Lake Fayetteville monitoring reveals peak months for harmful algal blooms

By John Lovett
University of Arkansas System Division of Agriculture
Arkansas Agricultural Experiment Station

FAYETTEVILLE, Ark. — Five years of water quality monitoring at Lake Fayetteville is shedding light on the cycles of waterborne nutrients and bacteria-produced toxins, offering a better way to measure the risk to recreational users.

WATER QUALITY — Brad Austin, research scientist with the Arkansas Water Resources Center, monitors the water quality as part of studies on Lake Fayetteville (U of A System Division of Agriculture photo by Paden Johnson)

Water quality scientists with the Arkansas Water Resources Center, a part of the Arkansas Agricultural Experiment Station, have been examining cyanobacterial harmful algal blooms, or HABs, in the 194-acre body of water since 2018. The lake was created in 1949 to supply the city’s water, but is now used for fishing, kayaking and other recreational uses.

“It’s a small watershed and recreational lake that is heavily influenced by human activity,” said Brian Haggard, director of the Arkansas Water Resources Center and a professor of biological and agricultural engineering. “Now, the watershed is urban, with still some agricultural lands, so it provides a unique opportunity to study a system that has become hypereutrophic.”

Hypereutrophic means the water has high concentrations of nutrients such as phosphorus and nitrogen. While these are necessary for plant growth, when there’s too much, they can spark a “bloom” — an explosive growth of cyanobacteria, which can produce toxins like microcystin. 

“Microcystins are the most studied cyanobacterial toxins, and many species of cyanobacteria can produce this toxin under certain conditions,” Haggard said. “There is a lot of nitrogen and phosphorus that can be released from the lake bottom, which might influence when cyanobacteria produced toxins.”

The nutrients which drive cyanobacterial growth can come from the watershed, especially during storm events which transport nutrients to the lake, he explained. However, the “legacy” nutrients, or nutrients stored within the lake bottom, can also drive harmful algal blooms and toxin production by the cyanobacteria.

Haggard said long-term monitoring of Lake Fayetteville offers practical guidance for people who use the lake, especially kayakers and dog owners, to avoid exposure to microcystins, which can make both people and animals sick.

Even though the City of Fayetteville, which owns the lake, put up a sign recognizing the potential for toxic cyanobacterial blooms, Haggard envisions a more comprehensive and data-driven approach.

“What we would like to move towards is something similar to what the forest service uses for fire risk,” Haggard said. “Are there some parameters we can measure rather easily that can help let us know if the chance of elevated toxins is high?”

Haggard said that expensive toxin analyses could be replaced by simple measurements such as water temperature and the fluorescence of phycocyanin, a pigment used for photosynthesis by cyanobacteria. These more cost-effective measurements could be used as a proxy to decide on whether the microcystin toxin concentration is too high in the lake for safe recreational use.

Since the Arkansas Water Resources Center began routine monitoring at the lake, microcystin has been observed in measurable concentrations greater than the reporting limit of 0.3 micrograms per liter throughout the year. In 2019, microcystin concentrations were measured up to 15 micrograms per liter at the lake — nearly double the recommended limit for contact in a recreational water.

Findings over five years

Haggard and his team at the Arkansas Water Resources Center published a study last year in the Journal of the American Society of Agricultural and Biological Engineers examining a subset of the monitoring data taken in summer 2020 at Lake Fayetteville. The study is titled “Microcystin shows thresholds and hierarchical structure with physiochemical properties at Lake Fayetteville, Arkansas, May through September 2020.”

“Lakes with HABs often have a pattern to when toxins are elevated, and Lake Fayetteville tends to have greater total microcystins during late spring, early summer and then again in fall,” Haggard said. “These peaks in total microcystin coincide with natural hydrodynamics of the lake, that is stratification – when the warm and cold layers set up – and turnover – when those layers remix bring nutrients from the bottom waters up to the upper layers.

“It’s not always this simple, but this has been the pattern at Lake Fayetteville. The cyanobacteria seem to produce more toxins during these periods.”

All lakes with deep enough water experience “turnover.” During the spring, the surface water warms when the deep water stays cooler. However, “when the colder water down there is not mixing with the surface any longer, you can lose all the oxygen.”

When the oxygen is gone or limited, a group of bacteria called facultative anaerobes use nitrates to “breathe,” removing nitrogen from the lake bottom waters through a process called denitrification. After the nitrate is gone, these bacteria seek manganese and iron to metabolize for energy.

Once the bacteria move to manganese and iron, they’re dissolving manganese and iron oxides in the sediments, which have phosphorus and ammonium and other things attached to them, Haggard explained. When metabolizing the manganese and iron, the anaerobic bacteria free up phosphorus and ammonium that goes into the lake bottom water and further builds nutrients.

“In the fall, when the lake mixes, this can bring nutrients up into the water,” Haggard said. “This happens when we see the fall peak in cyanobacterial toxins.”

Haggard’s co-authors on the microcystin thresholds study included Erin Grantz and Brad Austin with the Arkansas Water Resources Center; former graduate students Abbie Lasater with the University of Arkansas biological and agricultural engineering department, and Alyssa Ferri with the crop, soil and environmental sciences department; Nicole Wagner with the biology department at Oakland University; and Thad Scott with the biology department and Center for Reservoirs and Aquatic System Research at Baylor University.

Toxin-risk framework

CASE STUDY — Lake Fayetteville offers scientist with the Arkansas Water Resources Center a case study in an urban lake once mostly surrounded by agricultural land. (U of A System Division of Agriculture photo by Paden Johnson)

Members of Haggard’s team also recently published a peer-reviewed paper in the journal of the University Council on Water Resources. The paper focused on developing a strategy to help inform recreational users of Lake Fayetteville when total microcystins might be elevated. The study is titled “Chlorophyll and phycocyanin raw fluorescence may inform recreational lake managers on cyanobacterial HABs and toxins: Lake Fayetteville case study.” It is this initial study that the Arkansas Water Resources Center is building on to help create a toxin-risk framework like that used to warn of fire danger in forests.

“The goal is to help inform the recreational users when the risk of cyanobacterial HABs that might be producing elevated toxins is low, medium, high and very high,” Haggard said. “This way the signage about cyanobacterial HABs and toxins can be updated on a more timely basis, and it does not become a static sign that people often disregard.”

To learn more about Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website: https://aaes.uada.edu. Follow on Twitter at @ArkAgResearch. To learn more about the Division of Agriculture, visit https://uada.edu/. Follow us on Twitter at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit www.uaex.uada.edu.

Food safety scientists crank up steam, radio waves to kill salmonella amid spice recall

By Maddie Johnson
University of Arkansas System Division of Agriculture
Arkansas Agricultural Experiment Station

FAYETTEVILLE, Ark. — Bacteria can easily hibernate in low-moisture ingredients such as flour and spices, and food scientists have been working on ways to make them safer with novel technologies.

SPICE SAFETY — Surabhi Wason, Ph.D., used a combination of radiofrequency and steam to sanitize spices in packages while a doctoral student in the food science department. (U of A System Division of Agriculture photo)

Publication of a food safety study on radiofrequency pasteurization and novel steam technology highlights the recent national recall of black pepper for salmonella risk. The June 3 recall brought low-moisture foods to the forefront of public discussion, showing just because bacteria can’t grow well in dry foods doesn’t mean they don’t pose a threat.

Surabhi Wason was the lead author of the study titled “Radiofrequency inactivation of salmonella in black pepper and dried basil leaves using in-package steaming,” which was published in the Journal of Food Protection. She conducted experiments to develop in-package steaming for enhancing the efficiency of radiofrequency pasteurization of spices and evaluate its impact on the spice quality.

“Radiofrequency, also referred to as macrowave, is a long wavelength, non-ionizing electrical form of energy,” Wason said. “The significant application for radiofrequency technology is in the treatment of dry ingredients where microbes are considered dormant and are in the most difficult state to kill.”

Wason explained that the radiofrequency, or RF, generator creates an alternating electric field between two electrodes, causing the polar water molecules in the material to generate friction, which causes the material to heat rapidly and uniformly.

Wason is a former doctoral student of Jeyam Subbiah, head of the food science department, who served as corresponding author for the study. The food science department is encompassed both by the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture, as well as the Dale Bumpers College of Agricultural, Food and Life Sciences.

Rossana Villa Rojas, assistant professor of practice in the food science and technology department at the University of Nebraska-Lincoln, was a co-author of the study showing that radiofrequency pasteurization and novel steam technology can inactivate salmonella in low-moisture foods, including spices, without significantly compromising quality.

The findings were based on work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2020-67017-33256. McCormick & Company, Inc. supplied low-moisture food materials for the study.

How it works

When a salmonella is identified on a product quality testing, or during a foodborne illness outbreak, the industry has to recall all products since the last cleaning of the plant, Subbiah explained.

“Food processing plants that process low-moisture foods clean less frequently, often once a year, because water in the plant can increase food safety risks,” Subbiah said. “That means the industry has to recall several days to months of production, which could potentially mean that everything on the shelf, and thousands of other products that used that as an ingredient, have to recall, and it’s a huge financial loss. People don’t realize the magnitude of food safety.”

Under traditional methods, low-moisture foods must be exposed to high temperatures for long periods to kill bacteria. Salmonella and other pathogens like listeria can adapt to harsh environments and stay hidden for years, requiring severe processing to be killed, Subbiah said. Without inactivation, the pathogens can begin growing when met with ideal conditions, like the interaction with water that occurs when spices are used in soup.

Baby formula is another low-moisture food that can become dangerous when rehydrated. Subbiah said Cronobacter sakazakii contamination in baby formula can lead to severe illness and death for babies.

With traditional methods, severe heat treatment diminishes aspects of the food quality such as nutrient content and may damage the package because of the generation of steam, Subbiah said. Scientists can also pasteurize these foods through irradiation, or radiation exposure, but consumer acceptance is low, he added.

Subbiah found himself wondering whether the kind of packaging technology that is widely used for foods like microwavable vegetables could be adapted to allow for the same quick heating of dry foods with the additional step of resealing needed before their sale. To prevent steam buildup from eventually bursting packaging, experts developed a one-way valve that releases the steam and then reseals, which is at the heart of Subbiah’s study.

This new valve technology mimics the in-package sterilization of canned goods and uses radiofrequency heating. Conventional heating methods transfer heat to a product through its surface and take longer to reach the center, but radiofrequency heating generates heat inside an entire product mass evenly through friction generated by the vibrating water molecules in an electric field, much like microwave technology. This way, products are pasteurized while they are already in their final packaging and are heated uniformly, avoiding the risk of overheating the edges before heat reaches the center. This in-package processing cuts the risk of contamination that can occur when products are moved between the pasteurization and packaging stages, and foods are safe from contamination until customers open them.

“The gold standard is to package it in the final form and kill the bacteria, like canning,” Subbiah said.

“This technology shows promise for extending to other products like flour, cereal grains offering a robust solution for diverse food sectors," Wason added. "Moreover, one of the key advantages of radiofrequency pasteurization lies in its continuous processing capability. By implementing a conveyor belt system, products can move seamlessly through the RF chamber, ensuring consistent and efficient pasteurization.”

Sticky situation

Subbiah was first inclined to explore this topic of low-moisture food safety after witnessing the costs of a 2007 peanut butter recall.

QUALITY AND SAFETY — Jeyam Subbiah, head of the food science department, conducts research through the Arkansas Agricultural Experiment Station to improve food quality and retain safety. (U of A System photo)

Recalls for products such as packaged meat require consumers to avoid products processed on a specific day. With dry foods such as peanut butter, though, sanitation of production facilities may happen just once a year, or every few years, to avoid exposing the product to water. This means that in cases of recall, a years’ worth of product, and any other foods that feature it as an ingredient, might pose a health risk for consumers and a financial loss for producers.

The company ended up recalling all peanut butter produced as far back as January 2004, an expected loss of $50-60 million.

In addition to his work with the experiment station, Subbiah also collaborates with the Center for Low-Moisture Food Safety based out of Michigan State University, which includes a stakeholder advisory group of industry professionals that take work like Subbiah’s from the publication to real-world application phase.

To learn more about Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website: https://aaes.uada.edu. Follow on Twitter at @ArkAgResearch. To learn more about the Division of Agriculture, visit https://uada.edu/. Follow us on Twitter at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit www.uaex.uada.edu.