In January of 2021 the Alliance coordinated the installation of a wetland habitat enhancement project in Charles County, Maryland. Through a series of four vernal pools the project has created habitat for various amphibians and reptiles in the surrounding area. Vernal pools are seasonal, or ephemeral pools that form from rain or winter snow melt. They often charge with water during the late winter and spring, and then dry throughout the summer and into the fall (Johnson & Hayslette, 2021). Habitats such as vernal pools are ancient, naturally occurring, and unfortunately, now rare. Climate change, deforestation, and development pressures have caused many ecosystems and animal species to rapidly lose their habitat and vegetation which they need for survival. It is our hope that by recreating these naturally occurring habitats, we can give amphibians and reptiles the extra boost they need to live, reproduce, and thrive amongst a developing Chesapeake Bay watershed.


Vernal Pool Inhabitants

Vernal pools exist around the world, but in the Chesapeake Bay region alone a plethora of species require these ecosystems for their survival. Salamander species including Spotted salamander (Ambystoma maculatum), Marbled salamander (Ambystoma opacum), Eastern tiger salamander (Ambystoma tigrinum), Red salamander (Pseudotriton ruber), Jefferson salamander (Ambystoma jeffersonianum), and Four-toed salamander (Hemidactylium scutatum) are all considered obligate amphibians meaning that they require vernal pools for their life cycles. Since vernal pools drain throughout the year, they prevent fish from establishing and allow salamanders to breed in the pools without predators. The Eastern Tiger salamander, which happens to be one of the largest salamander species in North America is also endangered. Other native amphibians include frogs such as Wood frog (Lithobates sylvaticus), Northern Spring Peeper frog (Pseudacris crucifer), Green Treefrog (Hyla cinerea), American Bullfrog (Lithobates catesbeianus), Northern Cricket Frog (Acris crepitans), and Southern Leopard Frog (Lithobates sphenocephalus). Spotted turtles (Clemmys guttata), American Toad (Anaxyrus americanus), and Eastern Newt (Notophthalmus viridescens) also inhabit vernal pools along with invertebrates including insects, crustaceans, fairy shrimp, and daphnia. Vernal pools vary in size; while some can be 2 acres others are only a couple hundred square feet while still being a dynamic, ecologically diverse habitat (Johnson & Hayslette, 2021).

A female spotted salamander with her eggs below the surface of a vernal pool in Virginia. (Photo credit: Steven David Johnson, Professor of Visual and Communication Arts at Eastern Mennonite University).

Vernal pools are highly variable environments. They exist throughout the Chesapeake Bay region behind coastal beaches, within floodplain depressions, and on mountaintops (Johnson & Hayslette, 2021). It’s this same variability that allows them to connect terrestrial and aquatic habitats which hosts rare plant and animal species (Johnson & Hayslette, 2021). Like many places, developmental pressures in Charles County are leading to fragmentation of vital habitats. Habitat fragmentation occurs when infrastructure development inhibits species from traveling from one habitat to another. Vernal pools help to combat this threat by acting as a bridge or corridor to connect habitats which are otherwise separated. Spotted turtles, who spend their lives traveling between various wetlands to feed, reproduce, and thermoregulate, frequently utilize these ephemeral habitats. Vernal pools, which act as a seasonal wetland provide adequate habitat for the turtles to reside in before migrating to the next wetland. You can also find them basking in the sunshine on the logs and vegetation within the vernal pools. While spotted turtles along with lizards, and snakes are classified as reptiles, and salamanders, frogs, and toads are classified as amphibians, all are considered herptiles, more commonly known as herps.

Salamanders and newts use vernal pools in a similar fashion. As they emerge from underground burrows or from under logs in early spring, they migrate to vernal pools to breed. Females lay their eggs in clusters below the surface, attached to stems or leaf litter in the pools (Johnson & Hayslette, 2021). After the embryos hatch, they spend roughly 3 months as larvae, metamorphosize, and then leave the pools for terrestrial land (Johnson & Hayslette, 2021). Other species such as Wood frogs freeze within the vernal pools during the cold winter months. Because of this they are often the first species to inhabit the pools in early spring. As Wood frog tadpoles hatch they feed on a nearby food source, often salamander eggs. Although fish are not a threat to vernal pool species, life in this wetland still poses challenges for many species.

Although fish are not a threat to vernal pool species, life in these ephemeral wetlands still pose many threats. Here eastern newts are feasting on a nearby food source, spotted salamander eggs. (Photo credit: Steven David Johnson, Professor of Visual and Communication Arts at Eastern Mennonite University).

Other salamander species such as the Four-toed reside in the moosy, vegetated wetlands surrounding the vernal pool, rather than the water itself. While frogs and salamanders may be the more widely known organisms associated with vernal pools, invertebrates including insects, larvae, daphnia, and hydra contribute to these complex habitats as well. Some insect larvae, like the dragonfly, spend the beginning of their lives underwater before leaving vernal pools (Johnson & Hayslette, 2021). One crustacean in particular, the fairy shrimp (Eubranchipus vernalis) has developed the ability to travel from one remote vernal pool to another. As ducks and other waterfowl eat female shrimp, the eggs of the shrimp are able to survive in the duck’s digestive tracts. As the ducks fly to far off pools the fairly shrimp are excreted, allowing them to reproduce and contribute to the exchange of new genetic material.

Project Installation

Vernal pool hydrology varies based upon location. While some recharge through rainwater, and snowmelt, others fluctuate depending upon nearby groundwater, aquifers, and floodplain topography. Like all restoration projects, it’s essential for the success of the project that the topography, hydrology, ecology, and nearby features are taken into consideration during the design process. Other naturally occurring vernal pools exist on the property where installation took place, making it the ideal ecosystem to expand this specific type of habitat. During the project a portion of existing upland drainage was converted into a series of four, shallow, interconnected basins or vernal pools. As the shallow pools were dug each were packed with a clay liner to encourage water retention. The pools were connected through a series of weirs. The weirs enable water to retain in each pool before overflowing into the adjacent pool, providing a similar function to a dam. Although water depth may vary based upon precipitation, generally it should not exceed two feet. During construction geotextile fabric was placed under the weir to hold the materials in place. A wood beam, also referred to as a level spreader was placed across the weir, and secured with rebar anchors, anchoring the level spreader to the weir on both sides, allowing it to stay in place during rain events. A combination of various rocks including class 1 rip rap, and mixed chinking stone was then placed on top of the geotextile fabric to create the foundation of the weir. The toe log, used from a tree cut down on site, was placed parallel to the level spreader, and connects the weir to the adjoining pool. While designers worked to keep as many trees in place as possible, inevitably some were cut down for site access. Reusing materials onsite such as trees, branches, and soil as needed is always considered when the plans are being designed. Large logs from removed trees were placed within each pool to function as a basking log for spotted turtles to sun themselves, and inhibit thermoregulation. After construction soil stabilization matting was placed on disturbed soil to keep it in place. Native grass seeds were spread along the banks, followed by a layer of mulch. This vegetation will grow over the next few months as the weather warms and will further stabilize the soil around the pools.

The lowermost vernal pool #4 of 4 retaining water after heavy rains. (Photo credit: Mark Burchick, Environmental Systems Analysis, Inc).

Mixed stone was installed by our partners on the inside of the pool, along the face of the notch. Fabric was cut to expose the 6”x 6” level spreader. The toe log was installed parallel to the level spreader. Class 1 rip-rap was placed on top of the fabric to provide the foundation of the weir outfall. (Photo credit: Mark Burchick, Environmental Systems Analysis, Inc).

Threats to Vernal Pools

While vernal pools play an essential role in the life cycles of numerous species their existence faces major threats from climate change, land development, and deforestation. As climate change alters the traditional seasonality and duration of precipitation, the pools themselves are drastically changing (Johnson & Hayslette, 2021). Variations in precipitation are causing the pools to become dry in late winter and fully charged in the summer (Johnson & Hayslette, 2021). This in turn alters the way in which herps are able to utilize these pools. As salamanders emerge in early spring from their burrows and migrate to the nearby vernal pools, they find them dry; they no longer have the desired habitat to lay their eggs. If herps can no longer predict when their breeding habitats will be available, this raises a lot of questions as to how amphibian and reptile populations will be affected in the long term.

To better understand how human actions are affecting vernal pools and to preserve existing ones, we can protect wetlands and forest, and monitor how climate change is affecting vernal pool environments. Vernal pools and forests work together to create a rich, diverse, interconnected environment that can host numerous species while providing food and breeding habitat. Most vernal pool species rely on the terrestrial forests surrounding vernal pools as habitat after breeding season. Additionally, forests shade the pools preventing them from becoming too hot, or drying up all together. Leaf litter from the trees and soil composition enhance the wetland habitat. Without these surrounding forests vernal pools will lose the ability to sustain a diverse range of plants and animals.

The uppermost vernal pool #1 of 4 completed, stabilized, and holding water. A basking log was placed in the middle of the pool for spotted turtles to sun themselves. (Photo credit: Mark Burchick, Environmental Systems Analysis, Inc).

Only twenty five years ago even the top natural resource experts in the mid-Atlantic region knew very little about vernal pools. Today, the term and concept is more widely understood in the field, but there is little awareness of these habitats amongst the general public. This is an issue considering a majority of vernal pools exist on private land, and landowners are unaware of their significance. If we can better educate individuals, and communities on the copious benefits that these ancient habitats have on the overall ecosystem, we stand a much better chance at being able to preserve them.

While vernal pools face countless threats looking into the future, the sheer abundance that these habitats have to offer makes them something worth fighting for. Developments in technology through media and photography have made it easier than ever to document the captivating transformations that occur within these pools. While we all may not be able to trek deep into the woods in search of vernal pools, underwater images enable the general public to connect to these otherwise elusive places. With the intense threats naturally-occurring ecosystems are facing, now more so than ever is the time to use our resources to provide threatened habitats the extra support they need to self sustain themselves. The vernal pools constructed in Charles County, MD will continue to be monitored to ensure that they are not only self-sustaining, but will thrive, hosting a plethora of rare species, crucial to an overall healthy ecosystem.

Work Cited

Johnson, S. D., & Hayslett, M. S. (2021). Vernal Pools Documenting Life in Temporary Ponds. North American Nature Photography Association