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Sistema de Información Científica
Red de Revistas Científicas de América Latina y el Caribe, España y Portugal
WATER QUALITY CONSERVATION FOR BUBTAINABLE DEVELOPMENT
Gabriele 1. Engelmann
Am
Knappenberg 70, D-4600 Dortmund, Federal German Republic
1. Importance of water quality conservation
11. Preventive versus reactiye conservation strategies
111. Point sources and non-point sources of pollution
IV. Attempting a preventive water quality conservation strategy
1. Water quality monitordng
2. Data evaluation within a system context
3. Incorporation of environmental aspects into development
planning
V. Conclusions
1. Im~ortance
a
Water aualitv conservation
During the last twenty years public concern about the quality of
available freshwater resources has been constantly increasing,
due to the fact that ever more cases of serious pollution
problems became known. Water
-
like soil and air
-
is no longer
regarded as a practically inexhaustable resource which can be
disposed of without prior consideration.
Although the total volume of water on earth has been estimated to
be
1,400 millions cubic kilometers,
the amount of freshwater, easily accessible to human use is much
smaller (Table 1). This amount, however, has been regarded as
fairly constant, as it is constantly renewed via the hydrologic
cycle of precipitation
-
percolation
-
evaporation
-
condensation
-
precipitation. The main concern of water management used to be
the uneven distribution of freshwater over time and space (e.g.
flooding and draughts), and therefore hydrologic monitoring was
instituted rather early in most parts of the world with a view to
planning of regulatory measures and for providing sufficient
quantities of freshwater where and when it is needed.
With worldwide increasing population densities also water demand
for various uses was constantly rising, and questions of water
quantity management were given increasing priority.
However,
even a glance at table 1 reveals that not only accessibility but
also quality determines the availability of water for human use;
otherwise the enormous amount of water contained in the oceans
would not be excluded because of its salinity.
Table 2 shows the different water uses. It can easily be seen
that their requirements in terms of water quality are widely
different, the most vital water uses (domestic use and food
production) having the most exacting requirements. As table
3
shows, a large part of the world's population still has to live
without these basic requirements being satisfactorily met.
Table 1: Global water yesources
97.3% saline water
(oceans)
2.7% freshwater
of which:
77.2% stored in glaciers
and polar ice caps
22.4% soil moisture
.
and groundwater
of which:
65% below 750 m from
the surface
0.35% in lakes and swamps
0.01% in streams
0.04% in the athmosphere
0.4% of freshwater
(0.01% of al1 water)
Table 2: Water uses
-
domestic use
-
agricultura1 use (about 80% of global consumption)
-
industrial use
-
preservation of fish and wildlife
-
recreation and aesthetics
-
hydroelectric power generation
-
navigation
-
waste disposal
Table 3: Access to safe water suwwlv
develowina countries
(according WHO survey, 1976)
urban population
rural population
overall share of adequately
supplied persons
3 5%
Fig. 2: Model plots, illustratinq
flow
devendence
trans~ort
concentration
for
sources with
different
characteristics (a) flow dependence of concentration, (b)
flow dependence of transport, (c) linearization of
hyperbolic dilution curves
f
~OW
b
flow
--
___)
C
-
(1) Source of highly
variable contribution
to f low, but of
constant concentration
(e.g. surface run-off)
cl
=
constant
T1
=
Clfl
(2) Source of constant
input to the system,
diluted by surface
c
run-off. (e-g. ground-
."
..J
water)
m
L,
T2
=
c2f2
=
constant
1i
c
=
T2/(fl+f2)
C
u
C
(3)
A
constant source
O
(c2f2) diluted by a
u
less concentrated source
of highly variable flow
(c1f
1)
.
T3
=
c2f2
+
clfl
c3
=
T3/ (fl+f2)
However, different water uses do not only vary with regard to
their qualitative and quantitative requirements but also with
regard to the impacts they cause. In fact the relationship
between water uses and water conditions may be regarded as a
feedback system which only the natural self-purification
mechanisms prevent from collapsing, if no regulatory measures
such as wastewater treatment and treatment in water supply plants
are introduced (Fig.
1)
.
Fig. 1: Pelationshi~
between water
m
and water conditions
alter water conditions
>
water uses
determine possibility
of water uses
water conditions
1I.Preventive versus reactive conservation stratesies
From the foregoing paragraph it becomes evident that water
quality conservation is a must not only to provide an adequate
living standard to the majority of the world's population but
also to allow
sustainable
agricultural
and
industrial
development. At present this is regarded as a rather trivial
statement, however general recognition of this fact is rather
recent and based on painful experience. With view to large scale
epidemics, decreasing fisheries, contamination of aquatic and
agricultural products and salinization of irrigated lands, the
necessity of ameliorative measures became urgent, and water
quality aspects were given come priority.
Naturally most urgent cases attract most attention and have to be
considered first; in other words: we are forced to follow a
reactive strategy instead of spending sufficient time and efforts
on early problem detection and prevention. Still, most water
quality problems are not detected through evaluation of
T~~tTrlñg-~aWthroug+*-n~=
impacLs2hey~se
m-
water uses, i.e. at a rather late stage in the process of problem
development. However, once a problem has reached an acute stage,
efficient measures are time consuming and costly, whereas
regulatory measures at an early stage of problem development may
even represent economic savings.
Of course, those of us who are living in areas already affected
by serious problems have little choice of where to focus their
interest, but there are still large regions
-
especially in the
developing part of the world
-
where prevention is viable a
opt ion.
In this context one argument has to be mentioned, because it has
given rise to rather controversia1 discussions, namely that in
developing countries development itself should be the priority
target and should
not be hampered by environmental
considerations.
It is said that "the highly developed countries have used and
exploited their resources to the fullest possible extent and got
rich in the process.
Although
they are now ridden by
environmental problems, people there have a high living standard
and are not willing to accept a lower one for the sake of
environment.
It is hypocrisy, if such people advise against
rapid resource development by introducing al1 sorts of
enviromental concerns"
.
It cannot be denied that a purely protectionist attitude which
may be termed hypocrisy exists, but in general a sound
environmental programme is not opposed to developmont. Of
course, every environmentalist will advise against development
plans which drive at the complete exhaustion of the resoruce to
be developed, but on a long range such projects neither benefit
the economy of a country nor the living standards of its
population. Furthermore, in most cases it is possible to device
and alternative development scheme which yields sustainable
benefits, if environmental considerations are included into
development planning.
In fact, the ultimate target of a preventive water quality
conservation strategy is to maintain suitable water quality for
human uses by preventing excessive pollution, and not to protect
water quality by preventing human uses. Thus, it aims at
contributing to development and not at hampering it.
111. Point sources
a
non-voint sources
of
pollution
Effluentes from large human settlements and from industrial
plants are obviously pollution sources. Everybody working in the
field of environmental water chemistry would not need actual
measurementes to risk a fairly qualified guess about river water
quality below a point where such effluents are discharged
-u*=*
anc&i-t-=ases
-
W
_also
be able to suggest
adequate treatment measures. If a factory is newly installed,
decisions on the production process also determine the amount,
concentration and composition starts, it would be possible to
elaborate a corresponding waste treatment scheme, and
-
ideally
-
provide waste treatment from the very beginning. Also, if
production and waste treatment are planned and considered
simultaneously, it may be possible to match the specific
requirements to such a degree that economic benefits instead of
additional treatment costs result (e.g. biogas, a product of
anaerobic treatment, may be used as an additional energy source;
stabilization ponds may eventually be used for aquaculture of
water vegetables and fish, etc)
.
If a factory is already discharging untreated wastes over a
period of time, a monitoring station rnay be needed
-
not to
recognize the problem which is only too evident
-
but to
reinforce water legislation, cal1 for treatment measures and
supervise the results.
Al1 these cases have in common that
-
with our present state of
knowledge
-
it is possible to anticipate problems without
conducting long term investigations, and to suggest solutions
even though it rnay not be easy to enforce them. The situation is,
however, much more complicated, if we have to deal with non-point
source pollution which is the prevailing type of pollution in
rural areas. Non-point source pollution reaches a river via
surface run-off or via groundwater contribution to river flow.
It rnay be a direct result of human activities, but it rnay also be
a consequence of environmental changes which have been triggered
unintentionally. In such a case, the chain
-
or better the
network
-
of mechanisms which have contributed to water quality
deterioration cannot be easily detected, although we rnay already
be confronted with a full blown problem. In other cases the
origin of a problem rnay be evident
-
e. g. eutrophication through
run-off from agricultura1 lands where too much fertilizer is
applied
-
but ameliorative measures are difficult to design and
to reinforce. Wastewater treatment cannot be applied, as there is
no definite source of wastewater which could be treated.
In other words: our knowledge about the mechanisms of non-point
source pollution as well as our possibilities to anticipate
problems and interfere with them are much smaller than in cases
of point source pollution. This admittedly difficult situation
is discouraging many scientists from tackling the problem.
On the other hand, it is especially in the rural areas where the
importance of early problem detection and quality conservation in
surface waters is high:
-
small scattered settlements or frams cannot easily be supplied
with safe freshwater from supply plants, and people often have
to rely on untreated surface water for domestic use. (This
situation is reflected in table
3),
and
-
food (vegetables, meat, milk, freshwater fish, etc) is produced
in rural areas, and its quality and quantity depends on the
quality of available surface water.
Admittedly, in most rural areas, affected only or mainly by non-
point source pollution, acute water quality problems are still
localized and not widely spread. However, population density
(and consequently water demand and pollution) is worlwide on the
rise, and for many areas the possibility to chose a preventive
instead of a reactive water quality conservation strategy rnay be
lost in the near future.
IV. Attem~tinq
a
preventive water aualitv conservation strateav
1. Water quality monitoring
Obviously, in order to detect water quality problems at the
earliest possible stage, it is necessary to know the actual water
conditions and their changes over time. This knowledge cannot be
obtained by random checks, as the data obtained will be
influenced by too many unknown factors to lend themselves to
conclusive evaluation. Therefore, conducting regular monitoring
operations is prerequisite to obtaining a conclusive picture on
water conditions. Such operations include:
-
a set of sampling stations, chosen to reflect the typical
environmental conditions in the drainage area (e.g. geology,
topography, land use, population density, development potential
and development plans),
-
a set of relevant parameters (e.g. conservative ions,
indicators for: organic pollution, eutrophication, eventual
specif
ic problems) to be measured according to def ined
analytical methods, in order to render intercomparable results,
-
a regular sampling frequency, determined by seasonal changes in
rainfall and stream flow (e.g. monthly sampling to cover dry
and wet season conditions), and
-
a functional infrastructure which allows punctual sampling,
rapid transport of samples to the analytical centre(s),
facilities for reliable and punctual analysis of incoming
samples, and data recording.
As, in general, at least one annual cycle of measurements is
needed to cover seasonal changes in temperature and/or stream
flow, detection of long term changes and trends requires a
monitoring period of (at least) severa1 years. Ideally, such
operations should be instituted on a permanent level.
2. Data evaluation within a system context
Even the design of water quality monitoring network (e.g. the
selection of representative sampling stations and parameters to
be measured) requires inputs from other fields than water
chemistry, namely information on surface configuration, soils,
agriculture, forestry etc. For the evaluation of collected data
such information is even more
important.
A search for
significant trends and changes on a purely statistical basis
would require more data than one could reasonably hope to collect
within ten years of monthly sampling, and detection of courses
and mechanisms of such changes would be almost imposible. Thus,
the evaluation process would not be sensitive enough for early
problem detection.
Al least one other data set, namely hydrological and/or
meteorological data, should be available for evaluation of water
quality data. Dilution consequent on rainfall or concentration
during a long dry period of mainly evaporation account for many
concentration changes, and in many cases a thorough evaluation of
the qualitylquantity relationship already allows conclusions on
how pollutants reach a river. Ideally for every sample taken at a
certain station a corresponding flow value should be available;
where a hydrologic network already exists, water quality
monitoring stations will often be chosen to coincide with
hydrologic stations.
Where this is not possible, installa'ion
of a gauge and water
level recording, or even collection of meteorologic data from the
closest available station would give valuable information. In
addition, al1 available information on natural resources,
resource uses and eventual problems in the drainage area should
be considered as potentially relevant. In short: water quality
data should be evalluated in the context of the overall
environmental system.
The following example shows a problem which could be detected at
a rather early stage, although it was not directly due to human
activities but rather to natural conditions in a specific area.
It, therefore, arose somewhat unexpectedly and needed a
multidisciplinary effort to be fully understood:
The problem may be summarily described as salinization of surface
waters and surface soils on a plateau of 100-200 m elevation,
characterized by flat to gently rolling plains. Surface
configuration and soil properties in this area are suitable for
agricultura1 use, although rainfall distribution is erratic and
irrigation water has to be provided even during the rainy season,
in order to ensure a good harvest. Thus, irrigation development
was considered to be ot high priority, and the area became the
focus of large scale irrigation development projects, including
dam construction and water storage in reservoirs.
In this context, of course, the quality of irrigation water is of
high importance, and therefore water quality data were screened
with view to this question. It showed that during the dry season
the NaCl concentration of river water at some few sampling
stations approached the level at which salt becornes toxic to rice
plants (lg/L)
.
From the point of vzex
nfirrigation+Laíilt~i~g
~saidñot
FeEtobe
an acutely critica1 situation, as such
conditions occurred only at extreme low flow and seemed to be
confined to a few places only. However, it attracted attention
to salinity questions, and therefore salt concentrations and
their flow dependence were examined in more detail. This
evaluation showed that in al1 rivers of the area
-
even in those
where NaCl
-
concentrations never reached extraordinary values
-
salt concentrations decreased with flow whereas salt transport
increased with flow.
This pattern indicated that salt reached the river in two
different ways:
-
as salt transport increases with flow, surface run-off which
determines the high seasonal variations of stream flow must be
carrying salt to the river. This salt can only originate from
surface soils in the drainage area.
-.as salt concentration decreases with flow, there must be a
higly concentrated salt source of more or less constant flow
contribution which is diluted by surface run-off.
This was assumed to be seepage of saline groundwater.
On the basis of these assumptions, a mathematical model was
formulated which allows to calculate NaCl concentrations as a
result of flow and two site specific parameters, to be determined
through regression analysis (Fig. 2, Table 4). As can be seen
from Fig. 3, the data calculated according to this model
corresponded fairly well to the actually measured data.
Concurrently to this evaluation, exercise al1 available
information on salinity in the area was collected and a soil
survey and geological survey was conducted.
It was known that
the whole area is underlain by geological salt deposits, but
these had been considered previously to lie at too great a depth
to be of influence on surface conditions. Some heavily salt
affected, barren patches of surface soil had been regarded as a
completely independent phenomenon, due to evaporation of flood
water in poorly drained depressions over hundreds of years.
Even
the existence of saline wells in the area had not been considered
of importance, and had never been evaluated in the overall
context.
Now, considering al1 available information in a system
context, reevaluation of
previous assumptions apperared
necessary.
In fact, the findings from the new soil survey
explained satisfactorily the existence of saline soil patches and
saline wells, and also validated the results of water quality
data evaluation.
To briefly summarize these findings:
-
Salt bearing bed rock can be encontered close enough to the
surface to be exposed by erosion; in many cases it had been
exposed already.
-
Water which percolates the salt bearing geological formation
becomes saline. The brine may seep out at the footslope of
hills but may also travel large distances under ground, if an
impermeable clay layer prevents it from rising to the surface.
Shallow saline aquifers are frequent in the area. Where the
capping clay layer is disrupted or thin enough for capillary
rise to reach the surface a saline spot will form.
Thus, it became evident that salinity phenomena which appeared
localized and irrelevant to irrigation development, as long as
they were regardea separately, are in fact closely interrelated
(Fig. 4) and can be interpreted as the first indicators of a
potentially serious salinity problem. Careless irrigation
development may trigger the problem, as changes in the water
balance of the area
-
especially fluctuations of the shallow
groundwater table
-
have Fn important influence on salinization.
The problem described above is rather unusual, and thus the
resu1t.s obtained are valid and useful only for the area
concerned. Nevertheless, this example seemed suitable to
illustrate the advantages of data evaluation in a system context,
for the following reasons:
-
The problematic compound (NaCl) was not introduced to the water
by human activities, it could not even be regarded as a direct
consequence of agricultura1 development. Thus, without
considering the specific
geology
of the
area, NaCl
concentration could not be expected to be an especially
important parameter. It is doubtful whether simple screening of
water quality data or even comparison to a comprehensive list
of quality standards could have revealed the problem at such an
early stage, if evaluation had not been carried out with view
to already existing development plans.
-
Salinization of soils in connection with irrigation development
is not uncommon, but the mechanisms involved are normally of
different nature (i.e. evaporation of irrigation water results
in salt accumulation in poorly drained fields). Knowledge of
these ItnormalN mechanisms had been drawn upon to explain the
existente of saline spots. This preconceived explanation,
however, almost prevented detection of the true mechanisms of
soil salinization in this specific case. It proved untenable
as soon as other system components (geology, hydrogeology,
hydrology, water quality) were considered simultaneously with
soils.
3.
Incorporation of environmental aspects into development
planning
Early detection of potential problems and mechanisms of problem
development will not lead to water quality conservation, if the
knowledge is not used to elaborate a corresponding action plan
which
-
in case of non-point source pollution
-
includes
management measures in the drainage basin. Elaboration of such a
plan will be a multidisciplinary effort, as al1 system components
involved in the problem have to be considered simultaneously. If
knowledge on potential environmental problems is only obtained
and used to assess preconceived develpment projects (for instance
in form of an Environmental Impact Assessment, EIA), this will
often lead to rejection of development projects and thus
strengthen the
unproductive dispute "environment versus
development"
.
Following up on the example given earlier, one can imagine that a
large scale irrigation project, incluiding dam construction for
water storage, a delineated irrigation area and a conveyance
system had already been designed in some detail and were only
awaiting the results of an obligatory EIA for construction to
start. At this stage, the irrigation project would already have
received
large inputs of work and
funds, as detailed
topographical and geological surveys have to be conducted from an
engineering point of view, irrigation engineers have to design
the conveyance system, and eventually even a resettlement study
Eor people living in the future reservoir
area is necesary.
Thus, the general expectation would be for the project to go
ahead as soon as posible, the 'EIA being regarded as a bothersome
formality. At this stage, the perception that hydrostatic
pressure from the huge waterbody in the reservoir might drive the
saline groundwater to the surface, and that the irrigation area
might become barren instead of productive would be received
rather reluctantly. The best possible outcome of such a
situation would be avoidance of an environmental disaster by
stopping the irrigation project altogether, writing off previous
investments.
However, if it is still possible to decide for severa1 small
storage tanks instead of a large one, and to incorporate
knowledge of potential salinity problems into the siting of these
tanks instead of a large one, and to incorporate knowledge of
potential salinity problems into the siting of these tanks as
well as into the management of the irrigation areas, agricultura1
development can be achieved on a sustainable basis. At the same
time, surface water salinity can be kept at a tolerable level,
which
-
in turn
-
will benefit irrigation development and al1
other water uses.
Thus, it seems to be mainly a question of timely co-operation
whether accordance or confrontation between environment and
development issues will be achieved.
For a preventive water
quality conservation policy in areas of'mainly non-point source
pollution such co-operation is indispensable, as non-point source
pollution can only be regulated by managemente measures in the
drainage basin and not by water treatment.
V. Conclusions
Efforts to maintain suitable water quality in surface waters,
generally focus on water bodies which are already endangered by
obvious pollution sources. Much less attention is paid to those
water sources which appear comparatively unspoilt, as they
receive only or mainly non-point source pollution. As detection
of non-point source pollution and its mechanisms normally
requires long term monitoring activities and careful data
evaluation, such programes are often postponed in favour of more
urgent cases.
However, from and economic as well as from a technical point of
view, timely prevention of acutely critica1 situations (i.e. a
preventive strategy) is more rewarding than institution of
amelioratory measures after a problem has become acute (i.e. a
reactive strategy)
.
Although non-point source pollution poses specific difficulties
to early problem detection and regulatory interference, water
quality conservation can be achieved, if the strategy is based on
multidisciplinary co-operation from the very beginning. This
relates also
-
and especially
-
to co-operation with development
planners and decision makers, as sustainab1.e development relies
on maintainance of suitable resources, freshwater being one of
the most vital resources.
Table 4: Dewendence of salt concentration
transwort
flow
(theoretical deduction)
c1f 1+c2f2
c3
=
---------
(fl
+
f2)
~l(fl+f2)
-
c1f2
+
c2f2
=
----------------m-------
(fl
+
f2)
f
=
fl
+
f2
T
=
clfl
+
c2f2
J.
=
Cl
+
f2 (c2
-
c1)
---------
(fl
+
f2)
linear regression
:
y
=
c3
;
x
=
l/f
intercept: cl
slope: f2 (c2
-
cl)
T
=
c3 (fl
+
f2)
=
f2 (c2
-
Cl)
+
Cl (fl
+
f2)
linear regression
:
y
=
T
;
x
=
f
intercept:
f2 (c2
-
cl)
slope: cl
(A constant)
(A
constant)
cl: concentration of surface run-off
c2: concentration of groundwater
c3:
concentration of river water
f
:
stream flow
fl: flow contribution of surface runoff
f2: flow contribution of groundwater
(
constant)
T
:
Transport
Fig. 3: Com~arison between peasured
calculated
a
concentrations for two different river stations
t
iI 1
I
.
I
l
CP
0.77
+
21.74/flow
I
I
1
I
11
I
I
I
I
I
i
I
I
i
-i-x-
measured values
1
1
i
1
I
I
.-.
.-.
....
calculated values
-
1979'
-1980
'
'-1981
-
'
1987
-
Fig.4: A schematic view
of
svstem comvonentg and their
Jnterrelationchiv
CLIMATE
PLANT COVERAGE
>
Precipitation
SURFACE CONFIGURATION
/Iat
SURFACE
Irrigation
<-
SOIL ->Runoff,
Drainage
--+
SURFACE WATER
ExPosire
/T
by
Erocion
I
'.
~ercoiation
~eepage
Capillary Rice
seepage\
1
GEOLOGICAL
--+
SALT SOURCE
---t
Percolation
--
I
>GROUNDWATER
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