Vernal Pools—an Overlooked Natural Resource
(Conservation Currents, Northern Virginia Soil and Water Conservation District)
Vernal pools are a vital natural resource. They offer many important benefits including serving as a breeding site for several amphibian species as well as a habitat for rare and endangered plant species. Vernal pools also filter the rainwater that ultimately drains into our water supply. Unfortunately, they are frequently overlooked.
Vernal pools by definition are small, isolated wetlands that retain water on a seasonal basis. Sometimes referred to as “spring pools,” vernal pools fill up with melting snow and early rains during spring, then usually dry up by mid to late summer depending on the pool depth, permeability of the soil, and amount of rainfall. Some relatively deep pools may remain flooded for a few years but become completely dry in seasons with very low rainfall. Found on every continent except Antarctica, vernal pools come in sizes ranging from several square feet to several acres. The sites where they occur also vary greatly and include isolated depressions in the woods, kettle holes, and gravel pits.
Nearly 50 percent of the amphibians in the U.S. breed primarily in vernal pools because the pools are temporary and cannot support fish, the major predator to amphibian larvae.2 Some species like the wood frog and the spotted salamander are obligate species meaning they will not breed in any body of water other than a vernal pool.
Vernal pools also support several species of insects including predacious diving beetles and crawling water beetles. These insects, along with dragonfly nymphs and the larvae of several salamander species, are voracious predators of mosquito larvae referred to as “wigglers.” Certain species of adult frogs, toads and salamanders feed on adult mosquitoes as well. The many predators that reside at vernal pools make them a hostile environment for mosquitoes as compared to the many man-made mosquito breeding sites such as bird baths, clogged gutters, and swimming pools that are not properly winterized.
We need to recognize and preserve vernal pools for the vital and dynamic natural resources that they are. For more information, try these Internet links: