Modelling of A Wetland Through Sustainable Development
Burak Giineralp and Yaman Barlas
Bogazici University, Dept. of Industrial Engineering
80850 Bebek/Istanbul Turkey
Telephone: ++90 212 280 15 00 Facsimile: ++90 212 265 18 00
guneralp @boun.edu.tr, ybarlas @ boun.edu.tr
This project deals with management policies toward sustainable development in a
wetland. Wetlands are fragile ecosystems and constitute a great potential for economic,
cultural, scientific, and recreational value to human life. Conservation and effective
utilisation of natural resources can be achieved under sustainable development practices.
Achievement of these goals requires well understanding of system under study so a
holistic point of view is to be adopted. The geographical location of the region is in
Temperate Climate Belt and consists of a shallow lake and its surrounding, an important
nesting place for bird species. Fishing is a commercial activity. Ultimate goal of the
project is to seek balance between ecosystem and human activities in order to secure a
continuous improvement in well-being of the inhabitants while improving or at least
maintaining the ecosystem. To this end, a system dynamics model of the wetland system
will be constructed to analyse policy alternatives.
1. Introduction
Wetlands are extremely important because of their ecological functions and they form
rich ecosystems. They also constitute a great potential for economic, cultural, scientific,
and recreational value to human life. Similarly, shallow lakes form one of the most fragile
ecosystem types on earth and generally they are the first to perish under development
activities (Barbier et al., 1997). Shallow lakes have only recently drawn attention of
scientists; thus their ecology is still not well-known.
Recent studies on shallow lakes suggest that there may be two alternative equilibria over
a range of nutrient concentrations: A clear state dominated by macrophytes and a turbid
state dominated by high algal biomass. This has important implications on management
of shallow lakes (Scheffer ef al., 1993).
It is wise to ask: “Do our so-called development activities constitute a true development
while degrading our environment or are we digging our own graves?” Conservation and
effective utilisation of natural resources can simultaneously be achieved under sustainable
development practices. However, achievement of these goals requires careful analysis and
well understanding of the system regarding the region under study. The elements such as
wildlife, people, government etc. and relations amongst these elements are almost always
constitute highly complex systems. So a holistic point of view is to be adopted and
considerable amount of time must be devoted to field studies to analyse these systems and
provide solutions.
Among a number of principles of Sustainable Development, the ones which are strongly
associated with System Dynamics are the following:
There are three subsystems which are essential elements to be defined in a sustainable
development practice. These are social, ecological and economic elements. The social
subsystem deals with equity and disparity within the current human population and
between present and future generations. The ecological subsystem considers the
ecological conditions on which life depends. Finally, economic subsystem considers
economic development and other non-market activities that contribute to social well-
being. Moreover, the borders of the system under study must be carefully determined so
as not to break any major links between elements (Hardi ef al., 1998).
A crucial characteristic of a sustainable development practice is participation from
various disciplines and even from the society which is the subject of the study (Hardi et
al., 1998).
Systems thinking provides the proper philosophical perspective for Sustainable
Development practices. In system dynamics literature, sustainable development studies
has a distinct place. System Dynamics offers an important research potential and direction
in sustainable development practices (Saeed et al. ,1998).
2. The Study Region
The geographical location of the region is in Temperate Climate Belt. The wetland under
study is in the borders of Turkey, a developing country. The wetland consists of a shallow
lake named Uluabat (or Apolyont), rivers flowing in and out of the lake, groundwater,
and lands surrounding the lake. It is an important nesting place for bird species, some are
under threat of extinction. In spite of this crucial role, the wetland plays and although it
meets the Ramsar Criteria it was not under conservation status until recently. This
resulted in “development” activities which damaged the ecosystem and, in turn, the
habitat of endangered bird species. Crayfish population was an important element of the
lake ecosystem until 1986; the year when the population was hit by a fungi (Yarar et al.,
1997). The lake under continuous load of organic wastes is faced with threat of becoming
euthrophic (inan er al., 1997).
The inhabitants rely on fishing, agriculture and -until recently- crayfish harvest. On one
hand, fishing and its industry is quickly replacing the crayfish harvest and industry; on the
other hand, agriculture is the most pervasive way of subsistence among the inhabitants
although some villages, such as Gélyazi, almost totally rely on fishing (inan ef al., 1997).
Tomato cultivation is significant. Tomato cultivated on lands surrounding the lake is
processed by the plants near the lake to produce tomato paste. The production equals 80%
of Turkey’s tomato paste production. The irrigation is done by water pumped from the
lake. The intensive fertiliser and pesticide use may be potential sources for the pollution
of lake’s waters which will in turn affect the agriculture in the wetland. However, no data
is available yet (Demir er al., 1998, inan et al., 1997).
Another problem about the wetland is intensive fishing. This is one of the major factors
that has adverse effects on the fragile wetland ecosystem (Report on Inland Waters and
Fish Farms of Turkey, 1994).
The industry in the wetland mainly consists of processing plants. The agricultural yield is
processed in these plants. The -mostly organic- wastes of these plants also threatens the
wetland ecosystem. On the other hand, installation of treatment facilities are the most
important means to reduce the amount of wastes. Apart from these pollution sources,
rivers, carrying the toxic and organic wastes of industrial plants and households, located
in their catchment basins, further worsens the case in the lake (inan et al., 1997).
The inhabitants are aware of most of the problems of their region. However, they do not
know the full extend of problems. Hence, it is important to educate the inhabitants and by
this way raise awareness to desired levels with the endeavours of local organisations, and
NGO’s such as Society for the Protection of Nature (DHKD) and Development
Foundation of Turkey (TKV).
The ultimate goal of the project is to seek a balance between ecosystem and human
activities in order to secure a continuous improvement in well-being of the inhabitants
while improving or at least maintaining the ecosystem. To this end, using system
dynamics methodology, a model of the wetland system is being constructed by identifying
the main elements and the interactions among them; after validation, various policies will
be analysed to the model by altering some elements and/or relations.
3. Model Overview
The model has three subsystems as described above. These subsystems are Lake Ecology,
Economic and Social Structure on the periphery of the lake. Each subsystem consists of
several sectors.
Ecological elements of the lake and their interactions are modelled under Lake Ecology
subsystem. In conceptualisation and construction of ecology subsystem, limited studies
done on shallow lakes have been referred. It is not aimed to reveal a detailed model of the
shallow lake ecosystem. The ecosystem is represented detailed enough as to serve to the
purposes of the study. Economic Structure subsystem includes all activities of the
inhabitants which have an intensive economic value such as industrial facilities, farming
around the lake and fishing. Social Structure subsystem deals with the well-being of the
inhabitants which is tightly related with the functioning of other two subsystems.
3.1. Lake Ecology Subsystem
The subsystem consists of five sectors: Hydrology sector, nutrients sector, water plants &
zooplankton sector and fish & bird sector.
Hydrology sector is included in lake ecology subsystem. It is straight forward and
calculates inflow, outflow, volume, surface area and depth of the lake, and irrigation.
Phosphorus (P) and nitrogen (N) are the two major nutrients, bound by plants during
photosynthesis. In Lake Uluabat, the main sources for nitrogen are NOo, NO3, NH3
whereas the main source for phosphorus is PO,. Their concentration in the lake water and
their ratio are important parameters. They dictate the trophic state of the lake. A portion
of both phosphorus and nitrogen loads to a water body is stored in sediments. Moreover,
phosphorus and nitrogen in sediments is released back to water at a certain rate. The
sedimentation and release rates are determined by a number of factors. In general,
sedimentation rate is higher and this results in nutrient excess in sediments and a nutrient
supply to water body internally even if external loading no longer exists. The result is
prolonged danger of eutrophication. This is also the case in Lake Uluabat where
sedimentation rate is high. Therefore, stocks for phosphorus and nitrogen in sediment are
added to the model. The concentration of phosphorus and nitrogen in the lake water and
their ratio, P/N, are calculated in the nutrients sector.
Algal, macrophyte and zooplankton biomasses are calculated in the water plants &
zooplankton sector. Algal biomass is represented by the chloro a content of the lake water
which is found by a logarithmic relationship between algal biomass and P and N
concentration of the lake (Jorgensen, 1994). However, algae is controlled by its predator,
zooplankton. So, actual chloro a is the actual algal biomass that can be observed in lake
although potential chloro a level dictated by P and N concentrations may be higher.
Actual chloro a is flushed by the outlow of the lake.
Macrophyte biomass unit is PVI (Plant Volume Infested). It is a graphical function of P
and N concentration of the lake and the P/N ratio. It is also affected by the chloro a
content of the lake since algae is more efficient in getting nutrients from water than
macrophyte. As the chloro a level gets higher, macrophyte is able to get less nutrients.
Algal biomass has also an indirect effect on macrophyte biomass via lake water
transparency. Transparency is dictated by actual chloro a level and it’s unit is SE (Secchi
disk transperancy). The relationship between SE and chloro a is a hyperbolic function as
provided in Jorgensen, 1994. Macrophyte is able to colonise the lake water to a depth of
three times the SE although the changes in lake transparency is not instantly reflected in
the actual macrophyte biomass. It takes sometime for macrophyte to colonise newly
available spaces and to perish from spaces with insufficient light conditions. This
situation is reflected in the model by the use of a third order exponential smoothing
function with a delay of twelve months. This is not the case for algae since it is much
more flexible than macrophyte; that is it is able to respond to changes in its environment
almost instantly.
Macrophyte provides refuge for zooplankton against its predators, carp and small pike,
namely planktivorous fish, to a certain degree. Refuge effect increases with increasing
macrophyte biomass; however, when planktivorous fish biomass is high, the refuge effect
diminishes considerably no matter how high the macrophyte biomass (Schriver et al.,
1995).
Fish & Bird sector constitutes the top of the food chain and it is the sector of the ecology
subsystem, directly linked to economy subsystem at the same time because of the fish
industry. There are a number of fish species in the lake but two fish species are
economically significant. These are carp and pike. Carp is a planktivorous fish; that is, it
feeds mainly on zooplankton. It prefers turbid waters. On the other hand, pike preys on
other fish including carp and it prefers clear waters. However, small pike is
planktivorous. All these points are appropriately reflected in the model. Small pike and
small carp has separate stocks than adults of their species. This allows both to
differentiate the food sources and to set aside the small fish from reproduction.
Reproduction of fish takes place during spring months. This serves as an opportunity for
application potential policy alternative; that is to ban fishing during spring.
Fishing Pike
‘
/ _
Growth Pike, Ke — —
2
Pygmy Cormorant
A fé volume to be colonised
i Coot
Growth Carp _+
<
*"\ 4 (>)
—" AS)
== Death Carp
i
refuge effect
a
Zooplankton 4 zooplankton
. aM
macrophyte actual
POS Pinflow =PO4 P Outflow
(" \~~
P in sediment
Figure I. Causal-loop Diagram of Lake Ecology Subsystem
Growth of carp and pike are affected by the turbidity, or in other words transparency of
water via two different graphical functions of transparency.
Information on population dynamics and feeding habits of birds is very limited.
Therefore, it is decided to reflect their biomass as a linear function of their preys. Two
bird species are selected as indicators of bird presence on the shores of the lake. These
species are coot and pygmy cormorant. Coot feeds on macrophyte so its biomass is a
linear function of macrophyte biomass; and pygmy cormorant feeds on fish so its biomass
is a linear function of total fish biomass.
Information on habitat preference and population dynamics of crayfish is also vague. Also
taking into consideration that crayfish has almost swept from the lake as the result of the
fungi attack, it is not included in the model.
Most of the parameter values specific to the lake are missing, including carp and pike
stocks in the lake. Hence, either their values were taken from literature or some estimates
were done based on observations and available data. For example, fish stocks were
estimated based on amount of fish sold per year in the local fish market. Causal-loop
diagram of lake ecology subsystem is given in Figure I. Note that there are a number of
balancing loops in the food chain and a large reinforcing loop. Hydrology sector is not
included in the diagram.
3.2. Economy Subsystem
Three sectors constitute economy subsystem, being fishing, agriculture and industry
sectors. The structure of these sectors are resembling each other.
Tomato cultivation sector is taken as an example. Marketprice of tomato is a fixed
constant whereas Tomato cultivated per hectare is a function of irrigation. However,
fishing from the lake is affected by the stock level of fish in the lake. Total income
increases as total tomato cultivated increases. This increases welfare of inhabitants
relying on tomato cultivation which in turn increases attractiveness of tomato cultivation
for others. Nonetheless, this attractiveness is normalised with the attractiveness of other
activities. The multiplication of normalised attractiveness of tomato cultivation, which is
a number between 0 and 1, with total workforce determines the number of workforce in
tomato cultivation. The land on which tomato is cultivated is a function of the workforce.
Maximum value it can reach is the total arable land around the lake.
The main interactions between agriculture sector and the lake are irrigation and nutrient
rich waters returning back to the lake from irrigated and fertilised lands.
Fishing has a similar structure. Since it is certain that the lake has not the capacity to
sustain intensive fishing it is clear from Figure II that increased income draws more
workforce to fishing so the pressure increases on fish which in turn inevitably reduce total
fish caught as a result of diminished fish stocks. This is exactly what is observed in the
lake now. This will either virtually exterminate fish from the lake or reduce workforce in
fishing to a more ‘sustainable’ level. The outcome will be revealed as the model is
completed and appropriate analyses are done.
In the fishing sector, the allocation of total fish caught between carp and pike is based on
the ratio of both species’ biomasses.
Industrial plants near the lake are for processing crop from agriculture and fish from the
lake. An increase in either crop or fish is directly reflected as an increase on the
production of industrial plants. Therefore, in the agricultural and aquacultural industry,
the expansion of the industry depends on the amount of harvests and available workforce.
So if there occurs a decline in harvests this will affect the industrial facilities.
The same balancing structure applies here also with slight modifications. The main
interaction between industrial plants and the lake is the discharge of the plants. Being
mostly organic, this discharges play a significant role in the probable eutrophication of
the lake. Besides these plants, there are other industrial facilities outside the periphery of
the lake discharges of which reach the lake. These discharges are considered as input
from outside sources to the model.
Since other elements of the subsystem has a similar structure, only causal-loop diagram
for Tomato Cultivation is provided in Figure II. The construction of economy subsystem
has not totally completed yet.
<lrtigation> <Total Work!
Ecofogy subsystem i—— from Socfal subsystem
\e Tomato Cultivation Area’
‘Tomato Cultivated por Hecare s
{ Worklorce in Tomato Cultivation
; ED
COG
Total Tomato Cuitivated
Maikeiptice Toit Normalised Attractiveness Tomato Cultivation
‘
‘Total Income from Tomato Cultivation F from Social subsystem
Attractiveness of Tomato Cultivation
Figure II. Causal-loop Diagram of Tomato Cultivation from Economy Subsystem
3.3. Social Subsystem
Demographic indicators are in the social subsystem. Population, total workforce, welfare
of the society are all included in this subsystem. It also provides parameters required to
calculate allocation of workforce amongst economic activities. Indicators for policy
options such as awareness, and adoption are located in this subsystem. As for the
economy subsystem, its construction has not yet completed.
4. Implementation
The construction of the model is not totally complete. Various policy alternatives to
prevent over-exploitation of the lake’s resources were suggested on reports prepared by
Society for Protection of Nature, Development Foundation of Turkey, related government
organisations and universities. However, they depend on missing, even misleading data
and more important they lack a holistic approach which is the main advantage of this
study.
Being a part of a wider attempt to manage the resources of the region in a sustainable
way, the alternatives proposed by the above institutions will be investigated and analyses
will be carried out in collaboration with them after the model and its validation tests are
completed. Especially, Development Foundation of Turkey is in preparation phase for a
thorough sustainable development study of the region (TKV, 1998) and they commented
that this model will be of great use for them. Furthermore, it is believed that the model
will provide a basis for a common platform for the communication of experts and other
responsible officials who work in the region. Lack of such a platform seems to be the
biggest obstacle in present state and in the future in finding a solution for the better
management of the region.
5. Conclusion
Sustainable development opens new horizons in front of human civilisation. It is widely
recognised all around the world. This system dynamics modelling study on Lake Uluabat
is part of a larger attempt to manage the resources of the region in a sustainable manner
and is continuing with the co-operation of DHKD, TKV and other local institutions. The
current state of the study which is an MSc thesis is documented in this paper. The study is
continuing. Construction of lake ecology subsystem is completed; its verification has also
been done. Its validation tests were carried out using information on shallow lake
ecosystems in the literature and data from the lake although they are very limited and, in
some cases, unreliable.
The completion of the rest of the model is expected not to take long. Data collection has
already been completed and the remaining subsystems of the model is being constructed
which will be followed by validation testing and investigation of a number of policy
analyses. The study is expected to come to an end on August’99. After the completion of
the study the results will be shared also with Ramsar Convention Bureau along with other
organisations interested in the region.
Sustainable development has been a hot topic in recent years. Yet, maybe because it is so
popular there is a lot of uncertainty on how to achieve it. There are studies done on
Sustainable Development in System Dynamics literature, but extensive research potential
still exists on this socio-economic concept and how to apply it.
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