf of the co-
sponsoring organizations.
Printed on acid-free text paper, ma nufactured in accordance with ANSI/NISO Z39.48-
1992 and ANSI/NISO Z39.48-1984 (Permanence of Paper).
Ordering information
Water Quality Monitoring
A Practical Guide to the Design and Implementation of Freshwater Quality
Studies and Monitoring Programmes
1996, 400 pages
published on behalf of WHO by F & FN Spon
11 New Fetter Lane
London EC4) 4EE
Telephone: +44 171 583 9855
Fax: +44 171 843 2298
Order on line: http://www.earthprint.com/cgi-
bin/ncommerce3/ExecMacro/ep/owncats.d2w/report?orgnbr=103
FOREWORD
According to Agenda 21 of the United Nations Programme of Action following the Earth
Summit in Rio de Janeiro:
“The complex interconnectedness of freshwater systems demands that freshwater
management be holistic (taking a catchment management approach) and based on a
balanced consideration of the needs of people and the environment. The Mar del Plata
Action Plan has already recognised the intrinsic linkage between water resource
development projects and their significant physical, chemical, biological, health and
socio-economic repercussions”
The approaches and methods for water quality monitoring described in this handbook
are based upon the experience gained, over two decades, with the design and
establishment of the global freshwater quality monitoring network, GEMS/WATER. The
GEMS/WATER programme is co-sponsored by the United Nations Environment
Programme (UNEP) and the World Health Organization (WHO), together with the
United Nations Educational, Scientific and Cultural Organization (UNESCO) and the
World Meteorological Organization (WMO). One of the goals of GEMS/WATER is:
“to strengthen national water quality monitoring networks in developing countries,
including the improvement of analytical capabilities and data quality assurance”.

This handbook supports this goal by providing a practical tool for use in water quality
management by national and local agencies and departments dealing with water
quality issues.
Water Quality Monitoring and its companion guidebook Water Quality Assessments. A
Guide to the Use of Biota, Sediments and Water in Environmental Monitoring, Second
edition (edited by Deborah Chapman and published on behalf of UNESCO, WHO and
UNEP by Chapman & Hall, London, 1996) constitute principal methodology guidebooks
developed and used in the monitoring and assessment activities of GEMS/WATER.
Together they make a direct contribution to capacity building in the area of water
quality monitoring and assessment.
This book brings together the information necessary to design and implement a water
quality monitoring programme and provides a basis for water quality assessments and
studies of the impact of pollution on the natural environment. Freshwater quality is
addressed in a holistic way, considering both surface waters and groundwaters.
Emphasis is given to monitoring the natural environment and to detecting and
monitoring trends in water quality.
The book outlines general considerations related to water quality monitoring, provides
a general protocol for a monitoring programme and includes such elements as staff
requirements, staff training and the equipping of analytical laboratories. It also
includes consideration of the problems that may be encountered when implementing
programmes in remote areas and developing countries and when establishing water
quality monitoring programmes from scratch.
It is hoped that the approaches and methods described will be useful for anyone
concerned with water quality monitoring whether they have a scientific, managerial or
engineering background and including, particularly, field staff and those who may not
be water quality experts. Potential users may be from local, regional or national
government agencies, research groups, consulting firms or non-governmental
organisations. This book will be especially useful to those who plan and manage the
various aspects of water quality monitoring outside the framework of large established
programmes, as may be the case in many developing countries and for specific
projects and studies world-wide.
Material on sampling and analytical methods for the most important physical, chemical
and bacteriological variables has been brought together here in a convenient form,
with an emphasis on field techniques at a level suitable for those implementing water
quality programmes. An overview of the principles underlying, and the importance of
hydrological, biological and sediment measurements and their relevance to water
quality monitoring is also included. Information on some of the commercially available
analytical kits for use in the field is included in an appendix.
ACKNOWLEDGEMENTS
The co-sponsoring organisations, UNEP and WHO, wish to express their appreciation to
all of those whose efforts made the preparation of this book possible. Special thanks
are due to the Department of International Development and Co-operation, Ministry of
Foreign Affairs of Finland which provided generous and continued financial support to
the preparation of the book as well as for the organisation of several regional review
workshops. The Tampere University of Technology, Finland and the National Board of

Waters and the Environment, Finland both supported the initiation of this handbook.
Thanks are also due to Dr Veerle Vandeweerd of UNEP/GEMS for her enthusiasm and
energy during the initiation of the project which led to the preparation of this
document and for her tireless support throughout the subsequent development and
refinement of this book.
An international group of authors provided material and, in most cases, several
authors and their collaborators contributed to each chapter. It is difficult to identify
precisely the contributions made by individuals and we apologise for any oversights in
the following list of principal contributors.
Dick Ballance, formerly of World Health Organization, Geneva, Switzerland (editor, and
contributor)
Jamie Bartram, European Centre for Environment and Health, World Health
Organization, Rome, Italy, formerly of the Robens Institute, University of Surrey,
Guildford, UK (editor and contributor)
Ray Briggs, Robens Institute, University of Surrey, Guildford, UK (contributions to
Chapter 9)
Deborah Chapman, Environment Consultant, Kinsale, Ireland (contributions to Chapter
11)
Malcolm Clarke, University of Victoria, BC, Canada (contributions to Chapter 14)
Richard Helmer, Urban Environmental Health, World Health Organization, Geneva,
Switzerland (contributions to Chapter 1)
John Jackson, formerly of UNEP GEMS Monitoring and Assessment Research Centre,
Kings College London, UK (contributions to Chapters 11 and 14)
Merete Johannessen, Norwegian Institute for Water Research (NIVA), Oslo, Norway
(contributions to Chapters 3 and 9)
Falk Krebs, Federal Institute of Hydrology, Koblenz, Germany (contributions to Chapter
11)
Esko Kuusisto, National Board of Waters and the Environment, Helsinki, Finland
(contributions to Chapters 1, 2 and 12)
John Lewis, Data Processing, Aberdare, UK (contributions to Chapter 14).
Ari Mäkelä, National Board of Waters and the Environment, Helsinki, Finland
(contributions to Chapters 1, 2, 3 and 5)
Esko Mälkki, National Board of Waters and the Environment, Helsinki, Finland
(contributions to Chapters 1, 2 and 5)
Michel Meybeck, Université de Pierre et Marie Curie, Paris, France (contributions to
Chapters 2 and 3)

Harriet Nash, Wardel Armstrong, Newcastle-under-Lyme, UK (contributions to
Chapters 5 and 14)
Ed Ongley, Canada Centre for Inland Waters, Burlington, Ontario, Canada contributions
to Chapters 12, 13 and 14)
Steve Pedley, Robens Institute, University of Surrey, Guildford, Surrey, UK
(contributions to Chapter 10)
Alan Steel, Consultant, Kinsale, Ireland (contributions to Chapter 14)
Paul Whitfield, University of Victoria, BC, Canada (contributions to Chapter 14)
Dr Richard Helmer, WHO, Geneva, Dr Veerle Vandeweerd, UNEP, Nairobi and Dr
Jeffrey Thornton, International Environmental Management Services, Wisconsin
critically reviewed early drafts. Later drafts were reviewed by John Chilton, British
Geological Survey and Ms Harriet Nash, Wardel Armstrong, who made useful
suggestions concerning groundwater and basic data checks respectively.
Drafts of the text were reviewed at a series of regional workshops convened in the
framework of the GEMS/WATER programme in Tanzania (1992), Zimbabwe (1993),
Uganda (1994) and Jordan (1994). More than 60 people contributed to the review
process in this way and the orientation of the final document towards real, practical
problems is largely due to their efforts.
Thanks are due to Verity Snook, Mary Stenhouse and John Cashmore for secretarial
services to the review meetings and for secretarial and administrative assistance at
various stages of the project. The editorial assistance of Sarah Ballance is also much
appreciated during the preparation of the final manuscript. Thanks are also due to
Helen MacMahon and Alan Steel (preparation of illustrations) and to Deborah Chapman
(editorial assistance, layout and production management).
United Nations Environment Programme
World Health Organization
Chapter 1 - INTRODUCTION
This chapter was prepared by J. Bartram and R. Helmer
Freshwater is a finite resource, essential for agriculture, industry and even human
existence. Without freshwater of adequate quantity and quality sustainable
development will not be possible. Water pollution and wasteful use of freshwater
threaten development projects and make water treatment essential in order to produce
safe drinking water. Discharge of toxic chemicals, over-pumping of aquifers, long-
range atmospheric transport of pollutants and contamination of water bodies with
substances that promote algal growth (possibly leading to eutrophication) are some of
today’s major causes of water quality degradation.
It has been unequivocally demonstrated that water of good quality is crucial to
sustainable socio-economic development. Aquatic ecosystems are threatened on a
world-wide scale by a variety of pollutants as well as destructive land-use or water-

management practices. Some problems have been present for a long time but have
only recently reached a critical level, while others are newly emerging.
Gross organic pollution leads to disturbance of the oxygen balance and is often
accompanied by severe pathogenic contamination. Accelerated eutrophication results
from enrichment with nutrients from various origins, particularly domestic sewage,
agricultural run-off and agro-industrial effluents. Lakes and impounded rivers are
especially affected.
Agricultural land use without environmental safeguards to prevent over-application of
agrochemicals is causing widespread deterioration of the soil/water ecosystem as well
as the underlying aquifers. The main problems associated with agriculture are
salinisation, nitrate and pesticide contamination, and erosion leading to elevated
concentrations of suspended solids in rivers and streams and the siltation of
impoundments. Irrigation has enlarged the land area available for crop production but
the resulting salinisation which has occurred in some areas has caused the
deterioration of previously fertile soils.
Direct contamination of surface waters with metals in discharges from mining, smelting
and industrial manufacturing is a long-standing phenomenon. However, the emission
of airborne metallic pollutants has now reached such proportions that long-range
atmospheric transport causes contamination, not only in the vicinity of industrialised
regions, but also in more remote areas. Similarly, moisture in the atmosphere
combines with some of the gases produced when fossil fuels are burned and, falling as
acid rain, causes acidification of surface waters, especially lakes. Contamination of
water by synthetic organic micropollutants results either from direct discharge into
surface waters or after transport through the atmosphere. Today, there is trace
contamination not only of surface waters but also of groundwater bodies, which are
susceptible to leaching from waste dumps, mine tailings and industrial production
sites.
The extent of the human activities that influence the environment has increased
dramatically during the past few decades; terrestrial ecosystems, freshwater and
marine environments and the atmosphere are all affected. Large-scale mining and
fossil fuel burning have started to interfere measurably with natural hydrogeochemical
cycles, resulting in a new generation of environmental problems. The scale of socio-
economic activities, urbanisation, industrial operations and agricultural production, has
reached the point where, in addition to interfering with natural processes within the
same watershed, they also have a world-wide impact on water resources. As a result,
very complex inter-relationships between socio-economic factors and natural
hydrological and ecological conditions have developed. A pressing need has emerged
for comprehensive and accurate assessments of trends in water quality, in order to
raise awareness of the urgent need to address the consequences of present and future
threats of contamination and to provide a basis for action at all levels. Reliable
monitoring data are the indispensable basis for such assessments.
Monitoring is defined by the International Organization for Standardization (ISO) as:
“the programmed process of sampling, measurement and subsequent recording or
signalling, or both, of various water characteristics, often with the aim of assessing
conformity to specified objectives”. This general definition can be differentiated into
three types of monitoring activities that distinguish between long-term, short-term and
continuous monitoring programmes as follows:

• Monitoring is the long-term, standardised measurement and observation of the
aquatic environment in order to define status and trends.
• Surveys are finite duration, intensive programmes to measure and observe the
quality of the aquatic environment for a specific purpose.
• Surveillance is continuous, specific measurement and observation for the purpose of
water quality management and operational activities.
The distinction between these specific aspects of monitoring and their principal use in
the water quality assessment process is described in the companion guidebook Water
Quality Assessments. A Guide to the Use of Biota, Sediments and Water in
Environmental Monitoring, 2nd edition (edited by D. Chapman and published on behalf
of UNESCO, WHO and UNEP by Chapman & Hall, London, 1996).
It is important to note the emphasis given to collection of data for a purpose in the
definitions of water quality monitoring above. This purpose is most commonly related
to water quality management, which aims to control the physical, chemical and
biological characteristics of water. Elements of management may include control of
pollution, use and abstraction of water, and land use. Specific management activities
are determined by natural water quantity and quality, the uses of water in natural and
socio-economic systems, and prospects for the future.
Water quality requirements or objectives can be usefully determined only in terms of
suitability for a purpose or purposes, or in relation to the control of defined impacts on
water quality. For example, water that is to be used for drinking should not contain
any chemicals or micro-organisms that could be hazardous to health. Similarly, water
for agricultural irrigation should have a low sodium content, while that used for steam
generation and related industrial uses should be low in certain other inorganic
chemicals. Preservation of biodiversity and other conservation measures are being
recognised increasingly as valid aspects of water use and have their own requirements
for water quality management. Water quality data are also required for pollution
control, and the assessment of long-term trends and environmental impacts.
1.1 Elements of a water quality monitoring programme
Before the planning of water sampling and analysis can be started, it is necessary to
define clearly what information is needed and what is already available and to identify,
as a major objective of the monitoring programme, the gaps that need to be filled. It is
useful to prepare a “monitoring programme document” or “study plan”, which
describes in detail the objectives and possible limitations of the monitoring
programme. Figure 1.1 outlines the contents of this book in relation to the process of
developing such a plan, its implementation and the interpretation of the findings. If the
programme’s objectives and limitations are too vague, and the information needs
inadequately analysed, the information gaps will be poorly identified and there will be a
danger of the programme failing to produce useful data.
Many reasons can be listed for carrying out water quality monitoring. In many
instances they will overlap and the information obtained for one purpose may be useful
for another. Water quality monitoring data may be of use in the management of water
resources at local, national or international level. Where water bodies are shared by
more than one country, a water quality monitoring programme can yield information

that may serve as a basis for international agreements regarding the use of these
waters, as well as for evaluation of compliance with any such agreements.
Water quality monitoring is the foundation on which water quality management is
based. Monitoring provides the information that permits rational decisions to be made
on the following:
• Describing water resources and identifying actual and emerging problems of water
pollution.
• Formulating plans and setting priorities for water quality management.
• Developing and implementing water quality management programmes.
• Evaluating the effectiveness of management actions.
To fulfil these functions some preliminary survey work must first be done to provide
basic, background knowledge of existing water quality conditions (Figure 1.1).
Subsequent monitoring efforts will identify problems and problem areas, short- and
long-term trends and the probable cause of the problems. Once sufficient data have
been gathered, it is possible to describe the average conditions, the variations from
average and the extremes of water quality, expressed in terms of measurable physical,
chemical and biological variables. In the meantime, priorities may have been set, plans
may have been made and management programmes may have been implemented.
Ultimately, information from the monitoring programme is fed back into the
management system so that any necessary changes to priorities and plans can also be
made.

Figure 1.1 Links between the critical elements of water quality monitoring discussed
in the various chapters of this book
Specifications for the collection of data should be uniform so as to ensure compatibility
and make it possible to apply to any particular location the experience gained in
another. Networks for water quality monitoring should be developed in close co-
operation with other agencies actively collecting water data. This not only minimises
the cost of establishing and operating the network but also facilitates the interpretation
of water quality data. The particular hydrological measurements and water
characteristics required will differ from one water body to another. For example, in
rivers and streams it is necessary to measure the velocity of flow and intensity of
longitudinal mixing, while thermal regimes are important considerations when
monitoring lakes. Measurement of wastewater discharges containing nutrients may not
be necessary for many rivers but may be important in lakes (which act as traps for
nutrients) because the additional input of nutrients may accelerate the eutrophication
process.

Networks for water quality monitoring must conform to programme objectives (Figure
1.1). A clear statement of objectives is necessary to ensure collection of all necessary
data and to avoid needless and wasteful expenditure of time, effort and money.
Furthermore, evaluation of the data collected will provide a basis for judging the extent
to which programme objectives were achieved and thus justify the undertaking. Before
observations begin, it is also essential to specify the location of sampling stations, the
frequency of sampling and the water quality variables to be determined.
Monitoring programmes should be periodically reviewed to ensure that information
needs are being met. As greater knowledge of conditions in the aquatic system is
gained, a need for additional information may become apparent. Alternatively, it may
be concluded that some of the information being collected is unnecessary. In either
case, an updated monitoring programme document must be prepared and distributed
to the information users. If such users are not kept fully informed of the exact scope of
the programme they may expect more than it can deliver and may not support its
continuation.
1.2 Monitoring for management
The elements of water quality monitoring and assessment described above and
discussed in detail in the following chapters are only part of a wider picture of water
quality and quantity management, environmental protection and policy formulation
and of development concerns. The critical element stressed is the development of
objectives. It may be that long-term objectives (such as integrated monitoring for
environmental and health protection) may be set for the monitoring programme but
that the programme operates, and is practically structured, to meet specified short-
term objectives (such as monitoring for immediate health priorities). This illustrates
that water quality monitoring operates within a larger structure of policy decisions and
management priorities. A programme may need to be flexible to meet short-term
objectives but still be capable of developing over longer periods to meet new concerns
and priorities.
The elements outlined above and described in more detail in the following chapters
should be implemented flexibly according to the different priorities of the monitoring
programmes. The initial phases of surveys and design may extend over periods of
months or even years before a clear idea of needs and priorities is achieved. The time
required for other eleme nts of the monitoring and assessment process varies.
Sampling missions may take several days, as may sample transport to the laboratory.
Complete chemical analysis of a sample may take a week. Data treatment can take
weeks, depending on the amount of data that is to be dealt with, while interpretation
of results and the writing and publication of reports can take from a few months to a
few years. If operational surveillance is one of the aspects of a multi-purpose
monitoring programme, the field work, data assessment and reporting should be
accomplished within a time limit appropriate to the operational requirements. For
example, reports on the surveillance of drinking water quality should be made very
quickly so that corrective actions can be taken when a contaminated supply threatens
public health.
The importance of the use of information should be stressed. There is little point in
generating monitoring data unless they are to be used. It is essential that the design,
structure, implementation and interpretation of monitoring systems and data are
conducted with reference to the final use of the information for specific purposes.

In some countries, water quality standards may be laid down by national legislation. A
government authority is then charged with monitoring the extent to which the
standards are fulfilled. This is particularly common for water intended for drinking and
is carried out as a public health protection measure. The monitoring objectives in this
case will be concerned with detecting any deterioration in raw water quality so that
appropriate source protection or treatment can be applied. In other instances, it may
be necessary to develop a new water source in order to meet increasing demands; the
objective may then become that of monitoring the quality and quantity of sources that
might fulfil this need.
Where water quality legislation is rudimentary or non-existent, the water authority’s
mandate may be to develop legislation and regulations appropriate to the country’s
economic development plans. In this case the monitoring objectives will probably
focus, in the first instance, on acquiring background information on water quality. The
objectives will change as information on water quality is accumulated, as problems
emerge and solutions are developed, and as new demands are made on the water
resources.
1.3 Monitoring and assessment
This handbook concentrates on providing the practical information which is necessary
to design, to implement and to carry out monitoring programmes in freshwaters.
Emphasis is placed on the collection and analysis of water samples because, at
present, this activity forms the principal component of most monitoring programmes.
The fundamental techniques associated with the use of sediment and biota in
monitoring programmes are also presented in order to illustrate how they may be
incorporated into existing programmes based on water sample analysis. Further details
of the growing application of these approaches is available in the companion guidebook
Water Quality Assessments.
Monitoring, as a practical activity, provides the essential information which is required
for an assessment of water quality. However, assessments require additional
information, such as an understanding of the hydro- dynamics of a water body,
information on geochemical, atmospheric and anthropogenic influences and the correct
approaches for analysis and interpretation of the data generated during monitoring.
The companion guidebook gives further detail on the supporting information which is
required for the full assessment of water quality in rivers, lakes, reservoirs and
groundwaters, illustrated by examples of assessments from different world regions. A
detailed description of different approaches available for the interpretation of
monitoring data is also given.
Chapter 2 - WATER QUALITY
This chapter was prepared by M. Meybeck, E. Kuusisto, A. Mäkelä and E. Mälkki
“Water quality” is a term used here to express the suitability of water to sustain
various uses or processes. Any particular use will have certain requirements for the
physical, chemical or biological characteristics of water; for example limits on the
concentrations of toxic substances for drinking water use, or restrictions on
temperature and pH ranges for water supporting invertebrate communities.
Consequently, water quality can be defined by a range of variables which limit water
use. Although many uses have some common requirements for certain variables, each

use will have its own demands and influences on water quality. Quantity and quality
demands of different users will not always be compatible, and the activities of one user
may restrict the activities of another, either by demanding water of a quality outside
the range required by the other user or by lowering quality during use of the water.
Efforts to improve or maintain a certain water quality often compromise between the
quality and quantity demands of different users. There is increasing recognition that
natural ecosystems have a legitimate place in the consideration of options for water
quality management. This is both for their intrinsic value and because they are
sensitive indicators of changes or deterioration in overall water quality, providing a
useful addition to physical, chemical and other information.
The composition of surface and underground waters is dependent on natural factors
(geological, topographical, meteorological, hydrological and biological) in the drainage
basin and varies with seasonal differences in runoff volumes, weather conditions and
water levels. Large natural variations in water quality may, therefore, be observed
even where only a single watercourse is involved. Human intervention also has
significant effects on water quality. Some of these effects are the result of hydrological
changes, such as the building of dams, draining of wetlands and diversion of flow.
More obvious are the polluting activities, such as the discharge of domestic, industrial,
urban and other wastewaters into the water-course (whether intentional or accidental)
and the spreading of chemicals on agricultural land in the drainage basin.
Water quality is affected by a wide range of natural and human influences. The most
important of the natural influences are geological, hydrological and climatic, since
these affect the quantity and the quality of water available. Their influence is generally
greatest when available water quantities are low and maximum use must be made of
the limited resource; for example, high salinity is a frequent problem in arid and
coastal areas. If the financial and technical resources are available, seawater or saline
groundwater can be desalinated but in many circumstances this is not feasible. Thus,
although water may be available in adequate quantities, its unsuitable quality limits
the uses that can be made of it. Although the natural ecosystem is in harmony with
natural water quality, any significant changes to water quality will usually be disruptive
to the ecosystem.
The effects of human activities on water quality are both widespread and varied in the
degree to which they disrupt the ecosystem and/or restrict water use. Pollution of
water by human faeces, for example, is attributable to only one source, but the
reasons for this type of pollution, its impacts on water quality and the necessary
remedial or preventive measures are varied. Faecal pollution may occur because there
are no community facilities for waste disposal, because collection and treatment
facilities are inadequate or improperly operated, or because on-site sanitation facilities
(such as latrines) drain directly into aquifers. The effects of faecal pollution vary. In
developing countries intestinal disease is the main problem, while organic load and
eutrophication may be of greater concern in developed countries (in the rivers into
which the sewage or effluent is discharged and in the sea into which the rivers flow or
sewage sludge is dumped). A single influence may, therefore, give rise to a number of
water quality problems, just as a problem may have a number of contributing
influences. Eutrophication results not only from point sources, such as wastewater
discharges with high nutrient loads (principally nitrogen and phosphorus), but also
from diffuse sources such as run-off from livestock feedlots or agricultural land
fertilised with organic and inorganic fertilisers. Pollution from diffuse sources, such as
agricultural run-off, or from numerous small inputs over a wide area, such as faecal
pollution from unsewered settlements, is particularly difficult to control.

The quality of water may be described in terms of the concentration and state
(dissolved or particulate) of some or all of the organic and inorganic material present
in the water, together with certain physical characteristics of the water. It is
determined by in situ measurements and by examination of water samples on site or in
the laboratory. The main elements of water quality monitoring are, therefore, on-site
measurements, the collection and analysis of water samples, the study and evaluation
of the analytical results, and the reporting of the findings. The results of analyses
performed on a single water sample are only valid for the particular location and time
at which that sample was taken. One purpose of a monitoring programme is,
therefore, to gather sufficient data (by means of regular or intensive sampling and
analysis) to assess spatial and/or temporal variations in water quality.
The quality of the aquatic environment is a broader issue which can be described in
terms of:
• water quality,
• the composition and state of the biological life present in the water body,
• the nature of the particulate matter present, and
• the physical description of the water body (hydrology, dimensions, nature of lake
bottom or river bed, etc.).
Complete assessment of the quality of the aquatic environment, therefore, requires
that water quality, biological life, particulate matter and the physical characteristics of
the water body be investigated and evaluated. This can be achieved through:
• chemical analyses of water, particulate matter and aquatic organisms (such as
planktonic algae and selected parts of organisms such as fish muscle),
• biological tests, such as toxicity tests and measurements of enzyme activities,
• descriptions of aquatic organisms, including their occurrence, density, biomass,
physiology and diversity (from which, for example, a biotic index may be developed or
microbiological characteristics determined), and
• physical measurements of water temperature, pH, conductivity, light penetration,
particle size of suspended and deposited material, dimensions of the water body, flow
velocity, hydrological balance, etc.
Pollution of the aquatic environment, as defined by GESAMP (1988), occurs when
humans introduce, either by direct discharge to water or indirectly (for example
through atmospheric pollution or water management practices), substances or energy
that result in deleterious effects such as:
• hazards to human health,
• harm to living resources,
• hindrance to aquatic activities such as fishing,

• impairment of water quality with respect to its use in agriculture, industry or other
economic activities, or reduction of amenity value.
The importance attached to quality will depend on the actual and planned use or uses
of the water (e.g. water that is to be used for drinking should not contain any
chemicals or micro-organisms that could be hazardous to health).
Since there is a wide range of natural water qualities, there is no universal standard
against which a set of analyses can be compared. If the natural, pre-polluted quality of
a water body is unknown, it may be possible to establish some reference values by
surveys and monitoring of unpolluted water in which natural conditions are similar to
those of the water body being studied.
2.1 Characteristics of surface waters
2.1.1 Hydrological characteristics
Continental water bodies are of various types including flowing water, lakes, reservoirs
and groundwaters. All are inter-connected by the hydrological cycle with many
intermediate water bodies, both natural and artificial. Wetlands, such as floodplains,
marshes and alluvial aquifers, have characteristics that are hydrologically intermediate
between those of rivers, lakes and groundwaters. Wetlands and marshes are of special
biological importance.
Figure 2.1 Typical water residence times in inland water bodies.

Note: Actual residence times may vary. Residence times in karstic aquifers may vary
from days to thousands of years, depending on extent and recharge. Some karstic
aquifers of the Arabian peninsula have water more than 10,000 years old.
It is essential that all available hydrological data are included in a water quality
assessment because water quality is profoundly affected by the hydrology of a water
body. The minimum information required is the seasonal variation in river discharge,
the thermal and mixing regimes of lakes, and the recharge regime and underground
flow pattern of groundwaters.
The common ranges of water residence time for various types of water body are shown
in Figure 2.1. The theoretical residence time for a lake is the total volume of the lake
divided by the total outflow rate (V/ΣQ). Residence time is an important concept for
water pollution studies because it is associated with the time taken for recovery from a
pollution incident. For example, a short residence time (as in a river) aids recovery of
the aquatic system from a pollution input by rapid dispersion and transport of
waterborne pollutants. Long residence times, such as occur in deep lakes and aquifers,
often result in very slow recovery from a pollution input because transport of
waterborne pollutants away from the source can take years or even decades.
Pollutants stored in sediments take a long time to be removed from the aquatic
system, even when the water residence time of the water body is short.
River flow is unidirectional, often with good lateral and vertical mixing, but may vary
widely with meteorological and climatic conditions and drainage pattern. Still surface
waters, such as deep lakes and reservoirs, are characterised by alternating periods of
stratification and vertical mixing. In addition, water currents may be multi-directional
and are much slower than in rivers. Moreover, wind has an important effect on the
movement of the upper layers of lake and reservoir water. The residence time of water
in lakes is often more than six months and may be as much as several hundred years.
By contrast, residence times in reservoirs are usually less than one year.
2.1.2 Lakes and reservoirs
An important factor influencing water quality in relatively still, deep waters, such as
lakes and reservoirs, is stratification. Stratification occurs when the water in a lake or
reservoir acts as two different bodies with different densities, one floating on the other.
It is most commonly caused by temperature differences, leading to differences in
density (water has maximum density at 4 °C), but occasionally by differences in solute
concentrations. Water quality in the two bodies of water is also subject to different
influences. Thus, for example, the surface layer receives more sunlight while the lower
layer is physically separated from the atmosphere (which is a source of gases such as
oxygen) and may be in contact with decomposing sediments which exert an oxygen
demand. As a result of these influences it is common for the lower layer to have a
significantly decreased oxygen concentration compared with the upper layer. When
anoxic conditions occur in bottom sediments, various compounds may increase in
interstitial waters (through dissolution or reduction) and diffuse from the sediments
into the lower water layer. Substances produced in this way include ammonia, nitrate,
phosphate, sulphide, silicate, iron and manganese compounds.
Temperate lakes

Thermal stratification has been studied for many years in temperate regions where,
during spring and summer, the surface layers of the water become warmer and their
density decreases. They float upon the colder and denser layer below and there is a
resistance to vertical mixing. The warm surface layer is known as the epilimnion and
the colder water trapped beneath is the hypolimnion. The epilimnion can be mixed by
wind and surface currents and its temperature varies little with depth. Between the
layers is a shallow zone, called the metalimnion or the thermocline, where the
temperature changes from that of the epilimnion to that of the hypolimnion. As the
weather becomes cooler, the temperature of the surface layer falls and the density
difference between the two layers is reduced sufficiently for the wind to induce vertical
circulation and mixing in the lake water, resulting in an “overturn”. This can occur
quite quickly. The frequency of overturn and mixing depends principally on climate
(temperature, insolation and wind) and the characteristics of the lake and its
surroundings (depth and exposure to wind).
Lakes may be classified according to the frequency of overturn as follows (Figure 2.2):
• Monomictic: once a year - temperate lakes that do not freeze.
• Dimictic: twice a year - temperate lakes that do freeze.
• Polymictic: several times a year - shallow, temperate or tropical lakes.
• Amictic: no mixing - arctic or high altitude lakes with permanent ice cover, and
underground lakes.
• Oligomictic: poor mixing - deep tropical lakes.
• Meromictic: incomplete mixing - mainly oligomictic lakes but sometimes deep
monomictic and dimictic lakes.

Figure 2.2 The classification of lakes according to the occurence of thermal
stratification and mixing in the water column
Thermal stratification does not usually occur in lakes less than about 10 m deep
because wind across the lake surface and water flow through the lake tend to
encourage mixing. Shallow tropical lakes may be mixed completely several times a
year. In very deep lakes, however, stratification may persist all year, even in tropical
and equatorial regions. This permanent stratification results in “meromixis”, which is a
natural and continuous anoxia of bottom waters.
Tropical lakes
A common physical characteristic of tropical lakes is that seasonal variations in water
temperature are small, as a result of relatively constant solar radiation. Water
temperatures are generally high but decrease with increasing altitude. The annual

water temperature range is only 2-3 °C at the surface and even less at depths greater
than 30 m. Density differences are minimal because water temperature is almost
constant. Winds and precipitation, both of which tend to be seasonal, play an
important role in mixing. The very limited seasonal temperature variation also results
in a correspondingly low annual heat budget in tropical lakes. However, the relative
variation in the heat budget in consecutive years may be considerable, because the
peak value of heat storage may result from a single meteorological event.
In some tropical lakes, variations in water level of several metres may result from the
large differences in rainfall between wet and dry seasons. Such variations have
pronounced effects on dilution and nutrient supply which, in turn, affect algal blooms,
zooplankton reproduction and fish spawning.
During the dry season, wind velocities are generally higher than at other times of the
year and evaporation rates are at their maximum. The resulting heat losses, together
with turbulence caused by wind action, promote mixing.
The classification of lakes based on seasonal temperature variations at different depths
is not generally applicable to tropical lakes. A classification which considers size, depth
and other physical characteristics, such as the following, is more relevant.
• Large, deep lakes all have a seasonal thermocline in addition to a deep permanent
thermocline over an anoxic water mass. Recirculation of the deep water may occur but
the responsible mechanism is not clear.
• Large, shallow lakes have a distinct diurnal temperature variation. Temperature is
uniform in the morning, stratification develops in the afternoon and is destroyed during
the night. The fluctuation in water level may be considerable relative to lake volume
and the large flood plain that results will have profound effects on the productivity of
biological life in the water.
• Crater lakes generally have a small surface area relative to their great depth and are
often stratified. Despite such lakes being in sheltered positions, special weather
conditions can cause complete mixing of lake contents.
• High-altitude lakes in climates where there is only a small diurnal temperature
difference are unstable and experience frequent overturns. Where temperature
differences are larger, a more distinct pattern of stratification can be identified. There
may also be substantial losses of water by evaporation during the night.
• River lakes are created when areas of land are flooded by rivers in spate. When the
water level in the river goes down, the lake water flows back towards the river. This
annual or semi-annual water exchange affects the biological and chemical quality of
the water.
• Solar lakes. In saline, dark-bottomed lakes an anomalous stratification can develop.
A lower, strongly saline water layer may be intensely heated by solar radiation,
especially if it is well isolated from the atmosphere by the upper layer of lighter brine.
Temperatures as high as 50 °C have been recorded in the lower levels of solar lakes.