Last month, the section of Pearl River running through the city of Guangzhou in China was rapidly invaded by an explosion of water hyacinths. After two days of intense skimming (455 tons of water hyacinths removed on the 17th and 495 tons on the 18th), the river was still not fully cleared. Last month’s rainfall washed the plants downriver causing them to accumulate in the slow-flowing estuary, a common occurrence in flood season. From April to June of this year, water hyacinths accounted for 80 percent of the 15,000 tons of floating rubbish collected by Guangzhou city.
Introduced to China in the 1960s, the water hyacinth is now widely distributed in nineteen provinces across the country. Warming temperatures due to climate change have created favorable growing conditions for water hyacinths across most of China – plant mass can double in two weeks in water temperatures between 27 and 35 degrees Celsius. Floods of water hyacinths occur regularly in many important bodies of water, including Dianchi Lake and Yangtze River.
As an invasive species that multiplies rapidly, heavy infestations of water hyacinths have to be quickly removed from impacted water systems to prevent economic and environmental damage. While water hyacinths do remove nutrient pollutants (N, P, K, Mg, Cu, Zn, and Mn) from waters, outbreaks cover water surfaces and consume most of the dissolved oxygen leaving little for fish and other aquatic species, which die off as a result. Unless removed, water hyacinths release nutrient pollutants back into the water when they die. Massive outbreaks cause further economic harm by blocking water transportation.
Despite these serious drawbacks, water hyacinth invasions can be harnessed for environmental benefit and renewable energy production. Water hyacinths have high cellulose content, making them a potential renewable energy source. Currently however, technical and cost barriers have forestalled widespread development of this energy option.