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Can non-woven fabrics help prevent harmful algal blooms?

With 365 miles of shoreline, High Rock Lake is North Carolina’s second largest lake. It was constructed in the late 1920s to harness the Yadkin River with a hydroelectric dam to power nearby aluminum mines. Nearly 100 years later, High Rock Dam still provides power, and the lake serves not only as a reservoir, but as host to a variety of recreational activities, including bass fishing, bird watching, and boating.

However, waters at High Rock Lake are often less than idyllic.

“High Rock Lake has been declared an impaired lake by the Environmental Protection Agency for more than 20 years,” says Jaime Cardenas, a Mountains to Sea Fellow with North Carolina Sea Grant and the NC Water Resources Research Institute. Specifically, he adds, High Rock Lake has a problem with “cyanobacteria,” or blue-green algae.

When nutrients — namely nitrogen and phosphorus — accumulate in large amounts in freshwater, cyanobacteria can grow and spread uncontrollably, causing harmful cyanobacterial algae blooms (“cyanoHABs”). Like many types of algal blooms, cyanoHABs can deplete the oxygen supply in water, choking out other organisms, and also reducing the amount of light available to other aquatic species.

More importantly, cyanobacteria produce highly potent toxins, which, according to the EPA, can cause a variety of immediate health impacts, ranging from mild — diarrhea, headaches, and rashes — to life threatening. These toxins spread both through contact with the water and, during blooms, through the air.

Our knowledge about the long-term health effects of exposure to cyanobacteria is still developing. Recently, the Albemarle Regional Health Services and Duke University’s Lisa Satterwhite have been investigating a potential link in northeastern North Carolina between exposure to harmful algal blooms and an unusually high number of cases of ALS, also known as Lou Gehrig’s Disease. Satterwhite is also studying cyanoHABs as part of a new Community Collaborative Research Grant project with Colleen Karl, chairperson of the Chowan Edenton Environmental Group.

“Taking care of our water sources is the same as taking care of our own health,” Cardenas says. “Just because you aren’t out next to the water every day, doesn’t mean that it isn’t playing a role in your well-being.”

Elusive Origins

Cardenas, a doctoral researcher in the department of biology at Wake Forest University, says one of the greatest challenges in reducing pollution that causes algal blooms is that the source or sources often are unclear (or “non-point”).

The Yadkin River feeds High Rock Lake, which means excess phosphorous and nitrogen might be entering the system anywhere along the river, through run-off directly into the lake, or a combination of the two.

Cardenas says human activity, particularly new construction, drives nutrient pollution. “The more you develop an area, especially as you use fertilizers, which usually contain large amounts of nitrogen and phosphorus, the more you are going to pollute those areas as well,” he says.

As rain falls over farmland and home gardens, it washes fertilizers, pet waste, and other sources of these nutrients into waterways. But, Cardenas adds, filtering rainwater before it reaches the system can reduce the impact on High Rock Lake.

Melt-Blown Solutions

Cardenas is filtering storm water using melt-blown fabrics, which are less costly than traditional fabrics used to filter run off. Eunkyoung Shim from North Carolina State University’s Nonwovens Institute created the fabric. The process for creating melt-blown fabrics begins with melting down different plastics, then extruding the plastic mixture in thin streams and blowing air to intertwine the strands.

Cardenas is testing the fabrics in three stages.

“During the first phase, I was mostly interested in understanding the main water quality picture at High Rock Lake,” he explains. During this stage, he sampled 12 locations across the lake, including sites used by the Yadkin Riverkeeper Association to monitor water quality, as well as sites he suspected would have high levels of chlorophyll-a — the primary pigment found in cyanobacteria and an indicator for potential blooms.

After determining these hot spots, Cardenas took the samples of water back to test the nonwoven filters at lab-scale at Wake Forest. He started by evaluating their ability to act as a simple filter, with water moving directly through the fabric.

When the fabric passed that benchmark, he then moved on to testing its ability to remove nutrients when water is moving both through and across the filter.

“Imagine that you are mixing sugar and water in a glass with a spoon,” Cardenas offers as an analogy to this second test. By placing the filter in a water column and swirling water around it, Cardenas evaluates how well the filter captures nutrients when the water is moving less predictably, like it would in the environment.

In practice, civil engineers will install the fabric on grates for storm drains and retention ponds or add the fabric along inclines on the banks of lakes and streams. When it rains, the runoff will move across and through the filter from all angles.

Cardenas also incorporated additional treatments to the fabric, such as activated charcoal. Activated charcoal (or “activated carbon”) pulls harmful materials from contaminated air and water. This includes excess phosphorus and nitrogen, which will “sorb” or stick to the carbon atoms.

Cardenas found that the addition of activated charcoal did indeed help eliminate nitrogen and phosphorus, which otherwise both dissolve in water, making them difficult to remove using filtering alone. In fact, Cardenas’s process removed 51% of the nitrogen, 73% of the phosphorus — and 86% of E Coli bacteria — in just 15 minutes.

Cardenas is now expanding his testing, studying the filter’s ability to remove and prevent the growth of cyanobacteria over two weeks. The longer time period will show whether the fabric is effective not only against cyanobacteria that rely on the nutrients available in the water, but also against what he calls “late bloomers.”

Even after filtering out all the nutrients available in the water, late-bloomers can use nitrogen available in the atmosphere to continue growing and prolong an algal bloom. To maximize effectiveness, the filters must be able to combat these cyanobacteria, too.

Cardenas is currently culturing several common cyanobacteria in the lab and developing methods to reliably measure both their growth and removal.

When he has finished with his testing, researchers at Auburn University will use his findings to conduct large-scale evaluations. In addition, researchers at the University of South Alabama intend to recover and repurpose the nutrients that the fabric has filtered out during the experiments at Auburn.

Recipe for Resilience

Cardenas says preventing algae blooms has a wide range of impacts, beyond the ecological.

In addition to human health impacts, eliminating blooms at the source can have economic benefits. “The more you take care of a body of water, the less expensive it will be for you in the long run,” Cardenas says. “If we are able to prevent these algae blooms then less money will need to be spent on drinking water treatment.”

For Cardenas, establishing systems to remediate and protect our waterways is key to building resilient communities.

“It is always worth maintaining these water sources,” he says, “not only for our own benefit, but also to allow for future generations to reap the same benefits.”

More

Algal Blooms: How to Stay Safe

From Streets to Sea: Addressing Stormwater Runoff

Safeguarding Water

Leaking Landfills

Lily Soetebier is a contributing editor for Coastwatch and an award-winning science communicator for North Carolina Sea Grant. She holds a M.S. in technical communication from North Carolina State University.