Algal bloom at Curecanti National Recreation Area/NPS
National Park Service Staff Grappling With How To Control Toxic Algal Blooms
By Lori Sonken
Cape Cod National Seashore in Massachusetts has had red tides – highly toxic algae that color the ocean red – for decades, but not until 2019 did the park’s freshwater lakes encounter bright green, shiny, harmful algal blooms (HABs). Now, the lakes within the park’s boundaries face outbreaks yearly. Climate change is the suspected culprit.
“We thought we would never get them,” said Sophia E. Fox, Ph.D., the park’s aquatic ecologist. ”Our current thinking is that the warming water temperatures” – as high as 77 degrees Fahrenheit in the summer– are allowing the cyanobacteria to thrive and outcompete natural plankton communities.
People and animals love to swim in Snow, Gull, and Ryder ponds, but this past summer the national seashore issued temporary public health advisories to keep away from the blue-green scum in Ryder Pond. Exposure can cause rashes, nausea, vomiting, breathing difficulty, seizure, and even death. Two years ago, a dog died at Zion National Park in Utah after playing in a toxic bloom on the Virgin River.
Like all 50 states, national parks across the country are facing HABS, but the reasons for them are not uniform and the ways to manage them are still being discussed.
Both freshwater and saltwater HABs stem from the rapid growth of algae or cyanobacteria that can produce toxins harmful to people, animals, and the environment. The Centers for Disease Control and Prevention has identified three main types of blooms that can sicken humans, their pets, and wildlife:
- Cyanobacteria (sometimes called blue-green algae)
- Dinoflagellates (sometimes called microalgae or red tide)
- Diatoms (sometimes called microalgae or red tide)
The cyanobacteria blooms are most often behind the freshwater blooms that prompt health warnings.
Green algal bloom at Saint Croix National Scenic Riverway/NPS
Factors spurring HABs including nutrient concentrations – especially phosphorous and nitrogen -- coming from concentrated animal feeding operations discharging manure, agricultural runoff releasing fertilizer and manure, urban stormwater releases, and failing septic systems likely feed the algae and are thought to contribute to the problem. HABs can also be attributed to heavy rainfall or intense runoff due to spring snowmelt that carry nutrients into the water, warm waters, and low wind speeds that allow HABs to bloom.
Both heavy rainfall events and warmer waters are occurring more frequently due to climate change, said David Wolfe, emeritus professor in the School of Integrative Plant Science at Cornell University, in an email.
But pristine Voyageurs National Park, known for its exposed rock ridges, cliffs, wetlands, forests, streams, and lakes in northern Minnesota about 55 miles from the Canadian border has HABs, especially after heavy rains. There are no nearby agricultural operations or urban areas that could be driving the phenomena. It could be that the soil is nutrient rich and washing into the water, said Victoria Christenson, research hydrologist with the U.S. Geological Survey. It’s also possible that the cyanobacteria attach to nitrogen in the air.
Naturally occurring algae are an essential part of the food chain, produce as much oxygen as trees, and only a small percentage of the blooms become toxic, according to Christenson’s blog in Scientific American.
She co-leads a joint USGS/National Park Service field study sampling water from 21 parks nationwide, including Cape Cod National Seashore, Voyageurs, Acadia National Park, Canaveral National Seashore, Fire Island National Seashore, Olympic National Park, Padre Island National Seashore, Sitka National Historic Park, Apostle Islands National Lakeshore, Curecanti National Recreation Area, Isle Royale National Park, Lake Mead National Recreation Area, Perry’s Victory & International Peace Memorial, Sleeping Bear Dunes National Lakeshore, Buffalo National River, St. Croix National Scenic Waterway and Zion National Park.
Now in in its second year, the three-year-long study is evaluating the toxicity of hundreds of algal toxins, phytoplankton, and cyanobacteria in water collected at the parks. It’s not looking at the impacts of climate change, Christenson said.
“HABs are complex and so we can't link a specific HAB to climate change, but we do know that climate change dramatically increases heat, which is a major influence in algae growth in many systems, as well as changes precipitation regimes, which we also know is a major driver of many HAB events, ” said Danielle Buttke, who heads the One Health Program at the National Park Service.
Congress provided $300,000 for the USGS/NPS study, and additional support comes from in-kind contributions.
“The primary outcome for the USGS-NPS Nationwide Harmful Algal Bloom Project will be a HAB Toolkit that provides a set of consistent monitoring protocols that parks can access during a HAB event,” said Jamie Kilgo, marine ecologist with the NPS and co-leader on the study.
Roger and Leslie Frick are citizen scientists participating in the project at the St. Croix National Scenic Waterway in Minnesota every other week from July through early October. Often from their kayaks, they dip liter-sized bottles into the clear brown water to collect samples and measure the water’s temperature. They pedal their kayaks several miles downstream to drop off the samples they collect.
“We’ve never seen a bloom of blue-green algae,” said Roger, but some of their samples have tested positive.
“HABs can disappear from the naked eye” but still be there, explained Marian Shaffer, aquatic biologist at St. Croix. Home to more than 40 species of freshwater mussels and 100 native fish species, the park is “a pristine flowing river surrounded by a beautiful forest landscape, buzzing with the sounds of birds, that really captivates your soul,” she said.
The park is threatened by upstream agricultural runoff and manure from a proposed hog facility on a tributary that could exacerbate the blue green, almost iridescent HABs that float along the shoreline and are frequently distributed throughout the water column during the late summer.
In Colorado, algal blooms are found across the state. In 2018, Curecanti National Recreation Area began monitoring blooms that exceed the state’s thresholds for cyanotoxins in Blue Mesa reservoir, said Nicole Gibney, aquatic ecologist. Now, HABs are happening more frequently.
A closeup photo of cyanobacteria seen this September at Voyageurs National Park/NPS
In September, the park closed an area the size of three football fields within Blue Mesa Reservoir to swimming, water skiing, paddle-boarding, and wading due to a HAB. There have been reports of people experiencing nausea after swimming in Blue Mesa and dogs getting sick, but nothing definitive.
Sometimes the HABs look like thick green pea soup or spilled paint. Other times they turn turquoise and occasionally are yellow. “The bloom definitely has a smell. It’s very pungent, almost like damp decaying plants,” Gibney wrote in an email.
Scientists are trying to figure out what causes the bloom in Blue Mesa, but not in the deeper reservoirs – Morrow Point and Crystal – within Curecanti. It may be a combination of factors, including pH levels and water temperature that are triggering the toxins, said Gibney.
“More than half of the national parks have waters considered impaired” under the Clean Water Act, said Sarah Gaines Barmeyer, deputy vice president for conservation programs at the National Parks Conservation Association. Pollution coming from outside the parks often causes the impaired water quality, including HABs, she said.
Aside from harming the natural environment, HABs have economic costs, too. In late September, Olympic National Park in Washington state experienced a HAB caused by a diotom, a type of algae abundant in marine and freshwater ecosystems and a food source for razor clams harvested along the state’s coastline. A 2010 study examining the economic effects of razor clam beach closures in Grays Harbor and Pacific counties in Washington state due to HAB presence showed a loss of 339 full time jobs and $10.6 million in labor income.
The toxin does not hurt the razor clams, but “it does harm mammals (especially humans) that eat them,” said Steve Fradkin, ecologist and limnologist at Olympic National Park, in an email. Shellfisheries along the Washington coast closed for more than a week this past summer due to the presence of the toxin in razor clam flesh.
Olympic National Park does not allow shellfish harvests during the summer months due to HABs – sometimes appearing as red, brown, or green clouds in the water and extending as far as 10 miles. Though the reasons for the HABs are under study, Fradkin said they “are likely caused by a combination of water temperature, oceanographic features (upwelling, long-shore transport, etc.), nutrient levels, and fundamental changes to the structure of marine communities and their dynamics.”
Neither Cape Hatteras National Seashore nor Padre Island National Seashore have experienced HABS this past summer. Shelly Todd, Padre Island’s chief of resource management, suspects that outside group’s efforts to reduce nutrients entering the watershed may be partly responsible but this suspicion is not confirmed.
A brown cyanobacteria mat in the Virgin River at Zion National Park, where a dog died after coming into contact with an algal bloom/NPS
Along the U.S. Eastern Seaboard, Cape Canaveral National Seashore in Florida posts warning signs when needed that shellfish and pufferfish can be harmful if consumed, said Kristen Kneifi, resource management specialist, in an email. Studies have shown that people can become ill from eating shellfish contaminated with paralytic shellfish poison in a toxic algal bloom.
In the Northeast, Rachel Fowler, Ph.D., at the University of Maine and collaborators are studying HABs at three freshwater lakes – Jordan, Witch Hole, and Seal Cove Ponds -- within Acadia National Park. “Our objective is to get a better understanding of risk conditions for HABs in different types of lakes” and the early warning signs that a lake might cross the threshold into HAB conditions.
The good news is that “Jordan Pond is in great shape and is going to remain in great shape,” she said, noting that the lake is deep, has low nutrients, lots of dissolved oxygen and the bottom lake temperature that remain about 43 degrees Fahrenheit throughout the summer.
She has not reached any firm conclusions about her findings, but suspects Witch Hole Pond may be the most at-risk due to high nutrients, high temperature, and low dissolved oxygen -- water quality characteristics that are associated with HABs.
Meanwhile,”data from the NPS/USGS study is being analyzed around the country, though we don’t know yet when the findings will be released. The next step will likely be incorporating the results from this project in the NPS Harmful Algal Bloom Guidance, which provides information for park managers on bloom detection, response, and prevention,” Kilgo said.
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