Vernal Pools
Zach Nemec, Coastal Outreach Specialist, works in the Delaware River Basin, in the Philadelphia area. Zach works with partners and organizations to advance individual and public understanding of the importance of vernal pools. This photo shows Zach and a group of master watershed stewards conducting a site assessment at one vernal pool located in Delaware County.
About Vernal Pools
Vernal pools are a type of seasonal depressional wetland that are typically independent of a dedicated water source such as a stream or spring. These pools are instead reliant on seasonal snow melt and rain fall, which sustain them in the winter and spring. When the water evaporates or replenishes the underground aquifer, the vernal pool dries up.
A Safe Haven
Vernal pools are a temporary yet highly productive ecosystem and a safe haven for toads, frogs, salamanders, and some reptiles which rely on them for shelter, food, and as a place to mate, breed, and lay their eggs. Without vernal pools, some species may struggle to maintain their populations, and some might cease to exist.
For some amphibians, referred to as indicator species, access to vernal pools is integral to their reproductive success and survival. The Wood Frog or Marbled Salamander, both indicator species, spend much of their lives in woodland habitats or underground. Once a year they emerge and seek out vernal pools where they will find a mate, breed, and lay their eggs. Indicator amphibian species will oftentimes return to the same vernal pool where they were born; thus, the conservation of vernal pools is vital to the success of indicator species.
Yet other amphibians, referred to as facultative species, do not rely exclusively on vernal pools for their reproductive success and survival. Facultative species, like the Green Frog and Red-spotted Newt, mate, breed, and lay their eggs in streams, rivers, lakes, reservoirs, ponds, marshes, and swamps, relying on vernal pools for habitat.
Benefits of Vernal Pools
In addition to their importance to wildlife, vernal pools and other wetlands are important to humans. Vernal pools help reduce the impacts of heavy rain events in developed areas. They reduce flooding and erosion by slowing and absorbing excess rain or stormwater, and their sponge-like nature slowly filters out pollutants while replenishing underground aquifers. Vernal pools and other wetlands also help reduce the impacts of climate change by capturing and storing carbon dioxide.
Vernal pools and wetlands also contribute to our mental and physical well-being by offering a tranquil setting to observe and listen to the eloquent calls and sounds of wildlife that gathers in these dynamic ecosystems.
Threats to Vernal Pools
Despite their value and state regulatory protections, wetlands and vernal pools in Pennsylvania are at risk. Development, climate change, and invasive species are major threats to wetlands, particularly to vernal pools due to their small size and seasonality.
Land development
Clearing and replacing forested land with impervious surfaces can result in increased flow of stormwater runoff leading to a vernal pool. This increased flow carries excess sediment and pollutants, which is often more than the pools can filter and absorb. Land development can also mean a disruption or even blockage of the migratory pathways that amphibians and other wildlife depend on to reach the vernal pools, where they mate and reproduce.
Environmental Changes
Temperature shifts and annual precipitation fluctuations can impact the amount and duration of available water in vernal pools, which can disrupt amphibian life cycles. One example of this might be the failure of amphibians to hatch due to the eggs drying out during periods of drought. Changing conditions can also alter mating habits, breeding periods, and the distribution of species.
Environmental changes are also having an impact on species habits and distribution. For example, the mating calls of some amphibians may now be heard earlier, or at a time other than their typical breeding season. Some non-indicator species may react to environmental changes by moving to a new area, thus expanding or altering their current range.
Invasive Species
Invasive species can alter both the vernal pool ecosystem and the native species living there. For example, if an aquatic invasive plant is introduced to a vernal pool, it can easily take over and become the dominant or sole vegetation. This not only impairs the quality of the ecosystem, but it can also result in the loss of the vernal pool entirely.
For more information about vernal pools, contact Zach Nemec, Coastal Outreach Specialist.
Zach Nemec
Coastal Outreach Specialist (Delaware River Basin, Philadelphia region)
814-898-6887
Zach Nemec, Coastal Outreach Specialist working in the Delaware River Basin, joined Pennsylvania Sea Grant in July 2021. He is responsible for planning, developing, implementing, and evaluating regional outreach programs with a focus on watershed restoration and community resiliency in southeastern Pennsylvania. Zach also connects communities with local stakeholders to better understand and grow their resilience, economies, and well-being. Read Zach’s bio.
