With the July heatwave in Arkansas, algae bloomed along the Buffalo National River.
Lucas Driver of Little Rock, an ecologist with the US Geological Survey’s Lower Mississippi Gulf Water Science Center, said the filamentous algal blooms occur naturally in almost all freshwater bodies, but can reach troublesome levels under certain conditions.
“If these blooms get worse, you could see a negative impact on visitors to the state’s crown jewel, the Buffalo River,” he said.
The national park attracts around a million visitors a year. Most of them don’t go there for the seaweed.
“Bloom” refers to algal colonies that get out of control.
What most people see along the Buffalo River is non-toxic algae of the genus Spirogyra, Driver said. “Lime-green, slimy, hair-like filaments that can grow to several feet in length under certain conditions,” he said.
Sometimes they grow out of the river bed to the surface where they are called mats.
“That’s when people start getting upset,” Driver said. “It can be a real deterrent to people trying to swim or fish out there.”
After a storm, the algae can detach from rocks, pebbles or bedrock and float downstream like “little river tumbleweeds,” Driver said.
The algal bloom along the Buffalo River has been documented in field notebooks as well as previous historical accounts over the past several decades.
According to a 1978 report on the Buffalo River, “Exuberant spirogyra blooms are associated with deep pools with large rocks and a sand-silt base. … Access to cattle at Tyler Bend appears to be directly related to localized and extremely potent Spirogyra blooms.”
According to a 2018 national park press release, “Some algae are important for a healthy ecosystem and most species are harmless, although they are a nuisance to paddlers, swimmers and fishermen.”
“Most of our blooms are just pesky algae,” said Shawn Hodges, an ecologist at Buffalo National River. “It’s unsightly. It’s not aesthetically pleasing, but it’s there. … I’m not surprised to hear reports of algal blooms this time of year, especially when we have 100 degree days.”
“Especially in the height of summer you can find seaweed in some places and a little bit of seaweed isn’t a big deal,” said Driver. “Algal blooms are, to some extent, not a big deal. It’s a naturally occurring thing. It’s uncomfortable for people to be around. It can become what we call an ecological stressor under certain conditions.”
If algal blooms continue to grow along the river, they could deprive fish, frogs and invertebrates of oxygen. Driver said algae could crowd out organisms or disrupt their ability to access necessary habitats for foraging, reproduction or refuge from predators.
“We’re seeing blooms that can flare up in late summer and fall,” Driver said. “As it gets cooler, these blooms usually begin to die back in late fall and winter.”
Hodges said he has worked at the national park since 2004. He’s seen algal blooms this year and next, but says they’re more extensive now. Hodges said he’s never seen an algal bloom on the Buffalo that killed fish.
After anecdotal reports of large algal blooms on the river in 2016, 2017 and 2018, the Geological Survey — in partnership with the National Park Service — began periodically monitoring the river water and testing for algae. Government volunteers also help.
As part of the study, water quality will be checked for nutrients every four to eight weeks at two dozen sites along a 70-mile stretch of the river from the Hasty Bridge to Rush, Driver said. At 12 of these test sites, a visual assessment for algae will be conducted for approximately 500 meters of the river. A detailed investigation is carried out in areas where thread algae are present.
“It’s not a perfect snapshot,” said Driver. “It gives us a representation of the spatial extent of the algae. This is just a kind of snapshot, a path, a piece of the puzzle. There is a lot to do.”
He said suspected causes of algal blooms include heat, excessive sun exposure, low-flow hydrology and nutrients in the water. Nutrients include elements such as nitrogen and phosphorus.
“The watershed in general has a lot of different sources of nutrients, from agriculture, people — there’s septic tanks, chicken coops, pastures, hayfields that get fertilized,” Driver said.
He said the region’s karst terrain could allow nutrients to enter the river from underground sources such as sinkholes, caves and springs.
Hodges said algae provide food for fish.
“We have fish that only feed on algae,” he said. “There is always seaweed all year round. They’re always there, but sometimes the conditions are perfect for flowering. At this point we are still trying to figure out what the root cause is.”
In general, the Buffalo River is considered a very nutrient-poor watershed, Driver said.
“The Buffalo is immaculate,” he said. “That’s one of the reasons why it’s a national park. Water quality has historically been very, very good. It is still considered a very nutrient poor system.”
Driver said there’s no real rule for what constitutes too much algae, and algae is more common in lakes than rivers.
After a 2012 public survey, West Virginia ecologists determined that 40% filamentous algae coverage of a stream bed—regardless of flower length—is the point at which algae interferes with the recreational use of the stream.
“We don’t currently have such a definition,” Driver said of Arkansas.
Last week, a survey of the Buffalo River by ecologists found less than 10% algae coverage at some of the 12 test sites, Driver said. Elsewhere, algae covered more of the river bed, but specific estimates of cover had not been analyzed as of Friday.
“I wouldn’t consider what we’re seeing extraordinary, but the summer isn’t over yet,” said Driver.
He said the seaweed is generally denser on the lower Buffalo River, where it’s wider and shallower, with some deep pools.
“Based on our experience, algae are typically more common in the lower part of the river, downstream from Tyler Bend,” he said.
Driver said he saw some filamentous algae growing to the point where they formed mats on the water.
“I haven’t seen huge mats,” he said. “I’ve seen a couple of spots along the river bank where the seaweed has started to build up on the surface.”
Driver said the current phase of the water nutrient quality study is coming to an end and they are looking at ways to continue the research.
While the water study has been running for 4.5 years, more time is needed to collect data and examine relative trends, according to Driver.
Spirogyra is usually a nuisance, but other algae are classified as harmful.
“Algae, ranging from microscopic, unicellular organisms to large algae, are simple plants that form the basis of food webs,” according to the National Oceanic and Atmospheric Administration. “Sometimes, however, their roles are more sinister. Under the right conditions, algae can get out of control – and some of these ‘flowers’ produce toxins that kill fish, mammals and birds and can cause disease or even death in humans in extreme cases. Other algae are non-toxic but use up all the oxygen in the water as they break down, clogging the gills of fish and invertebrates, or suffocating coral and underwater vegetation. Still others stain water, form huge, smelly piles on beaches, or contaminate drinking water. Collectively, these events are referred to as harmful algal blooms, or HABs.”
While NOAA is mostly talking about the ocean there, some harmful algae can be found in freshwater streams.
Cyanobacteria, often referred to as “blue-green algae,” occur naturally in most freshwater streams, including the Buffalo River. It can produce toxins, is considered a harmful alga, and caused problems in buffalo in 2018.
“…A species of blue-green algae (also called cyanobacteria) has been identified in the river,” according to a July 27, 2018 press release, quoting Hodges. “This species has the potential to produce cyanotoxins that can be harmful to humans and pets. Unfortunately, one cannot tell if the algae would produce cyanotoxins just by looking at them. Some visitors this month have reported illness after swimming in areas with algae.”
Environmentalists thought a large pig farm that closed in January 2020 could be responsible for a nutrient spike in the Buffalo River.
In 2012, the state allowed C&H Hog Farm to operate a farm near Big Creek, a tributary of the Buffalo River. The farm was permitted to house up to 6,503 pigs, although it normally operated at around 3,000.
After years of controversy, the Arkansas Department of Environmental Quality denied C&H permission to continue operating the farm in 2018.
The next year, Arkansas paid C&H $6.2 million for the farmland to be used as a wildlife sanctuary to protect the river.
From 2016 to 2018, Driver participated in a study of Big Creek and the Buffalo River.
The study examined monthly nutrient concentrations and periphyton response in the Buffalo River both upstream and downstream of its confluence with Big Creek. Periphyton refers to aquatic organisms, including plants, algae, and bacteria, that adhere to underwater surfaces such as rocks in a river bed.
“Basically we went out and scraped algae off rocks,” Driver said. “It was standardized. There was a certain number of rocks that we would pick up from the creek bed.”
Some of what they found was to be expected.
“Nutrients in Big Creek were higher than in the main stem, but that’s not surprising and not uncommon for Buffalo River tributaries,” Driver said.
And in the Buffalo River?
“There was no significant difference in upstream and downstream nutrient concentrations, but there seemed to be a small difference in the downstream periphyton communities, which could indicate a response to even small changes in nutrient concentrations,” Driver said.
Cassie Branstetter, a spokeswoman for Buffalo National River, said she has had no complaints about algal blooms this year.
Branstetter said the park made no attempt to remove algae.
“Algae could be removed with algaecides, but in a natural environment that would be very detrimental to the ecosystem,” she said. “These are typically used in fountains and other artificial water features to make them look beautiful.”