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Estimation and prediction
of eutrophication in West Lake
Luu Lan Huong, Do Kim Anh, Truong Tuan Anh
College of Science, VNU

ABSTRACT. The water quality of lakes in Hanoi has been declining. In that, eutrophycation
is the most popular. One of the effective tools for its accessing and predicting is the use of
mathematical models. This paper used the Vollenweider model, Empirical watershed model
and Jorgensen model to determine the eutrophycation of West Lake by Phosphorous
concentration in the lake water.
The results given by the models show that the ability of Eutrophication of West Lake is very
high, because the content of Phosphorous in the lake exceed allowable value of standard
(0.03mg/l) many times. The results of Jorgensen model are: P = 13132-18894kg/year (rainy
season), P = 9450-23580kg/year (dry season) and the results of Empirical watershed model
are: P=0.45-1.71mg/l (rainy season), P = 0.64-2.45 mg/l (dry season). Thus, the results of
the two models are similar and close to the results measured in the field. The prediction
results of the eutrophication of West Lake by Jorgensen model are simulated by Software
Stella II, which showed that the eutrophication in West Lake could be controlled by reducing
waste sources to the lake and raising amount of fishes.
1. Introduction
Eutrophication is the aging process by which shallow lakes gradually become dry
land because of the accumulation of sediment and organic material. Nutrient
enrichment contributes to the process as it causes excessive growth of algae and
aquatic plant. Under natural conditions, this aging process occurs over geologic time
(CETIA, 2005). However, the process can be greatly accelerated by human activities in
watersheds. To save the lake ecosystem, there is a need of estimation and prediction of

water quality of West Lake, including: Phosphorous and Nitrogen concentration, DO,
pH, are under not very good condition.
3.2. Estimating eutrophic state by chemical parameter (Phosphorous)
3.2.1. The standard amount of Phosphorous loading to the lake
We used Vollenweider model to calculate the standard amount of nutrients loading
to the lake. It is found that if the lake receives more than 1482kg of Phosphorous
(according to the condition of rainy season) or 786kg of Phosphorous (under condition of
dry season) per year, it will be eutrophic.
3.2.2. Estimating loads of Phosphorous
a. Estimating loads of Phosphorous by Empirical model
Phosphorous loading to West Lake is from 4 sources: soil, atmosphere, humans
and cattle. For each, there is an exporting coefficient, representing the average amount
of Phosphorous in every hectare of land for the lake per year. By using these
coefficients and data of West Lake, we found that West Lake would receive about P =
6020.4 - 22942.2kg/year in the condition of rainy season and 5789.4 - 22106.2kg/year in
the condition of dry season.
b. Estimating loads of Phosphorous by Jorgensen model
Jorgensen and Empirical models use the same method for estimating the amount
Estimation and prediction of eutrophication in West Lake
VNU. Journal of Science, Earth Sciences, T.XXIII, N
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1, 2007
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of nutrients loading to lakes. However, the exporting coefficients and the classification
of nutrient sources are different. There are three types of nutrient sources in Jorgensen
model: from soil, rain and humans. Thus, the results of the two models are different.
Results of Jorgensen model are: P = 13132 - 18894kg/year (rainy season) and P = 9450 -
23580kg/year (dry season).
3.2.3. Calculating Phosphorous concentration

to investigate and then build a system of more suitable coefficients for West Lake.
Luu Lan Huong, Do Kim Anh, Truong Tuan Anh
VNU. Journal of Science, Earth Sciences, T.XXIII, N
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3.3. Estimating and predicting eutrophication of West Lake by biomass of
phytoplankton
Biomass of phytoplankton is an indicator of eutrophication, so it is possible to
estimate and especially predict eutrophication by phytoplankton model. In this
research, we use CLEAN model of phytoplankton with a variety of major components of
lake ecosystems:
pppzppnetp
BMUGPdtdB )(/
,,
−−−= ,
where B
p
: biomass of phytoplankton; P
net,p
: growth rate of phytoplankton; G
p,z
: rate of
grazing phytoplankton by zooplankton; Up: rate of settlement, Mp: rate of mortality
without zooplankton.
After combining the data of West Lake and CLEAN model, we used Stella II
software to simulate the change in biomass of phytoplankton. There are 3 cases of
results in which the Phosphorous conditions are different:
• First case: Phosphorous concentration is constant.

1
1
2 2 2 2
3 3 3 3
Graph 1

Figure 1. First case: Phosphorous concentration is constant. Biomass of Phytoplankton is rather high.
Estimation and prediction of eutrophication in West Lake
VNU. Journal of Science, Earth Sciences, T.XXIII, N
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12:16 AM 4/12/03
0.00 15.00 30.00 45.00 60.00
Years
1:
1:
1:
2:
2:
2:
3:
3:
3:
0.00
0.10
0.20
0.00
0.50

3:
3:
0.00
0.10
0.20
0.00
5.00
10.00
0.00
0.25
0.50
1: Bp 2: ca 3: dot khaithac lon
1
1
1
1
2
2
2
2
3
3
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3
Graph 1

Figure 3. Third case: Suggest a case for sustainable development of West Lake. Phytoplankton biomass has
decrease slowly when fish eating phytoplankton and humans catching fish are added.
4. Conclusion
- Results from mathematical models of total phosphorus amount and phosphorus

Vietnamese).
[2] Hannon, B., Ruth, M. (1997), Modeling Dynamic Biological Systems. Springer-Verlag
New York, New York, 399 pp.
[3] Ho Thanh Hai et al. (2001), Preliminary assessment of external nutrient Nitrogen and
Phosphorous discharged into Ba Be Lake, Institute of Ecology and Biological resources,
5pp. (in Vietnamese).
[4] Jorgensen, S.E. (1983), Application of Ecological Modeling in Environment Management,
part A. Elsevier Scientific Publishing Company, Amsterdam, 735 pp.
[5] Nguyen Xuan Nguyen, Tran Duc Ha (2004), Quality of rivers, lakes water and
environmental protection of the water, Publishing house of Science and Technology,
Hanoi, 200 pp. (in Vietnamese).
[6] Park, A.R. (1974), A generalized model for simulating lake ecosystems, Simulation
Councils, pp. 33-50.
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