Examensarbete
TVVR 12/5012
Study on the Blue-green Algal Bloom
Control in Lake Taihu, Jiangsu, China
2012-06-11
___________________________________________________________________
Tianjiao Qian
Division of Water Resources Engineering
Department of Building and Environmental1 Technology
Lund University
Avdelningen för Teknisk Vattenresurslära
TVVR-YY/500n
ISSN-1101-9824
Study on the Blue-green Algal Bloom Control in Lake
Taihu, Jiangsu, China
Tianjiao Qian
Supervisor: Kenneth M Persson
Examiner: Linus Tielin Zhang
Acknowledgements
I would like to express my gratitude to all those who helped me during my writing of
this thesis. My deepest gratitude goes first to my supervisor, Professor Kenneth M
Persson, for his great encouragement and guidance. I also would like to express my
heartfelt gratitude to my examiner Professor Linus Tielin Zhang for his patient
answering my questions and helpful instructions.
Secondly, I want to acknowledge with deep gratitude the assistance given to me by
Director of the Algae control Management Office, Kuang ming and the Senior
Engineer, Ni Qijun. They helped me a lot during the course of the thesis.
Finally, I wish to extend my thanks to my family and friends for their support and
help so that I can finish my thesis project successfully.
.
Abstract
Lake Taihu is the second largest lake in China. With the fast urbanization and industry
development in the river basin, the lake started getting polluted in the early 1990s and
is now highly eutrophicated. People live on this lake are facing a terrible problem that
they have blue-green algal blooms almost every summer. During that period, the
water in the lake becomes mushy and smelly and drinking water safety is threatened.
After some studies and surveys, several alternative solutions such as water transfer
and diversion, restoration by large aquatic vegetations, water algal separation,
pollution source control and integrated management are provided and discussed. All
the solutions put forward have their advantages and disadvantages. Pollution source
control is the fundamental solution while water algal separation act well in a short
time when blue-green algal blooms happen. Other methods like biomanipulation need
further study.
Key words: Taihu eutrophication blue-green algal control
Content
Acknowledgements
Abstract
List of Figures and Tables
1. Introduction ................................................................................................................ 1
1.1 Lake Taihu........................................................................................................ 1
1.2 Lake Taihu River Basin.................................................................................... 2
1.3 Wuxi Water Body Distribution and Water Treatment Plants ........................... 4
1.4 Problem Description ........................................................................................ 7
1.5 Capacity Building of Water Resources and Environmental Management in
Lake Taihu............................................................................................................ 10
2. Aims and Objectives ................................................................................................ 12
3. Current Situation ...................................................................................................... 13
4. Causes of algal blooms ............................................................................................ 17
4.1 Pollutions ....................................................................................................... 17
4.2 Geographical and Climatic Impact ................................................................ 19
5. Policy Issues............................................................................................................. 21
6. A Comparative Example: Dianchi Lake, Yunnan, China ......................................... 22
6.1 Description of Dianchi ................................................................................... 22
6.2 Eutrophication History ................................................................................... 22
6.3 Comparison with Taihu Lake ......................................................................... 23
6.4 Treatment Against Algal Blooms ................................................................... 24
6.5 Conclusion for Dianchi .................................................................................. 25
7. Alternative Solutions ................................................................................................ 26
7.1 Water Transfer and Diversion ........................................................................ 26
7.2 Integrated Management by Catchments......................................................... 27
7.3 Pollution Source Control................................................................................ 28
7.4 Restoration by Large Aquatic Vegetations ..................................................... 30
7.5 Biomanipulation ............................................................................................. 31
7.6 Water Algae Separation .................................................................................. 31
7.7 Other Methods ............................................................................................... 32
8. Analysis & Suggestions ........................................................................................... 33
9. Conclusion ............................................................................................................... 36
References .................................................................................................................... 38
List of Figures and Tables
Figures
Figure 1: Location of Lake Taihu in China ............................................................ 1
Figure 2: Water system of the Taihu basin .......................................................... 3
Figure 3: Wuxi Water System ................................................................................ 5
Figure 4: Overview of the northern part of Lake Taihu, the main water treatment
plants (WTP) and their water intakes in Wuxi city. ....................................... 6
Figure 5: The microscopic images of blue-green algae. ........................................ 7
Figure 6: The concentrations of ammonia nitrogen ............................................. 14
Figure 7: The concentration of CODm ................................................................ 14
Figure 8: The concentrations of TP...................................................................... 14
Figure 9: The concentrations of TN ..................................................................... 15
Figure 10: The percentages of chemical oxygen demand (COD), ammonia
nitrogen(NH3-N), total nitrogen(TN) and total phosphorus(TP) from
domestic, industrial and agricultural sources, respectively. ......................... 17
Figure 11: Regional map of Lake Taihu in Wuxi ................................................. 20
Figure 12: the sceneries of Dianchi Lake ............................................................ 22
Figure 13: Comparison between traditional water hyacinth and the species with
purple root .................................................................................................... 24
Figure 14: A picture of purple-root water hyacinth ............................................. 25
Figure 15: The locations of four catchments ....................................................... 28
Tables
Table 1: The concentrations of TP ....................................................................... 16
Table 2: The amount of domestic pollution in 2010 ............................................ 18
Table 3: The amount of industrial pollution in 2010 ........................................... 19
Table 4: The amount of agricultural pollution in 2010 ........................................ 19
Table 5: Lake residence period of some Chinese lakes ....................................... 23
Table 6: Chinese sewage discharge standard for municipal wastewater plants ... 30
1. Introduction
1.1 Lake Taihu
Located in the Yangtze delta in the eastern China, the most economically developed
region in the country, Lake Taihu has become the second largest lake in China since
the previous second large lake, Dongting Lake, has been decreasing in size these years.
Lake Taihu is the key source of drinking water for some of the major cities like
Suzhou, Wuxi and also for the metropolitan city, Shanghai. It is a highly eutrophic
lake with a mean depth around 2m, an area of 2,250 km² and a volume of 4.4 billion
m3. (Pu and Yan1998; Qin and others 2007) It is world famous for its gorgeous
sceneries along the shoreline and there are several tourist attractions surrounding the
lake.
Figure 1: Location of Lake Taihu in China
(source: www.jiangsu.net/map/regions/laketaihu.php)
Lake Taihu is linked by different waterways from adjacent provinces and cities which
makes it a very characteristic district known as “Jiangnan Water Village”. Water flows
1
into Lake Taihu through 15 rivers from Suzhou, Wuxi and Changzhou in Jiangsu
Province. (Cheng, et al., 2009)
Scientific studies show that the original structure of Lake Taihu is the result of a
meteor impact based on the discovery of shatter cones, shock metamorphosed quartz,
microtektites, and shock metamorphic unloading fractures. (Wang and Erkang, 2002)
Due to sediments and reclaiming farmland in the lake, the shape of the lake has been
changing. Now, the actual water area of Lake Taihu is approximately 3159 km2.
1.2 Lake Taihu River Basin
1.2.1 Geography
Taihu basin lies at the center of the Yangtze River Delta and has an area of 36,900
km2. It is composed mainly of plains and characterized by favorable natural
conditions, well-known as the ‘Land of Fish and Rice’ in China. The Taihu basin is
high in the west and low in the east. In landform, it is divided into the hilly country
and the plain. The most of the mountain lands have a range in height from 300m to
700m above sea level. The main peak of Tianmu Mountain can reach an altitude of
about 1500m above sea level. On the other hand, the Lake Taihu plain is low in the
center and high in circumference just like a plate. The plain takes 67% of the total
basin area and the surface elevations are all below 10m, higher in the west ranging 5
to 8m and ranging from 2.5 to 3m in the middle-east. (TBA, 2012)
1.2.2 Climate
The Taihu basin lies in the subtropical monsoon climatic zone. It is clearly
demarcated in four seasons, being cold and arid in winter, hot and humid in summer.
The mean annual temperature has a range from 15 to 17 centigrade, and increases
from north to south. The average annual precipitation in the Taihu basin is 1181mm,
and the precipitation is uneven in seasonal distribution that 60% is attained in May to
September. The ratio of maximum and minimum precipitations can reach 2.4 while
that of runoff can be 15.7. (TBA, 2012) The average evaporation capacity ranges from
1151 to 1576mm, being highest in the north and lowest in the hilly region in the
southwest, varying greatly in seasons, up to 3-4 times in summer than in winter. (She,
et al., 1991)
1.2.3 Water System
The water system of the Taihu basin is a lake network system that the Lake Taihu is
its center. The source of Lake Taihu is derived from Shaoxi and Nanxi, flowing
through several rivers and canals to the east part of Lake Taihu and also via the
Huangpu River and the Liuhe finally into the Yangtze River and the East China Sea.
The upstream water system lies to the west of the lake and the downstream to the east.
In the whole basin, the water area almost occupies one-sixth of the total area which is
about 6200 km2. The largest man-made river course, the Jiangnan Canal, is 312km in
length and links up the rivers and lakes in the basin. There are 15 main rivers flowing
into Lake Taihu in Suzhou, Changzhou and Wuxi of Jiangsu Province, totally 69
towns. (Cheng, et al., 2009)
Figure 2:
Water system of the Taihu basin
(source: http://www.shanghaiwater.gov.cn/web, edited by Qian,2012)
1.2.4 Social Economy
The Taihu river basin is not only the place in China where the economy is in fullest
flourish but also the region where the essence of agriculture is located. This region is
gifted with favorable natural conditions concentrated with cities and towns like
Shanghai, Wuxi and Suzhou. It plays a reading role in the industrial and agricultural
production in the country. The region covers less than 0.4% of the total area of the
whole national territory with a population accounting for 2.9% that of the entire
country which is more than 36 million people. The population density has reached
978 per square kilometer. This region is of great importance in China in terms of
levels in culture, science and technology, economic strength, standards of
urbanization as well as the per capita national income, etc. The Gross Domestic
Product (GDP) of this region has achieved 4.09 thousand billion Chinese Yuan (CNY)
that is about 10% of the total Chinese economy in 2010.(Jiangsu,2011)
1.3 Wuxi Water Body Distribution and Water Treatment
Plants
Situated in the north of Lake Taihu, south of the Yangtze River, Wuxi has countless
rivers, streams, brooks and creeks. It has a nick name “Jiangnan Water Village”. The
total surface area of water body covering the city is about 1089.26 km2 which takes
22.82% of the whole city area.
1.3.1 Yangtze River
The Yangtze River is the longest river in China. The part that flows through Wuxi city
is about 35 km. The width of the river surface is 2 to 4 km while the depth has a range
from 30 to 40 m. According to hydrological observation data, the annual average
runoff of the Yangtze River is 973 billion m3.
1.3.2 Lake Taihu
Lake Taihu is the largest lake in south China with 2338 m2 water surface area. Wuxi
city occupies 613 km2 of the total area which includes Meiliang Bay, Lake Gonghu,
Lake Zhushan and Lake Lihu, etc. Lake Taihu is regarded as a natural reservoir that
can store 4.423 billion m3 of water when its water level reaches 2.99 m and 8.3 billion
m3 when the depth is 4.65 m. The mean depth of the lake is 1.89m. During the rainy
season in April every year, the water level begins to rise and reaches the peak in late
July. The lowest water level happens in the dry season around February or March. The
highest water level occurred in the year 1991 which was 4.97m and the lowest 1.87m
in the year 1934. (Zhang, et al., 2010)
1.3.3 The Grand Canal
The segment of Grand Canal flows through Wuxi is 41 km long. The width of the
canal bottom ranges from 35m to 94m. The Grand Canal is considered as the main
navigation and drainage channel, so it plays a really significant role in Wuxi Water
body.
Figure 3: Wuxi Water System
(source: Wuxi Government.2011)
1.3.4 Water Treatment Plants
There are 4 large water treatment plants in Wuxi that serve the major drinking water
now, Nanquan WTP, Xidong WTP, Xuelang WTP and Zhongqiao WTP. The Nanquan
water intake is situated at the entrance of Meiliang Bay and is connected with the
intakes of Zhongqiao and Xuelang WTPs with 16km and 14 km long pipes
respectively. Located at the northeast part of Lake Taihu, the Xidong water intake
transfers source water to its plant. The Zhongqiao WTP has a treatment capacity of
600,000m3 per day and supplies water for most of the urban area while the Xuelang
WTP has a capacity of 250,000m3 per day and supplies the southern portion of the
city. The Xidong WTP has a capacity of 300,000m3 per day and supplies the
sub-district of the east Wuxi. (Zhang, et al., 2010)
Figure 4: Overview of the northern part of Lake Taihu, the main water treatment plants
(WTP) and their water intakes in Wuxi city.
(source: Zhang, et al., 2010)
1.4 Problem Description
At present, some lakes all over the world are marred with eutrophication problem and
algal blooms. Lough Neagh is the largest lake in Great Britain. Excess nutrients
especially the excess discharge of P and some pollution events have affected the water
badly. Eutrophication is considered as the key factor of water quality degradation.
There are also lakes for instance in Japan, Canada and the US bothered with
eutrophication. Eutrophic lakes always carry too many nutrients that lead to algal
blooms. The water quality in Lake Taihu has been deteriorating these years and the
lake is in a highly eutrophication level now. Algal blooms particularly blue-green
algal blooms become the most troublesome problem. They take place every summer
and seriously threaten the drinking water safety in the Taihu basin.
1.4.1 Blue-green Algae
Blue-green algae are bacteria that can be considered as simple ancient aquatic
species that occur naturally in waters, rivers, lakes, trees, hot springs and snow, etc.
They can vary considerably in shape, colour and size and reproduce exponentially.
Figure 5: The microscopic images of blue-green algae.
(source: www.derm.qld.gov.au/water/blue_green/blue_green.html)
Blue-green algae are actually types of bacteria known as Cyanobacteria. They
usually look green and sometimes may turn blue when scums are dying. Water
bodies may generally have taste and odour problems with large concentrations of
blue-green algae. Meanwhile, some species are capable of producing toxins that
endanger human health by contaminating drinking water sources. (Queensland
Government, 2006)
Because of their small size, cells of blue-green algae only can be seen with the aid of
a microscope. Some types of blue-green algae have tiny gas vesicles in their cells,
allowing them to change the position in water in response to light intensity and
nutrient concentration. The blue-green algae obtain a competitive advantage in
obtaining light and nutrients when having this buoyancy-regulating mechanism.
(Queensland Government, 2006)
When there is an increase in the number of algae cells, a phenomenon named
‘bloom’ takes place. If blue-green algal blooms start in water bodies, a number of
problems could come up. They would stem flow in drainage systems, make pumps
and sluices clogging, interfere with navigation fishing and also do damage to other
structures or activities. The process of overgrowing blue-green algae consumes a
large amount of oxygen in the water that left little to other aquatic creatures. When
the necrons and carcasses start to rot, the oxygen concentration get even lower and
the water would have unpleasant tastes and odours which seriously reduce the water
quality. What’s more, as the bloom dies, the cells tend to become 'leaky'. Some of
the algae species can produce toxins will release toxins into the water body. It may
take several months for the natural population of bacteria to degrade the toxins. So
the drinking water production from Lake Taihu may be affected by toxins in the raw
water.
1.4.2 Eutrophication
Eutrophication can have an effect on the sensory traits and environment of water body,
water quality of drinking water, fishery and so on. (Cheng, et al., 2009)
“ Eutrophication is the process by which a body of water acquires a high
concentration of nutrients, especially phosphates and nitrates. These typically promote
excessive growth of algae. As the algae die and decompose, high levels of organic
matter and the decomposing organisms deplete the water of available oxygen, causing
the death of other organisms, such as fish. Eutrophication is a natural, slow-aging
process for a water body, but human activity greatly speeds up the process.” (Art,
1993)
Blue-green algal blooms go hand in hand with eutrophication. Species of blue-green
algae may dominate and increase excessively in water body under following
circumstances. First when the nutrient level is high, particularly phosphorus and
nitrogen are sufficient for the population growth. Secondly, the turbulence of water
is fairly low or water’s lack of mixing. Thirdly, the weather patterns are stable for a
long time, especially with a warm temperature. But blooms also can occur in cooler
weather. (Queensland government, 2006)
Nowadays, human activities do really have an important influence on the environment
of water body. More phosphates and nitrates are poured into water body along with
the rapid development of economy. For the last century, developed countries such as
the US, Japan, Germany, Holland, Finland have spent a large amount of money on the
studies on algal bloom control. Though the technologies they put forward can solve
the problem on a certain extent, they still seem to be not that perfect.
Eutrophication occurs more frequently in most developing countries due to their
industrial structure. In those countries, agriculture often takes the majority part that
brings in excess phosphates and nitrates into water bodies. Because of outdated
technologies, developing counties need additional amount of chemical fertilizer to
maintain the grain output which produces even more phosphates and nitrates that
makes the situation even worse.
1.4.3 Water crisis in 2007
The most serious water event happened in Jiangsu in recent years may be the water
crisis in the year 2007. The water crisis swept Wuxi city in a sudden. Two millions of
people had a shortage of clean drinking water for almost one week. On 16th May, the
water from the intake of Meiliang Bay started to get turbid and smelt badly. The
Xiaowanli Water treatment plant stopped supplying water due to the bad water quality.
It was investigated that large amount of blue-green algae around the water intake of
Xiaowanli WTP died and get rotted rapidly. According to a report from the related
department on 28th May 2007, water quality from Gonghu WTP was really bad, the
ammonia nitrogen index went up to 5 mg/l while DO (dissolved oxygen) down to 0
mg/l. Three days later, the ammonia nitrogen index was still 6.55mg/l high, and DO
went back to 0.33mg/l. (Zhang, et al., 2010)
During the first few days of the water crisis, the tap water in the urban area looked
swampy. Certainly, it was not portable even after being boiled. Panic buying for
bottled water happened and nearly cleared the shelves in every store. In the following
days, the tap water still smelt really badly but became less swampy because of the
chemicals adding into it. Though the tap water was not as turbid as before, people
were not able to drink it, have shower or cook with it. Citizens in Wuxi were really
worried and anxious to know when they could have safe and clean drinking water
again.
A large volume of water was transferred into Lake Taihu from the Yangtze River to
dilute the high algal concentration. Other measures like water diversion from
Meiliang Lake were also carried out. To rehabilitate the water supply as soon as
possible, experts came across the country to deal with the problem. Though the tap
water was no longer turbid, bad smell from chemicals added to get rid of algae still
left. Nobody can drink that kind of water trustingly.
1.5
Capacity
Building
of
Water
Resources
and
Environmental Management in Lake Taihu
Under the great emphsis of the CPC Central Committee and State Council, the
seriousness of the water pollution in Taihu Lake has been fully recognized. Nowadays,
many departments are taking responsible for protecting the water resources in Taihu
Lake. It is required that the Taihu Lake basin should be restored in an
environmental-friendly and energy-efficient way. Every capacity building should clear
and definite the overall requirement, objectives, main tasks and key measurements
through the whole project of water protection and algae control. Since the Lake Taihu
is under the concurrent jurisdiction of two provinces and Shanghai, the big project
needs cooperation and may have difficulties during process.
The Wuxi government has set up a group to deal with affairs that involve renovation,
planning, implement projects on water resources and algae control and coordination
with other departments. In algae control, there are mainly three departments in Wuxi
that are in charge, the Algae control Management Office, the Wuxi Environmental
Protection Bureau and the Wuxi Water Conservation Bureau.
Other related departments in the sub-region of Wuxi also have to participate in the
water resource protection to pledge relevant project can be executed well. In the
‘Wuxi special programming of water environment in Taihu Lake’, it is stated clearly
that the part which is under Wuxi government’s administration is managed in
regionalization. In each region, there will be specialized section to take action. All the
results from investigations and monitoring should be reported to the superiors
regularly.
2. Aims and Objectives
Water is essential to human beings and other living lives on earth. Though covering
97% of the earth surface, only about 3% of the earth water is fresh water while 68.7%
of that water is in icecaps and glaciers that people can hardly use. Less than 0.3% of
all freshwater is in rivers, lakes, and the atmosphere. (Gleick, P.H., ed., 1993) Under
this circumstance, lakes are really vital for natural resources of freshwater. Having the
largest population in the world, China just occupies very little fresh water on earth.
Current per capita water resources in China only take 28% of the world average
standard. Among all the 660 cities in the country, more than 400 are short of
freshwater. The Taihu Lake basin accounts for about 3% of the national land area and
8% of the national population, so the water shortage seems urgent.
Algal blooms have bothered the local government and citizens for quite a long time.
The phenomena of algae aggregation started taking place several years ago. It was not
that terrible like these years, so the local government did not take this problem
seriously. In spite of ten years of treatment costing billions of Chinese Yuan, the
pollution in Taihu Lake continues. So far, many universities, laboratories,
organizations and companies have bonded to study algae bloom control and they do
have some achievements now. But there is still no conclusion on which is the most
quickresponsed and efficiency technology or method to deal with algal bloom.
In this report, several technologies and methods invented are introduced and evaluated.
Comparisons among these technologies and methods are given to find out the most
efficient solution to algal bloom. The efficiency to remove algae, costs, whether it is
friendly to the environment and other important factors will be taken into
consideration. Hopefully this report can achieve a little contribution to the field of
algal bloom control for the future.
3. Current Situation
Nowadays, the local government and the citizens have paid more intention to water
quality than ever. The quality of surface water is classified into five levels in Chinese
national standard. The case Ⅰ and Ⅱ water can be used as drinking water source.
According to a report posted on the website of
the Environmental Protection
Department of Jiangsu Province on 6th November 2011, the CODm index reached
case Ⅲ, the total P case Ⅳ while the total-N index still stayed in a poor condition
which was worse than case Ⅴ on the first year of 2011. The eutrophication level of
the whole lake was evaluated as light.
In the 53 monitoring sections around lake and at the administrative borders among
which 50 of them are measured in practice, the three indices of TP, TN and CODm in
the 47 measured sections can reach the national standard of case Ⅲ water.
The EOS/MODIS satellite has been monitoring the appearance blue-green algae
aggregation and observed the phenomena for 15 times in 2011. The average size of
aggregation area was 7.9 km2, and the largest was 23 km2. The west coast region was
the part that algal blooms occurred most frequently. Comparing to the same period
last years, the algal blooms still took place in a small scale and gathered sporadically,
but at the same time, the concentration of the algae decreased, especially that in the
head water site decreased by 25.5%. (EPDJP, 2011)
The following figures 6, 7, 8 and 9 show the mean concentrations for four items
ammonia nitrogen, CODm, total P and total N for each month through a whole year
from 2007 to 2011. There are 33 observation points in the 9 sections of Lake Taihu.
(Water Resources Protection Bureau of Taihu Basin, 2011)
Figure 6: The concentrations of ammonia nitrogen
(source: WRPBTB, 2011)
Figure 7: The concentration of CODm
(source: WRPBTB, 2011)
Figure 8: The concentrations of TP
(source: WRPBTB, 2011)
Figure 9: The concentrations of TN
(source: WRPBTB, 2011)
There is a read line in each figure that stands for a critical concentration of water
quality case Ⅲ. From the four figures, it can be concluded that the concentrations of
ammonia nitrogen and CODm can always be below the critical line while those of
total N are always higher than the standard. And the concentrations of total P are
mostly above the critial line.That means the water quality in Lake Taihu cannot
satisfy the basic standard of Case Ⅲ. According to the Environmental quality
standards for surface water in P.R.China(GB 3838-2002), the Case Ⅲ water is the
worst surface water that can be used for drinking water source, others even worse
than Case Ⅲ are not allowed to be used as drinking water source before treatment.
Table 1 shows the annual concentrations of P and water quality levels for the last two
decades.
Table 1: The concentrations of TP (Wuxi Gov)
Concentration(mg/L)
1990
water quality level
Ⅳ
1991
Ⅲ
0.025-0.05
1992
Ⅳ
0.05-0.1
1993
Ⅳ
0.05-0.1
1994
Ⅴ
0.1-0.2
1995
Ⅴ
0.1-0.2
1996
Ⅴ
0.1-0.2
1997
Ⅳ
0.05-0.1
1998
Ⅴ
0.1-0.2
1999
Ⅳ
0.05-0.1
2000
Ⅴ
0.1-0.2
2001
Ⅴ
0.1-0.2
2002
Ⅳ
0.05-0.1
2003
Ⅳ
0.05-0.1
2004
Ⅳ
0.05-0.1
2005
Ⅳ
0.05-0.1
2006
Ⅳ
0.05-0.1
2007
Ⅳ
0.05-0.1
2008
Ⅳ
0.05-0.1
2009
Ⅳ
0.05-0.1
2010
Ⅳ
0.05-0.1
year
0.05-0.1
According to a report form Nanjing Institute of Geography & Limnology. Chinese
Academey of Sciences, the total amount of TP into Lake Taihu every year is about
1029 tons and 668 tons out. The blue-green algae contains 0.66-0.81% of phosphorus,
so when 1 ton of water-algae mixture is harvested, 0.33 kg of phosphorus can be
removed. (Li and Huang, 2007) To improve the water quality in Lake Taihu, an
amount larger than 361 tons should be removed every year.
4. Causes of algal blooms
4.1 Pollutions
Around the 1960s, people started to pour heavy pollutants into Lake Taihu. Up to now,
a variety of pollutants have been discharged into it.
Figure 10: The percentages of chemical oxygen demand (COD), ammonia nitrogen(NH 3-N),
total nitrogen(TN) and total phosphorus(TP) from domestic, industrial and agricultural sources,
respectively.
(source: Cheng, et al., 2009)
An investigation was done based on 2007 general survey of pollution sources,
statistical yearbook and the data from some related departments. (Cheng, et al., 2009)
Figure 10 demonstrates the results, the pollution discharge amount of 15 rivers
flowing into Taihu Lake from Suzhou, Wuxi and Changzhou of Jiangsu Province.
Pollutant emission in the planning region is large. For the contribution to the emission
amount, domestic, industrial and agricultural pollutions take the first, second and third
place respectively.
Wuxi is a developed city in southern Jiangsu Province. The pollution sources can be
classified into point source and non-point source. They are mainly from urban sewage,
rural sewage, industries, agriculture, shipping traffic and tourism, etc.
 Domestic pollution
In recent years, with the rapid development of urbanization of Wuxi city, the
permanent resident population has been growing and their living standards keep
improving which lead to a great growth in sewage discharge and waste production. In
table 2, it can be clearly seen how much domestic pollution the residences produce in
2010.
Table 2: The amount of domestic pollution in 2010 (Wuxi gov, 2011)
Population
Region
COD
(thousand) (ton/year)
NH3-N
TN
TP
(ton/year)
(ton/year)
(ton/year)
Urban
area 3542.3
16841.84
1419.03
3295.02
155.04
Yixin
1235.5
14665.58
1138.78
1799.3
154.95
Jiangyin
1594.8
15371.62
1165.35
1869.9
154.68
Total
6372.6
46879.03
3723.16
6964.22
464.67
 Industrial pollution
The industries in Wuxi city develop well and the scale of enterprises is expanding
year by year. Now, there are 7225 largest companies in the city. Though new
industries in biomedicine, new energy and new material are growing dramatically, the
high-pollution industries such as chemical, textile are still occupying a substantial part
in the entire industries.
Table 3: The amount of industrial pollution in 2010 (Wuxi gov, 2011)
Region
COD
NH3-N
TN
TP
(ton/year)
(ton/year)
(ton/year)
(ton/year)
Urban area
3926.2
360
901
21
Yixin
2526.9
175.5
329.2
10.9
Jiangyin
8524.4
274.9
844.6
40.3
Total
15977.4
810.4
2074.7
72.2
 Agricultural pollution
Agricultural pollution refers to the nutrients like nitrogen and phosphorus that
infiltrate into soil in the agricultural production activities. It includes farming,
aquaculture, and is one of the major factors resulted in water pollution.
Table 4: The amount of agricultural pollution in 2010 (Wuxi gov, 2011)
COD
Region
NH3-N
(ton/year) (ton/year)
TN
TP
(ton/year)
(ton/year)
Urban area
529.32
7.63
53.37
9.88
Yixin
1189.63
45.42
254.24
34.93
Jiangyin
359.09
2.54
31.03
6.15
Total
2078.04
55.59
338.64
50.96
4.2 Geographical and Climatic Impact
In the late spring or summer times, when the sunshine is abundant and temperatures
are appropriate, the algal bloom begins in the lake Taihu. Despite the pollutant sources
into the lake being controlled, the appearance of bloom is still happen. The
frequencies of showing may have small differences, but they are basically in an
increasing trend. Blue-green algal blooms usually last for several weeks, sometimes
months, depending mainly on the weather or flow conditions if no actions are taken.
Cooler, windy weather or increased flow may reduce the opportunities or prevent
blooms from happening.
Figure 11: Regional map of Lake Taihu in Wuxi
(source: Google map,edited by Qian)
Seen in figure 11, the orange arrows represent the wind direction in summer. It blows
southeast monsoon during the hot period. The Meiliang Bay and Gonghu Bay are like
two bowls that gather most of the algae growing in summer due to the wind direction.
So these two regions are the place where algal blooms show most frequently. Most of
all, as a result of the urban heat land effect around Meiliang Bay, the temperature is
usually higher than surrounding area that provides a more comfortable environment
for algae growing.
5. Policy Issues
There are a series of laws and policies aiming at water resources protection and algae
control. The policies may be put into action in regulations, economic measures,
information and education measures as well as assigning obligation to different
stakeholders.
In the year 1984, China’s National People’s Congress Standing Committee issued
Water Pollution Prevention Law of the People’s Republic of China. On the basis of
this law, provinces and municipalities should follow its principles to enact their own
regulations suitable for local situation. If local governments already have their
standards for water pollutant emissions, the local standards should be implemented.
(Durgin, 2010) If they don’t, then the central government has the right to enact
regulations that the local governments should obey.
Up to now, the Jiangsu Government, the Wuxi local government, those who should
take responsible for Taihu Lake basin and the Chinese central government have
already legislated on a series of laws protecting water resources in Taihu Lake,
especially laws regarding to pollutant emissions.
6. A Comparative Example: Dianchi Lake,
Yunnan, China
Dianchi is another important lake in China. It has been bothered with algal blooms for
years even earlier than Lake Taihu. People started to study algal blooms when it
happened in Dianchi Lake for the first time around 1970s. Now several decays have
passed, the condition in this lake is as worrying as before though efforts have been
taken to improve the water quality. One effective method dealing with algal bloom is
the application of a special species of water hyacinth.
6.1 Description of Dianchi
Dianchi lies in the downstream of a fast developing city of China, Kunming. Its water
surface is approximately 306 km2 and is the largest lake in Yunnan Province. It plays a
quite significant role in this province and has municipal functions of urban water
supply, industrial and agriculture water supply, flooding control, tourism, hydro power
generating and so forth. Dianchi Lake is one of the most eutrophication lakes in China.
The condition may be even worse than Lake Taihu.
Figure 12: the sceneries of Dianchi Lake
(source: Baidu pictures,2011)
6.2 Eutrophication History
As is mentioned before, the lake is in the downstream of a fast developing city. With
the development of the city in the early 1970s, pollutants were pouring into the lake
without hesitation. When people realized the poor water quality in the lake, it was too
late. P, N and other heavy metals had deposited on the bottom of the lake and were not
easy to remove. The lake has started to get eutrophic in the early 1970s and has been
under seriously terrible condition since then. Now, the water can only be marked as
case worse than Ⅴ which means it is not suitable to use as drinking water source.
6.3 Comparison with Lake Taihu
 Location and size
Dianchi located in the southwest in China, also southwest to Lake Taihu, it is the
largest freshwater lake in that region. It is 297 km2 in size and 1.57 billion m3 in
volume. Comparing with Lake Taihu, Dianchi is much smaller, only about one tenth
of Taihu. Since it can be regarded as one of the earliest freshwater lakes that were
polluted and became eutrophic, the local government of Yunnan province has been
studying in algal bloom control for quite a long time. Therefore, the lake is a
representative case in algal bloom control.
 Retention period
Table 5: Lake residence period of some Chinese lakes (Ye, 2011)
Lake
Taihu
Dongtihu
Retention
period
309days
20days
Boyanghu Hongzehu
57days
35days
Chaohu
Dianchi
168day
2.5years
One reason why the Dianchi is deeply eutrophic is that it has a really long retention
period, 2.5years. Table 5 shows the retention period for several important lakes in
China. Study this table we may find out that Lake Taihu and Dianchi have a relatively
long retention period than others. That may also explain why these two lakes are in a
highly eutrophication status. It is not only because of the heavy pollution but also the
long retention time which reflects a low ability of regeneration.
6.4 Treatment against Algal Blooms
The most successful solution applying in the algal blooms is the utilization of water
hyacinth with purple roots. The first picture is a comparison between traditional water
hyacinth and the species with purple root. The new species was cultivated by Yunnan
institute of ecological agriculture by GPIT (Gene Phenotype Induce Technique). The
differences are not only the well developed root system which is 20 times larger than
traditional one, but also growing with much smaller leaves just one tenth comparing
traditional ones above water
surface that can reduce evaporation. The well
developed root system can reach 70 centimeters long and keep growing for nine
months without rotting. The water hyacinths use their root system to transfer oxygen
to the water surface and absorb blue-green algae at the same time.
Figure 13: Comparison between traditional water hyacinth and the species with purple root
(source: http://ssthj.com)
Figure 14: A picture of purple-root water hyacinth
(source: http://jstianshi.cn)
6.5 Conclusion for Dianchi
After two decades’ efforts, many methods including physical, chemical and
mechanical ones have been tried to solve the blue-green algal blooms but the results
seemed disappointing. The application of purple-root water hyacinths is the most
efficient approach so far. It can reduce the concentration of TP and TN by 60%-75%
in about 6 days and 94% in 20 days. The water hyacinths are able to purify the water
in the lake from ‘green’ to ‘transparent’ and satisfy the standard of Case Ⅲ water in
one week time.
Purple-root water hyacinths is efficient in water quality improvement, however, there
are risks. For instance, a large-scale cultivation may lead to clogging and if their
growths are not well controlled, species invasion may take place and bring series of
problems that threaten other aquatic species.
7. Alternative Solutions
Years ago, algal blooms took place almost every other year in Lake Taihu. People
could find no way to stop it but just watch. When the bloom came, hundreds of
fishermen were hired to harvest blue-green algae with simple tools by hand. It had a
poor efficiency and 99% of what they harvested was water. They put the algae water
mixture in temporary sites like col or use them to water trees which might cause
secondary pollutions. So how to prevent algal bloom and harvest algae becomes really
significant. Now, the local government, some organizations and other municipalities
have come out some up-to-date and effective solutions to algal bloom. Some of the
alternative solutions are applied to prevent algal bloom, some of them are applied in
time of the bloom explosion and the rest are applied when bloom has already
occurred.
7.1 Water Transfer and Diversion
In the year 2000, the Wuxi government started a project called “water diversion from
Yangtze River to Taihu”. As the name implies, the project transfers water in the
Yangtze River to the Lake Taihu. The aim of the project is by means of water
diversion to enhance water carrying capacity.
This water diversion project takes the advantage of an existing project—Wangyuhe
Project that introduces Yangtze water in river network, and through other projects to
provide freshwater into Lake Taihu. (Zhou, et al., 2010)
During the water crisis happened in 2007, this project become a quite quick way to
dilute the polluted water. When the water crisis happened, a large amount of water
flowed into Lake Taihu that diluted the concentration of the pollutants as well as the
blue-green algae. The meanwhile, water quality in Gonghu water treatment plant
upgraded from case Ⅴ to case Ⅲ and that of Xiaowanli and Xidong water treatment
plants were also improved. After one-year water diversion from the second half year
in 2007 to the first half year in 2008, the concentrations of potassium permanganate
index, total-P and total-N have gone down from 7.04mg/L, 0.106mg/l and 4.10mg/l to
3.35mg/L, 0.087mg/L and 2.87mg/L respectively. (Zhou, et al., 2010) These indices
showed that the water quality had obviously improved.
Since the project started, the water level of Taihu Lake has a raising tendency. With
the drainage effect that Meiliang pump station adds, water in Gonghu and Meilianghu
flows faster. Due to this diversion project, the water volume of Taihu Lake in May to
August 2007 went up to 3.86 billion km3 which was 1.04 billion larger than the same
period in 2006.
The advantage of water diversion and transfer is that it can promote water mixing and
moving. When new water is introduced in the old system, it brings new life and
species make the water body ‘dynamic’. The high nutrients are diluted by this way.
7.2 Integrated Management by Catchments
In the history of Lake Taihu management, each department always does efforts
separately rather than cooperatively. So the idea of ‘manage by catchments’ is put
forward. Now, four catchments are delimited as Zhihugang (Z), Lihuxincheng (L),
West Wangyuhe (W), and West Yixin catchments (WY).
The Z catchment is an old region of Wuxi city. It is understood that this portion is
industrially developed and has a high load of pollution with a dense population. So
the water quality of this part remain poor in case Ⅴ or worse. The water quality
improvement task in this region seems the hardest. By means of industrial
restructuring and centralized sewage treatment, the Zhihugang catchment hopes to
gain a better water environment.
The L catchment is the region that develops very fast these years. This region is
regarded as an open, ecological modern new district in Wuxi. The region is
constructed to be a nice place for both entertainment and business. There are now lots
of small rivers in this area. The water system is flourishing but lack interaction. The
point of dealing water quality problem is to build new water system and bring in
water from outside to renew the old one so that the system can earn a better
self-purification.
The Wangyuhe River is the only passage linking the Yangtze River and Taihu. Every
year, water is transferred into Taihu from Yangtze River through Wangyuhe River. So
the water quality in this river is vital. But lots of factories are built in this region and
wastewater is discharged into the river. In this case, wastewater control is the key
factor in the management.
The last catchment, West Yixin, almost has the same problems as Wangyuhe does.
Yinxin is a subordinate town of Wuxi and also has lots of industries there.
Figure 15: The locations of four catchments
(source: Wuxi Government, 2011)
7.3 Pollution Source Control
 Industrial pollution source control
To reduce the industrial pollution, industries that produce higher pollutants should be
shut down or faced to build wastewater treatment plants for their effluents. In the
Lake Taihu basin, the most pollutional industries are textile, electroplating, printing
and chemistry industries which are called “high consumption, high polluting, high
risk; low production, low efficiency” industries. Given the economy development at
the same time, closure and reorganization of factories and companies selectively are
proper for pollution source control. For those projects that related to the high polluting
industries, the local government should create rules or regulations to ensure the
pollutants discharge are under control.
 Domestic pollution source control
Comparison among table 2, 3 and 4 illustrates that the domestic pollution dominates
in the pollution emission. Therefore, the domestic pollution control seems to be the
most crucial. In the urban area, the best way dealing with sewage water is to set up a
sophisticated centralized treatment system. In the next five years, the government is
planning to set up 14 new waste water treatment plants that can handle 4.155 million
tons more wastewater per day. By then, the entire city can handle 16.375 million tons
of wastewater every day. Having a strong ability in wastewater treatment, a high
coverage system with pipes should be built in the same time. The system should be
able to connect all the houses and apartments in the city, gather and transfer sewage
water to treatment plants. Another key point of domestic pollution source control is
how to deal with the sludge from treatment plants. An environmental friendly solution
is ought to be harmless and has no secondary pollution.
 Agricultural pollution source control
Agricultural pollution mostly comes from aquaculture and fertilizers. So to use
fertilizers properly and make aquaculture in an environmental friendly way is the best
solution to pollution control. Firstly, in the grain growing region, fertilizer must be
provided corresponding to the need and use organic fertilizer or green manure as
much as possible. Promote to use new fertilizer that can be easily absorb and
degraded by nature. Also, the N and P can be decreased by buffer strips and wetland
constructing around the area.
 Sewage discharge standard
In the Chinese standard GB18918-2002, there are 12 basic items which are BOD5,
CODCr, SS, plant animal oil, Petroleum, LAS, TN, NH3-N, TP, pH, chromaticity and
fecal coliform. The new built wastewater treatment plant should meet the standard of
standard A of first class which is defined in the discharge standard. The four indicators,
BOD5, TN, NH3-N and TP are the items that the treatment plant focusing on because
they are difficult to reduce. Table 6 lists the discharge standards for those four items.
Table 6: Chinese sewage discharge standard for municipal wastewater plants
(GB18918-2002, created by Qian)
Unit: mg/L
Indicator
Standard A of first class
BOD5
10
TN
15
NH3-N
5
TP
0.5
7.4 Restoration by Large Aquatic Vegetations
The overgrown blue-green algae can be controlled by aquatic macrophyte vegetation.
In a phytocoenosium, plants or bacteria can release chemicals to inhibit or excite other
cells’ growths. (Liang and Liang, 2011) This phenomenon is called ‘allelopathy’ and it
happens naturally in ecosystem. Aquatic plants have effects on the population of algae
by competition for nutrients, sludge settling and allelochemicals releasing. Aquatic
plants generally absorb nutrients more easily than algae, so they can inhibit the
growth of algae in this way. So far, there have been three leading methods in algae
control by ‘allelopathy’ of aquatic plants. First is grow aquatic plants in the untreated
water body, and then uses the allelochemicals the plants release to inhibit the growth
of algae. That kind of plants can not only absorb the nutrients in the water and provide
transportation for them but also take advantages of the allelochemicals to achieve
water restoration and purification. Secondly, introduce dead and dry plant materials
into the untreated water, and utilize the allelochemicals the materials release when
they decay to control the overgrowth of algae. The last method is to put
allelochemicals extracted from plants to inhibit algae growth directly.
Purple-root water hyacinths are now the regular vegetation used in blue-green algae
control in China. They are proved to be the optimal choice for algae control in the
Dianchi Lake case and now are widely used in other lakes troubling with the same
problem.
7.5 Biomanipulation
Another way of algal bloom control is using the principle of biomanipulation. Shapiro
and Wright (1984) defined the term ‘biomanipulation’ as “the deliberate exploitation
of the interactions between the components of the aquatic ecosystem in order to
reduce the algal biomass”. The idea is to introduce other species into the food chain in
the lake, for instance, some fish or shellfish. These fish and shellfish usually are feed
on algae directly or indirectly. By this way, the overgrowth of algae can be controlled.
It is widely applied at home and aboard that use filter feeding fish to control algal
bloom. And the results indicate efficiency and effectiveness. As a filter feeding
animal, shellfish have a strong ability in water treatment or filtration. It is able to take
in phytoplankton by filtration and create biological sediments that make particles
move down to the bottom so that improve the water quality. This process also has a
positive effect on the structure and function of the aquatic ecosystem. It is a win-win
method in one side the water quality can be improved, on the other side people can
feed fish or shellfish on algae.
7.6 Water Algae Separation
The principle of Water-algae Separation Method is based on flotation and
pressurefiltration. There are basically two parts in the whole Water-algae Separation
process.
First, the blue-green algae are harvested by machines. But what the machines
harvested is a combination of water and algae that contains 99% of water. So they
are gathered to be dewatered. If the water after dewatering can reach the quality
Case Ⅲ standard, it will be discharge into Lake Taihu directly. If not, it would be
transferred to the treatment plants to have further treatment. The sludge after
dewatering can be used for marsh gas power generation or producing organic
fertilizers.
The water-algae separate station called JinYuan was built in 2008. And by the year
2012, 8 stations have been built including JinYuan Station. They can treat 12000
tons of water-algae mixture per day. (people.com, 2012) And the constructions of 3
other stations are in process. From 2007 to 2012, 205.5 tons of P and 822.5 tons of
N have been removed from Lake Taihu by harvesting algae.
7.7 Other Methods
Other approaches dealing with blue-green algae are applied like using bioreactor and
take the advantages of the biofilm adhering on the carrier to absorb and decompose
algae. In some cases, algae will be swallowed by the protozoa growing on the biofilm.
This biofilm method can also get rid of the toxins algae release. This kind of biofilm
technology was first invented in the early 1970s in Japan.
Another way of dealing algal bloom is desilting and reducing sediments. Since the
sediments containing a large amount of phosphorus and nitrogen, this solution can
certainly lower the eutrophication level of the water body and reduce the possibility of
the occurrence of algal bloom.
Water ecological restoration is considered as an imperative project that plays an
important role in algal bloom control. Once the water environment in Lake Taihu is
enhanced, of course the appearance of algal bloom will become less and less. As a
matter of fact, the restoration project is indeed complicated which needs a long time
and deep study.
8. Analysis & Suggestions
Since the Wangyuhe River is the only passage connecting Lake Taihu and the
Yangtze River and water can only flow in one direction, therefore, it is impossible to
diverse cleaner water from Yangtze River and discharges polluted water to the
Yangtze at the same time. So when water is transferred in to the lake, the polluted
water in the lake would flow to the Gonghu bay that intensifies the eutrophication
level in the bay. And during the no water transfer period, polluted water is discharged
into Yangtze River through Wangyuhe River. In this process, a large amount of N and
P may settle in the bottom of Wangyuhe River and may be flushed back to Gonghu
Bay during water transfer period. The fact that the Gonghu Bay has been the region
where algal bloom shows most frequently, no one wants to see it further polluted.
According to a report (Gao et al. 2006), the concentration of TP in Yangtze River has
already reached 0.094 mg/L which is higher than that in Lake Taihu, 0.08mg/L. It
means the solution ‘water transfer and diversion’ may not decrease the concentration
but increase it on the contrary if the water discharged into Yangtze River has a mean
concentration of 0.08mg/L. To make the solution water transfer and diversion more
satisfactory, first, more water way must be created linking the Yangtze River and the
lake. The existing Wangyuhe River should be broadened. By these methods, the
tempo of water transfer could be faster and the ability of water self-purification can be
strengthened. On the other hand, there may have flood in a certain period, so how to
balance in the water transfer and flooding control need further consideration.
Pollution source control is the only solution that gets the root of the problem. At
present, the dominate pollution source is domestic ones. But as far as I concerned, the
government still focus on industrial pollution control. Industrial pollution must be
paid great attention due to their harmfulness while the government should not neglect
domestic pollution. Domestic pollution is related to every average person therefore
the public awareness become the strategic point. Under the supervision of some
departments, every citizen would aware of the importance of water resources and
environmental protection. Up to now, the Jiangsu and central government has
published a series of laws protection water resources in Lake Taihu. There are also
laws about water pollution emission. And why is the water quality still in a poor
condition in the lake? Of course, it may have loopholes in these laws, whereas, the
existing laws are not well obeyed is the primary cause. Laws and regulations are
published to obey but not to break. Companies and enterprises always put their benefit
beyond obligation. The government must gain more efforts to punish those who
contaminate the environment. We now should get rid of the ‘treatment after pollution’
pattern and take everything would do harm to the environment into consideration in
advance.
Along with the intensification of eutrophication, the need of algal bloom control will
become more and more urgent. The physical treatment such as water algae separation
may be the most effective when a bloom happens, but it is a huge task to remove the
algae in such a big lake like Taihu. And it also takes too much time for an operation
period. What’s more, to get rid of blooms as soon as possible, a large sum of money
should be invested to invent advanced machinery. The chemical solutions have the
advantages of fast responding and obvious effect but may lead to secondary pollution
which we do not expect at all. The biological approaches seem to be the best: apparent
effect, no secondary pollution, broad prospects and profound academic significance.
But they are not quite well developed and people still need time to study.
Before the extensive and long lasting algal bloom comes, several measures could be
taken action to narrow down the area of bloom or cut the appearance time. First is to
continue water transfer and diversion that keep the nutrient concentrations in a lower
level. Second is monitoring the growth of algae and the region they grow. Then focus
on how they move and where could have algal aggregation. Algal aggregation often
happens in the southern part of the lake, measurements should be taken in case of
spreading to the other parts.
Years ago, there was no such heavy pollution into the lake so that the lake was able to
degrade the pollutants by self-purification. But now, with the big bang of population,
the city has more functions than before and produces much more pollutants than ever.
Lots of the pollutants are discharged into the lake that far beyond lake’s
self-purification ability. Before we discharge the waste into the lake, we certainly
should keep it in mind that we are living in this environment. If we give the nature
waste, they will pay back. Be nice to the nature, be nice to ourselves.
Other high-efficiency methods do well in the lab. But when it applies on a huge water
body like Lake Taihu, the results seems unsatisfactory. Because the quantity of
hormone plantings release is quite small, it will disperse in a large water body and
reach a tiny concentration that cannot work. This method also needs an appropriate
environment for the plantings releasing hormone while in the Lake Taihu, the
temperature, pH or other conditions are unpredictable, so it is not sure whether the
plantings can function well.
9. Conclusion
 Management of eutrophication is the priority in algal bloom control.
According to the situations described in former chapters and sections, it can be clearly
seen that the algal blooms happen in Lake Taihu need urgent attention and treatment.
Because the outbreak of algae is due to eutrophication basically, the management of
eutrophication should be considered as the first priority in the treatment. It is a
comprehensive and heavy task of time.
 Pollution source control is the fundamental solution.
The fundamental measure of algal bloom control is stopping all kinds of pollution
pouring into the Lake Taihu from the beginning. In the economically blooming time,
it is burdensome for the local government to remove all the pollutant-produce
industries around the lake. But it is feasible to have a series of regulations and laws to
restrict the behaviors of those companies and factories. Those types of regulations and
laws should strictly qualify the pollutants especially phosphorous and nitrogen those
may lead to eutrophication and the amounts they are allowed to produce.
 Water algae separation is the most sufficient method if algal blooms have already
taken place, a combination with well-supervised cultivation of purple-root water
hyacinths works better.
Now, the most efficient and economical method dealing with algal bloom is a
combination of several approaches. For a short term treatment, the algae water
separation technology is considered as the first choice. When coming to a long term
control, the pollution control is absolutely the fundamental and thorough solution.
Since it has been proved that the purple-root water hyacinths are valid for algal
control, they should be cultivated in the Lake Taihu in case of blooms. But one thing
to notice is, keep an eye on the growth of purple-root water hyacinths, they are new
species in the lake, and should not impede other species’ normal growth. When it
comes to a situation that the blue-green algal bloom has already taken place, the fast
and efficient solution is to push the blooms to some places where can easily operate
the algae harvesting ships as soon as possible, never let the situation get worse.
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