By guest author Jenny Adkins, PWS, MAD Scientist Associates. Learn more about the author below.
- What are vernal pools?
- What makes vernal pools difficult to recognize?
- Which species inhabit vernal pools?
- What makes a vernal pool a unique habitat?
- How to identify a vernal pool during a wetland delineation
What Are Vernal Pools? – Definition and Characteristics
Have you ever heard the ensemble of frogs calling in the early spring, found yourself mesmerized by the quiet fluttering of fairy shrimp below, or felt the freezing cold water as you waded through stillness? Then you, my friend, likely experienced the magic of vernal pools.
Vernal pools, sometimes referred to as “ephemeral pools,” are special wetlands which are often present in woodland depressions and floodplains. These fill with water in the spring, and dry up during the warmer months. They play a critical role in sustaining amphibian and invertebrate populations, many of which are species that are vernal pool obligates and not found elsewhere.
How Vernal Pools Form, and Species They Support – Amphibians, Invertebrates, and More
What makes these wetlands unique can also be their undoing, as they are not always readily recognized in the field, and may be unknowingly impacted by land use changes.
These special ecosystems typically fill with inches to feet of water from snowmelt and rainfall in the spring. Once inundated, they’re readily colonized by breeding amphibians like spring peepers, wood frogs, mole salamanders, newts, aquatic insects, fishing spiders, crustaceans, fingernail clams, and aquatic worms—just to name a few. The temporary nature of these pools deters inhabitation of major predators like fish and larger frog species, making them a relatively safe place to breed for many of these “denizens of the shallow.”
Identifying Vernal Pools During a Wetland Delineation – Field Indicators
When drier, warmer periods ensue, water levels drop via evapotranspiration and infiltration. The myriad of larval species metamorphose and travel to their next destination outside of the pools—or in the case of many invertebrates, take on a dormant form until the following spring. 
What’s left is often a dry depression with darkly stained leaf litter. To the trained eye, there are likely other clues that indicate “wetland.” These may include:
- Water marks (dark staining) on tree trunks
- Presence of clams (family Sphaeriidae) in soil
- Presence of hydrophilic (i.e., water-loving) vegetation, such as buttonbush (Cephalanthus occidentalis) and Brome-like Sedge (Carex bromoides)
Should you be performing a delineation or other ecological survey and notice some of these features, be sure to closely investigate. Many of the indicators of vernal pools are present in the Army Corps of Engineer Regional Supplement methodology as primary and secondary indicators of hydrology, which is often the least obvious characteristic of these wetlands in the drier months.
Tip: Use Ecobot’s built-in reference tools from the USACE Regional Supplements to support your field identifications. Try it out.
Recognizing and properly characterizing these unique habitats will undoubtedly protect populations of vulnerable species, preserving biodiversity and keeping the sounds of spring alive.
Note from Ecobot: Current federal environmental policy excludes protection for the majority of vernal pools. Some state and local governments have laws and programs protecting vernal pools. Learn more about how wetland protections vary by state in the interactive StoryMap, “How does SCOTUS’ Sackett v. EPA Decision Affect You?”
About the Author
Jenny Adkins, PWS, has served as Lead Ecologist at MAD Scientist Associates for over a decade. She is skilled in plant identification, restoration planting plans, and management practices for invasive species control. MAD Scientist Associates has served the state of Ohio since 1998, providing high-quality wetland and ecological consulting services to clients in the public and private sectors. MAD frequently shares their expertise on vernal pools at educational events across Ohio.
