The U.S. National Parks have outstanding scenery and unique natural features – protected in perpetuity. People go to them to camp, hike, fish, watch wildlife, ski, learn, boat, paddle, row, dive, climb, and stand in awe of America.
Besides preservation and recreation, the parks serve as living laboratories. With diverse ecosystems and strong protections, they are ideal environments to study natural processes, human impacts, and the intricate and infinite connections between them.
This month, the National Park Service turns 100 years old and to celebrate, we are sharing some of the studies conducted in National Parks by the St. Croix Watershed Research Station over the past two decades.
“Looking at global change in National Parks, we can rule out so much local land-use effects,” says station director Dr. Dan Engstrom. “We see either how the natural system works or how the natural system is disturbed by large-scale problems – like climate change.”
1. Watching glacial lakes grow old
Berg Bay inlet of Glacier Bay and one of the NPS boats the researchers used to access remote study sites. (Photo courtesy Dan Engstrom)
Amid the fjords and mountains of southeast Alaska, glaciers do a slow dance with the Pacific Ocean. For the past two centuries, in Glacier Bay National Park and Preserve, the ice has mostly retreated from the sea, due to natural forces. Where a sheet of ice once covered the 65-mile long Glacier Bay fjord, today it finds refuge in mountain valleys.
O n lands revealed from under retreating glaciers, new ecosystems develop, just like after the last Ice Age in North America. Questions about how landscapes evolve from barren to bountiful have brought ecologists to Glacier Bay since 1916 (incidentally, the same year the Park Service was created).
Glacier Bay was first protected by the federal government because of its importance for research, at the urging of the Ecological Society of America and its president, University of Minnesota plant ecologist William Skinner Cooper. Cooper first visited the bay after reading John Muir’s writings about an expedition to the area in 1899.
Engstrom has studied Glacier Bay since 1983 and continues to return occasionally for research into how lakes change over time, starting when they are first born from beneath the retreating ice. Surprising and counterintuitive revelations that lake waters become gradually more dilute and biologically less productive in a landscape’s first centuries earned a paper on the subject the cover story in the journal Nature in 2000, a “once-in-a-lifetime” accomplishment.
The park’s remote location, highly pristine nature, and position on the edge of the Pacific, thousands of miles “downwind” from China and other industrialized countries in Asia, has also made for revealing research about atmospheric mercury. The toxic element, carried great distances from coal-burning power plants and other dirty smokestacks, can be measured in the lakes and streams of southeast Alaska. Study results show that mercury deposition rates in the mid-1990s were more than 2.5 times higher than in preindustrial times, with even larger increases over last couple of decades.
2. Making sense of mercury
Engstrom "demonstrates the proper use of duct tape" to Bruce Monson (Minnesota Pollution Control Agency) on Tooth Lake in Voyageurs National Park. Despite its remote location, the lake has among the highest measured fish-mercury levels of any lake in Minnesota.
Wild lakes surrounded by undeveloped landscapes and the potential to learn more about mercury have also brought Engstrom to several other National Parks, including northern Minnesota’s Voyageurs and Lake Superior’s Isle Royale.
There, Engstrom and colleagues studied lake sediment cores to determine changes in how much mercury falls from the sky – far from any smokestacks or other sources. Even in these protected parks, fish in some lakes can be risky to eat because of this toxic element in their flesh.
The research revealed how the surrounding landscape can make a big difference in the safety of fish consumption. Those lakes with extensive peatlands in their watershed had higher fish mercury levels, indicating the importance of wetlands in forming methylmercury, which can concentrate in animals as it works up the food chain.
A related long-term study in the nearby Marcell Experimental Forest demonstrated how increased atmospheric inputs of sulfate, a mercury “co-pollutant”, can greatly increase the production of methylmercury in peatlands.
“We now know that many of our northern lakes have received a “double-whammy” from long-distance industrial pollution – with more mercury and more of it being converted to its highly toxic methyl form,” Engstrom says.
It was only because the ecosystems studied were functioning naturally that the effects of mercury and sulfate could be pinpointed. The findings have played an important role in understanding how sulfate from mining discharge can have serious environmental consequences.
3. Microscopic monitoring
Station director Dan Engstrom (standing in the canoe) collects a sediment sample in Isle Royale National Park with scientist Mark Edlund and canoe technician Dave Edlund. (Photo courtesy Joan Elias, NPS)
There are a lot of ways to measure the health of a National Park – studying its flora and fauna and monitoring for changes are especially effective. Researchers and park managers often inventory birds, plants, and other wildlife to observe increases and decreases in critical species.
The Great Lakes Inventory and Monitoring Network of the National Park Service leads this work at nine national park units in Michigan, Indiana, Minnesota, and Wisconsin. It monitors and analyzes various “Vital Signs” to help parks make scientifically-informed management decisions.
For more than 10 years, research station scientist Dr. Mark Edlund has been partnering with the network to monitor some of the smallest plants possible: diatoms, his favorite group of algae. Because every diatom species creates a unique glass-like shell that lasts long after the alga is dead, they can be extracted from the mud on the bottom of lakes and identified.
Diatoms are also super sensitive to environmental changes like acidity, water clarity, nutrients, and other water quality measures. Different species thrive in different conditions. By studying diatoms from lake sediment cores, Edlund is able to look at diatom fossils that lived in lakes over the past 200 years, identify the species, and describe how the water has changed during the past few centuries.
“We typically see two periods of changes in these lakes – and it’s not when the park was established,” Edlund says. “European settlement is always the big thing, always tied to landscape change – logging and agriculture. Then we’re seeing this more recent change in the National Park lakes, and trying to understand that.”
The work led to a study Edlund did with station scientist Jim Almendinger, matching climate data to diatoms in the sediment, and describing how things like temperature and the depth of the thermocline have changed in the lakes. The protected parks and isolated lakes, with minimal human development on land, are essential to seeing if global climate change is affecting these wild waters.
4. Botulism, invasive species, and dead birds
Scientist Mark Edlund examines a fresh sediment core from the bottom of Lake Michigan on board the Environmental Protection Agency research vessel R/V Lake Guardian. (Photo courtesy Alaina Fedie)
Since around 2000, there has been a disturbing increase in the number of bird kills at Lake Michigan’s Sleeping Bear Dunes National Lakeshore and elsewhere in the Great Lakes. The birds have been poisoned by botulism, an illness caused by naturally-occurring bacteria, a problem more commonly associated with poor food preparation and storage.
But at Sleeping Bear Dunes, the real culprits are non-native zebra and quagga mussels, and a small bottom-dwelling fish called the round goby. Based on research by station scientist Mark Edlund and colleagues, the disease and the die-offs are the result of complex food-web interactions.
By examining sediment cores from the bottom of Lake Michigan near the shores of the National Park and reconstructing the lake’s history from analysis of the sediment, Edlund observed a major change in the environment starting in the 1990s. That was the same time invasive mussels and gobies first arrived in the ballast water of ships from eastern Europe.
How do mussels and fish kill gulls and waterfowl? First, the mussels filter the water, consuming algae and other material. The water quickly becomes much clearer, meaning light can reach to greater depths. Algal species shift to those growing on the lake bottom in near-shore areas.
Eventually, thick mats of green filamentous algae begin to develop. The algae are harmless alive, but their death creates another condition necessary for botulism.
“When they die, they accumulate on beaches and on the lake bottom and they start rotting, which consumes oxygen from the bottom water,” Edlund says. “For the bacteria to produce the botulism toxin, you have to have no oxygen.”
The non-native round gobies, a fish that happens to eat the non-native zebra mussels, can consume the poison when they eat infected mussels. The illness causes them to flop around near the surface where they are readily eaten by waterfowl – and that’s probably how the disease has killed more than 80,000 birds on the Great Lakes since 1990.
5. St. Croix River science
Backwaters and braided channels near the Research Station provide endless opportunities for exploration. (Photo by Greg Seitz)
It’s hard to say where to start when it comes to the National Park unit literally in the Research Station’s backyard. Station lands extend to the banks of the St. Croix National Scenic Riverway and its scientists work a few hundred yards from its Wild & Scenic waters.
The St. Croix and its 8,000 square mile watershed have been a central focus of the Research Station since its founding in 1989 – and the subject of many studies. Working in partnership with the National Park Service, state agencies in Wisconsin and Minnesota, and regional conservation organizations, the Station has been a key player in efforts to understand challenges facing the river and to help devise solutions.
Polluted runoff has been identified as one of the biggest problems for the past 20 years. In Lake St. Croix, the lower 25 miles before the St. Croix joins the Mississippi, the water turns seasonally green with noxious algae as nutrients from farm fields, urban areas, wastewater treatment plants, and other sources spur excess growth.
Lake St. Croix is now the subject of an EPA-approved effort to reduce phosphorus inputs and improve the water. Station scientists have been central to this effort, from doing the original research to determine historic levels of nutrients, to measuring current conditions, to modelling effective tactics for improving the health of the river.
Curiously, even as cleanup efforts have proceeded and the phosphorus in the river has been gradually reduced, algae blooms have continued to occur, and perhaps more frequently. Decades of study have revealed clues about this confounding connection and led to better scientific understanding of how such riverine lakes function.
In limnology, more phosphorus usually means more algae, and vice versa. But Lake St. Croix is a complex system, not one river nor one lake, but four deep pools connected by shallow channels. This affects how long water resides in each pool, if and when each pool stratifies, and how nutrients are cycled between the water, bottom sediments, and the algae themselves.
6. Revealing rock pool ecology
Mark Edlund takes measurements at a rock pool in Apostle Islands National Lakeshore. (Photo by Alaina Fedie)
The most popular place to visit in any park on Lake Superior is usually along the shoreline. Visitors watch waves, throw rocks, and contemplate the distant horizon. Underfoot, some shoreline areas also contain dozens to hundreds of small rock pools that are important and sensitive habitat for specialized plants, frogs, algae, and other creatures.
Seldom more than a few feet across, these shallow depressions in the bedrock look a lot like tide pools on an ocean coastline, and also serve as a unique habitat for plants and animals. But they have much different hydrology and biology.
There are actually three distinct types of rock pools, ranging from the “splash zone” nearest the lake to the “lichen zone” at the upper edge where lake waves never reach. The life forms calling each pool type home are different too, as Mark Edlund found during a 2011 study of three of Lake Superior’s National Park units intended to establish a baseline of where rock pools were, how they function, and what organisms depend on them.
“There are a lot of really specialized diatoms, and the species present were night and day different between splash zone and the lichen zone,” Edlund says.
By visiting rock pools at Isle Royale National Park and Apostle Islands and Pictured Rocks National Lakeshores once a month for a year, Edlund and colleagues assembled a trove of data that is still providing insights. Edlund is working to describe new diatom species based on the work. And now armed with this information National Park resource managers can better protect the unique and delicate chemistry and biology of these little lakes.
In addition to the possible disturbance by human visitors, Edlund also points out that numerous shipping routes go right by some of the places they studied. With the potential for future oil shipping on the Great Lakes, the findings give a clearer idea of the fragile habitats threatened by a spill.