Battling the Bloom
Writing and photography by Jesse Weber
A Chinese folk song extols the beauty of Lake Taihu by describing white sails gliding across blue water, bountiful fish and shrimp, and scents of fruit and rice wafting in the breeze. Ancient Chinese poems romanticize Taihu as a place of breathtaking scenery and rich cultural heritage.
Today, the scene on China’s third-largest lake is much different. The white sails can still be found, but churning motors are now more common. Instead of a clear blue, the water is a murky concoction of greens. Once-verdant hills beneath cerulean skies on the horizon have now faded into a haze of gray.
This is the panorama that lies before Steven Wilhelm, professor of microbiology, and Jennifer DeBruyn, assistant professor of biosystems engineering and soil science. They have traveled halfway around the world in order to scoop from the teeming pea-green soup of algae that laps at the sides of their boat.
Lake Taihu is besieged by a type of cyanobacterium, commonly referred to as blue-green algae, that grows out of control every summer. Known as an algal bloom, this phenomenon has become progressively worse over the last fifty years and has spoiled the lake’s former reputation as a natural wonder.
Wilhelm and DeBruyn represent a team of UT researchers that have been traveling to Taihu since 2008 to investigate the causes of the algal blooms and determine potential strategies to control them. Funded by the National Science Foundation, the scientists are collaborating with several institutions in the US and China.
Although multiple types of cyanobacteria are present in Taihu’s vernal blooms, Microcystis spp. is among the most common and the most problematic. This single-celled alga is fed by sewage and agricultural runoff that introduce an over-abundance of phosphorus and nitrogen—nutrients essential for growth—into the lake. This chemical buffet feeds enough algae to make the water turbid green yearround, which blocks sunlight from entering the water and smothers beneficial aquatic plant life.
Disruption of the natural ecosystem has been detrimental to the once-bountiful fisheries of Taihu, but this is only part of the problem. “In terms of human impact, Microcystis produces a huge variety of toxins,” says graduate student Morgan Steffen.
The toxins, called microcystins, are a byproduct of the cyanobacterium’s metabolism. Some of these toxins are known to cause liver damage in humans, while others are thought to be carcinogenic. Since Taihu supplies municipal water to more than ten million people, along with drinking water for livestock, there is great potential for serious health concerns.
Microcystis thrives in the summer months when temperatures reach above 79 degrees Fahrenheit. This is not good news as average global temperatures are predicted to continue to rise for the foreseeable future.
“The Taihu region has had more marked, consistent warming than most places on earth in recent years,” Wilhelm explains. With an average depth of less than three meters, Taihu’s water is particularly susceptible to rapid and dramatic warming. In fact, water temperatures during the summer of 2013 reached 95 degrees Fahrenheit.
Warm, shallow water loaded with nutrients from human and animal waste makes Taihu a giant Petri dish not only for algae, but also for disease-causing bacteria like E. coli that enter along with runoff.
“With water temperature so close to that of the human body, the lake is perfect for pathogens that affect humans,” Wilhelm explains.
Wilhelm and the team from UT are primarily involved with ongoing monitoring and experimentation concerning nutrient concentrations and temperature in the lake. “But unlike past efforts,” Wilhelm says, “this team uses state-of-the-art techniques in molecular biology to determine how the entire microbial community, not just one cell type, is involved in driving bloom proliferation.”
By manipulating variables in isolated pods, the researchers can determine how the algal community will respond to various nutrient conditions and how changes like further warming will affect populations.
The outlook for Taihu is uncertain. A number of abatement techniques have been tried, including flushing more water through the lake by diverting the nearby Yangtzee River, absorbing algae into sediment by sinking clay in the lake, and engineering wetland buffers that consume nutrients to improve water quality. These attempts have produced localized reductions in Microcystis populations, but nothing has proved effective for treating the lake as a whole.
American and Chinese scientists studying Taihu agree that the only permanent solution would be a drastic reduction of pollution from emissions and runoff. Considering an ever-rising population of more than forty million people in the Taihu basin that lives in the midst of an industry-heavy economy, this challenge seems insurmountable.
In the meantime, algae population monitoring and mitigation experiments continue with the hope of one day restoring the lake. Scientists are optimistic that techniques developed at Taihu can be replicated around the world. “Taihu is a looking glass into the future,” Wilhelm says. “We can expect to see these blooms happening elsewhere as populations, pollution, and temperatures increase around lakes worldwide. This is an opportunity to work with the Chinese in their efforts to deal with this problem and plan for how we ourselves should react down the road.”
Unfortunately the situation in Taihu is far from unique. Algal blooms occur in freshwater bodies worldwide, and are fueled largely by the same factors that influence Taihu. Notable examples in North America are Lake Erie, Lake Winnipeg, the San Francisco Bay estuary, and Grand Lake St Marys in Ohio.
The critical lessons being learned in China are paramount to preventing the green growth and its dangerously toxic water. Perhaps Taihu’s future reputation will include both natural beauty and scientific significance. Millions of plant, animal, and human lives around the world are depending on it.