Hydrology-From Measurement To Hydrological Information (7)


This chapter discusses general aspects of water quality sampling and specifi c aspects related to the
sampling of rivers, streams, lakes, reservoirs and
groundwaters. More detailed discussions can be
found in the references (WMO, 1988; UNEP/WHO/
UNESCO/WMO, 1992) and in more specialized
publications related to biological water quality
(American Public Health Association and American
Water Works Association, 1999; Genin and others,
1997). Guidance on chemical or isotopic sampling
and analytical techniques are provided in a long list
of references by the International Atomic Energy
Agency (IAEA).

There are several approaches to water quality
monitoring. Monitoring can be accomplished
through a network of strategically located longterm stations, by repeated short-term surveys, or by
the most common approach, a combination of the
The location of stations and samplings should take
into account the following factors:
(a) Accessibility and travel time to the laboratory
(for deteriorating samples);
(b) Available staff, funding, fi eld and laboratory
data handling facilities;
(c) Inter-jurisdictional considerations;
(d) Population trends;
(e) Climate, geography and geology;
(f) Potential growth centres (industrial and
(g) Safety of personnel.
Sampling frequency depends on the objectives of
the network, the importance given to the sampling
station, the levels of the measured values, the
spacial variability of the studied parameters and,
most importantly, on the available funding.
Without sufficient previous information, an arbitrary frequency is chosen based on knowledge of
the local conditions. This frequency may be adjusted
after a sufficient number of samples have been
taken and analysed and note has been taken of the
substances present, their concentrations and the
observed variability.
The choice of sampling stations also depends on
the present and planned water use, the stream or
lake water quality objectives or standards, the accessibility of potential sampling sites (landowners,
routes, airstrips), the existence of services such as
electricity, and already existing water quality data.
Figure I.7.1 shows the steps to follow for the choice
of sampling sites.
7.2.1 Water-quality parameters
The parameters that characterize water quality may
be classifi ed in several ways, including:
(a) Physical properties, for example, temperature,
electrical conductivity, colour and turbidity;
(b) Elements of water composition, such as pH,
alkalinity, hardness, Eh or the partial pressure
of carbon dioxide;
(c) Inorganic chemical components, for example, dissolved oxygen, carbonate, bicarbonate,
chloride, fluoride, sulfate, nitrate, ammonium,
calcium, magnesium, sodium potassium, phosphate and heavy metals;
(d) Organic chemicals, for example, phenols,
chlorinated hydrocarbons, polycyclic aromatic
hydrocarbons and pesticides;
(e) Biological components, both microbiological,
such as faecal coliforms, and macrobiotic, such
as worms, plankton and fish, or vegetation.
7.2.2 Surface-water quality
The programme objectives will often precisely
defi ne the best locations for sampling in a river or
lake system. For example, in order to determine the
effect of an effl uent discharge on a receiving stream,
sampling locations upstream and downstream of
the discharge would be required. In other cases,
both location and frequency of sampling will be
determined by anti-pollution laws or by a requirement for a specific use of a water body. For example,
a permit to discharge surface waters may outline
details of monitoring, such as location, number of
samples, frequency and parameters to be analysed.
Sampling strategies are quite different for different
kinds of water bodies and media, for example,
water, sediment or biota. If the objective concerns the impact of human activities on water quality in
a given river basin, the basin can be separated into
natural and altered regions. The latter can be further
subdivided into agricultural, residential and industrial zones. In acid-deposition studies, an important
factor is the terrain sensitivity to the deposition.
Figures I.7.2 and I.7.3 give some examples of how
sampling stations could be located to meet specific
objectives on river and lake systems.
Collecting relevant information on the region to
be monitored is an essential step in water quality
assessment. This information includes the geological, hydrological and climatic aspects. In addition,
demographic conditions and planned water use
(water intakes, waste outlets, main drainage, irrigation schedules and fl ow regulation) are also

Figure I.7.1. Scheme for the selection of water quality sampling sites

For surface waters, the distance downstream to the
point of complete mixing is roughly proportional
to the stream velocity and to the square of the
width of the channel. For shallow rivers, waters
attain homogeneity vertically below a source of
pollution. Lateral mixing is usually attained much
more slowly. Thus, wide swift-flowing rivers may
not be completely mixed for many kilometres
downstream from a pollution point source. Lakes
can be vertically stratified owing to temperature or
high-density saltwater intake.

Figure I.7.2. Monitoring site: rivers
Figure I.7.3. Monitoring site: lakes

Various protocols are recommended to determine
representative sampling in the cross-section of the
river. For example, six samples analysed in duplicate, taken from three positions across the river and
at two depths or mid-depth samples at the quarter
points, or other equal distance points across the
width of the river. If a representative sample cannot
be obtained, it is advisable to select another site,
either immediately upstream or downstream. The
other alternative is to obtain a flow-weighted
composite sample from samples collected at verticals on the cross-section.

Longitudinal mixing of irregular or cyclic discharges
into a river will have a secondary influence on the
location of a sampling site. Their effects need to be
taken into account in deciding the frequency of
sampling and in interpreting the data.
For lake stations, the recommended practice is to
sample for fi ve consecutive days during the warmest part of the year and for fi ve consecutive days
every quarter. Alternatively, they should be sampled
at least six times a year, together with the occasional
random sample, to cover the periods such as open
water prior to summer stratification, during mixing
following summer stratification, under ice, and
during the periods of snow melt and runoff.
Similarly, additional samples of rivers should be
taken, if possible, after storm events and during
snow melt and runoff. When parameters are plotted against time, some cyclic variation may be
apparent amidst the random fluctuations.
The detection of cyclic events requires a sampling
interval that is no longer than one third of the
shortest cycle time and a sampling period at least
ten times as long as the longest cycle. Therefore,
long-period cycles will not be verified in the initial
surveys, but become apparent during the operation
of the network. In order to detect the cyclic variations, some random sampling is desirable, for
example, on different days of the week or at different times of the day.

7.2.3 Precipitation quality
Specific aspects concerning the quality of precipitation, particularly sampling equipment, are discussed
in 3.16. In general, sampling sites should be selected
to give accurate and representative information
concerning the temporal and spatial variation of
chemical constituents of interest. Important factors
to take into consideration are prevalent wind trajectories, sources for compounds of interest, frequency
of precipitation events (rain, snow or hail), and other meteorological processes that influence the
deposition. The following criteria should be
(a) No moving sources of pollution, such as routine
air, ground or water traffic, should be within
1 km of the site;
(b) No surface storage of agricultural products, fuels
or other foreign materials should be within
1 km of the site;
(c) Samplers should be installed over fl at undisturbed land, preferably grass-covered,
surrounded by trees at distances greater than
5 m from the sampler. There should be no wind activated sources of pollution nearby, such
as cultivated fields or unpaved roads. Zones
of strong vertical eddy currents, eddy zones
leeward of a ridge, tops of wind-swept ridges
and roofs of buildings, particularly, should be
avoided because of strong turbulence;
(d) No object taller than the sampler should be
within 5 m of the site;
(e) No object should be closer to the sampler than
a distance of 2.5 times the height by which the
object extends above the sampler. Particular
attention must be given to overhead wires;
(f) The collector intake should be located at least
1 m above the height of existing ground cover
to minimize coarse materials or splashes from
being blown into it;
(g) Automatic samplers require power to operate
lids and sensors and, in some cases, for refrigeration in the summer and thawing in the winter.
If power lines are used, they must not be overhead. If generators are used, the exhaust must
be located well away and downwind from the
(h) To address issues on a continental scale, sites
should preferably be rural and remote, with no
continuous sources of pollution within 50 km
in the direction of the prevalent wind direction
and 30 km in all other directions.
It may not be possible to meet all of these criteria in
all cases. The station description should refer to
these criteria and indicate the exact characteristics
of each location chosen as a sampling site.
In the case of large lakes, the precipitation over the
lake may not be as heavy as along the shores and
the proportion of large particles may be smaller. In
order to sample in the middle of a lake, the sampler
can be mounted on a buoy, rock, shoal or small
Precipitation sampling can be taken for each rain
event or over a monthly period. In this case, rain is
preserved for the same period before being analysed.
The analysis of event-precipitation samples enables
pollutants associated with a particular storm to be
determined, and a wind-trajectory analysis can
determine probable sources. However, this
sampling regime is very sensitive. The same statistical considerations concerning frequency of
sampling apply here as for surface-water
7.2.4 Groundwater quality
The quality of groundwater is subject to change and
deterioration as a result of human activity. Localized
point sources of pollution include cesspools and
septic tanks, leaks in municipal sewers and waste
ponds, leaching from garbage dumps and sanitary
landfills, seepage from animal feedlots, industrial
waste discharges, cooling water returned to recharge
wells, and leaks from oil tankers or pipelines. Larger
geographical areas may suffer degradation of
groundwater quality because of irrigation water
returns, recharge into aquifers of treated sewage or
industrial effluents, and intrusion of seawater in
coastal zones or from other highly saline aquifers.
Water samples can be collected from free-flowing
artesian wells or pumped wells. The wells should be
pumped long enough to ensure that the sample is
representative of the aquifer and not of the well.
This is particularly necessary for open wells or
where a well has a lining subject to corrosion.
Portable pumps are needed in case of non-equipped
wells. For sampling at different depths, mechanical
or pneumatic equipment should be used to isolate
specifi c sites. Sampling in shallow aquifers and
saturated zones between impermeable layers can
often be obtained by lowering a piezometer to the
desired depth. The basic parameters used to defi ne
surface water quality can also be used for groundwater monitoring with the exception of turbidity,
which is not usually a problem.
A good deal of hydrogeological information may
be necessary to plan a groundwater sampling
programme. Data on water levels, hydraulic gradients, velocity and direction of water movements
should be available. The velocity of groundwater
movement within the aquifers is highly variable. It
can vary from 1 m y–1 in fl at regions with low
recharge to more than 1 m s–1 in karst aquifers. An
inventory of wells, boreholes and springs fed by the
aquifer should be drawn up and details of land use
should be recorded.
For the collection of water samples (and water
levels), an existing well is a low-cost choice,
although they are not always at the best location or made of non-contaminating materials. A well that
is still in use and pumped occasionally is preferable
to one that has been abandoned. Abandoned or
unused wells are often in poor condition with
damaged or leaky casings and corroded pumping
equipment. It is often difficult to measure their
water levels and there may be safety hazards.
Changes in groundwater can be very slow and are
often adequately described by monthly, seasonal or
even annual sampling schedules. In some cases,
such as alluvial aquifers with large inputs from
surface drainage, the temporal variation of water
quality can be very relevant.

7.2.5 Sediment quality
Most of the selection criteria outlined in previous
sections also apply to sampling for sediments (5.5.3
and 5.5.4). Therefore, only additional special recommendations will be described here.
For rivers where sediment-transport data are
required, it is necessary to locate the sampling sites
near a gauging station so that accurate stream discharge information is available at all times.
Sampling locations immediately upstream from
confluences should be avoided because they may
be subject to backwater effects. In streams too deep
to wade, sampling sites should be located near
bridges or cableways. When sampling from bridges,
the upstream side is normally preferred. Sampling
in areas of high turbulence, such as near piers, is
often unrepresentative. Attention should also be
paid to the accumulation of debris or trash on the
piers, as this can seriously distort the fl ow and
hence the sediment distribution. An integrated
sample obtained by mixing water from several
points in the water column according to their
average sediment load can be considered as a
representative sample as long as there is good
lateral mixing.

The best places to sample bottom deposits in fast flowing rivers are in shoals, at channel bends and at
mid-channel bars or other sheltered areas where the
water velocity is at its minimum.
Sampling sites should be accessible during floods,
since sediment-transport rates are high during these
For identification of peak pollution loads in rivers,
two cases must be considered:
(a) For pollution from point sources, sampling
should be done during low-flow periods, when
pollution inputs are less diluted;
(b) When pollutants originate from diffuse sources,
such as runoff of agricultural nutrients or
pesticides, sampling must be focused on flood
periods during which the pollutants are washed
out of the soil.
If one of the objectives is to quantify the transport of
sediment in the river system, it should be noted that
peak concentrations of sediment do not necessarily
correspond with times of peak flow. Also, a series of
high fl ow rates will lead to progressively lower sediment peaks – an exhaustion effect arising from the
depletion of material available for re-suspension. For
lakes, the basic sampling site should be located at
the geographic centre of the lake. If the lake is very
large (area > 500 km2), several base stations may be
needed. If various sediment types are to be sampled,
then data from acoustic surveys (echo-sounders) can
be used both to identify the type of surfi cial material
(sand, gravel or mud) and to indicate the presence of
layering below the surface.

Secondary sampling sites should be located between
the base station and major tributary inlets or pollutant sources. A common strategy is to place points
down the long axis of the lake with occasional cross
lines. Three to fi ve stations should usually give a
good approximation to the sediment quality of an
average size lake. For statistical validity, however, a
larger number of sampling sites will probably be

Sampling frequency in lakes is influenced by the
concentrations of suspended sediment which is
generally low. Sediment traps should be operated
during the periods of maximum and minimum
algal productivity and at times of high input of
sediment from rivers. Repeat sampling of bottom
sediments in lakes needs to take into account the
rates of sediment accumulation. Basins in cool,
temperate climates often have accumulation rates
in the order of 0.1–0.2 mm y–1. A re-sampling period
of fi ve years would then be too soon to provide
worthwhile new information, unless the presence
of a new pollutant were to be tested.

Sampling is the process of collecting a representative quantity of water from a river, lake or well.
Sampling methods are determined by a number of
factors, including the type of material being
sampled, the type of sample and the quality parameter being analysed, which in turn determine the
equipment and procedures to be used.

Sampling procedures should be adapted to different
components such as the following:
(a) Steady: the components do not change with
(b) Nearly steady: the components change with
time but can be stabilized during a period of
24 hours or less after appropriate treatment;
(c) Unsteady: the components change rapidly and
cannot be stabilized.
Groups (a) and (b) include components that are
laboratory tested, whereas those included in group
(c) must be measured in situ.
7.3.1 Types of water samples Grab samples
Grab samples are appropriate when it is desired
to characterize water quality in a particular location. They are also used to establish the water
quality history based on relatively short time
intervals. A discrete grab (or spot) sample is
taken at a selected location and depth. A depth integrated grab sample is collected over the
depth of the water column at a selected location
and time. Composite samples
A composite sample is obtained by mixing several
samples to obtain an average value of water quality over the sampling period. Discrete or
continuous sampling can be used and the mixing
proportion is calculated on a time or discharge
basis. A portion of the composite sample is then
analysed. An obvious advantage is in the economy of reducing the number of samples to be
analysed. However, composite samples cannot
detect changes in parameters occurring during
the sampling period.
There are two main types of composite samples:
sequential and fl ow-proportional.
A sequential composite is constituted by
continuous, constant sample pumping, or by
mixing equal water volumes collected at regular
time intervals.
A flow-proportional composite is obtained by
continuous pumping at a rate proportional to the
fl ow, mixing equal volumes of water collected at
time intervals that are inversely proportional to the
rate of flow, or by mixing volumes of water proportional to the flow collected at regular time
7.3.2 Collecting a representative water
For sampling at sites located on a uniform,
well- mixed reach of stream, the collection of depth integrated samples in a single vertical may be
adequate. For small streams, a grab sample taken at
the centroid of flow is usually adequate.
In other cases the number of samples taken will
depend on the width, depth, discharge, amount of
suspended sediment being transported and aquatic
life present.
Three to five verticals are usually sufficient; fewer
are necessary for narrow or shallow streams.
One common method is the equal-width-increment method, in which verticals are spaced at equal intervals across the stream. The equaldischarge-increment method requires detailed
knowledge of the streamflow distribution in the
cross-section to subdivide the cross-section into
verticals spaced in proportion to the incremental
7.3.3 Sampling for the analysis of water
stable isotopes
To complete the study of water quality, it is interesting to consider the stable isotopes of a water molecule
(oxygen-18 and deuterium). For instance, in coastal
areas, the analysis of water stable isotopes – both in
surface and groundwater – is useful to detect whether
the salinity of inland waters is due to anthropic
pollution, agriculture activities or upstream saline
water. Isotopes also permit the localization of aquifers, the study of surface and groundwater linkage or
the detection of natural processes affecting waters
such as mixing or evaporation. Detailed information
on the use of stable isotopes relevant to this subject
is provided in the references (Mook, 2000).
Isotopic analyses require specialized laboratories,
but the required water samplings procedures are
quite simple. Sampling procedures that take account
of the specific protocol for isotope sampling and
conditioning are as follows:

(a) Use painted glass bottles or high-density plastic
(10 to 60 ml), generally 50-ml containers and
hermetic sealing caps (reinforced by an interior
plastic plug);
(b) Rinse the containers three times with the water
to be sampled;
(c) Fill the bottle to the brim; this avoids evaporation, which could enrich the residual water and
vapour pressure. If transported by air, bottle should not be filled and the cap should be insulated with a paraffi n film;
(d) Snow samples should be collected in clean
plastic bags (using non-contaminating gloves),
then gradually melted before being put into
(e) Ice samples are preserved in the frozen state to
reach the laboratory;
(f) Samples should not be filtered except when
they have been in contact with oil (used for
protection against the evaporation of collected
(g) Sample may be preserved for a long time (more
than a year) in a cool, dark environment.
7.3.4 Radioactivity measurement
Detailed instructions for the analysis of radioisotopes associated with water quality together with
recommended containers and preservation methods are provided in the references (United States
Geological Survey, 1984; IAEA, 2004) and further
reading at the end of this chapter Sources of radioactivity in water
Sources of radioactivity in water may be natural or
due to human activities. The main natural sources
are derived from the weathering of rocks containing radioactive minerals and the fallout of
cosmic-ray nuclides. The major sources of radioactivity due to human activities are: uranium mining,
nuclear-power industries, nuclear weapons testing, and the peaceful applications of nuclear
materials and devices, for example, energy
The principal radionuclides introduced naturally
into surface water and groundwater are uranium,
radium-226, radium-228, radon, potassium-40,
tritium and carbon-14. All but the last two derive
from radioactive minerals. In areas where radioactive
minerals are abundant, natural uranium is the
major radioactive constituent present in water.
Tritium and carbon-14 are produced by the
interaction of cosmic-ray neutrons with nitrogen in
the upper atmosphere. The tritium (3H) isotope, a
constituent present in water, is eventually rained
out as precipitation. Radioactive carbon is
incorporated into atmospheric carbon dioxide.
Both tritium and radioactive carbon are also
produced by thermonuclear power testing and are
currently used for groundwater dating (time elapsed
between aquifer recharge and water sampling).
Since 1970 the nuclear power industry has probably
been the larger source of tritium. Strontium-90 and
Cesium-137 are the major man-made radioisotopes
of concern in water.

The geochemical behaviour of a daughter element
may be grossly different from that of the radioactive parent element, although its occurrence,
distribution and transport may be governed by
those of the parent. The International Commission
on Radiological Protection recommends the
maximum permissible concentration values in
water. Collection and preservation
of samples for radioactivity
Acceptable containers (generally four-litre bottles)
are made of polypropylene, polyethylene or Tefl on.
They should be pretreated in laboratory by filling
them with concentrated nitric acid for a day, rinsing with detergent, and then rinsing several times
with highly purified water.
For tritium, samples should be collected in high density plastic bottles holding between 0.5 and 1.0 l.
For carbon-14, according to specialized laboratory
requirements, one procedure is to take one litre of
water in high precision bottles or to dissolve about
2.5 g of precipitate into more than 100 l of water in
case of low carbon content.
The principal problem encountered in preserving
these samples is adsorption on the walls of the
container or on suspended matter. To analyse the
total radio-element quantities and to minimize
adsorption, 2 ml of concentrated HCl per litre of
sample, or nitric acid to one per cent concentration, are added.
Generally, to minimize analysis cost, it is advisable
to analyse an annual composite sample by mixing
aliquots from each monthly sample.

Figure I.7.5. Kemmerer sampler

If a significant level of radioactivity over environmental levels is found, the samples making up the composite are analysed individually to locate the sample(s) that has (have) the higher than expected
radioactivity level.
7.3.5 Field sampling equipment and
techniques Grab samplers
Grab samplers may be classified as those appropriate only for volatile constituents, such as for dissolved gases and others for non-volatile constituents. Both discrete (surface or specific depth) and
depth-integrating types of samplers are available.
Both may be used to collect water for the determination of non-volatile constituents.
To obtain an approximate depth-integrated sample,
an open sampling apparatus should be lowered to
the bottom of the water body and raised to the
surface at a constant rate so that the bottle is just
filled on reaching the surface. A sampling iron can
be used for this purpose: it is a device, sometimes
made of iron, used to hold sample bottles. The
sample bottles are placed in the sample iron and are
secured by the neck holder. In some cases, sampling
irons may have provision for additional weights to
ensure a vertical drop in strong currents.

Depth integration may not be possible in shallow
streams where the depth is insufficient to permit
integration. In such cases, care must also be taken
not to disturb the river bottom when taking a
sample. One suggestion in such cases is to dig a
hole in the bottom, let the stream settle, and sample
down to the top of the hole.

Figure I.7.4. Van Dorn bottle

Discrete samplers are used to collect water samples
at a specific depth. An appropriate sampler is
lowered to the desired depth, activated and then
retrieved. Van Dorn, Kemmerer and pump samplers
are frequently used for this purpose:
(a) Van Dorn bottle – The Van Dorn bottle
(Figure I.7.4) is designed for sampling at a depth
of 2 m. Its horizontal configuration should be
used when samples are taken at the bottom, at
the sediment-water interface;
(b) Kemmerer sampler – It is one of the oldest
types of messenger-operated vertical samplers.
It is commonly used in water bodies with a
depth of 1 m or greater. The Kemmerer sampler
(Figure I.7.5) is available in volumes ranging
from 0.5 to 8 l;
(c) Pumps – Three types of pumps – diaphragm,
peristaltic and rotary – are available to collect
samples from specified depths. In general,
diaphragm pumps are hand operated. The
peristaltic and rotary pumps require a power
source and consequently have limited fi eld
utility. Peristaltic pumps are not recommended
for the collection of samples for chlorophyll
analysis because damage to the algal cells
may occur. All pumps must have an internal
construction that does not contaminate the
water sample. Input and output hoses must
also be free of contaminants.
The Van Dorn samplers have an advantage over the
Kemmerer bottle in that their lids do not lie in the
path of the fl ow of water through the sampler,
which can cause eddies and disturbance.
A multiple sampler (Figure I.7.6) permits the simultaneous collection of several samples of equal or
different volumes at a site. Each sample is collected
in an individual bottle. When the samples are of
equal volume, information concerning the instantaneous variability between the replicate samples
can be obtained. The sampler may be altered to
accommodate different sizes and numbers of bottles
according to the requirements of specific
programmes. This may be done by changing cup

sizes, length of cup sleeves and the confi guration
and size of openings in the clear acrylic top. Dissolved-oxygen sampler
A typical sampler for dissolved-oxygen concentration and Biochemical Oxygen Demand (BOD)
is illustrated in Figure I.7.7. This sampler must be
pulled up open, thus some mixture with the
upper water layers is possible. If certain grab
samplers are fitted with bottom drain tubes, they
may be used by running the sample into the
bottom of the analysis container. The samples
should be collected in narrow-mouthed BOD
bottles that have bevelled glass stoppers to avoid
entrapment of air in the samples. Sampling of
shallow streams is not advisable with this sampler.
In this case, sample agitation (bubbling) should
be minimized by gently tilting a BOD bottle
downstream. Automatic samplers
Automatic samplers range from elaborate instruments with fl exible sampling programmes, which
require external power and permanent housing, to
simple, portable, self-contained devices, such as a
submerged bottle with a rate of fi lling determined
by a slow air bleed. These devices are often
programmed to sample over a 24-hour period.
They reduce costly personnel requirements if
frequent sampling is required. If the site has automatic fl ow-measurement capability, some automatic
samplers can provide fl ow-proportional samples.
Both composite- and individual-sample models are
available. Sampling procedures as influenced
by station, location and season
In the field, the sampling situation determines
which of several different sampling techniques is
required. Some of the practical sampling considerations related to location and season of sampling are
outlined below. Detailed procedures for sampling
are given in the Manual on Water Quality Monitoring:
Planning and Implementation of Sampling and Field
Testing (WMO-No. 680).

Sampling from bridges is often preferred because of
the ease of access and safety under most conditions
of fl ow and weather. However, vehicular traffic is a
potential hazard and should be considered.
Boats provide more flexibility and reduce the time
of travel between sampling points. The sampling
point must be identified by triangulation from
landmarks, and here also the hazards of navigation,
high flows and storms have to be considered (8.5).
Aircraft, including helicopters, are expensive, but
fast and flexible. Tests have shown that the disturbance of water under helicopters does not
significantly affect even dissolved-oxygen water
samples. Bank-side sampling should only be used
when no alternative is possible. The sample should
be taken in turbulent water or where the water is
fast and deep. A sampling iron is often used
when water samples are collected from shores,
stream banks and wharves.

Figure I.7.6. Multiple sampler

Sampling of ice and snow under winter conditions
requires somewhat different techniques. The safety
precautions outlined in 8.9 should be followed.
Overlying snow should be removed from the ice
surface to provide a suitable working area.
7.4.1 General preparation
(a) Obtain specifi c instructions on sampling
(b) Prepare an itinerary according to the sampling
schedule (also 2.4.3);
(c) Prepare lists of required equipment and materials;
(d) Ensure that all sample bottles have been cleaned
in accordance with standard procedures;
(e) Ensure that the laboratory has prepared the
chemical reagents and standards needed for the
(f) Prepare a checklist (7.4.3 below).
7.4.2 Selection of sample volumes
The volumes of the particular samples required
depend on the type and number of parameters to
be analysed, the analytical method and the expected
concentrations of the constituents in the water.
Laboratory personnel will specify the sample
volume required. The required sample volume can
be determined by listing all of the parameters that
are preserved in the same way, totalling the volume
needed for preparation and analysis, and then
multiplying by two for duplicate and three for triplicate analyses. The following points should be kept
in mind:
(a) When contact with air is to be avoided, the
sample container should be completely fi lled;
(b) When samples require vigorous shaking before
taking aliquots for analysis, the container
should not be completely fi lled;
(c) Where both requirements must be met, the
bottle should be completely fi lled, but pieces of
clean, sterile inert solid such as beads should be
(d) When the sample contains discrete particles,
for example, undissolved materials, bacteria
and algae, a volume of sample larger than usual
maybe needed to minimize errors.
7.4.3 Checklist prior to fi eld trip
(a) Check and calibrate meters (pH, specific
conductance, dissolved oxygen and turbidity)
and thermometers;
(b) Replenish supplies of reagents for dissolved oxygen determinations as well as reagents for
chemical preservation;
(c) Obtain fresh buffer solutions. The pH values
for the buffers should be close to the values
expected in the fi eld;
(d) Obtain KCl solution for pH probes;
(e) Obtain road maps, station-location descriptions, fi eld sampling sheets, sampling bottles,
labels, samplers, preservation reagents, pipettes
and equipment manuals;
(f) Obtain writing materials, extra rope and a
comprehensive toolbox;
(g) Obtain electrical cables if the equipment has
in-fi eld charging capabilities;
(h) Obtain ultrapure water (resistivity of 18.2 MΩ)
and prepare clean beakers for pH, blanks and
buffer measurements;
(i) If fi eld fi ltering is required, obtain fi ltering
gauge and perfectly clean fi lters;
(j) If microbiological sampling is to be done,
obtain sterile bottles and ice chests. Ice chests
are recommended for all sample storage;
(k) Check the contents of the emergency fi rst-aid kit.
7.5.1 Automatic monitoring
The use of one particular instrument requires that
the water be pumped and that the measurements
be made on shore. Other instruments use probes
immersed in the water body and the measurements are made in situ. A more recent type is a
self-contained, battery-operated instrument that
can be operated as much as 300 m below the
Currently, automatically measured parameters
include pH, temperature, specific conductance,
turbidity, dissolved oxygen, chloride, redox potential, stage, sunlight intensity and ultraviolet
7.5.2 Field-measured parameters
Conductivity, pH, dissolved oxygen, temperature,
turbidity, colour and transparency can change on
storage of a sample, and should therefore be measured in the field as soon as possible after the sample
The sample collector should also look out for any
unusual features of the water body being sampled
or any changes since previous sampling periods.

These qualitative observations might include
unusual colour, odour, surface films and floating
objects. Any special environmental conditions,
such as rainfall, heavy winds, storm runoff, or ice
break-up, should be noted. pH measurement
In unpolluted natural waters, the pH is largely
controlled by a balance between carbon dioxide,
carbonate and bicarbonate ions. The concentration
of carbon dioxide can be altered by exchanges at
the air-water interface and by photosynthesis and
decay processes. Changes in the pH are caused by
acid rain, industrial wastes, mine drainage or leaching of minerals. The pH is an important criterion of
the quality of water since it affects the viability of
aquatic life and many uses of the water. Being
temperature dependent, pH measurement must be
strictly associated to the sample temperature at the
sampling moment. Optimally, the pH is determined
in situ, using a digital meter with a combined electrode permitting simultaneous temperature
The pH may also be determined colourimetrically
by using pH indicators and buffer standards for
visual or colourimeter comparison. This method is
generally less accurate and is limited to waters with
a low content of coloured substances and with little
turbidity. In the field, the instrument should be
recalibrated before each reading with appropriate
buffer solutions and according to the instructions
in the operating manual. The temperature of the
buffer solutions and electrodes can be adjusted by
submerging the bottles of buffer and electrodes in
the water sample.
Extreme care must be taken to prevent the water
from entering the buffer bottles. If the electrodes
have not been used recently or have been allowed
to dry for several days, they may require 10 to 20
minutes to stabilize. The meter should be
protected from extreme temperature changes
during measurement as these affect the stability
of the electronic system and measurement
When combined electrode assemblies have been
stored dry for a long period, the glass membrane
should be soaked in a 3 mol/l KCl solution for
12 to 24 hours before use. pH meters may have
a probe-storage reservoir that should be filled
with electrolyte. Glass electrodes that have not
been conditioned before use may not stabilize
properly and may require frequent
If the pH meter shows a drift and the probe has
been stored and correctly conditioned, the probe
itself may require topping up with additional
3 mol/l KCl solution.
If there is persistent drifting, the electrode should
be soaked in ammonium hydroxide. As with any
piece of equipment, the probe should be protected
from sludge, frost and rough handling at all times. Conductivity measurement
Conductivity is an indicator of salt, acid and base
non-organic concentration of ions dissolved in
water. The relationship between conductivity and
the concentration of dissolved solids is usually
linear for most natural waters.
In situ conductivity measurement is preferable.
Being temperature dependent, the conductivity
meter should give a value for either a reference
temperature (generally 20°C or 25°C) or the sample
temperature, which must be recorded simultaneously. This is important to calculate and compare
sample conductivity at a given reference time.
Before any measurements are taken, the sample
containers and probe should be rinsed several times
with the water sample. The water sample in which
the pH was measured should not be used to measure the specifi c conductance, as KCl diffuses from
the pH electrode.

The instrument should be recalibrated in the field
before each reading. The KCl standard solutions,
with the specific conductance closest to the values
expected in the field, should be used. Equipment
for measuring conductivity must receive the same
care and maintenance required by all sensitive
instruments. Accurate readings require that the
meter be protected from sludge, shocks and

The accuracy of measurement will depend upon
the type of instrument, the way in which it has
been calibrated and the actual conductivity value
of the sample. If care is taken in selecting and calibrating the instrument, an uncertainty of ±5 per
cent of full scale should be possible over a temperature range of 0°C to 40°C with automatic temperature
compensation. Dissolved-oxygen measurement
Dissolved-oxygen concentration is important for
the evaluation of surface water quality and of waste
treatment process control.

There are two methods for dissolved-oxygen measurement: the fi rst is in situ by using a polarographic
or potentiometric (oxymeter) probe. The second is
by using a Winckler chemical analysis. In the
Winckler method the addition of reagents (Mn++
solution and basic iodure solution) in the sample at
the moment of its grab permits its oxygen fi xation.
Analysis will then be performed in the laboratory
on a sample preserved by light. There is also a fi eld
method based on the same principle, namely, the
Hach method using pre-dosed reagents.
As concentrations may show large changes during
the day, in situ time measurements are advisable.
For the chemical method, three water samples
should be collect with the dissolved-oxygen sampler
( Measurement of the dissolved-oxygen
concentration of the samples is done by using a
dissolved-oxygen meter or a Winkler chemical
analysis. The recorded dissolved-oxygen value
should be the average of at least two readings that
are within 0.5 mg/l of each other.
In the electrochemical methods the probe responds
to activity of oxygen, not concentration. Freshwater
saturated with oxygen gives the same reading as
saltwater saturated with oxygen at the same pressure
and temperature, although the solubility of oxygen
in saltwater is less. Thus, salinity, temperature and
atmospheric pressure should be considered when
In the Winkler chemical method there are interferences when samples are highly coloured or turbid,
or contain readily oxidizable or other interfering
substances. This method is largely used in laboratories for its accuracy in measuring dissolved-oxygen
The probe method can be used when results are
within ±0.5 to 1.0 mg l–1 of the true value and are
suffi cient for the purposes of the study. If the sample
has a relatively high dissolved-oxygen concentration, the accuracy is adequate, but in some cases
the dissolved-oxygen concentration is shown to be
very low; then it is important to use a new and carefully calibrated probe. Temperature measurement
Temperature measurements may be taken with a
great variety of thermometers. These include alcohol-toluene, mercury-filled, bimetallic strip or
electrical thermometers. The last category includes
thermocouples and less portable varieties, such as
thermistors, quartz and resistance thermometers.
Some meters, such as those used to measure
dissolved oxygen, pH, Eh and specifi c conductance,
have temperature-measuring capabilities.
Before its use, the thermometer is rinsed with a
portion of the water sample. The thermometer is
immersed in the sample for approximately one
minute or until the reading stabilizes. The thermometer must not be placed in any of the sample
bottles being shipped to the laboratory. The value
should be recorded in degrees Celsius on the field
In general, the accuracy of water-temperature
measurements of 0.1°C will not be exceeded.
However, in many circumstances, an uncertainty of
0.5°C can be tolerated and there are many instances
where statistical temperature data are quoted to the
nearest 1°C. Thus, it is important to specify the
operational requirements so that the most suitable
thermometer can be selected. Turbidity measurement
Turbidity is an optical measure of suspended sediment such as clay, silt, organic matter, plankton
and microscopic organisms in a water sample.
Turbidity virtually affects all uses of water and adds
to the cost of water treatment. Whenever possible,
turbidity should be measured in situ. Turbidity can
be measured by visual methods (in Jackson turbidity units or JTU) or nephelometric methods (in
nephelometric turbidity units or NTU). Using the
Jackson Candle Turbidimeter, the distance through
the suspension at which the outline of the standard
candle becomes indistinct is compared with standard suspensions.
Nephelometric methods are preferred because of
their greater precision, sensitivity and application
over a wide turbidity range. They measure light
scattering by the suspended particles. However,
instruments of different design may give different
results for the same sample. Colour in the sample as
well as variations in the light source can cause
errors. Both problems can be minimized by using
an instrument that simultaneously measures the
scattered and transmitted light, with both scattered
and transmitted beams traversing the same path
To operate the turbidity meter, calibration curves
for each range of the instrument should be prepared
by using appropriate standards. At least one standard in each range to be used should be tested,
making sure that the turbidity meter gives stable
readings in all sensitivity ranges. The sample should be shaken vigorously before analysis. Readings
should always be made after the same time period
following the homogenizing of the sample (for
example, 10 seconds) to ensure uniform data. It is
important to pour off the sample quickly and to
measure the turbidity of the sample in triplicate.
The performance of a given turbidimeter will
depend on the frequency of calibration with a
formazin standard and the way that the sample is
presented to the instrument. As a general guide,
nephelometers used under laboratory conditions
should be accurate to within ±1 formazin turbidity
unit (FTU) in the range 0 to 10 FTU, and to ±5 FTU
in the range 0 to 100 FTU at 95 per cent confi dence
level. The uncertainty of absorption meters will
vary considerably, but should give at least ±10 per
cent of full scale for any given range of turbidity.
In practice, the performance of turbidimeters
depends, to a large extent, on their optical confi guration and, in the case of instruments that accept a
fl owing sample and give a continuous reading, on
their ability to withstand fouling of optical surfaces
by algal growth and sediment build-up, which
would otherwise result in calibration drift and
insensitivity. Colour measurement
The true colour is observed after fi ltration or centrifugation. Colour results from the presence of
metallic ions, humus and peat materials, plankton
and industrial wastes. Colour is important for potable water supplies, washing or processing, or
recreational purposes.
The hues ordinarily present in natural waters can
be matched by mixtures of chloroplatinic acid and
cobaltous chloride hexahydrate. Because this
method is not convenient for fi eld use, colour may
be obtained by visually comparing standard glass
colour discs with tubes fi lled with the sample.
Waters mixed with certain industrial wastes may be
so different in hue from platinum-cobalt mixtures
that comparison is inappropriate or impossible. In
this case, a fi lter photometer may suffi ce, although
a double-beam spectrophotometer would be preferable if the samples can be taken to the laboratory. Transparency measurement
Transparency of water is determined by its colour
and turbidity. A measure of transparency can be
obtained from depth in metres at which a 20- to
30-cm diameter disc – called a Secchi disc and
usually painted in black and white quadrants –
disappears when lowered slowly and vertically into
the water. Standard type on white paper is sometimes used instead of the disc. The measurement is
usually made in lakes and other deep-water bodies
and is useful in assessing biological conditions. General summary of fi eld procedures
Regardless of the specifi c parameters of interest, a
routine should be followed at each sampling station.
The following is a general summary of procedures
to be followed at each station:
(a) Calibrate meters;
(b) Standardize sodium thiosulphate when using
Winkler analysis for dissolved oxygen;
(c) Run fi eld or in situ measurements for pH,
conductivity, dissolved oxygen, temperature
and turbidity;
(d) Rinse all bottles with sampled water except for
those that contain preservatives or those used
for dissolved oxygen and bacteria analyses;
(e) Collect and preserve samples according to the
instruction manual;
(f) Complete fi eld sheet accurately according to
the instruction manual;
(g) Put bottles in appropriate shipping containers;
(h) Label boxes and complete fi eld sheets with all
required information.
Environmental monitoring is mainly based on
physical-chemical analysis techniques to evaluate
the concentration of pollutants, sediments and
living organisms in water. The major inconvenience
of these methods may be their lack of information
about the actual chemical impact on living
organisms. Furthermore, certain groups of toxic
pollutants are not detectable. This occurs because:
(a) These molecules infl uence living organisms at a
concentration below detection limits;
(b) There may be completely new molecules;
(c) The evolution of these toxic pollutants in the
environment is little known (in this case the
problem is to identify the by-products to be
Thus, the great variety of potential pollutants in the
monitoring media makes these methods highly
costly. Lastly, if chemical analyses inform about the
existence or non-existence of a pollutant in different ecosystem compartments (water, soil, sediments
or organisms), they are in any case insufficient to

predict the actual impact of the toxic substances on
the organism, since the numerous interactions
between pollutants and pollutants/organism have
not been considered. Biological analyses can integrate the interactions between all the present
pollutants and organisms and can diagnose the
pollution impact on the organisms living in the
ecosystem more realistically.
Biomonitoring is the study of the living response to
all the degrees of biological organization (molecular, biochemical, cellular, physiological, histological,
morphological and ecological) to pollutants. This
defi nition (McCarthy and Shugart, 1990) identifi es
the following levels of observations:
(a) At the intra-individual level a biomarker is the
biological response detected at a level below the
individual to a substance present in the environmental product (van Gestel and van Brummelen, 1996). This response measured in an
organism or in its products shows a change in a
normal state, for example, the modifi cation of
an enzymatic activity owing to a defence process in the organism. Biomarkers are also specifi c
molecular, biochemical, physiological, histological and morphological changes in animal
and vegetal populations observed after exposure to pollutants;
(b) At the level of individuals or organisms a bioindicator is performed by measuring the vital
functions of a biological entity which, owing
to its ecological specifi city, reacts to a pollutant with a relevant specifi c modifi cation of its
vital functions (Kirschbaum and Wirth, 1997),
for example, an alteration in the growth of a
microinvertebrate organism;
(c) At the level of populations and settlings, the
hydrobiological analysis obtains integrative
data on global water quality. There are biological indexes permitting the study of all or parts
of the species settled in an ecosystem and the
variations of their composition and structure
owing to an anthropic factor. It is thus possible to defi ne quality classes by the normalized
inventory of certain species. For example, the
Environmental Biological Index uses macroinvertebrate fauna as an environmental compartment integrator; a standardized sampling
considering different types of settling habitats
shows the ecosystem quality by the presence or
absence of faunistic indicator groups.
In the current phase of biological monitoring, the
studies using biomarkers concern the research of
new methods to evaluate the health of organisms
and practical applications to a larger amount of
comproved techniques of pollution monitoring.
Routine biomarker methods are still limited, but
current studies show that it is already possible to
detect polluted areas considering the health of
organisms living there. The methods based on the
studies at the organism or population level are used
in biomonitoring network. Microbiological and
macrobiota sampling will soon be developed.
Furthermore, there are also methods concerning
the global evaluation of the environmental river
self-epuration capacity. BOD, developed in this
chapter, is the most widely used method.
7.6.1 Microbiological analysis
The presence of living fecal coliform bacteria indicates inadequately treated sewage. The complete
absence of coliforms, and especially of fecal coliforms, is mandated by the World Health
Organization for any drinking water supply. Other
micro-organisms responsible for human diseases
are sometimes found in water, for example the
cholera and typhoid agents, salmonella, pseudomonas, and certain single-celled animals, such as
those that cause amoebiasis.
In order to accurately refl ect microbiological conditions at the time of sample collection, it is very
important that all water samples submitted for
microbiological analysis be collected as aseptically
as possible.
Microbiological samples are usually collected in
sterile 200- or 500-ml wide-mouthed glass or nontoxic plastic bottles with screw caps. Plastic
containers should be checked to make sure that
they do not shed microscopic particles capable of
confusing some kinds of bacterial counts. Metal
and certain rubber containers may exert a bacteriostatic effect. If capped, the bottle cap should have
an autoclavable silicone rubber liner. If tapered, the
bottle mouth should be covered with sterile heavyduty paper or aluminium foil secured with either
string or an elastic band.
Whenever possible, water samples should be
analysed immediately after collection. If immediate
processing is impossible, then samples should be
stored in the dark, in melting ice. Storage under
these conditions minimizes multiplication and dieoff problems up to 30 hours after collection. Samples
should never be frozen. If samples are suspected of
containing concentrations greater than 0.01 mg l–1
of heavy metals, such as copper, nickel or zinc, their
bacteriostatic or bactericidal effects should be minimized by the addition of 0.3 ml of a 15 per cent
solution for each 125 ml of sample of ethylene

diamine tetra-acetic acid (EDTA) (Moser and
Huibregtse, 1976). Residual chlorine should be
destroyed by the addition of 0.1 ml of a 10 per cent
solution of sodium thiosulfate for each 125 ml of
7.6.2 Macrobiota
There are several categories of multicellular species
that may be monitored for a number of different
reasons. Fish, as the top of the aquatic food chain,
are indicative of a variety of water quality conditions, dependent on their type and age. Benthic
macroinvertebrates (organisms living on or near
the bottom that are retained by a standard sieve)
are indicators of recent pollution events because of
their low mobility and sensitivity to stress.
Periphyton are sessile plants, growing attached to
surfaces, and those that grow in the mat attached to
it are some of the primary producers of aquatic
organic matter, particularly in shallow areas.
Macrophytes are large plants, often rooted, that
cover large areas in shallow water and may interfere
with both navigation and recreational uses of a
water body. Plankton are small free-fl oating plants
and animals. Phytoplankton are primarily algae
whose growth is an indirect measure of, among
other things, the concentration of nutrient chemical constituents. Zooplankton are found at all
depths in both lentic and flowing waters.
Many of these organisms can be troublesome in
water treatment. For example, algae clog filters,
consume extra chlorine, adversely affect odour and
taste of water, and some are toxic. Other species
may be carriers of disease-causing organisms, such
as the snails that carry guinea worm larvae or
Fish can be collected actively, with seines, trawls,
electro-fishing, chemicals, and hook and line, or
passively, with gill nets, trammel nets, hoop nets
and traps. Macroinvertebrates may be sampled
qualitatively by many methods, depending on their
habitats and other parameters. In addition to nets,
two methods are multiple-plate samplers and basket
samplers. These are left suspended in place by fl oats
for periods of four to eight weeks, and then are carefully raised to the surface with a net underneath for
dislodgement of the specimens.
Plankton can be collected by using the water
samplers described above in 7.3. There are also
specially designed samplers, such as the Juday
plankton trap, which encloses at least 5 l of sample
at the desired depth and fi lters out the plankton. It
is rather expensive and awkward to handle from a
boat. Zooplankton require large samples, and a
metered nylon net can be employed. Periphyton
can be sampled by exposing anchored or fl oating
slides at the site for at least two weeks.
For macrophytes, a garden rake can be used in shallow water and dredges can be used in deeper water.
From a boat, a cutting knife on the end of a pole or
a simple grapple can be used. For some purposes,
the self-contained underwater breathing apparatus
has been found to be useful.
It is recommended that a suitable stain such as rose
bengal be added before any fi xatives. At a later date,
the preserved animals can be picked out by personnel with less biological training because the colour
causes them to stand out against the background.

Table I.7.1. Techniques generally suitable for the preservation of samples

Tables recommending methods for the preservation
of specimens of macrobiota are included in
Table I.7.1. Some practitioners prefer the use of
lugol solution rather than formaldehyde for periphyton and plankton.

7.6.3 Biochemical oxygen demand
The discharge of polluting organic matter into a
water body instigates a natural purifying action
through the process of biochemical oxidation.
Biochemical oxidation is a microbial process that
utilizes the polluting substances as a source of
carbon, while consuming dissolved oxygen in the
water for respiration. The rate of purification
depends on many conditions, including the temperature and the nature of the organic matter. The
amount of dissolved oxygen consumed by a certain
volume of a sample of water for the process of
biochemical oxidation during a period of five days
at 20°C has been established as a method of measuring the quality of the sample, and is known as the
biochemical oxygen demand test or BOD. Oxidation
is by no means complete in fi ve days and for some
purposes longer periods of incubation may be used.
The incubation period may be indicated by a suffi x,
for example, BOD5 or BOD20, and the results are
expressed as mg of oxygen per litre of sample.
BOD is defined as the total amount of oxygen
required by micro-organisms to oxidize
decomposable organic material. The rate of
biochemical oxidation is proportional to the
remaining amount of unoxidized organic material.
Thus, the BOD test is used to estimate the amount
and rate of de-oxygenation that would occur in a
watercourse or lake into which organic material is
discharged. However, the predictions of the effects
of such discharge are more complicated and may
involve many other factors not involved in the determination of BOD.

For example, suspended organic material can be deposited onto a stream bed in a slow-moving stream just downstream from
the source of discharge, where it may have a
considerable effect on the local dissolved oxygen
content. The presence of benthos, rooted plants
and planktonic algae also influence the dissolved
oxygen regime on a daily basis.
Serious complications in the BOD test can also
occur as a result of the presence of nitrifying bacteria that will oxidize ammonia and organic nitrogen
compounds to nitrite and nitrate.
Industrial effluents may also present problems
because of potentially high concentrations of
pollutants, which may suppress biochemical oxidation in the receiving water under natural conditions.
In these circumstances, the sample may have to be
diluted with pure water and “seeded” with sewage
effl uent that contains the active micro-organisms
required to start the biochemical oxidation process.
Special sample preparation techniques may have to
be developed to suit the sample to be tested. Methods of measurement
Several methods have been developed for the measurement of BOD. The one most commonly used is
the dilution method, but manometric techniques,
while still mainly used for research, may have
advantages in some circumstances, for example the
control of sewage effluent. Ideally, the sample
should be analysed immediately after it has been
taken from the effluent, watercourse or lake. If this
is not possible, the sample must be kept at a temperature of 3° to 4°C to slow down the biochemical
oxidation processes. If BOD of a sample is estimated
to be greater than about 7 mg l–1, appropriate dilution and/or seeding of the sample are necessary. An
excess of dissolved oxygen must be present in the
sample at the end of the test period for the BOD
value to be valid.
BOD is calculated from the measurement of volumetric dilution of the sample and the difference
between the dissolved-oxygen concentrations of
the sample ( before and after a five-day incubation period. During this period, a temperature of
20°C should be maintained, and atmospheric
oxygen should be excluded from the sample, which
should be kept in the dark to minimize the effect of
photosynthetic action of green plants. However,
the oxygen consumed by the respiration of algae is
included in the test. For samples in which nitrification may occur during the test, allylthiourea (ATU)
is added to the sample prior to incubation. In this
case, the resulting apparent BOD is indicative of
carbonaceous polluting matter only. The rate of
biochemical oxidation can be estimated on the
basis of incubating five identical BOD samples and
measuring the dissolved oxygen in the first bottle
on day 1, the second bottle on day 2, the third
bottle on day 3, the fourth bottle on day 4, and the
fifth on day 5. The logarithm of BOD should plot
against time as a straight line. Extrapolation of the
straight line to ultimate time results directly in an
estimate of the ultimate carbonaceous BOD, which
is a measure of the total amount of oxygen required
to oxidize decomposable organic material. Accuracy of measurement
The BOD test is rather inexact. If statistical signifi –
cance is to be made of the results, several samples
must be diluted and incubated (and seeded, if necessary) under identical conditions, and an average
BOD calculated. To achieve higher accuracies, it has
been suggested that the manometric test should
replace the dilution method. It should be borne in
mind that the two methods are not always directly
comparable (Montgomery, 1967). The manometric
method can give an indication of the biological
oxidizability of a sample in a period shorter than
five days.

7.7.1 Filtration
Sample filtration is recommended for separation of
dissolved from particulate matter. Centrifuging
requires more equipment, settling requires more
time, and both cannot be easily calibrated and may
increase contamination hazards. The filtration
should be carried out in the field during or immediately after sample collection and must be followed
by appropriate sample preservation procedures.

The total concentrations of metals may be determined by using a second unfiltered sample collected
at the same time. This sample will undergo an acid
digestion in the laboratory permitting particulate

Samples requiring analysis for organic constituents
are filtered immediately after collection by using a
glass fibre filter or a metal membrane. The fi ltrate
maybe analysed for dissolved organic constituents,
and the filtre supporting the particulate fraction is
available for particulate-organic analysis.

The adsorption of dissolved substances on the filter
material can be a serious problem.
The best materials to be used for mineral substances
are organic filters (polycarbonate, cellulose acetate
or Teflon) and glass fibre filters for organic
The fi lter and filtration apparatus require laboratory pretreatment and should be rinsed with a
portion of the collected sample before the filtrate is
collected, by discarding the fi rst 150 to 200 ml of
filtrate. Either an electrical or a manual pump must
be used to create the vacuum in the filtration apparatus. If an electrical pump is employed, filtration
will require access to electrical services or the operation of a mobile power unit. Vacuum may cause
changes in the pH due to loss of carbon dioxide,
and result in the precipitation of some metals. For
this reason and to reduce losses due to adsorption
on the walls of the container, metal samples are
often acidified.
7.7.2 Preservation techniques
Between the time that a sample is collected in the
field and analysed in the laboratory, physical,
chemical and biochemical changes may take place.
Consequently, this time should be minimized as far
as practicable, or sample preservation must be
For several determinants, preservation is not possible and the measurements must be made in the
field. Even when the constituent is reasonably
stable, it is usually necessary to preserve the samples.
This is done by various procedures, such as keeping
the samples in the dark, adding chemical preservatives, lowering the temperature to retard reactions,
freezing samples, extracting them with different
solvents, or using fi eld column chromatography. Containers
The use of appropriate containers is very important
in preserving the integrity of the sample especially
when constituent concentration is low. Specifications
are generally provided by laboratories. Many publications contain recommendations on which type
of container should be used for particular cases
(Clark and Fritz, 1997).
The major types of container materials are plastic
and glass. Borosilicate glass is inert to most materials and is recommended when collecting samples
to be analysed for organic compounds. Polyethylene
is inexpensive and adsorbs fewer metal ions. It is
used for samples that will be analysed for inorganic
constituents. Polyethylene containers should not
be used to trace organic samples, such as pesticides
and some volatile substances that can diffuse
through plastic walls. Light-sensitive samples
require opaque or non-actinic glass containers.
Narrow-mouthed bottles with pointed glass stoppers are used for dissolved gases. Containers for
microbiological samples must withstand
For tracking elements, only low- or high-density
polyethylene (LDPE and HDPE) should be used.
Today disposable containers are available. Before
use, they must be pre-decontaminated. They must
be kept, for at least 24 hours, in an ultrapure 10 per
cent solution of HNO3, then rinsed in ultrapure
(18.2 MΩ) water and preserved in polyethylene
bags until their fi eld use (Pearce, 1991).
Bottle caps are a potential source of problems. Glass
stoppers may seize up, particularly with alkaline
samples. Cap liners other than Tefl on may introduce contaminants or absorb trace samples. The
smaller the concentrations in the sample of the
species to be determined, the more important these
aspects become. Chemical addition
This method is used for most dissolved metals
and phenoxy acid herbicides. Some samples for
biological analysis also require chemical
As a general rule, it is preferable to use relatively
concentrated solutions of preserving agents.
Corrections for the dilution of the sample by the
small volume of preserving agent will then be small
or negligible.
Potential interference of the preservative with the
analysis requires that procedures be carefully
followed. For example, an acid can alter the distribution of suspended material and can lead to
dissolution of colloidal and particulate metals.
Thus, the order of fi rst fi ltration and then acidifi cation becomes very important. Freezing
When analysis is impossible in a reasonable period
of time, freezing is recommended for the analysis of
main anions, that is, chloride, sulfate and nitrates.
However, this is not a general preservation technique because it can cause physical-chemical
changes, for example, the formation of precipitates and loss of dissolved gases that might affect the
sample composition. In addition, solid components
of the sample change with freezing and thawing,
and a return to equilibrium followed by high-speed
homogenization may be necessary before any analysis can be run. Water samples should never be
frozen in glass bottles. Refrigeration
Refrigeration at 4°C is a common preservation technique. In some cases it may affect the solubility of
some constituents and cause them to precipitate.
Refrigeration is often used in conjunction with
chemical addition. Practical aspects of preservation
An important aspect of preservation is adherence to
a consistent routine to ensure that all samples
requiring preservation receive immediate treatment. This is particularly important when a
chemical preservative is added, as such additions
may not produce an easily detectable change in the
appearance of the sample. It may be advisable to
mark or fl ag each preserved sample to ensure that
none is forgotten or treated more than once.
Safe and accurate fi eld addition of chemical preservatives also requires special precautions. Pre-calibrated
and automatic pipettes ensure accurate fi eld addition, as well as eliminating the safety hazard of
pipetting acids by mouth. It is often convenient to
add the preservative in the laboratory before the
sample containers are taken to the fi eld. Another
alternative is to use colour-coded or labelled, sealed
vials containing pre-measured preserving agents.
Although more expensive, this method has the
advantage of simplifying the fi eld procedure and
reducing the possibility of error and contamination.

Teledetection permits the characterization of the
spatial and temporal changes obtainable by other
methods. However, it is not accurate in terms of
local ground measures. Furthermore, it should be
implemented with satellite image readings to interpret images in water quality and soil measurement
terms. Remote-sensing application for suspended
matter evaluation is discussed earlier in Chapter 5.
More detailed information is provided on applications such as vegetation characterization, salinity
and water temperature.
Satellites can be divided into two groups, depending on their energy source. Passive satellites need
sunlight to capture object images on the Earth’s
surface. They generally operate in the visible and
infra-red domain of EMS and supply the so-called
“optic” images. Active satellites have their own
energy source. They operate in the microwave
domain of EMS and supply the so-called “radar”
Furthermore, satellite images can be differentiated
according to four basic criteria:
(a) Range gating corresponding to pixel size. There
are small sized (1 km or more, such as NOAA,
SPOT vegetation or meteorological images),
medium (20 m or more, such as Landsat MSS
and TM or SPOT 1 to SPOT 4 images) or outsized
range gating (10 m or less, such as in SPOT 5 or
(b) Spectrum gating corresponding to the wavelength in which images have been taken;
(c) Passage frequency of the satellite;
(d) Radiometric gating corresponding to the
detector ability to catch the received radiant
The choice of satellite image is determined by many
factors. First, the size of the studied area should be
considered. It will not be possible to study a 20-km2
marsh with a NOAA image based on low-range
gating. Spectrum gating will be chosen according to
the programme objectives. For example, an optical
image is advisable to study water turbidity. Finally,
the equalization between the time variables of the
studied phenomenon and the satellite passage
frequency over the studied area are required.
7.8.1 Water-quality study in the
visible and infra-red domain
From the visible domain to the near IR, the radiometric response of pure water is like that of a black
body absorbing the whole incident radiation. This
well-known property is used to easily locate the
presence of water on a satellite image.
Different factors, such as water salinity and turbidity, soil composition or vegetation presence, alter
water radiometric response, which can therefore be
used to inversely characterize these factors.
The best positive correlation between radiometric
response and turbidity is in the green range (Bonn,
1993). This will indirectly provide indications on
salinity. In fact, salinity and turbidity are generally
inversely correlated. When salinity arises, it results
in flocculation followed by sedimentation of suspended matter and the lowering of the turbidity
of the water.

Water radiometric response in the near IR may be
perturbed by suspended matter and also by a shallow bottom (Chuvieco, 2000). For shallow waters,
absorption is low and refl ectance is large (due to
high bottom refl ectance). However this effect is
complex, as soil radiometric behaviour is infl uenced
by its chemical composition, texture, structure and
humidity. Therefore, a clay soil, for example, will
have quite a low refl ectance, compared with a sand
soil. The soil refl ectance range is very large between
light soils (sand, limestone or even gypsum), highly
refl ecting solar radiation, while dark soils (clay, rich
in organic matter) absorb nearly the full amount of
radiation (Bonn and Rochon, 1993).
In the radiometric domain, vegetation refl ectance is
reduced in the visible spectrum, but is very high in
the near IR. As regards vegetation, low response in
the visible range results from strong absorption of
chlorophyll, especially in the red range, whereas
the high response in the near IR is due to the internal cell structure of leaves. Thus, to study the
presence of vegetation in shallow waters it is advisable to use optical images (Shutko, 1986, 1990;
Gross and others, 1987).
The assessment of chlorophyll quantity in the
ocean and estuaries has been carried out from different images, especially Coastal Zone Colour Scanner
(CZCS) or AVHRR images (WMO, 1993). This assessment is limited to cases where suspended matter
concentration is low enough not to mask the refl ectance corresponding to that of chlorophyll (Ritchie
and others, 1992). Macrophytes and aquatic vegetation can be generally studied following these basic
principles (Ackleson and Klemas, 1987).
7.8.2 Water-quality study in the
microwave domain
In waters, the microwave domain permits a certain
penetration. Superfi cially it is possible to differentiate
a rough from a smooth surface by a lambertian or
symmetric response, respectively. For example, a
radar image may be used if roughness is due to the
presence of waves. These applications have also
been exploited to detect surface anomalies such as
those due to indiscriminate oil discharge. It has
proved, both theoretically and practically, that
microwave radiometry can be used to study salinity
and general water mineralization (Shutko, 1985,
1986, 1987). In fact, microwave emissivity is
sensitive to water conductivity variations, and thus
to water composition.
Teledetection in the thermal IR domains and microwave radiation can be used to evaluate surface water
temperature (examples in Engman and Gurney,
1991). Microwave radiation is less sensitive to
atmospheric conditions and thus it will be more
often used, but its resolution is rough compared
with that of the IR (Shutko, 1985, 1986).
References and further reading
Ackleson, S.G. and V. Klemas, 1987: Remote sensing of
submerged aquatic vegetation in Lower Chesapeake
Bay: A comparison of Landsat MSS to TM imagery.
Remote Sensing of Environment, Volume 22,
pp. 235–248.
American Public Health Association and American Water
Works Association, 1999: Standard Methods for the
Examination of Water and Wastewater. Twentieth
edition, Washington DC, CD-ROM.
Bonn F., 1993: Précis de Télédétection. Volume 2: Applications
thématiques, Presses de l’Université du Québec/AUPELF,
Sainte-Foy, Québec.
Bonn F. and G. Rochon, 1993: Précis de Télédétection.
Volume 1: Principes et méthodes, Presses de l’Université
du Québec/AUPELF, Sainte-Foy, Québec.
Chuvieco E., 2000: Fundamentos de la Teledetección Espacial,
Third edition, Ediciones RIALP, Madrid.
Clark, I. and P. Fritz, 1997: Environmental Isotopes in
Hydrogeology. Lewis Publishers, Boca Raton, Florida.
Engman, E.T. and R.J. Gurney, 1991: Remote Sensing in
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Genin B., C. Chauvin and F. Ménard, 1997: Cours d’eau
et indices biologiques: Pollutions, Méthodes, IBGN.
Etablissement National d’Enseignement Supérieur
Agronomique, Centre National d’Etudes et de
Ressources en Technologies Avancées,
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Gross, M.F., M.A. Hardisky, V. Klemas and P.L. Wolf, 1987:
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Hydrological Cycle: Principles and applications.

IHP-V, Technical Documents in Hydrology No. 39,
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land via microwave radiometry: the principles of
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Proceedings of Study Week on Remote Sensing and its
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Shutko, A.M., 1990: Offer on hardware, software and
services on survey of soil, vegetation and water
areas — from aircraft. Institute of Geoinformatics,
Nongovernmental Center for Research and Institute
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