Haley Plaas hits the road before sunrise to get an early start on the drive from Morehead City to Edenton, North Carolina. After two hours of farmland views along country backroads, she finally arrives at her destination — a small residential neighborhood on the banks of the Chowan River. Balancing plastic tubs filled with research equipment, she hauls her gear through a backyard. At the edge of the grass, Plaas gets her first view of the water — streaked with the tell-tale bright green hue of a cyanobacterial bloom.
“Nice!” she exclaims. “I know it’s weird to say but this gets me so excited. This is perfect.”
Plaas, a PhD student at the University of North Carolina at Chapel Hill’s Institute for Marine Sciences (IMS), studies the potential respiratory threat caused by harmful algal blooms.
Commonly called blue-green algae — although formed by cyanobacteria rather than algae — these are freshwater blooms that emit toxins. While a green scum on the water’s surface is the most obvious indication, even seemingly clear water can be infected. Quite common in the South where temperatures are warm most of the year, they are found worldwide.
They are also becoming more frequent and severe due to humans. Nutrients like nitrogen and phosphorus from fertilizer, untreated sewage, stormwater runoff, and even air pollution can cause the blooms to grow out of control. In addition, they favor warm water temperatures caused by climate change, as well as increased rainfall bringing more runoff nutrients into waterways from sources like farms and lawns.
“People equals nutrients,” says Hans Paerl, a professor of marine and environmental sciences at IMS. “The more people you pack into a watershed, the more nutrients end up getting generated and discharged.”
Out-of-control growth can be detrimental to aquatic ecosystems in a number of ways. Because they form on the water’s surface, cyanobacteria outcompete desirable aquatic plants by shading them, thereby cutting off the plants’ ability to grow through photosynthesis. Another issue is bioaccumulation — when toxins are magnified in their intensity as they move up the food chain. Additionally, when the blooms die their decomposition can greatly reduce the concentration of dissolved oxygen in the water and kill fish, shellfish, and other aquatic life.
They also pose a danger to human and animal health by producing neurotoxins and liver toxins. Last year, multiple dogs died after swimming, and some evidence points to their deaths being caused by acute liver failure after exposure to a harmful bloom. Exposure over long periods of time can also promote tumor growth and cancer.
While many studies examine intoxication through ingestion or skin contact, Plaas’ work looks at a different angle: aerosol.
Wave action causes air bubbles to become trapped beneath the water’s surface. As these bubbles rise through the water column they collect all sorts of particles, including cyanobacterial cells. The bubbles then burst at the surface, creating a spray of microscopic aerosol that carry these cells into the air — sometimes up to two miles.
Since May, Plaas and a team of community scientists from the Chowan Edenton Environmental Group have collected aerosol and water samples every two weeks from various points along the Chowan River.
Back in the Paerl Lab, Plaas will quantify the amount of toxins emitted to help determine if they pose a public health risk. Currently, no guidelines for aerosolized bloom toxins exist from the United States Environmental Protection Agency, Centers for Disease Control and Prevention, or the World Health Organization.
Plaas is also analyzing how different amounts and ratios of nutrients and water salinity impact cyanobacterial growth.
“If we can figure out what types of nutrients are making these blooms thrive, then we can work backward from that and figure out how to prevent them from getting that concentration of nutrients,” she says.
While they are becoming more frequent, there are a multitude of preventative steps to mitigate these blooms — the most important being reducing nutrient inputs into waterways. The most effective strategy, Paerl says, is using less fertilizer and applying fertilizer in a timely fashion — such as avoiding fertilizing during storm-prone periods like hurricane season.
“You’ll always worry that you haven’t put enough on but, believe me, I’ve been doing this for a long time and you don’t need much,” he says.
Another solution is advanced wastewater treatment that removes phosphorus and nitrogen from discharge, something he says many North Carolina wastewater treatment plants are already doing. Creating artificial wetlands or riparian buffers — essentially, natural vegetation — around agricultural lands and urban areas can capture runoff and remove nutrients before entering waterways or groundwater. Some farmers also rotate crops and grow nitrogen-fixing plants like soybeans to add nitrogen back into the soil naturally instead of through fertilizers.
“We know a lot about how to start controlling blooms but the will has to come to deal with it,” Paerl says. “Given that we are running out of freshwater resources in many places, there’s certainly more pressure to do something about controlling them.”
Hans Paerl is a Kenan Distinguished Professor of marine and environmental sciences at the UNC Institute of Marine Sciences.
Haley Plaas is a PhD student of environmental science and engineering at the UNC Institute of Marine Sciences.