Cấu trúc quần xã thực vật phù du trong các hồ chứa ở cao nguyên Lâm Viên, tỉnh Lâm Đồng (2)_unprotected

INTRODUCTION
Currently, the pollution from agricultural activities and sources of domestic waste
in the Lam Vien highland has caused eutrophication to some water bodies, altering
structure and function of aquatic ecosystems, in that phytoplankton communities are
affected directly and indirectly. The common phenomenon is the excessive growth of
phytoplankton groups, usually cyanobacteria, damaging to other organisms in the
water bodies. To control this situation, we need identifying sources of impacts on
basins and aquatic organisms. In basins, phytoplankton is an important link in food
web and is also the subject that affected by environmental factors. Phytoplankton
groups have different reactions when environmental conditions impact on them,
through changes in composition, distribution, and growth. Therefore, integrated
analysis of phytoplankton responses to environmental factors can elucidate
furthermore the effects of environmental conditions on phytoplankton. From there,
identifying which environmental factors that impact on the entire of aquatic
ecosystem.
Worldwide, the study factors that impact on phytoplankton was done quite soon
and mostly in temperate areas. These researches are less and later in the tropics. There
are a lot of lakes and reservoirs in Vietnam but are not yet much researches about
them. In particular, the studies on relationship between environmental factors and
phytoplankton as well as between phytoplankton and other organismal groups have
not been mentioned adequately. Most researches are focusing on taxonomy.
Until now, the researches on the impact of environmental factors on
phytoplankton community structure in Vietnam as well as in Lam Vien highland
based on year database have not been implemented. Therefore, the study "Structure of
phytoplankton communities in reservoirs at Lam Vien highland, Lam Dong Province"
in addition to contribution on taxonomy for the flora of freshwater microalgae in Tay
Nguyen area of Vietnam, it also help understanding clearly the responses of
phytoplankton to environmental conditions as well as identifying dominant
environmental factors that impact on aquatic ecosystems.
At the practical level, identifying which main impact on aquatic organisms,
including phytoplankton community, will be the basis of science, support to

management, protection of biodiversity of water resources in Lam Vien highland.
 Aims of study
- Identifying characteristics of phytoplankton community structure in reservoirs at the
Lam Vien highland.
- Determineing factors that impact on community structure of phytoplankton in the
reservoirs.
 Thesis contents
1


- Species composition, density and distribution of phytoplankton in Xuan Huong
reservoir, Tuyen Lam reservoir and Dan Kia reservoir.
- The status of the waters of Xuan Huong reservoir, Tuyen Lam reservoir and Dan
Kia reservoir.
- The relationship between phytoplankton and environmental characteristics of each
reservoir.
- The impact of nutrition and grazing on growth of phytoplankton
- Simulation and forecasting trends of change in ecosystem of reservoirs by
modeling.
 Scientific contributions and applied aspects
- Complementing database for tropical phytoplankton flora in general, tropical
highland in particular. Providing some information for phytoplankton researches and
applications.
- Determining impacts of environmental factors on water bodies as well as on
phytoplankton, the basis for building management solutions, effective use and proper
exploitation of local water sources.
- Contributing to find causes of excessive growth of phytoplankton in lakes and
resaervoirs, the basis for restricting outbreak of phytoplankton, especially
cyanobacteria blooms in reservoirs at Lam Vien highland.
CHAPTER I. OVERVIEW

1.1 The characteristics of tropical lakes and reservoirs
1.1.1 Overview
1.1.2 The temperature, stratification and mixing in water column
1.1.3 Radiation and clarity
1.1.4 Nutrition and solutes
1.1.5 Food webs, top-down and bottom-up control in lakes and reservoirs
1.2 Morphological characteristics and classification of freshwater phytoplankton
1.2.1 Morphological characteristics and classification of freshwater phytoplankton
1.2.2 Groups of freshwater phytoplankton
1.3 Ecology of phytoplankton
1.3.1 Light and photosynthesis of phytoplankton
1.3.2 Influence of temperature, stratification and mixing on phytoplankton
1.3.3 Metabolism and nutritional absorption of phytoplankton
1.3.4 Survival strategies of phytoplankton
1.4 Variation in phytoplankton community over time
1.4.1 The short-term changes (changes in molecules and cells)
1.4.2 Changes in medium term (phytoplankton community succession)
1.4.3 The long-term fluctuations (fluctuates by year)
1.5 Spatial distribution of phytoplankton
2


1.5.1 Voluntary movement of phytoplankton in water column
1.5.2 Passive movement of phytoplankton in water column
1.5.3 Loss phytoplankton in basins
1.6 AQUATOX model
1.6.1 AQUATOX model overview
1.6.2 Application of AQUATOX model
1.7 Some characteristics of studied area
1.7.1 Natural conditions of Lam Vien highland

1.7.2 Characteristics of reservoirs in Lam Vien highland
1.8 Situation of phytoplankton study in the world and Vietnam
CHAPTER 2. MATERIALS AND METHODS
2.1 Studied subjects
Phytoplankton and characteristics of water in 3 reservoirs, Xuan Huong, Tuyen
Lam and Dan Kia.
2.2 Materials and methods
2.2.1 At the field
At each reservoir, sampling at 3 stations. At each station, sampling and measuring
water parameters at 2 layers. Frequency of survey is once a month, from 11/2013 to
10/2014. Flow rate, water temperature, depth of reservoir, Secchi depth, pH, DO,
turbidity, light intensity were measured by handheld electronic devices. Collecting
water samples for analyzing chemical and biological parameters.
2.2.2 Experiments
2.2.2.1 Fixing cells, qualitative and quantitative phytoplankton
Samples were fixed with 1% Lugol solution and formaldehyde solution of acetic
acid (FAA) 2%. Phytoplankton identification was based on classification keys of
freshwater phytoplankton. Quantitative forms, one liter of water was fixed by Lugol
1% and 2% FAA, within about 48 hours, siphon off above portion of water to remain
100 ml of water. Let standing within 24 hours and then siphon off 20 ml remain
water. Taking 1 ml of this one for counting by using Sedgewich – Rafter chamber.
2.2.2.2 Fixed cells, qualitative and quantitative zooplankton
Samples of quantitative zooplankton were fixed by a solution to final
formadehyde concentration is 4%. Analysizing zooplankton at Marine Plankton
Department, Institute of Oceanography. Zooplankton taxa were photographed, the
quantitative zooplankton results are managed on MS-Excel.
2.2.2.3 Analysis of chemical parameters
Nutrition parameters are defined according to APHA (1995, 2005). Determination of
chlorophyll a by UV-Vis 1020 – H, according to APHA (1995). Fecal coliform is
determined by culturing multiple tubes method, most probable number, 9221 APHA (1999).

Pesticide residues were analyzed at Environmental Research Institute, Dalat University.
3


2.2.2.4 Experiments to determine plankton biological rates
Bottom-up experiments arranged by Severiano (2012). Top-down experiments
arranged by Landry & Hasset (1982) and Evans et al., (2003).
2.2.2.5 Calculation of phytoplankton biomass
Phytoplankton biomass is calculated according to Wetzel et al., (2001).
2.2.2.5 Running AQUATOX model
AQUATOX model was applied to assess impact of flows into Dan Kia reservoir.
2.2.2.6 Application of statistical softwares and models
Analyzing significant differences between two properties by analysising variances
(ANOVA) base on MS-excel. Data normalization, correlation analysis, regression by
Statgraphic 5.0 statistical software. Canonical-correlation analysis (CCA) between
phytoplankton and environmental factors base on CANOCO 4.5 software. Correlation
analysis - RDA (Redundancy Analysis) for estimating biomass variability of
morphological groups of phytoplankton and environmental factors was performed
base on CANOCO 4.5 software. Analysis Shannon index (H'), Simpson dominance
index (D) with Primer 6.0 software.
CHAPTER 3. RESULTS AND DISCUSSION
3.1 Species composition, density and distribution of phytoplankton in the reservoirs
3.1.1 Species composition of phytoplankton in Xuan Huong, Tuyen Lam and Dan Kia
3.1.1.1 Species composition of phytoplankton in Xuan Huong reservoir
Total
taxa
of
phytoplankton in
Xuan
Huong

reservoir are 112,
belonging to 7
phyla, including
Chlorophyta (60
taxa,
53%),
Cyanophyta (18
taxa,
16%),
Euglenophyta (16
taxa,
14%),
Bacillariophyta (8
taxa
accounting
for 7%). Dinophyta (4 taxa, accounting for 4%). Both Cryptophyta and Chrysophyta
has 3 taxa, accounting for 3% of total taxa of phytoplankton (Figure 3.1).
Species composition of phytoplankton in Xuan Huong reservoir is a typical one of
phytoplankton in lentic waters with dominant species belong to green algae, and also
has characteristics of eutrophic water-bodies with advantage of Cyanophyta density.
4


Cyanobacteria density accounting for 80% of phytoplankton in the reservoir
throughout the year (Figure 3.1B). Of the seven phyla in Xuan Huong reservoir,
Chrysophyta density is the lowest. Although Euglenophyta do not contribute
significantly in density, they contributed significantly in biomass due to their cell size.
Of three reservoirs, Xuan Huong had the highest number of taxa, as well as the
density phytoplankton concentrated in a few taxa. Xuan Huong reservoir receives
water from upstream sides. So, phytoplankton species composition perhaps related to

addition of these taxa from its basins.
Overall, the number of phytoplankton species in Xuan Huong reservoir is high but
there are many species in low frequency, this maybe related to additional species
temporarily from basins. The density and biomass of phytoplankton are concentrated
in some taxa of Cyanophyta phylum, the group dominant throughout the year.
3.1.1.2 Species composition of phytoplankton in Tuyen Lam reservoir
There are 6 phyla
in Tuyen Lam
reservoir, with 43
taxa.
Among
them,
Chlorophyta
contained
25
taxa, accounting
for
58%;
Bacillariophyta
and Cyanophyta
contained 6 taxa,
accounting
for
14%; Dinophyta
and Chrysophyta
contained 3 taxa, accounting for 7% and 2 taxa, accounting for 5% respectively.
Euglenophyta phylum only has 1 taxon, representing 2% (Figure 3.2).
Phytoplankton in Tuyen Lam reservoir also featured lentic waters with advantage
belonging to Chlorophyta phylum (Figure 3.2A). According to density, Cyanophyta
has the highest density (Figure 3.2b) but base on biomass, Dinophyta was the most

dominant group (Figure 3.2C). Some Chlorophyta genera are common, they are
Desmids group (Desmidium, Coelastrum, Elakatothrix, Pleurotaenium, ...), these
genera usually present in less dirty waters (Reynolds, 2006).
There are two dominant phyla in Tuyen Lam reservoir, Cyanophyta and
Dinophyta. However, while filamentous cyanobacteria was dominant in Xuan Huong
5


reservoir, colony cyanobacteria was dominant in Tuyen Lam reservoir. Two
Dinophyta dominant genera are Ceratium and Peridinium.
3.1.1.3 Phytoplankton species composition of Dan Kia reservoir
Dan Kia reservoir has 44 taxa, distributed in 7 phyla, including Chlorophyta, 17
taxa, accounting for 39%; Bacillariophyta, 11 taxa, accounting for 25%; Cyanophyta,
6 taxa, accounting for 14%; Chrysophyta, 5 taxa, accounting for 11%; Dinophyta, 2
taxa, accounting for 4.5%; Euglenophyta also 2 taxa, 4.5% and 1 Cryptophyta taxon,
representing 2% of total number of phytoplankton species in Dan Kia reservoir.
Though number of Chlorophyta taxa was lower than the others, this phylum was still
dominant
in
number of species
(Figure
3.3a).
Bacillariophyta
was dominant in
Dan Kia reservoir
both in species
composition,
density
and
biomass.

Cryptophyta
accounting
for
only 2% of total
taxa but they
contributed not less in density and biomass of phytoplankton (Figure 3.3a, 3.3b and
3.3C) .
In short, species composition of phytoplankton was not the same in three
reservoirs. Th number of phytoplankton species was the highest in Ho Xuan Huong,
112 taxa. Two remaining reservoirs had similar numbers, 43 and 44 taxa respectively
for Tuyen Lam and Dan Kia. Especially, comparing with similar reservoirs in the
region (Le Thuong, 2010) showed that while Chrysophyta and Cryptophyta were
found in studied reservoirs but they are completely absent in Eanhai reservoir, Easoup
reservoir and Dak Ming reservoir. Maybe, these groups distribute typically in some
high mountains, low heat background around year. Percentage of phyla in studied
reservoirs is similar to reservoirs in the region, especially there is abundance and
diversity of Chlorophyta in all.
3.1.1.4 Biological diversity of phytoplankton in the reservoirs

6


No
seasonal
differences
in
species diversity
index
of
phytoplankton in

Xuan
Huong
reservoir (T-test,
p = 0.106) and
Dan Kia reservoir
(T-test,
p
=
0.285), but this
difference
occurred in Tuyen Lam reservoir (T-test, p = 0.016). Species diversity index of
phytoplankton was highest in December in Tuyen Lam reservoir (2.24) and the lowest in
October in Xuan Huong reservoir (0.51). H’ index of Tuyen Lam reservoir, Dan Kia
reservoir was higher of Xuan Huong reservoir (T-test, p = 0.048; p = 0.004). Meanwhile,
there was no difference between Dan Kia reservoir and Tuyen Lam reservoir (T-test, p =
0.382) on this index. Phytoplankton species diversity of Xuan Huong reservoir was the
lowest among them.
3.1.1.5 Characteristics of phytoplankton community structure base on morphological
- function groups
The biomass dominant spiecies of phytoplankton in Xuan Huong reservoir, Tuyen
Lam reservoir and Dan Kia reservoir were sorted by morphological - function groups
of Reynolds et al., 2002, Salmaso & Padisak, 2007 and Kruk et al., 2010. Table 3.6,
morphological - function groups presence in the studied reservoirs base on three
systems.
Table 3.6 Morphological - function groups presence in the studied reservoirs

According to Reynolds et al., (2002), D and Y group were in Xuan Huong
reservoir and Dan Kia reservoir but completely absent in Tuyen Lam reservoir. D and
Y are the groups that characterized distribution in the shallow, turbid reservoirs, and
7

susceptible to change or are affected by outside activities. In this case, environmental
and biological data in Dan Kia, Xuan Huong are consistent with above statements.
Among groups according to Reynolds et al., (2002), only LM present in three
reservoirs, this group is known commonly present in high level of nutrition. Thus, LM
is not a good indicator for nutritional status but it is an evidence that functional
morphological groups reflects nature of ecosystem. The groups only present in Xuan
Huong reservoir is H1 (typically in eutrophic, shallow, non-stratified reservoir), W1
(rich organic) and W2 (shallow, medium - eutrophic nutrient water bodies) all fit
physic, chemical conditions that has been investigated for the reservoirs. Similarly, N
group (distributed at mixing reservoirs, 2-3 m thickness), was present only in Tuyen
Lam reservoir. WS group (in rich organic water bodies from decomposition process of
plant; neutral pH), was present only in Dan Kia reservoir.

Figure 3.5 RDA chart of environmental
factors and functional - morphological
groups according to Reynolds et al.,
(2002). Trans = Transparency Secchi, L
= light intensity, T = temperature, Cond
= conductivity, DO = dissolved oxygen,
TP = total phosphorus, phosphate PO4 =;
TN = total nitrogen, NH4 = ammonium
nitrate NO3 =

Overall, the survey results on hydraulic, physic, chemical conditions in studied
reservoirs fitted with ecological characteristics that morphological - function groups
indicated. However, there were some groups that featured in each water body where
8

they present no resemblance to the survey results. For example, A group (at Xuan
Huong and Dan Kia) distribute in clean, deep, poor nutrient water bodies (Reynolds et
al., 2002) while these reservoirs are not clean, shallow and eutrophic. So, we can not
completely rely on this system for monitoring quality, which should be combined
with multivariate analysis between morphological-function groups and environmental
factors. Multivariate analysis techniques are often applied is RDA (Legendre, 1998).
RDA analysis results between environmental factors and functional-morphological
groups according to Reynolds et al., (2002) at Xuan Huong reservoir (Figure 3.5A)
shows that in the first axis, morphological-function groups (including A group)
correlate mainly with light intensity, concentration of nitrate and TN. Meanwhile, the
second axis correlates mainly with TP. RDA chart (Figure 3.5C) also shows that A
group correlate with nitrogen and phosphorus. Thus, the presence of A group maybe
related to nutritional status of water bodies. Overall, three functional - morphological
systems can be applied to evaluate characteristics of aquatic ecosystems.
3.1.2 Variation of phytoplankton density in Xuan Huong, Tuyen Lam and Dan Kia
3.1.2.1 Variation of phytoplankton density in Xuan Huong reservoir
Except Cyanophyta and Chlorophyta, all remaining phyla in Xuan Huong
reservoir did not differ according to layer (Table 3.8).
Table 3.8 Density of phytoplankton in Xuan Huong reservoir

The dominance of Cyanophyta density is one of the characteristics of
phytoplankton in Xuan Huong reservoir. At time of algae blooms, density of
Cyanophyta at the surface increased up to hundreds of millions of cells/liter. The
studied results showed that shallow, eutrophic, turbidity and no stratification reservoir
9


could be characteristics enabling algae blooms in Xuan Huong reservoir. These
conditions are close to ecological characteristics for excessive development of

Cyanophyta (Reynolds, 2006). Density of phytoplankton groups in Xuan Huong
reservoir varied according to season (Table 3.8). Density of most groups did not differ
according to layer, except Cyanophyta (ANOVA, p = 0.039) and Chlorophyta
(ANOVA, p = 0.001).
3.1.2.2 Variation of phytoplankton density in Tuyen Lam reservoir.
Among phyla of phytoplankton in Tuyen Lam reservoir, Cyanophyta and
Chrysophyta did not differ according to layer (Table 3.9). On other hand, only
Cyanophyta (ANOVA, p = 0.022) and Chlorophyta (ANOVA, p = 0.046) are different
according to season at the surface layer and cell density higher than in dry season.
Table 3.9 Density of phytoplankton Tuyen Lam reservoir

Density of Chlorophyta, Bacillariophyta, Dinophyta fluctuated according to layer,
at the surface layer was higher than at the bottom layer. Density of diatoms in bottom
layer varied according to season (ANOVA, p = 0027), in dry season is higher in rainy
season.
Phytoplankton density of Tuyen Lam reservoir was much lower than in Xuan
Huong reservoir. Cyanophyta is also dominant group in this one. However, while
filamentous cyanobacteria is dominant in Xuan Huong reservoir, colony
cyanobacteria is dominant in Tuyen Lam reservoir. Perimidium and Ceratium are
dominant genera in density and biomass, due to size of their cells. These genera is
typical for organisms that has K strategy, advantage in environments that density of
higher organisms and concentration of nutrients is low relatively (Sigee, 2004).
3.1.2.3 Variation of phytoplankton density in Dan Kia reservoir
Density of Bacillariophyta and Dinophyta are different according to season and
layer, at the surface layer is higher than at the bottom layer. In particular, density of
10


Bacillariophyta was higher in dry season than in rainy season. Density of algal cells in
Dan Kia reservoir was very low. Most of algal density was higher in rainy season than

in dry season, cell density in the surface layer was higher than in the bottom layer
(Table 3.10).
Density and biomass of Chrysophyta was quite high in Dan Kia reservoir.
Chrysophyta are known as adapting to changes of nutrient concentrations in water.
Especially, Dinobryon is a mixotrophic genus (Kristiansen, 2005), dominant
throughout year. While concentration of inorganic nutrients (N, P) in Dan Kia
reservoir unlimited growth of phytoplankton, sources of remaining energy, such as
light, is very noticeable. Dan Kia reservoir is also very high turbidity, this is the factor
limiting penetration of light into water. In this case, the mixotrophic lifestyle will
advance over nursing. Diatom is dominant in Dan Kia reservoir both density and
biomass. Some diatom species are suitable for high turbidity conditions and rich
nutrient (Bellinger & Sigee, 2010). Obviously conditions, environmental water of Dan
Kia reservoir is quite suitable for the growth of diatoms.
Table 3.10 Density of phytoplankton in Dan Kia reservoir

In short, most of phytoplankton groups in the reservoirs have seasonal
fluctuations. While filamentous cyanobacteria was dominant in Xuan Huong
reservoir, colony cyanobacteria was dominant in Tuyen Lam reservoir. Besides, in
Tuyen Lam reservoir also appeared more a dominant one, that is Dinophyta. While,
Diatoms and Chrysophyta are dominant in Dan Kia reservoir.
3.2 Assessment water status of Xuan Huong, Tuyen Lam and Dan Kia reservoir
3.2.1 Water status of Xuan Huong reservoir
Hydraulic, physical, chemical and biological parameters of water in Xuan Huong
reservoir were surveyed from 11/2013 to 10/2014, are shown in Table 3.11.
11


Table 3.11 Hydraulic, physical, chemical and biological parameters of water in
Xuan Huong reservoir
Hydraulic, physical,

chemical and
biological
parameters

Min

Max

Average ±SD

1.0

4.9

2.86±1.46

Significant
differences
p≤0.05
Seas
Layer
on
*
0.616

0.25

0.6

0.45±0.11

0.001

*

1466

31033

8147±7898

0.006

*

19.69±2.60
19.65±2.58

15.57
15.53

22.13
22.1

18.86±2.32
18.16±2.27

0.321
0.075

0.465

9.53
9.50

8.97±0.45
8.91±0.48

6.28
6.30

8.80
9.57

7.94±0.83
7.83±0.96

0.001
0.001

0.675

4.60
4.77

6.33
6.24

5.36±0.56
5.37±0.44

3.89
4.12

6.54
6.86

5.07±0.65
5.18±0.72

0.188
0.389

0.314

231.67
216.33

254.00
252.67

234.33±13.6
235.00±11.9

174.33
174.67

238.17
240.00

200.17±20.4
201.13±20.1

0.001
0.001

0.880

33.57
33.83

89.73
104.67

57.55±19.29
59.35±21.26

20.86
23.10

60.97
104.33

39.76±14.62
49.27±25.85

0.003
0.224

0.221

1.91
1.78

10.98
11.94

6.10±3.16
6.32±3.24

3.07
3.93

18.95
23.74

12.30±4.42
12.51±5.52

0.001
0.001

0.862

0.23
0.18

5.12
5.80

2.07±1.55
2.31±1.68

0.74
0.79

3.17
3.24

1.95±0.74
2.01±0.68

0.749
0.472

0.624

3.97
3.01

18.73
18.89

10.56±4.71
11.07±4.53

7.76
8.38

24.43

30.94

17.85±4.62
18.19±6.15

0.001
0.001

0.781

0.33
0.56

2.08
1.99

1.10±0.58
1.24±0.47

0.17
0.17

2.53
3.39

1.10±0.60
1.42±0.99

0.975
0.522

0.14

3.35
4.06

8.33
8.08

5.38±1.70
5.76±1.31

0.69
0.51

3.68
13.47

2.26±0.92
3.75±3.63

0.001
0.048

0.096

1.13/1
1.08/1

2.87/1

2.46/1

1.98±0.66
1.91±0.54

3.55/1
1.59/1

22.77/1
20.52/1

10.32±6.24
9.05±7.32

0.014
0.057

0.771

*
*

*
*

*
*

0.00
*

22.68
*

10.23±7.68
*

*
*

12
12

2400
2400

1198±1067
1076±1124

313
300

2400
2400

1949±577
1794±710

0.010
0.024

0.519

49.51
19.84

247.93
173.34

165.96±55.5
114.56±43.2

32.79
15.61

161.19
131.71

103.37±39.65
55.27±30.73

0.001
0.001

0.001

0.00
0.08

3.14

8.50

1.15±1.19
3.83±2.77

0.83
1.25

13.75
12.92

7.34±3.68
6.99±3.50

0.001
0.006

0.805

0.00
1.08

19.92
18.20

3.60±4.87
6.98±5.56

0.00
1.33

9.80
13.44

5.20±2.81
5.70±3.06

0.221
0.381

0.079

0.00
0.00

17.50
9.32

3.33±4.54
3.55±2.95

1.67
0.33

28.22
27.13

10.92±7.16
10.21±6.94

0.001
0.001

0.842

0.00

35.33

5.95±10.56

0.89

10.33

5.29±2.68

0.788

0.999

Dry season
(From November to March)

Rainy season
(From November to March)

Min

Max

Water depth (m)

0.9

4.6

Average
±SD
2.61±1.44

Secchi depth (m)

0.25

0.4

0.34±0.06

Light intensity (lux)

353

4213

2215±940

15.07
15.20

22.80
22.87

7.81
7.57

Water temperature (°C)
Surface layer
Bottom layer
pH
Surface layer
Bottom layer
DO (mg/l)
Surface layer
Bottom layer
Conductivity
(µS/cm)
Surface layer
Bottom layer
Turbidity (NTU)
Surface layer
Bottom layer
NO-3-N (mg/l )
Surface layer
Bottom layer
NH+4-N (mg/l )
Surface layer
Bottom layer
TN (mg/l )
Surface layer

Bottom layer
PO3-4-P (mg/l )
Surface layer
Bottom layer
TP (mg/l )
Surface layer
Bottom layer
N:P
Surface layer
Bottom layer
Pesticides (µg/l)
Surface layer
Bottom layer
FC (MPN/100ml)
Surface layer
Bottom layer
Chlorophyll a (µg/l)
Surface layer
Bottom layer
Cladocera(indi./l)
Surface layer
Bottom layer
Copepoda (indi./l)
Surface layer
Bottom layer
Rotatoria (indi./l)
Surface layer
Bottom layer
Larvae (indi./l)
Surface layer

12

*


Bottom layer

0.16

27.83

6.37±6.78

0.98

9.12

4.99±2.41

0.395

(*): No data
3.2.1.1 Hydraulic, physical, chemical and biological characteristics of water in Xuan
Huong reservoir
Xuan Huong is a shallow reservoir, average depth of 2.86 m. Typically, shallow
tropical reservoir none thermal stratification. High pH values is a notable
phenomenon in Xuan Huong reservoir, pH values in the surface layer is difference
according to season (ANOVA, p = 0.001) and layer (ANOVA, p = 0.001), average
value of pH in dry season was higher than in rainy season. The highest pH values at

time of algal blooms. At the time, biomass of phytoplankton belonged to mainly
several taxa of Cyanophyta. Three compounds that containing nitrogen did not differ
according to layer (ANOVA, p = 0.862), (ANOVA, p = 0.624) and (ANOVA, p =
0781) respectively for ammonium, nitrate and TN. The ratio N/P of the surface layer
has seasonal differences (ANOVA, p = 0.014), the average value in dry season (1.9/1)
was lower than in the wet season (10.32/1). This N/P ratio is suitable for the growth
of cyanobacteria (Paerl, 1996), and cyanobacteria is also the dominant group in Xuan
Huong reservoir.
In summary, Xuan Huong is a shallow, turbid, non-stratified reservoir, high
nutrient concentrations, quality water is very low, nutrient concentrations is suitable
for the growth of Cyanophyta. According to OECD (1982), Xuan Huong is a super
eutrophic reservoir in terms of chlorophyll a, TP concentration and Secchi depth.
3.2.1.2 Biological characteristics in Xuan Huong reservoir
Concentration of chlorophyll a in Xuan Huong reservoir is very high and different
according to layer and season. The average chlorophyll a was higher in dry season
than in rainy season in the surface layer. There were presence of four groups of
zooplankton in Xuan Huong reservoir, including Cladocera, Copepoda, Rotatoria and
Larvae. These groups did not differ spatial distribution in water column, p> 0.05
(Table 3.11). In there, density of Cladocera and Rotatoria varied according to season,
higher in rainy season.
3.2.2 Water status of Tuyen Lam reservoir
The results of physical, chemical and biological parameters of water in Tuyen
Lam reservoir from 11/2013 to 10/2014 are shown in Table 3.12.
Table 3.12 Hydraulic physical, chemical and biological parameters of water in
Tuyen Lam
Hydraulic, physical,
chemical and biological
parameters

Dry season

(From November to March)

Rainy season
(From November to March)

Min

Max

Average ±SD

Min

Max

Water depth (m)

7.80

9.50

8.65±0.63

8.00

13.00

Average
±SD
9.88±1.28

Secchi depth (m)

0.80

2.40

1.55±0.34

1.10

3.50

1.75±0.6

13

Significant
differences
p≤0.05
Season

Layer

0.004

*

0.015

*


Light intensity (lux)
Water temperature (°C)
Surface layer
Bottom layer
pH
Surface layer
Bottom layer
DO (mg/l)
Surface layer
Bottom layer
Conductivity (µS/cm)
Surface layer
Bottom layer
NO-3-N (mg/l )
Surface layer
Bottom layer
NH+4-N (mg/l )
Surface layer
Bottom layer
TN (mg/l )
Surface layer
Bottom layer
PO3-4-P (mg/l )
Surface layer
Bottom layer
TP (mg/l )
Surface layer

Bottom layer
N:P
Surface layer
Bottom layer
Pesticides (µg/l)
Surface layer
Bottom layer
Chlorophyll a (µg/l)
Surface layer
Bottom layer
Cladocera(indi./l)
Surface layer
Bottom layer
Copepoda (indi./l)
Surface layer
Bottom layer
Larvae (indi./l)
Surface layer
Bottom layer

776

2286

1636±531

1343

50966

14180±1765

0.001

*

16.43
16.4

20.53
20.4

18.41±1.30
18.26±1.19

16.27
16.00

22.67
21.60

19.11±1.95
18.96±1.28

0.060
0.067

2.940

6.96

6.46

7.97
8.10

7.49±0.3
7.32±0.49

7.10
6.12

7.87
8.25

7.30±0.33
7.18±0.61

0.049
0.189

0.460

5.55
5.61

7.10
7.20

6.32±0.39
6.30±0.43

5.16
5.06

7.73
7.17

6.55±0.70
6.50±0.66

0.013
0.047

0.390

59.00
59.00

64.33
63.67

61.51±1.42
61.38±1.23

58.67
59.33

64.67
64.33

62.70±1.72
62.65±1.15

0.236
0.026

0.100

1.19
0.91

2.22
2.06

1.64±0.34
1.54±0.34

0.06
-

1.85
2.08

1.35±0.56
1.36±0.63

0.019
0.003

0.430

0.07
0.17

0.46
0.46

0.22±0.1
0.25±0.07

0.1
0.07

0.64
0.89

0.3±0.19
0.29±0.22

0.007
5.480

0.370

1.87
1.89

3.03
3.09

2.30±0.46
2.29±0.51

1.38
0.74

3.37
3.67

2.30±0.63
2.26±0.94

0.998
0.957

0.19
0.13

0.92
1.14

0.55±0.26
0.56±0.32

-

1.23
1.15

0.46±0.45

0.51±0.41

0.015
0.152

0.360

0.60
0.67

1.05
1.53

0.88±0.18
1.04±0.32

0.39
0.41

2.17
2.30

1.02±0.59
1.09±0.63

0.629
0.887

0.580

2.09/1
1.89/1

4.05/1
3.18/1

2.85/1±0.76/1
2.29/1±0.51/1

0.98/1
0.72/1

5.12/1
4.65/1

2.90/1±1.27/1
2.91/1±1.59/1

0.932
0.429

0.640

*
*

*
*

*

*

4.1E-4
*

5.7E-4
*

5.1E-4±8.5E-5
*

*
*

11.21
3.74

37.88
16.02

21.21±7.43
7.82±3.59

11.21
3.73

52.33
22.43

23.71±11.21

8.81±5.26

0.102
0.045

0.000

0.17
0.00

1.25
1.17

0.64±0.31
0.64±0.29

0.83
1.00

3.08
3.33

1.82±0.65
1.96±0.67

0.001
0.001

0.903

0.75
0.75

3.50
2.83

2.07±0.66
2.07±0.56

1.67
2.42

12.79
8.25

5.02±2.44
4.65±1.72

0.001
0.001

0.915

1.25
1.33

3.17
3.33

2.37±0.53

2.28±0.61

1.42
1.25

3.71
3.33

2.62±0.57
2.49±0.52

0.191
0.250

1.000

0.915

*

(*) No data
3.2.2.1 Hydraulic, physical, chemical characteristics of water in Tuyen Lam reservoir
There was no difference in temperature between the layers (ANOVA, p = 2.940),
known that Tuyen Lam reservoir is deeper than Xuan Huong reservoir about 3.5
times. Except chlorophyll a, all parameters were not different according to layer, but
different according to season. Ammonium and phosphate concentrations also differed
according to season but only at the surface layer. Concentration of phosphates was
higher in bottom layer in both seasons. In summary, Tuyen Lam is not turbid, not
stratified reservoir, and irregular disturbance; its depth is medium, nutrition ranged
from moderate to eutrophic conditions.

3.2.2.2 Biological characteristics of water in Tuyen Lam reservoir
14


Concentration of chlorophyll-a was different in water column (ANOVA, p =
0.001; Table 3.12), higher than in the surface layer. Not seasonal differences of
chlorophyll a in the surface layer (ANOVA, p = 0.102), while at the bottom layer, has
the seasonal differences. This phenomenon maybe relate to characteristics of
phytoplankton community structure in Tuyen Lam reservoir. In this reservoir,
Dinophyta (Peridinium, Ceratium) and Cyanophyta (Microcystis) are dominant
species in density. Both groups have ability to move in the water column. Microcystis
can move at 3 m/h speed, and favourite low light intensity (Walsby, 1994). Thus,
chlorophyll a fluctuations in season at the bottom layer maybe relate to the
distribution of two above groups. For zooplankton, comparing to Xuan Huong
reservoir, it is the absence of Rotatoria. Cladocera and Copepoda fluctuated according
to season in the layers (ANOVA, p = 0.001). Larvae do not fluctuate over time.
3.2.3 Water status of Dan Kia reservoir
The results of hydraulic physical, chemical and biological parameters of water in
Dan Kia reservoir from 11/2013 to 10/2014 are shown in Table 3.13.
3.2.3.1 Hydraulic, physical, chemical characteristics of water in Dan Kia reservoir
Water levels varied considerably according to season (ANOVA, p = 0.044),
Secchi depths are low (0.38 and 0.34 m) and not different (ANOVA, p = 0.294).
Table 3.13 The results of hydraulic physical, chemical and biological parameters of
water in Dan Kia reservoir

Min

Max

Average ±SD

Min

Max

Average ±SD

Water depth (m)

1.0

8.0

4.38±2.53

1.5

10

6.35±3.03

Significant
differences
p≤0.05
Season
Layer
*
0.044

Secchi depth (m)

0.25

0.6

0.38±0.12

0.2

0.5

0.34±0.11

0.294

*

Light intensity (lux)

993

21333

4370±5793

367

31866

11372±11924

0.043

*

15.07
15.47

22.27
22.00

19.84±2.48
19.40±2.17

15.57
15.47

22.13
21.93

18.86±2.32
18.13±1.95

0.027
0.049

0.602

6.45
6.38

7.97
7.77

7.25±0.44
7.12±0.44

6.06
6.60

7.07
7.14

6.44±0.30
6.53±0.35

0.001
0.001

0.969

5.59
5.50

7.37
6.92

6.22±0.44
6.13±0.34

5.75
5.79

6.77
6.57

6.07±0.29
6.11±0.26

0.331
0.865

0.289

19.67
21.67

4.67
42.33

30.67±6.88
30.98±6.50

37.00
37.33

53.67
54.67

42.06±4.34

42.11±4.44

0.001
0.001

0.932

20.04
19.01

42.69
77.83

42.68±22.54
44.29±22.69

20.83
21.07

70.13
185.67

70.13±50.98
73.52±47.58

0.059
0.035

0.792

0.21
0.19

2.22
2.34

0.85±0.71
0.88±0.71

0.11
0.16

2.15
1.97

0.78±0.57
0.87±0.57

0.739
0.972

0.645

0.81
0.78

2.81
2.89

1.63±0.67

1.64±0.65

0.01
0.00

7.51
7.54

3.32±2.39
4.23±2.49

0.007
0.000

0.379

Hydraulic, physical,
chemical and
biological parameters

Water temperature (°C)
Surface layer
Bottom layer
pH
Surface layer
Bottom layer
DO (mg/l)
Surface layer
Bottom layer
Conductivity (µS/cm)

Surface layer
Bottom layer
Turbidity (NTU)
Surface layer
Bottom layer
NH+4-N (mg/l )
Surface layer
Bottom layer
NO-3-N (mg/l )
Surface layer
Bottom layer

Dry season
(From November to March)

Rainy season
(From November to March)

15


TN (mg/l )
Surface layer
Bottom layer
PO3-4-P (mg/l )
Surface layer
Bottom layer
TP (mg/l )
Surface layer
Bottom layer

N/P
Surface layer
Bottom layer
Pesticide (µg/l)
Surface layer
Bottom layer
FC (MPN/100ml)
Surface layer
Bottom layer
Chlorophylla(µg/l)
Surface layer
Bottom layer
Cladocera(indi./l)
Surface layer
Bottom layer
Copepoda(indi./l)
Surface layer
Bottom layer
Rotatoria (indi./l)
Surface layer
Bottom layer
Larvae (indi./l)
Surface layer
Bottom layer

1.45
1.39

4.78
4.88

2.97±1.02
3.02±1.06

0.54
0.87

11.22
11.20

5.07±3.48
6.12±3.43

0.031
0.002

0.373

0.71
1.13

3.74
3.61

1.85±0.96
1.98±0.87

0.89
0.72

9.19
9.47

2.87±2.53
2.85±2.61

0.146
0.223

0.932

1.50
1.47

4.05
4.10

2.31±0.84
2.33±0.86

1.27
1.34

9.87
10.51

3.46±2.72
3.58±2.73

0.126

0.097

0.879

0.74/1
0.69/1

2.33/1
2.17/1

1.42/1 ±0.71/1
1.28/1±0.67/1

0.42/1
0.44/1

2.37/1
3.06/1

1.45/1 ±0.71/1
2.05/1±0.92/1

0.951
0.353

0.383

*
*

*
17.92

*
*

0.018
0

33.15
6.25

13.11±16.13
1.25±2.79

*
*

9
3

150
93

39.27±38.91
34.07±26.91

43
23

1100
1100

342.57±352.95
325.38±307.38

0.002
0.000

0.859

3.74
0

24.92
26.70

11.82±6.64
9.25±8.55

7.47
0

59.81
74.76

17.80±10.70
11.21±15.59

0.064

0.662

0.072

0.00
0.42

3.14
2.92

1.15±1.19
1.57±0.78

1.33
1.41

4.83
4.94

2.76±0.98
2.76±0.92

0.000
0.000

0.650

0.08
0.33

2.67
9.33

1.27±0.65
2.83±2.57

1.42
1.17

52.36
34.58

12.47±12.86
11.13±10.02

0.002
0.004

0.955

0.00
0.00

0.50
9.32

0.08±0.16
3.55±2.95

1.67

0.33

28.22
27.13

10.92±7.16
10.21±6.94

0.222
0.243

0.334

0.00
0.00

1.08
14.08

0.26±0.39
1.17±3.59

0
0

2.58
4.16

0.98±0.75
1.27±1.11

0.002
0.898

0.193

*

(*): no data
Dan Kia reservoir is turbid frequently while chlorophyll a concentration are very
low. Thus, turbidity of Dan Kia reservoir can be caused by suspended solids. pH
values ranged from slight acid to slight alkaline. This condition is suitable for the
growth of Chrysophyta. Surveying composition and density of phytoplankton showed
regular presence of Synura genus in Dan Kia reservoir and Tuyen Lam reservoir
while not seeing this taxon in Xuan Huong reservoir. Ammonium and phosphate
concentrations were high within the dry season, but did not differ according to layer
and season (Table 3.13). Some parameters of quality water exceeded Vietnamese
Standard for drinking water (QCVN08:2008/BTNMT).
In short, Dan Kia is a muddy, medium depth, none stratified reservoir, some
parameters of nutrition were in medium level, others were in eutrophic level. Maybe
agricultural activities around the basins causing a nutritional imbalance of nitrogen
and phosphorus.
3.2.3.2 Biological characteristics of water in Dan Kia reservoir
Adequate presence of four zooplankton groups are Cladocera, Copepoda,
Rotatoria and Larvae in Dan Kia reservoir. While Rotatoria is dominant in Xuan
Huong reservoir, they have low density in Dan Kia reservoir and absolutely no
presence in Tuyen Lam reservoir.
16

3.3 Characteristics of phytoplankton community and the impact factors
3.3.1 Chlorophyll a and environmental factors
The results of multivariate regression analysis for 3 reservoir, including
chlorophyll a is the dependent variable, environmental factors are the independent
variables, are shown in table 3.14.
Table 3.14 Correlation between chlorophyll a and environmental factors
Reservoirs/layers
Xuan Huong
Surface layer
Bottom layer
Tuyen Lam
Surface layer
an Kia
Surface layer

Correlation equations

R2 (%)

P

Chla = -345.043 + 0.005* Conductivity*Turbidity +
144.3*log(Temperature) (1)
Chla = -345.043 + 0.005* Conductivity*Turbidity +
144.3*log(Temperature) (2)

40.46

0.0002

65.83

0.0001

Log(Chla) = 1.5924 + 0.277*pH - 0.273*TN (3)

23.81

0.0112

Log(Chla) = 2.333 + 0.029*Crypt (4)

20.94

0.0050

At Xuan Huong reservoir, chlorophyll a concentrations in the surface layer and the
bottom layer correlated with conductivity, turbidity and temperature, the largest R2
value at the bottom layer is 65.83% (p = 0.0001). Correlation equations (1) and (2)
show that chlorophyll a in Xuan Huong reservoir correlated with temperature.
Meanwhile, concentration of chlorophyll a in Tuyen Lam reservoir correlated with pH
and TN. Thus, nitrogen is the main factor that dominated growth of phytoplankton in
Tuyen Lam reservoir. At Dan Kia reservoir, chlorophyll a concentration in the surface
layer has a relationship with Cryptophyta (Equation 4, Table 3.14).
3.3.2 Correlation between density of phytoplankton (by phylum) and environmental
factors
Database of phytoplankton density in the layers of the reservoirs were
standardized for multivariate regression analysis. The results are shown in Table 3:15.
Table 3:15 Results of multivariate regression analysis between phytoplankton groups
and environmental factors

Groups of
phytoplankton
Xuan Huong
Cyanophyta
Surface layer
Bottom layer
Chlorophyta
Surface layer
Cryptomophyta
Surface layer
Tuyen Lam
Cyanophyta
Surface layer
Bottom layer

Correlation equations between phytoplankton density &
environmental factors

R2

P

53.74

0.0001

57.46

0.0001

Log(Chlorophyta) = 0.878 + 0.588*DO (7)

20.33

0.0141

Log(Cryptophyta) = 3.943 - 1.087*log(TP) (8)

42.69

0.0004

Log(Cyanophyta) = 7.967 - 6.106*log(NO3) (9)
Log(Cyanophyta) = 4.675 + 2.771*log(Turbidity) - 1.630*TN (10)

31.92
51.30

0.0006
0.0001

Cyanophyta = -3259.990 - 1429.510*PO43- +
491.351*Temperature - 1212.670*log(TP) (5)
Sqrt(Cyanophyta) = 51.2801 - 9.266*DO + 2.774*Temperature
- 0.315*log(NO3-)*TN (6)

17


Chrysophyta

Surface layer
Dan Kia
Bacillariophyta
Surface layer
Bottom layer
Dinophyta
Surface layer
Chrysophyta
Surface layer
Bottom layer
Cryptomophyta
Surface layer
Bottom layer

Log(Chrysophyta) = 1.193 + 1.871*PO43- (11)

26.43

0.0348

Log(Bacillariophyta) = -0.587 + 0.554*pH - 0.413*log(TN) (12)
Bacillariophyta = 11.762 - 6.007*NO3- + 3.245*TN (13)

45.60
47.61

0.0001
0.0001

Log(Dinophyta) = -1.009 +

0.097*SQRT(Conductivity)*log(Turbidity) (14)

76.66

0.0001

Log(Chrysophyta) = 1.041 + 0.414*Cladocera (15)
Log(Chrysophyta) = 5.568 + 0.629*Cladocera - 0.916*DO (16)

45.58
70.11

0.0001
0.0001

Cryptophyta = 99.494 - 1.293*T - 9.818*pH (17)
Log(Cryptophyta) = 5.506 - 0.005* Temperature *pH*DO (18)

60.36
36.36

0.0001
0.0023

In Xuan Huong reservoir, density of Euglenophyta, Dinophyta and Bacillariophyta
did not correlate with environmental factors in both layers. Chlorophyta and
Cryptophyta density in the surface layer have negative correlation with DO and TP (7,
8 equation). Cyanophyta correlated with environmental factors clearly. In particular,
Cyanophyta density of surface layer correlated with phosphorus inversely (Equation
5), Cyanophyta density of the bottom layer inversely correlated with nitrogen

(Equation 6). In addition, Cyanophyta in two layers was dependent on temperature.
Thus, both chlorophyll a and Cyanophyta density depended on temperature and
nutrition in Xuan Huong reservoir. In Tuyen Lam reservoir, Chrysophyta density
correlated with concentration of phosphate and some environmental factors,
especially they inversely correlated with nitrogen concentration. Bacillariophyta
depended on pH and nitrogen in Dan Kia reservoir (equation 12 and 13). Dinophyta
correlated with turbidity and conductivity of Dan Kia water (Equation 14) while
Cryptophyta can not resist to pH variations (equation 17 and 18).
3.3.3 Correlation between phytoplankton density and environmental factors
The results of CCA analysis between phytoplankton species composition and
environmental factors in the reservoirs are shown in Figure 3.18, 3.19, 3.20.
In the surface layer of Xuan Huong reservoir (Figure 3.18A), most of the
environmental factors were dominant species composition in months of dry season
and are located in the first axis. The advantage in these months belong to
Euglenophyta and Cyanophyta as Euglena sp., Euglena caudata, Trachelomonas sp.,
and Oscillatoria boryana, Pseudanabaena catenata. At rainy season, light intensity
was maximum, nitrate and TN varied in opposite direction with ammonium, dominant
species belonged to Microcystis aeruginosa, Pseudanabaena limnetica along with
appearance of Cyclotella sp. In months of rainy season and the first months of dry
season, with abundant presence of Cyanophyta taxa as Pseudanabaena sp., Anabaena
sp. Anabaena genus known can fix N in case of ratio N/P of water is low. The ratio
18


N/P in Xuan Huong reservoir at that time (June and July) was lower than in other
months.

Figure 3.18 The CCA graph of phytoplankton species composition and
environmental factors in Xuan Huong reservoir. (A) surface layer, (B) bottom
layer

Phytoplankton species composition in the surface layer of Tuyen Lam reservoir
(Figure 3.19A) was more diverse than in the bottom layer (Figure 3.19B). In the surface
layer, Pinnularia sp. and Cymbella sp. positioned near the light intensity vector. This
species occurred in April and May, when light intensity increases. Meanwhile, they
were not present at the bottom layer, proved to that they are photophilic taxa.
Phytoplankton at the surface layer of Tuyen Lamreservoir was dominated by most of
environmental factors in the final months of rainy season and the beginning of dry
season (Figure 3.19).
Coelastrum cambrium, Cosmarium pseudoconnatum, Pandorina charkowiensis
and Ceratium hirundinella were found at the 2nd axis (Figure 3.19) related to
concentration of low nutrients in July. Microcystis aeruginosa, Microcystis
wesenbergii, Oscillatoria sp. on the graph (Figure 3.19A) showed their superiority
density related to temperature and pH of water. When these elements were added at
the beginning of rainy season (April), accompanied by an increase in density of above
genera.
Seasonal variation of species composition in Dan Kia reservoir is shown quite
clearly in the CCA axis. pH value at the first axis and temperature at the second axis
increase in rainy season with dominant species is Rhizosolenia sp. In the last months
of rainy season, turbidity increased, this appropriate to Dinophyta as Peridinium sp.,
Ceratium sp. and Bacillariophyta as Cyclotella sp. Thus, turbidity is the dominant
factor on phytoplankton species composition in Dan Kia reservoir.

19


Figure 3.19 The CCA graph of phytoplankton species composition and
environmental factors in Tuyen Lam reservoir. (A) surface layer, (B) bottom layer
3.4 Impacts of nutrition and grazing on phytoplankton
3.4.1 Nutrition and growth of phytoplankton
Figure 3.21 shows no has difference among supplement and complement

experimental treatments of zooplankton in rainy season (dry season experiments were
also similar). The pair of treatments added only N or P were also no different from no
supplementation. However, additional treatments simultaneously N and P had
significant differences from non-supplement, in both experiments of rainy season
(ANOVA, p = 0.002) and dry season experiments (ANOVA, p = 0.012).

Figure 3.21 Variability of phytoplankton biomass at 6/2014 experiment for Tuyen Lam
reservoir. N=nitrogen (N-NO3-), P=phosphorus (P-PO43-), Z = zooplankton, C=control
The results showed that in Tuyen Lam reservoir, grazing of zooplankton did not
adjust biomass of phytoplankton, that is the role of nutrients. Thus, the results obtained
from experimental treatments and fields showed that bottom up control is a key driver in
Tuyen Lam reservoir.
20


3.4.2 Grazing of zooplankton on growth of phytoplankton
Apparent growth rate of organisms groups in series of experimental dilutions
(rainy and dry season) with average death rate is shown in Table 3.18.
Table 3.18 The equations describing the regression line of apparent growth of
plankton groups (preys) in different dilutions in two periods of experiment
Time of
experiments

Preys
filamentous
cyanobacteria

Dry season
(24/2/2014)

cyanobacteria
Bacteria
Algae
filamentous
cyanobacteria

Rainy
season
(30/8/2014)

cyanobacteria
Bacteria
Algae

Serie of
dilutions

The regression equation
between apparent growth
rate (k) with dilutions

R2

p

0.2µm
0.01µm
0.2µm
0.01µm
0.2µm

0.01µm
0.2µm
0.01µm
0.2µm
0.01µm
0.2µm
0.01µm
0.2µm
0.01µm
0.2µm
0.01µm

y = 1.932 – 2.376x (19)
y = 1.463 – 7.905x (20)
y = 0.107 – 0.177x (21)
y = 0.3  1.165x (22)
y = 1.992  0.821x (23)
y = 1.905 – 8.855x (24)
y = 2.437  0.769x (25)
y = 0.738 – 0.873x (26)
y = 0.182 + 0.205x (27)
y = 1.737  2.664x (28)
y = 0.894 – 4.702x (29)
y = 1.087 – 2.339x (30)
y = 1.745 – 7.976x (31)
y = 2.256 – 3.363x (32)
y = 0.6433  2.531x (33)
y = 0.8317  0.304x (34)

0.7405

0.9068
0.1536
0.6321
0.5667
0.9818
0.8708
0.2722
0.0334
0.9974
0.9694
0.7198
0.9559
0.9698
0.9672
0.1380

0.8267
0.0491
0.9937
0.1632
0.4671
0.0498
0.1020
0.8747
0.8235
0.9501
0.0499
0.6896
0.0487
0.9013

0.0496
0.2791

Average mortality (d-1)
by
Virus

Zooplankton

0.713

-

-

-

0.258

-

-

-

-

-

-

0.394

-

0.167

-

0.591

During dry season
None increase in apparent growth rate of filamentous Cyanobacteria in the 0.2
micron dilution. Conversely, the apparent growth of this group in the 0.01 micron
dilution increased. The regression line of 0.01 micron series of dilution (Equation 20,
24) shows, viruses effected on filamentous Cyanophyta and bacteria. Indirect
mortality of filamentous Cyanophyta and bacteria by viruses were estimated
respectively 0.713 d-1 and 0.258 d-1. In contrast, zooplankton have no significant
impact on filamentous Cyanophyta, bacteria, Cyanophyta and other phytoplankton
during this experiment.
During rainy season
Grazing of zooplankton was identified as lethal for bacteria (Equation 31), other
Cyanophyta (Equation 29) and eukaryotic phytoplankton (Equation 33). Zooplankton
indirectly lethal for bacteria, unicellular Cyanophyta and eukaryotic algae was
estimated 0.167; 0.394 and 0.591 d -1respectively. In summary, lysis of virus was the
main cause of death for populations of filamentous Cyanophyta, bacteria in dry
season. Meanwhile, the grazing was the lethal source to single-cell cyanobacteria,
microalgae and bacteria in rainy season.
3.5 Simulation trends of ecosystem of Dan Kia reservoir by AQUATOX model

21


The first scenario, the current situation, the load of nutrients of all 5 streams was
introduced into the reservoir. The second scenario, the quality water was controlled to
reduce to 1/3 of nutrient load in S4 and S5 without affecting flows.

a) All sources were introduced into Dan Kia reservoir (status)

a) Reducing to 1/3 of nutrient load in S4 and S5 streams
Figure 3.23 Quality water of the surface layer of Dan Kia reservoir according to scenarios
The first scenario
Most concentration of
NH4+, NO3- and PO43from the model and the
survey (Figure 3.23a)
were suitable. The
model results reflected
quite well concentration
of ammonium, nitrate
and
phosphate.
Accordingly, the model
can forecast quality
water of reservoir in the
22


future. The results forecast that NH4+, NO3- and PO43- will increase in the future even
if the scale of impacts are similar to the current situation (Figure 3.23a).
Phytoplankton were simulated including Bacillariophyta, Chrysophyta and

Dinophyta (Figure 3.24). Phytoplankton biomass increases in January and higher in
April. There was relatively consistent between chlorophyll a concentration from the
model and monitoring. On other hand, chlorophyll a concentration from the model
varied simultaneously with Bacillariophyta, Dinophyta.

The simulation resuts of zooplankton groups showed that Copepod and Cladocera
biomass (Figure 3.25) was the highest in March, respectively 5.5 mg/l and 2.25 mg/l.
These values fell to the lowest in August and September. Most zooplankton biomass
from the model were higher than actual results from 0.1 to 30%
The second scenario
When controlling to reduce the load of nutrients to 1/3 of S4 and S5 streams,
concentration of ammonium, nitrate and phosphate decreased significantly. Nitrate
concentrations were lower than the allowed threshold of A1 level at all months.
Phosphate concentration still exceed the allowed standard of B2 level from 1.2 to 1.8
times. When nutrient concentrations of water decreased, the model results showed
that phytoplankton and zooplankton biomass also decreased.
Decreasing the load of nutrients of S4 stream and S5 stream is only one of many
possible scenarios to simulate proposed quality water as expected from AQUATOX
model.
CONCLUSION
Recorded 7 phyla of phytoplankton in the studied reservoirs, including
Cyanophyta, Chlorophyta, Bacillariophyta, Euglenophyta, Dinophyta, Chrysophyta
23


and Cryptophyta. Of these, 112 taxa of Xuan Huong reservoir, 43 and 44 taxa
respectively in Tuyen Lam reservoir and Dan Kia reservoir. Each reservoir has its
own characteristics of phytoplankton community structure. The structure of
phytoplankton community in each reservoir is dominated by a few certain factors.
While density of filamentous Cyanophyta and Euglenophyta were dominant at Xuan

Huong reservoir, colony Cyanophyta and Dinophyta dominated in Tuyen Lam
reservoir. Diatoms and Chrysophyta were dominant at Dan Kia reservoir. Species
diversity of phytoplankton in Xuan Huong reservoir is the lowest, higher and similar
each other in Tuyen Lam reservoir and Dan Kia reservoir.
The phytoplankton groups according to morphological - function groups reflected
nature and characteristic of aquatic ecology at certain levels. When considering
evaluate the relationship between phytoplankton community structure and
environmental factors, the system of Reynolds et al., (2002) and Kruk et al., (2010)
should be used.
All studied reservoirs are not stratified. Most hydraulic, physical, chemical
parameters of water did not differ according to layer but differing according to
season. Each reservoir owns ecological characteristics, including:
- Xuan Huong is a shallow, turbid, high pH reservoir. The main factor caused
turbidity is phytoplankton biomass. The ratio N/P of water is suitable for growth of
Cyanophyta.
-Tuyen Lam reservoir has an average depth, few turbidity and low nutrient
concentration among the reservoirs.
-Dan Kia reservoir frequently is turbid, this is not related to phytoplankton
biomass. Nutrient concentrations are high in months of dry season.
Composition, density and biomass of phytoplankton in the reservoirs respect to
environmental factors. Each reservoir was dominated by a few certain factors.
Turbidity dominated on phytoplankton community structure in three reservoirs.
Temperature effects on phytoplankton community structure of Dan Kia reservoir and
Xuan Huong reservoir. Conductivity dominated on phytoplankton community of
Xuan Huong reservoir, Dan Kia reservoir and pH value dominated on phytoplankton
of Dan Kia reservoir. The concentration of compounds containing nitrogen and
studied reservoirs. Unclear roles of adjustment of zooplankton on phytoplankton in
the reservoirs. This control was selective in Xuan Huong reservoir. There was no
impact of zooplankton on filamentous Cyanophyta, but grazing were identified as the
main lethal source for bacteria, single-celled cyanobacteria and others algae, with an

estimated 0.167d-1; 0.394d-1and 0.591d-1 respectively. Meanwhile, virus is a major
cause of death for populations of filamentous Cyanobacteria and bacteria. Indirect
mortality of filamentous Cyanophyta and bacteria by virus estimated are 0.713 d-1 and
0.258 d-1 respectively.
24


AQUATOX model was used to simulate quality water of Dan Kia reservoir
including the load of nutrients, content of chlorophyll a, and biomass of zooplankton
and phytoplankton. The results showed that, when controlling to reduce the loads,
concentration of ammonium, nitrate and phosphate was lower than the allowed
thresholds of surface water standards.
NEW FINDINGS OF THE THESIS
- This is the first study in Vietnam on impact of environmental conditions on natural
phytoplankton community structure by analyzing aggregated responses of
phytoplankton and environmental factors in the reservoirs at Lam Vien highland.
- Indicating structural characteristics of phytoplankton community in the reservoirs at
Lam Vien highland by approaching and applying softwares, tools, experiments and
new methods.
- This is the first study in Vietnam assessing the biological rates in reservoirs
-The first time, the forecasting model of freshwater food web was applied in Vietnam.
LIST OF WORKS HAS BEEN PUBLISHED
1. Tran Thi Tinh, Doan Nhu Hai, Le Ba Dung, 2015. Mortality impact of viral
and microzooplankton upon bacteria and phytoplankton in a eutrophic in central
highland. Journal of Biology, Vol 37, No. 2, 2015 (200-206).
2. Tran Thi Tinh, Doan Nhu Hai, Le Ba Dung, 2015. Seasonal variation of
phytoplankton in Tuyen Lam reservoir in Da Lat, Vietnam. Journal of Biology, Vol
37, No 4, 2015 (414-424).
3. Tran Thi Tinh, 2014. Assess the state of eutrophication of some reservoirs in
Dalat by TSI and AQ index. Journal No. 13, May 12-2014 (36-43), Tay Nguyen

University, ISSN 1859-4611.
4. Tran Thi Tinh, Doan Nhu Hai, Bui Nguyen Lam Ha, Nguyen Thi Thanh
Thuan, 2016. Impact assessment of Dan Kia inflows and application
AQUATOX model in managing water quality. Journal of Biology, Vol 38 No. 1,
2016 (61-69).

25