Chaoxuan Guo, Guangwei Zhu, Hans W. Paerl, Mengyuan Zhu, Li Yu, Yibo Zhang, Mingliang Liu, Yunlin Zhang & Boqiang Qin
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Extreme weather event may induce
Microcystis blooms in the Qiantang River,
Southeast China
Chaoxuan Guo, Guangwei Zhu, Hans
W. Paerl, Mengyuan Zhu, Li Yu, Yibo
Zhang, Mingliang Liu, Yunlin Zhang &
Boqiang Qin
Environmental Science and Pollution
Research
ISSN 0944-1344
Volume 25
Number 22
Environ Sci Pollut Res (2018)
25:22273-22284
DOI 10.1007/s11356-018-2216-7
1 23
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Author's personal copy
Environmental Science and Pollution Research (2018) 25:22273–22284
https://doi.org/10.1007/s11356-018-2216-7
RESEARCH ARTICLE
Extreme weather event may induce Microcystis blooms in the Qiantang
River, Southeast China
Chaoxuan Guo 1,2 & Guangwei Zhu 1 & Hans W. Paerl 3,4 & Mengyuan Zhu 1 & Li Yu 1 & Yibo Zhang 1,2 & Mingliang Liu 5 &
Yunlin Zhang 1 & Boqiang Qin 1
Received: 22 July 2017 / Accepted: 2 May 2018 / Published online: 27 May 2018
# Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
A severe cyanobacterial bloom in the mainstem of a large Chinese river was first reported from China. The Qiantang River is the
longest river in the Zhejiang province, southeast China. It provides drinking water supply to ~ 16 million people, including
Hangzhou city. Fifteen sites along the Qiantang River (including upper, middle (Fuchunjiang Reservoir), and lower reaches and
tributaries) were sampled between August 13 and September 9, 2016 to conduct a preliminary examination of the outbreak of
Microcystis blooms. Laboratory investigation revealed that Microcystis spp. are dominant in the Fuchunjiang Reservoir (an
overflow reservoir on the mainstem of the Qiantang River) with an extremely high cell density of 2.3 × 108 cells/L, leading to
a severe bloom in the mainstem of the Qiantang River. Investigations of the meteorological, hydrological, and nutrient charac-
teristics associated with the bloom indicated that extremely dry (6.8 mm rainfall from August 13 to September 9, 2016) and hot
(32 consecutive days of temperatures > 30 °C from July 20 to August 31, 2016) weather might be the key factors triggering the
bloom. Additionally, the extremely low flow of the tributary, Lanjiang River (142 ± 56 m3/s from August 13 to September 9), and
its high nutrient background, favored the bloom. While nutrient reductions are important, the most immediate and effective
management approach might be to implement appropriate minimal flow conditions to mitigate the blooms.
Keywords Cyanobacterial . Blooms . Mainstem . Hydrology . Nutrients . Reservoir . Extreme weather
Introduction inputs favor proliferation of algal blooms in lakes, estuaries,
and rivers, leading to degradation of water quality and render-
Cultural eutrophication, a worldwide problem in inland wa- ing it unfit for drinking and impairing use in industrial, agri-
ters, is caused by phosphorus and nitrogen over-enrichment cultural, recreational, and other purposes (Likens et al. 1971;
(Carpenter et al. 1998; Dodds et al. 2009). Excessive nutrient Schindler and Lean 1974; Reynolds 1987; Smith et al. 2016;
Qin et al. 2013). Until now, no consensus has been reached
regarding the physicochemical thresholds for establishing an
Responsible editor: Vitor Manuel Oliveira Vasconcelos
algal bloom, which is usually indicated as a rapid increase in
* Guangwei Zhu
algal biomass, and recognized as a visual discoloration in the
gwzhu@niglas.ac.cn water by algal pigments (Reynolds et al. 1994; Johnk et al.
2008). Among the bloom-forming phytoplankton taxa, nu-
1 merous cyanobacterial genera produce toxic secondary me-
State Key Laboratory of Lake Science and Environment, Nanjing
Institute of Geography and Limnology, Chinese Academy of tabolites (cyanotoxins) which pose a potential threat to the
Sciences, Nanjing 210008, Jiangsu, China aquatic environment and risk to human health (Jurczak et al.
2
University of Chinese Academy of Sciences, Beijing 100049, China 2005; Graham et al. 2010). Harmful cyanobacterial blooms
3 (CyanoHABs) have mainly been reported in eutrophic lakes,
Institute of Marine Sciences, The University of North Carolina at
Chapel Hill, Morehead City, NC 28557, USA reservoirs, and estuaries, such as Lake Erie (Millie et al. 2009;
4 Michalak et al. 2013; Bertani et al. 2016) and Lake Taihu (Xu
College of Environment, Hohai University, Nanjing 210098, Jiangsu,
China et al. 2015; Zhu et al. 2014) in China and Lake Biwa (Maeda
5 et al. 1992) in Japan. Blooms are generally less common in
Institute of Environmental Protection Science of Hangzhou,
Zhejiang 310005, Hangzhou, China river systems because the hydrodynamics (constant verticalAuthor's personal copy
22274 Environ Sci Pollut Res (2018) 25:22273–22284
mixing; high flow and short residence time) usually deter the tributaries (Yang et al. 2012) or by the dinoflagellate
mass bloom development (Salmaso and Braioni 2008; Gymnodinium sp. in the estuaries (Tang et al. 2003); however,
Mitrovic et al. 2011). Nevertheless, in recent years, an increase the Xiaojiang, Pengxi, Xiangxi Rivers, which are all tribu-
in the frequency and diversity of blooms in rivers and river- taries of the Yangtze River, are now largely dominated by
reservoirs has been reported. Among them, diatom blooms, cyanobacteria (Hu et al. 2017; Xiao et al. 2016; Cui et al.
such as those observed in the Hanjiang River in China (Yang 2016; Zhou et al. 2017). As to the mainstem Yangtze River
et al. 2012), the James River in the USA (Filippino et al. and other Chinese Rivers (i.e., Hanjiang River), a few reports
2017), the Oder River in Poland (Sun et al. 2013), and the are mainly diatom-dominated blooms (Zeng et al. 2006; Yang
New Zealand Rivers (Bray et al. 2016), usually occur in et al. 2012), whereas cyanobacterial blooms are yet to be
spring. Blue-green algal blooms tend to dominate in summer found. Additionally, most of these reports corresponded to
or autumn and have been observed in the Xiangxi River, a relatively short durations and conducted in the backwaters of
tributary of the Three Gorges Reservoir (Cui et al. 2016) in tributary-river conjunctions.
China; in the Neuse River, North Carolina (Pinckney et al. The Qiantang River is the longest and the most important
1997) and Potomac River, Virginia, DC (Krogmann et al. river in Zhejiang province, one of the most populated and
1986) in the USA; the Nakdong River in South Korea (Ha developed regions in southeast China. It is the key source of
et al. 1999, 2002; Jeong et al. 2007; Tekile et al. 2015; Hong drinking water for more than 16 million people and provides a
et al. 2016); and the Darling–Barwon and Murray Rivers in fundamental regional connection from inland to the coastal
Australia (Bowling and Baker 1996; Donnelly et al. 1997; ecosystem. Previous studies on the Qiantang River have pri-
Bowling et al. 2016; Crawford et al. 2017). marily focused on pollution (Huang et al. 2010; Su et al.
A number of environmental factors, including nutrient 2011), nutrient history (Jia et al. 2017), and hydrological and
over-enrichment, higher water temperatures, and poor flush- meteorological trends (Xu et al. 2013; Xia et al. 2015), with
ing during droughts, have been identified as causes of these few reports on actual phytoplankton dynamics (Sheng et al.
river blooms (Smith 2003; Paerl et al. 2001; Kosten et al. 2010; Li et al. 2014). In this paper, we provide the first report
2015). Increase in human nutrient inputs is considered to be of a large-scale cyanobacterial bloom event in the mainstem of
the main driver of cyanobacterial blooms in inland waters, and a major river in China. The cyanobacterial bloom, which oc-
the relative importance of nitrogen vs. phosphorus (or both) curred in 2016 in the mainstem of the Qiantang River and its
inputs has been debated (Smith et al. 2016; Paerl et al. 2016a). tributaries, spanned ~ 100 km and lasted nearly a month. The
Despite measures taken to reduce cyanobacterial blooms, their bloom posed a significant risk to domestic water consumers
frequency and duration are increasing. This has been partly and prompted major concerns for management actions by
attributed to the impacts of global climate change on the dis- public authorities in Zhejiang province. In this study, we (i)
tribution and intensity of cyanobacterial blooms (Paerl and describe the Microcystis bloom process, including the occur-
Huisman 2009; Brookes and Carey 2011; Paerl and Paul rence, extent, and environmental conditions leading up to the
2012; Havens and Paerl 2015). Most studies on the impacts bloom in the Qiantang River, and (ii) analyze the relationship
of climate change on aquatic systems have focused on global between the meteorological and hydrological conditions that
warming, tropical cyclones, and heat waves, all of which favor may induce the Microcystis bloom process and consider pos-
CyanoHABs (Klausd et al. 2008; Johnk et al. 2008; Zhu et al. sible causal factors in a large river with high nutrients.
2014; Beaver et al. 2013; Havens et al. 2016). However, less Understanding how extreme events and climate variability
attention has been paid to climatic/hydrological extremes, affect CyanoHAB events in the Qiantang River will help pre-
such as variations in precipitation, drier droughts, and/or low- dict the impacts of high-frequency and high-magnitude
er inflows which are likely to promote CyanoHABs (O’Neil blooms on aquatic ecosystems, especially in light of highly
et al. 2012; Reichwaldt and Ghadouani 2012; Paerl and Paul variable and extreme future climate scenarios, and provide
2012; Paerl et al. 2016b). Because many rivers are partly reg- useful information on better management of river mainstems
ulated by low-stand dams in certain sections of their tributaries from an integrated catchment perspective.
and/or mainstems (Hong et al. 2016; Jeong et al. 2007), me-
teorologically extreme abnormities can directly alter the hy-
drological regime and consequently result in ecological and Material and methods
environmental disasters, especially under high nutrient load-
ing conditions. Description of the study site
Most of eutrophication and algal bloom studies in China
have focused on lakes and reservoirs, including well-known The Qiantang River is the largest (605 km) river in Zhejiang
large lakes such as Taihu, Chaohu, and Dianchi (Yang et al. province, southeast China, and has a catchment area of
2008; Zhang et al. 2016; Luo et al. 2017). Until now, blooms 55,560 km2. The river meanders from the hilly Xiuning coun-
in Chinese rivers have largely been dominated by diatoms in ty (1630 m a.s.l.) to Hangzhou Bay plain and then flows intoAuthor's personal copy
Environ Sci Pollut Res (2018) 25:22273–22284 22275
the East China Sea. Located in a typical subtropical East Asian Lake Eutrophication Survey of China^ methods (Jin and Tu
region, the catchment receives an annual precipitation of 1990). Biological parameters measured were chlorophyll-a
1200–2200 mm, 60% of which occurs in March–July. The (Chl-a), phytoplankton cell density, and species composition.
winter and spring seasons experience a Bprogrammed Water from the 15 sites was sampled daily from August 13 to
drought^ and receive about 20% of the annual rain (Xu et al. September 9, and every 3 days from September 10 to 19, 2016
2013; Xia et al. 2015). The Qiantang River consists of three for Chl-a measurement which comprised extraction with hot
sections, i.e., the upper Xinanjiang (XAJ) River, middle 90% ethanol as described by Jespersen and Christoffersen
Fuchunjiang (FCJ) River, and lower Qiantang River. XAJ (1987) followed by spectrophotometry at wavelengths of
Reservoir (Lake Qiandao) in the upper XAJ River and 665 and 750 nm. Phytoplankton were sampled and identified
Fuchunjiang Reservoir (a lowhead reservoir) in the middle once on August 22, 2016 across 11 sites (S1–S2, S5–S7, S9–
FCJ River regulate the upper and middle reaches, respectively, S11, and S13–S15). Phytoplankton samples were fixed in situ
of the Qiantang River (Fig. 1). The annual mean freshwater with Lugol’s iodine solution (1%, V/V) and deposited for 48 h
discharge of the Qiantang River is 38.7 × 108 m3 and the (APHA 1992). Cell density was counted directly in a 0.1-ml
freshwater discharge varied from 24.3 × 108 to 63.1 × 108 m3 counting chamber using an Olympus BX53 microscope at ×
from 2003 to 2016. The Qiantang River serves as a key source 400 magnification. The algal taxonomic identification was
of water for more than 16 million people. It supplies domestic conducted according to Hu and Wei (2007) and Hu (2011).
drinking water and is used for industrial, agricultural, and
recreational purposes. Meteorological and hydrological data
Field sampling and laboratory analysis Daily discharge and water-level data were obtained from three
hydrological stations, i.e., XAJ Dam, FCJ Dam, and Lanxi
A total of 15 sites along the Qiantang River (Fig. 1) were stations, for the years 2001–2016. Data on daily air tempera-
sampled between August 13 and September 19, 2016. Five tures, precipitation, and sunshine duration for the years 2001–
sites (stations S1–S5) at the Lanjiang River (the largest tribu- 2016 were available from Tonglu, Lanxi, and Jiande stations
tary of the Qiantang River), two sites (stations S6–S7) at the located in the Qiantang River catchment. The hydrological
upper XAJ River, five sites (stations S8–S12) at the FCJ and meteorological data before and during the bloom periods
Reservoir area, and three sites (stations S13–S15) at lower were specifically analyzed from late July to early September.
Qiantang River were selected (Fig. 1).
The total nitrogen (TN) and total phosphorus (TP) were Statistical analyses
measured daily for ten sites (S1–S5, S7, S9, S13, S14, S15)
from August 13 to September 19, 2016. TN and TP were Mean values and standard deviations were calculated using
determined in the laboratory according to the BStandard of Microsoft Excel 2013 program. The differences in discharge,
Fig. 1 Sketch of the Qiantang
River and the relevant sampling
sites (S1, Yanggang; S2,
Shencun; S3, Ditian; S4, Hongwu
Bridge; S5, Jiangjunyan; S6,
Mamu Bridge; S7, Meicheng
Wharf; S8, Sanjiangkou; S9,
Fuchunjiang (FCJ) Dam; S10,
Lengshui; S11, Zixu; S12,
Yanlingwu; S13, Tonglu Water
Plant; S14, Fuchunjiang Bridge;
S15, Jiuxi Water Plant)Author's personal copy
22276 Environ Sci Pollut Res (2018) 25:22273–22284
water level, and air temperature across different years during the upper, Chl-a concentrations at S7 were similar to those in
the bloom period (August 13–September 9) were analyzed by the FCJ Reservoir (44.05 ± 15.07 μg/L). Concentrations less
Wilcoxon signed-rank non-parametric test in R-studio than 10 μg/L were recorded in the Qujiang River (S1) (for the
0.97.551 (R i386 2.15.2) software. entire sampling period) and in the upper XAJ River (S6) be-
fore August 20 and after August 27. Temporal Chl-a concen-
trations fluctuated from August 13 to September 9, followed
Results by a decline from September 10 to 19, 2016. The bloom in the
FCJ Reservoir/River was most severe from August 13 to 20,
Summer 2016 Microcystis bloom in the Qiantang covering a distance of ~ 100 km in the mainstem and extend-
River ing from XAJ Dam to the lower Qiantang River. The bloom
scenarios at the mainstem stations S8–S12 (before FCJ Dam)
A severe large-scale cyanobacterial bloom occurred in the and stations S5 and S7 (upper) were relatively stable from
Qiantang River during the summer of 2016. The bloom de- August 21 to September 9. After September 10, the bloom
veloped on August 13 and declined from September 10 to 19 gradually dispersed, with Chl-a concentrations in all sections
(Fig. 2). This was estimated from the sampling conducted dropping to below 10 μg/L following heavy rainfall from
along the tributaries (Qujiang River, Lanjiang River, and September 10–19.
Jinhua River), and the mainstem (XAJ River, FCJ Reservoir, Laboratory investigations revealed that phytoplankton cell
FCJ River, and Qiantang River). During the cyanobacterial densities varied from 6.0 × 104–4.8 × 108 cells/L from the trib-
bloom period, Chl-a concentrations in different sections of utaries to the mainstem of the Qiantang River (Fig. 3, left). A
the river ranged from 0.1 to 171.00 μg/L (30.62 ± peak was found at FCJ Reservoir (S10), and the lowest con-
28.57 μg/L). The Chl-a concentrations showed a progressive centrations were observed at the Qujiang River (S1).
increase from the tributaries (34.55 ± 30.40 μg/L) to the Microcystis was completely dominant, with an extreme cell
mainstem FCJ Reservoir (55.60 ± 35.92 μg/L), followed by density of 2.3 × 108 cells/L (S10), resulting in severe blooms
a sharp decrease in the lower (12.04 ± 9.40 μg/L) (Fig. 2). In in the FCJ Reservoir. Blooms in different mainstem sites (S6,
Fig. 2 Chlorophyll-a variation from August 13 to September 19, 2016 in the tributaries and the different mainstem sections (upper, XAJ River;
Reservoir, FCJ Reservoir; lower, FCJ River and lower Qiantang River) of the Qiantang RiverAuthor's personal copy
Environ Sci Pollut Res (2018) 25:22273–22284 22277
Fig. 3 Cell densities of phytoplankton and Microcystis and algal compositions during blooms in the tributaries and the mainstem of the Qiantang River
on August 22, 2016
S7 in upper, S9–S11 in middle, and S13–S15 in lower) were the Qiantang River, the nutrient levels in the middle FCJ
also dominated by Microcystis spp., and the percentages of Reservoir remained high (S9) (TN, 2.87 mg/L; TP,
cyanobacteria in the phytoplankton community were 73.8– 0.125 mg/L), as compared to the values in the upper XAJ
97.9% in the upper XAJ River, 97.5–98.2% in the middle River (S7) (TN, 1.96 mg/L; TP, 0.101 mg/L) and the lower
(FCJ Reservoir), and 73.8–97.2% in the lower Qiantang FCJ River (S13, S14) (TN, 1.80 mg/L; TP, 0.066 mg/L) and
River (Fig. 3, right). In the middle FCJ Reservoir, the domi- the Qiantang River (S15) (TN, 1.66 mg/L; TP, 0.082 mg/L).
nant cyanobacteria were not Microcystis alone especially in When compared with TN and TP data for 2001–2015, the
S11. Laboratory investigations found that there existed three decreased nutrient levels in 2016 were sufficient to support
dominant species in S10, i.e., Microcystis spp., the algal blooms (Xu et al. 2015).
Pseudanabaena spp., and Dolichospermum spp., with
Microcystis cell density of 2.3 × 10 8 cells/L, whereas Hydrological regimes during summer 2016
Microcystis spp. and Pseudanabaena spp. were both dominat-
ed in S11 with Microcystis cell density of 4.77 × 107 cells/L Based on the multi-year mean discharge from the three sta-
(Fig. 3, left). In the upper S6, the algal cell density was much tions, the inflows of FCJ Reservoir were primarily contributed
lower, and no severe bloom occurred despite the predomi- by Lanjiang River (63%) and Xinanjiang River (34%). The
nance of Microcystis. Cyanobacteria were also found to be average daily discharges (2001–2016) in FCJ Dam, XAJ
dominant in the tributary Lanjiang (S5), where the bloom Dam, and Lanxi stations were 897 ± 964, 307 ± 279, and
was first noted before August 13, and Microcystis cell densi- 565 ± 764 m3/s, respectively. The general flow regime pat-
ties reached up to 3.72 × 107 cells/L. Green algae were dom- terns in FCJ River and Lanjiang River were similar, with the
inant (86.8%) in the Jinhua River (S2) blooms, whereas no exception of the upper Xinanjiang River runoff being
blooms were found in the Qujiang River, which was dominat- completely regulated by hydroelectric plant operations
ed by green algae and diatoms (Fig. 3, right). (Fig. 5). The runoff in the Qiantang River catchment was quite
The concentrations of TN and TP varied across different different in 2016 in comparison to runoff in 2001–2015
sites in the Qiantang River (Fig. 4). The results indicate that (p < 0.01, Table 1). Floods arrived earlier from April to July,
from August 13 to September 19, 2016, the mean TN and TP 2016 with a peak runoff of 8660 and 6540 m3/s in FCJ Dam
in the Qiantang River reached 2.52 and 0.121 mg/L, respec- and Lanxi station, respectively, and then dropped sharply to
tively. The eutrophication status was most severe in the tribu- extremely low water levels. Average daily discharges from
taries (TN, 3.02 mg/L; TP, 0.153 mg/L); the highest values FCJ Dam, Lanxi station, and XAJ Dam (River) were 670 ±
were noted in the Jinhua River (S2, S3, S4) (TN, 3.62 mg/L; 156, 142 ± 56, and 537 ± 79 m3/s, respectively, during the
TP, 0.194 mg/L) and the lowest values in the Qujiang River bloom period in 2016 (Fig. 5). Discharge of the main tributary
(S1) (TN, 2.12 mg/L; TP, 0.069 mg/L). As for the mainstem of of Lanjiang River (Lanxi station) in 2016 exhibited the lowestAuthor's personal copy 22278 Environ Sci Pollut Res (2018) 25:22273–22284 Fig. 4 TN and TP concentrations in different sections of the Qiantang River (a tributary; b upper; c middle/reservoir; d lower) from August 13 to September 10, 2016 and in 2001–2016 value on record since 2001 from August 13 to September 9, bloom period in 2016; this was significantly lower when com- whereas the runoff from the mainstem Qiantang River (FCJ pared to the same period in 2001–2015 (p < 0.01) (Table 1). Dam) in 2016 also decreased significantly as compared to the same period in 2001–2015 (p < 0.01) (Table 1). Additionally, Meteorological conditions in summer 2016 the average daily water levels (2001–2016) at FCJ Dam and Lanxi station were 23.43 ± 0.70 and 23.03 ± 0.28 m, respec- The precipitation from January to September 2016 was tively. The water level difference between FCJ Dam and 1588.1 mm higher than the 2001–2015 annual mean values Lanjiang River (Lanxi) was 0.285 m during 2001–2015, (1308.1 mm). April–June contributed 1015.03 mm, which whereas the difference reached 0.041 ± 0.03 m during the was ~ 63% higher than the corresponding values for 2001– Fig. 5 Discharge at FCJ Dam, XAJ Dam, and Lanxi station, 2016
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Environ Sci Pollut Res (2018) 25:22273–22284 22279
Table 1 Differences in discharges at FCJ Dam, XAJ Dam, Lanxi station, and water level gap between Lanxi station and FCJ Dam from August 13 to
September 9 of 2001–2015 (mean ± SD) and 2016
Year FCJ Dam (m3/s) XAJ Dam (m3/s) Lanxi station (m3/s) Water level gap(m)
2001–2015 755 ± 601 299 ± 172 454 ± 509 0.285 ± 0.43
2016 670 ± 156 537 ± 79 142 ± 56 0.041 ± 0.03
p < 0.01 < 0.01 < 0.01 < 0.01
2015. The meteorological drought from July 20 to September backgrounds from the tributaries supported the bloom out-
9, 2016 was the most intense since 2001, with only 65 mm of burst. In the Qiantang River catchment, heavy rainfall oc-
rainfall recorded. During the bloom proliferation period, no curred between April and June, 2016, which was 63% higher
rainfall occurred from August 13 to 20 and a mere 6.8 mm was when compared to rainfall in the years 2001–2015. The flood
observed from August 20 to September 9, 2016 (Fig. 6). season brings significant amounts of nutrients into the river,
Meanwhile, the sunshine intensity and duration were higher coinciding with elevated turbidity in the tributaries and the
(379.3 h) from July 20 to August 31, 2016, especially in mainstem. From July 20 to August 12, 2016, a mere
August (253 h). This was higher when compared to 2001– 58.2 mm rainfall was observed in the Qiantang River catch-
2015 annual mean values, possibly due to very little rainfall ment (Fig. 5), resulting in a sharp decrease of inflow from the
in August, 2016. Moreover, the summer in 2016 was the lon- Lanjiang River. Additionally, when the lower tributary inflow
gest since 2001. From July 20 to August 31, 2016, the mean joined the relatively constant inflow from the regulated up-
air temperature was 30.9 °C, with 32 continuous days exceed- stream (XAJ Reservoir), a persistent, low-moving stagnant
ing 30 °C, and higher than the yearly mean of 29.1 °C from region was formed at the junction of the Lanjiang River and
2001 to 2015 (Fig. 7). the mainstem. The algal bloom was first observed in S5, in
Lanjiang River before August 13. Because blooms would
thrive in warmer conditions (Paerl and Huisman 2008), higher
Discussion temperatures as well as longer sunshine durations could favor
algal proliferation in the tributaries and the mainstem in the
The extreme weather events (drought conditions, longer sun- ensuing days. During the bloom period, the inflows from the
shine, persistently higher temperatures, and reduced inflow) Lanjiang River were less than 200 m3/s and very low com-
were probably the key factors triggering the bloom in the pared to 2001–2015. The water level difference between FCJ
Qiantang River. In addition, persistently high nutrient Dam and the Lanjiang River (Lanxi) was 0.041 ± 0.03 m,
Fig. 6 Comparison of precipitation in 2001–2015 (mean ± SD) and 2016 across different periods, April 1–June 30, July 20–August 12, August 13–20,
August 21– September 9, and September 10–19Author's personal copy 22280 Environ Sci Pollut Res (2018) 25:22273–22284 Fig. 7 Temperature and sunshine duration from July 20 to August 31, 2001–2016 which was nearly insignificant. Moreover, the accumulated background nutrient concentrations (Fig. 4), because temperatures exceeding 30 °C for 32 consecutive days and higher flows favor fast-growing diatoms and/or green al- persistent drought before and during the blooming are likely gae, while lower regions experience replacement by to favor phytoplankton community dominated by cyanobacteria (Sherman et al. 1998). The rest of the cyanobacteria (Havens and Paerl 2015; Srifa et al. 2016). Lanjiang River and the mainstem FCJ Reservoir are no Heavy rainfall (131.7 mm) from September 10 to 19 in 2016 exceptions under stagnant regimes, with Microcystis in the catchment spared the Qiantang River from the bloom. bloom spreading over to the middle reaches of the The 2016 bloom event in the Qiantang River was the Qiantang River under conditions of continuously high first reported cyanobacterial bloom in the mainstem of a temperatures, while cyanobacteria that form blooms accu- large Chinese river. In China, reports of blue-green algae mulated at the surface due to their high buoyancy river blooms have been restricted to the backwaters of (Mitrovic et al. 2011; Carey et al. 2012). A temporary tributaries and river-reservoirs (Hu et al. 2017; Xiao bloom was also found in the upper Qiantang River (S6) et al. 2016; Cui et al. 2016). As to the mainstem from August 20 to 27, 2016 (Fig. 2) although cell densi- Chinese rivers, bloom reported are limited to diatom ties of phytoplankton and Microcystis were much lower blooms such as in Hanjiang River and Three Gorges on August 22, 2016 (Fig. 3, left), probably due to the Reservoir (mainstem Yangtze River) (Yang et al. bloom spreading upstream from the FCJ Reservoir. In 2012;Zeng et al. 2006). Nonetheless, no cyanobacterial the lower Qiantang River, two water plants were inevita- bloom was reported in any mainstem Chinese rivers be- bly threatened by potential CyanoHABs as Microcystis, fore 2016. The dominant Microcystis spp. in the Qiantang through exhibiting relative lower cell densities, dominated River reached an extreme cell density of 2.3 × 108 cells/L instead of diatoms (Fig. 3). and the Chl-a concentrations exceeded 170 μg/L from Hydrodynamics play a key role in bloom outbreaks, August 13 to September 9, 2016. During the occurrence declines, and ultimately, their mitigation. Rivers are gen- of a bloom, the differences in the phytoplankton commu- erally considered as unlikely habitats for cyanobacteria, nities of upstream and downstream rivers are likely to be because high flow, short residence times, and persistent maximal during low-flow periods (Tornes et al. 2014). In vertical mixing discourage cyanobacterial dominance the middle of the Qiantang River, investigations during (Steinberg and Hartmann 1988). Reports of severe 2006–2007 indicated that cyanobacteria and diatoms Microcystis blooms in rivers have been primarily ob- dominated in summer with densities ranging from served in stagnant reservoirs such as in the regulated 0.21 × 105 to 3.01 × 107 cells/L (Sheng et al. 2010), and Nakdong River (Ha et al. 1999; Jeong et al. 2007; Hong diatoms dominated in the lower Qiantang River during et al. 2016), where blooms frequently proliferate under 2004–2010 (Zhang et al. 2015). The in situ investigations drought and hot weather conditions during summers. of samples collected on August 22, 2016 revealed that the Such blooms are commonly found in reservoirs and in Qujiang River (S1) contained the lowest TP in the entire fully regulated rivers. The hydrological processes of FCJ catchment, resulting in little to no bloom impacts (Fig. 3). Reservoir/River are more like a river than a reservoir. The At the Jinhua River tributary, the river flow was slightly hydrological regime of the mainstem Qiantang River was faster than downstream Lanjiang River. Consequently, a synchronous with inflows from the Lanjiang River (Fig. relatively fast-growing green algae (Scenedesmus spp.) 5), which provided 63% inflow to the mainstem. instead of the slow-growing cyanobacteria (Microcystis However, the outflows from XAJ Dam, as well as the spp.) was proliferous in the Jinhua River at higher inflows from the upper reaches of the Qiantang River
Author's personal copy
Environ Sci Pollut Res (2018) 25:22273–22284 22281
(XAJ River), are fully regulated, with fluctuations in order Wuxi city in 2007 was an example of such event (Yang
to satisfy hydropower plant operations in XAJ Dam. The et al. 2008). When the blooms occurred in the mainstem of
lowhead FCJ Dam partially lets the mainstem river flow Qiantang River, extensive measures were taken to mitigate
as freely as the Lanjiang River. The monsoon in southeast blooms in the entire catchment, through measures such as
Asia strongly influences hydrological processes in rivers, algal bloom harvesting, hydrological regulation, pollution
and the regulation of reservoir outflows according to rain- control, emergency monitoring, and advanced treatment pro-
fall patterns are likely to influence the control of phyto- cessing in the water plants (Chen et al. 2016; Upadhyay et al.
plankton in the mainstem of rivers at any given time 2013; Ji et al. 2017). An emergency monitoring system for the
(Jeong et al. 2007; Hong et al. 2016). The flow pulses entire catchment was set up soon after August 13, 2016.
(flushing) in the summer mainstem of rivers and reser- Additionally, immediate measures were initiated in the catch-
voirs can help suppress phytoplankton blooms ment to reduce nutrient inputs to the river. More than 4000 m3
(Grabowska and Hanna 2016; Domingues et al. 2014). of fresh cyanobacterial blooms were harvested from FCJ
Flushing of the FCJ Reservoir has been conducted by Reservoir from August 13 to 20, 2016. Moreover, the associ-
regulating outflows from FCJ Dam that are greater than ated treatment techniques such as active carbon adsorption,
inflows from the XAJ River and the Lanjiang River ultrafiltration, and CyanoHABs detection facilities have been
(August 14–16, 2016, Fig. 5) in order to keep a minimum implemented for water plants. Emergency practices and expe-
velocity of ~ 0.1 m/s in the FCJ Reservoir. An optimal riences for the mitigation of blooms in the Qiantang River
flushing strategy of FCJ Reservoir remains to be quanti- catchment could use the Korean approach for dealing with
fied and awaits future modeling, simulation, and practice toxic cyanobacterial blooms (Hong et al. 2016), as well as
efforts. Still, the practice of hydrological regulation in the what has been proposed for the Three Gorges Reservoir in
Qiantang River could be helpful for judicious manage- the Yangtze River (Ji et al. 2017).
ment in regulated rivers with one or multiple dams facing
the threat of possible bloom outbreaks.
Extreme weather could possibly affect our ability to control Conclusions
blooms. The nutrient concentrations, water temperature, hy-
drological regime, and stratification in inland eutrophic waters A severe bloom occurred in the mainstem and the tributaries of
could all be disturbed by extreme weathers (Wood et al. 2017; Qiantang River between early August and mid-September
Yang et al. 2017). Achieving a desired low level of algal 2016. Investigations revealed that Microcystis were highly
biomass and fewer occurrences of blooms in the future would dominant in Fuchunjiang Reservoir/River, and the middle
probably require greater cutoffs of nutrient inputs from the reaches of Qiantang River, with a maximum cell density of
catchment than are needed under frequent extreme weather 2.3 × 108 cells/L. The extreme combinations of reduced precip-
events (Hong et al. 2016; Yang et al. 2017). In Lake Taihu, itation, lower inflow, persistent high temperatures, and longer
nutrient reduction magnified the impact of extreme weather on sunshine may induce the bloom, turning the entire area of the
cyanobacterial bloom formation (Yang et al. 2016). During the middle mainstem Qiantang River as well as its tributaries into a
past 3 years (2013–2015), with the rapid economic develop- stagnant reservoir with Microcystis blooms. Additionally, the
ment in the Qiantang River catchment, some measures were persistently sufficient nutrient levels in the tributaries supported
taken for water pollution control and environmental protection bloom proliferation. To control algal bloom outbreaks in rivers,
in relevant regions within the catchment, and nutrient loads hydrological regulation might be effective; however, critical
were gradually reduced (Fig. 4), especially for phosphorus. informational gaps of relevant scientific research and practice
Even then, the nutrient levels in Qiantang River remained high need to be filled. In the long run, substantial catchment nutrient
and suitable for algae blooms (Xu et al. 2015). In the future, reductions will be needed in order to develop an effective and
intensified water treatment for sewage effluents would be permanent bloom reduction strategy.
needed to reduce nutrient inflow from the catchment to the
river (Hong et al. 2016). A framework of thresholds and Acknowledgements We would also like to thank the Environmental
guidelines aimed at mitigating or preventing blooms could Monitoring Center of Zhejiang province, the Hydrological Bureau of
Zhejiang province, and the Meteorological Bureau of Zhejiang province
provide criteria to environmental monitoring, drinking water
for their data support.
supply works, and public communication systems for the en-
tire catchment (Funari et al. 2017; Qin et al. 2010). Funding information This work was jointly supported by the
As the only drinking water source for more than 16 million International Science and Technology Cooperation Program of China
people and one of the most developed regions of China, the (2015DFG91980), the National Key Research and Development
Program of China (2017YFC0405201), the Key Research Program of
normal tap water supply in the Qiantang River catchment is
Frontier Sciences, CAS (QYZDJ-SSW-DQC008), and the National
important, yet can be seriously impacted by toxic Natural Science Foundation of China (grants 41671494, 41230744, and
cyanobacterial blooms. Lake Taihu drinking water crisis in 41501532).Author's personal copy
22282 Environ Sci Pollut Res (2018) 25:22273–22284
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