Pennsylvania Wetlands: Vernal Pools

Overview

Vernal pools are shallow depressions on the surface of the land that fill with snow melt and rainwater. The majority are seasonal in nature and only appear in the spring and fall months. These temporary wetlands are very important to the lifecycle of amphibians, insects, and unique crustaceans that lie dormant most of the year. Protecting and conserving vernal pools is crucial for maintaining biodiversity and preserving delicate species.

Hydrology

Vernal pools are typically closed systems and fill through precipitation via runoff from snowmelt and rainfall. Some interact with the water table and fill up with water when the water table is at its peak during rainy seasons. The pools cycle through processes of water accumulation, limited retention, and loss through infiltration and evaporation. Given the temporary nature of vernal pools they tend to be low in nutrients and be slightly more acidic due to the decomposition of organic materials like mosses, leaves, and wood. Water chemical composition can be influenced by local geology, seasonal fluctuations, and localized land uses.

Ecology

Plant communities in vernal pools vary greatly and are dependent on the ecoregion an individual vernal pool is found.

Many vernal pools are void of trees but are typically surrounded by them and this offers shade to keep water temperatures down. Moisture tolerant and wetland loving shrubs may grow throughout vernal pool depressions. Shrubs like buttonbush, willows, dogwoods, and even moisture tolerant upland blueberry bushes are often found in Pennsylvania vernal pools. Tree and shrub trunks and downed woody debris is often densely covered with moss. There are also several herbaceous plants that thrive in vernal pools, typical species included bulrushes, wool-grass, sedges, ferns, and occasionally skunk cabbage.

Vernal pools are vital to the lifecycle of various amphibian and invertebrate species, provide temporary homes for reptile species, and an easily accessible water source for mammals and birds.

• Amphibians that rely on vernal pools for their lifecycle include mole salamanders, such as: Spotted, Jeferson’s, and Marbleds; newts, like the Red-spotted; many frog species, indicator species being Wood, Spadefoots, and Spring Peepers.

Marbled Salamander Photo: PA Fish and Boat Commission

Red Eft, Red-spotted Newt Photo: Brad Kunsman

• Many invertebrates utilize vernal pools as water is needed early in their lifecycles, these include various insects and crustaceans. A unique and notable species indicative of vernal pools is the Fairy Shrimp.

Fairy Shrimp Photo: Chesapeake Bay Program

• Reptiles will take advantage of habitat provided by vernal pools. Turtle species, such as: Painted, Spotted, Wood, Box, and Snapping; snakes, like Garter, Dekay’s (Brown), Ring-Necks, and Green will be seen passing trough to take advantage of abundant water and food resources.

Garter Snake Photo: Brad Kunsman

Visit

Visit them before they’re gone for the summer.

• Western Pennsylvania: Wolf Creek Narrows Natural Area - Interactive Preserve Map
• Central Pennsylvania: Kings Gap State Park - Kings Gap State Park Guide
• Eastern Pennsylvania: Minsi Lake Vernal Pool Preserve

Reference

Various. "Vernal Pool Ecology." Pennsylvania Natural Heritage Program, Pennsylvania Department of Conservation and Natural Resources, Pennsylvania Game Commission, Pennsylvania Fish and Boat, Western Pennsylvania Conservancy, www.naturalheritage.state.pa.us/VernalPool_Ecology.aspx. Accessed 15 Apr. 2024.