Shifting nutrient balance shapes plankton blooms
Pollution from Chinese factories is changing the nutrient balance in the ocean, say scientists who studied depositions of chemicals and plankton blooms in the East China Sea. These waters are increasingly threatened by harmful algal blooms that choke off vital fish populations, according to the new study, led by researchers at the University of California, Irvine.
“There has been massive growth in emissions from China’s factories and cars over the past few decades, and what comes out of the smokestacks and tailpipes tends to be richer in nitrogen than phosphorus,” said Katherine Mackey, assistant professor of Earth system science at UCI and lead author of the study, published recently in Frontiers in Marine Science.
Together with researchers from the Woods Hole Oceanographic Institution, and China’s Fudan and Nanjing universities, Mackey took a close look at the deposition of particles in the ocean downwind of China’s enormous industrial and population centers.
Wind-blown pollutants, along with rivers running into the sea, is changing the region’s ecology, they found. As the balance of nutrients change, certain aquatic plants and plankton thrive and crowd out others.
“When you start having changes in the food web, you can see differences in the fish catch,” Mackey said. “Harmful algal blooms and nuisance species that are cropping up can produce toxins or just aren’t the type of food fish prefer to eat, so people have been noticing changes in the ecosystem in recent years.”
According to the study, tiny metal particle pollution from industrial processes tend to dissolve more quickly than dust from such natural sources. These human-generated substances give certain species of phytoplankton a competitive edge over others, leading to increasingly frequent and more intense algal blooms.
The researchers reviewed satellite data and government records dating back decades and found a clear correlation between the expansion of the country’s industrial output and the growth of unwanted algae blooms.
In a makeshift lab on the Shengsi Islands off coastal Shanghai at the mouth of the Yangtze River, the team members collected samples and incubated them in the lab to determine how certain conditions could lead to a plankton imbalance.
The study concluded that adverse changes in the ocean ecosystem can be traced back to industry and agriculture and that the only way the process can be reversed is for humans to start addressing land-based pollution.
Mackey said climate change could play a growing role in the transformation of the East China Sea.
“As the climate warms, we might start seeing more of these nuisance blooms,” she said. “It’s like a double whammy. If you have higher temperatures favoring certain types of phytoplankton and you’re monkeying with their nutrient supply, there are going to be unintended consequences.”