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On the morning of May 29, 2007, after enduring a hot and sticky night, residents in the four-million strong city of Wuxi, Jiangsu Province, on the shore of China's Lake Tai, awoke to find their water taps emitting an intolerably foul smell.
The culprit turned out to be a massive bloom of the toxin producing cyanobacteria Microcystis spp. which was polluting China’s third largest freshwater lake - the city's sole water supply. Some two million residents, well used to their city water supplies smelling of chlorine, earth and must, found the odour so objectionable they turned to bottled water for at least a week. At their peak, concentrations of CODMn, TN and TP were 13.1 mg L-1, 10.6 mg L-1 and 0.54 mg L-1 respectively, between three and five times the average concentrations for that time of the year in Tai. The bloom didn't entirely vanish until September.
Causal factors for the early arrival of the cyanobacterial bloom included an excess of nutrient enrichment, an unusually warm spring, and prevailing winds which washed the bloom onto the shoreline near the intake of the water plant, researchers Boqiang Qin et al eventually found. Warming possibly related to climate change and poor water management also bear some blame.
Worse, efforts to flush the lake by diverting water from the nearby Yangtze River had ultimately proved misguided, instead creating a current which transported the bloom into the intake, exacerbating the drinking water contamination problem.
Their report urged both the human and climatic factors influencing the blooms and their impacts on water supply in this and other large lakes threatened by accelerating eutrophication become the focus of long-term management.
"The Chinese face some real water quality challenges in the Lake Tai basin," says eWater CRC Application Leader, Catchments and Climate, and Senior Hydrologist, Department of Environment and Resource Management (QLD) Dave Waters. "The rapidly expanding urban population combined with the pressures from agriculture are impacting on water quality in the lake, including elevated nutrient levels leading to algal blooms just as we experience in Australia.
“I am also very impressed at the numerous field trials that were being undertaken to look at innovative techniques for the removal and or reuse of nutrients at a whole of farm scale.”
Environmental factors to blame
Lake Tai spans 2,250 km², has an average depth of just 2 metres, and is a key drinking water source for up to 10 million people. There are about 90 islands scattered across its surface, ranging in size from a few square kilometres to several square kilometres. Linked to China's massive Grand Canal, the lake is the source of a number of rivers, including Suzhou Creek. Rapid economic growth - especially in tourism, fisheries and shipping - in recent years has exacerbated its pollution woes.
At the same time waste from urban centres and nearby agricultural and industrial segments of the rapidly growing local economy has led to dramatic increases in nutrient loading, accelerating eutrophication. Cyanobacterial blooms can be a sign of advanced eutrophication of freshwater lakes and reservoirs used for drinking water supplies, fishing and recreational purposes.
The source of the tainted drinking water in Lake Tai, it eventuated, was the Gonghu Water Works, Gonghu Bay, which treats one million cubic meters of water per day. Boqiang Qin et al’s investigations uncovered a decomposed cyanobacterial scum comprising foam-covered black agglomerates flowing slowly towards the intake of the water works. These agglomerates had a strong offensive odour and were composed of cyanotoxin producing, bloom-forming cyanobacterial genus Microcystis.
"A combination of environmental factors, including human activities and extreme climatic conditions, caused a massive, toxin producing cyanobacterial bloom dominated by Microcystis spp., which produced microcystins that led to a major drinking water crisis at Tai," Boqiang Qin et al concluded. "At least two decades of excessive nutrient loading have created the potential for these cyanobacteria blooms. Because nutrient loading currently exceeds cyanobacterial growth requirements, the magnitude, spatial extent and duration of these blooms is mainly controlled by physical factors, including temperature, wind intensity and direction and irradiance. As observed worldwide, a general warming trend reflecting climate change (Bates and others 2008) favors regional cyanobacterial bloom expansion, and longer periods of bloom persistence (Jőhnk and others 2008; Paerl and Huisman 2008). Conditions at Tai appear to reflect this trend.
"Because toxin producing strains of Microcystis are now present almost year-round in Tai, and animals and humans in the Tai basin drink untreated lake water, the risk from MCs may be high for these groups. Concentrations of microcystins, exceeding the WHO acceptable level of 1 lg L-1, have been measured in association with previous blooms (Song and others 2007), and it is possible that these elevated levels occurred during the 2007 bloom."
The government reacted by treating the algae outbreak as a priority concern, establishing a National Restoration Action Plan, led by the National Development and Reform Commission (NDRC), to achieve remediation of Lake Tai.
Enter the Australian China Environmental Development Partnership (ACEDP), a five-year, $25m Australian Government, AusAID initiative aiming to support and enhance policy development in China in environmental protection and natural resources management. Due to continue until 2012, the partnership is working towards supporting China environmental work in areas of mutual interest to China and Australia, and designed to respond to shifting policy priorities and emerging issues.
Another focus is the building of enduring partnerships between Australian and Chinese agencies, institutions and individuals engaged in environmental policy development and implementation. Activities under the partnership include pilot studies and projects, study tours, training courses, conferences, work attachments, exchange programs and scientific cooperation and policy dialogue mechanisms.
Under the Lake Tai Water Pollution Treatment Project, the ACEDP intervention supports the National Restoration Action Plan and aims to:
The project is being led by China's NDRC and lead Australian contractor is Australian Urban System (AUS) Cluster led by Earth Systems Consulting Pty Ltd.
eWater CRC was invited by Earth Systems to attend an ACEDP workshop held in China in November 2010 to promote the suite of software tools eWater are developing and demonstrate how they are being applied across Australia to assist in managing water quality issues similar to those face in Lake Tai.
The Chinese delegation was keenly interested in the eWater CRC modelling suite and as a result, eWater has been invited to undertake a pilot project in the region over the next 12 months to be led by Dave Waters.
The project will look to train a number of the Chinese delegates in the use of Source Catchments and build capacity locally. The aim is then to demonstrate how the model can be applied to assess a range of alternative management strategies and the associated water quality impacts.
In support of this project, the ACEDP has established an on-line forum for concerned scientists and water managers involved in algal bloom management to share information and latest research, the ‘Eutrophication Portal’. The portal is accessible on the ACEDP website www.acedp-partnership.org/en/default.aspx to registered users. At present it comprises specialists from Australia, China, Hongkong and the USA. Interested individuals who want to join the portal should contact the ACEDP program manager at firstname.lastname@example.org.
Qin B, Zhu G, Gao G, Zhang Y, Li W, Paerl H, Carmichael W (2009) A Drinking Water Crisis in Lake Tai, China: Linkage to Climatic Variability and Lake Management
Hu Y, Wang S, Wang W and Jiang H (2010) Characterization of Phosphorus Removal in the Rivers Inputting into Lake Tai
Gaoa, Y, Zhua G, Bo-Qiang Q, Pang Y, Gonga Z, Zhanga Y. (2007) Effect of ecological engineering on the nutrient content of surface sediments in Lake Taihu, China.