Vernal Pools at Ohio University

by Morgan Spehar

A short hike away from the observatory, down a trail so overgrown it is hard to see where the path begins, lie two basins of receding water, surrounded by rings of cracked mud with lush plant life growing throughout. At first glance, they look like naturally occurring ponds, but upon further inspection there seem to be less natural looking hills and troughs dug out of the landscape, and there are surveyor’s flags around the edges. 

The two bodies of water are called vernal pools, dug out of the Land Lab at The Ridges, where many Ohio University faculty and students conduct outdoor research. Half pond and half wetland, the vernal pools dry up during the summer and fall, providing the perfect habitat for some of Ohio’s native amphibians. 

Molly Gurien, a professor in Ohio University’s Department of Biological Science, created the pools in October of 2014. 

“The name amphibian means ‘dual-life cycle’,” Gurien said, “so they are born in water, but then they usually go upland once they’re mature, for the overwintering part of their lifecycle. With no fish predators, amphibians can breed in those pools and their larvae are mostly safe from being eaten. Vernal pools are really important in Ohio and other parts of the country as really good amphibian breeding habitat.”

Deforestation and habitat alteration for farming and housing purposes have significantly changed the landscape in Ohio over the last 50 to 100 years. Wetlands and vernal pools have been drained and filled in, leaving the species that use the habitats with very little space to survive.

But the ecology behind replacing the pools is tricky. If the water temperature gets too hot, the pools lose their oxygen, an important resource for amphibians, which breathe partly through their skin in a process called cutaneous respiration. The pools could also drain or dry up too quickly, stranding amphibian larvae in the middle of the forest. Depth matters too; the deeper pool at The Ridges is only about 12 inches deep at full water capacity and the shallower pool only gets to around 7 inches. 

Having native plants is important to the ecosystem, too, because if a wetland doesn’t have aquatic plants, it just becomes a pond. Different species of sedges, which are flowering, grass-like plants, have taken over the vernal pools, along with bur reed, arrowhead and spatterdock. All of these plants were brought in with soil from another wetland in Ohio to create the habitat.

Gurien knows that the habitat is critical to some species. 

“A vernal pool obligate is a species, typically an animal, that is dependent on a vernal pool for part of its life cycle,” she said. “So, in this case, these species have to breed in vernal pools, they won’t breed anywhere else.” 

These obligate amphibian species include spotted salamanders, mole salamanders, wood frogs and eastern spadefoot toads. Only one species, the spadefoot, is listed as endangered by the Ohio Department of Natural Resources. Gurien designed and built the lower of the two pools with the spadefoot toad in mind.

“The spadefoot have adapted to have a very short breeding period. They get in, they lay their eggs, those eggs mature and they get out within a couple of weeks, so they can use pools that are only wet for a couple of weeks and keep all the other predators out.”

There are some older vernal pools in the Land Lab as well, which are remnants of fish ponds from back when The Ridges was the Athens Lunatic Asylum. When the asylum stopped maintaining the grounds, the ponds dried up and left depressions in the ground that were just the right depth for mini wetlands. It’s possible that the amphibian populations that already existed at these pools could help bolster populations at the newer ones. 

Since the pools were created, they have hosted many macroinvertebrates (aquatic, larval form of insects), red salamanders, green frogs and wood frogs. Gurien is still waiting on the spadefoot toads, though. It could take a few years, but she’s hopeful that someday they’ll return to their previous population levels and can be taken off of the endangered species list for good.   

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