“Old dark sleepy pool...
Quick unexpected frog
Goes plop! Watersplash!”
-Bashō, Japanese Haiku
Vernal ponds are temporary wetlands that provide a vital role in our environment. Although once a common element occurring within our landscapes, most vernal ponds and larger wetlands have been claimed by society. In exchange, these ecological marvels have been replaced by endless miles of road, skyscrapers, parking lots, industrial complexes and millions upon millions of rows of Zea mays. Fortunately, the tide has shifted a bit in recent years and society has begun to show a restored interest in large wetlands and their ecology. As is the case with small, pollinator patches that most everyone can implement regardless of their lot size or budget, small “pocket ponds” can be established within the landscape at a minimal cost and effort. When designed and constructed properly, a vernal pond will look and function just like their naturally occurring counterparts.
A Landscapes Kidneys
Historically, vernal ponds and larger wetlands were formed by the ebb and flow of overflowing rivers, large lakes, and vast oceans. Others were created by natural weather events such as earthquakes, lightning induced fire, and chemical reactions that occurred within the soil. In most cases vernal ponds are shallow, temporary, and are separate from streams and rivers. Because of this, most were drained and filled during the agrarian boom of the late 19th century with advancements in farming techniques and the introduction of mechanized machinery. This backfilling of wetlands continued into modern times as monoculture farming encroached upon countless acres to meet the demands of an ever-growing population that called for more and more food. Larger vernal ponds, because of their size and ability to hold water, were converted into permanent ponds or lakes by government entities and private landowners.
In the continental U.S. alone, we have lost well over 50% of our historical 220 million wetland acres. Healthy wetlands serve as our landscapes “kidneys” by capturing, holding and filtering water. This “slow release” of surface water during heavy rain events allows time for the water to gradually seep into the surface thus recharging the groundwater supplies. In addition, the slow release reduces runoff, lessening soil erosion and further assists in filtering sediments, chemicals and nutrients within the soil. Research has shown that wetlands can trap at least 50% of dissolved phosphates and 70% of dissolved nitrates that are running off nearby lands before they have a chance to enter our nation’s waterways.
Other incentives to establishing vernal ponds within your landscape are that they provide protection from floods by holding excess rainwater during heavy rain events, they sequester soil carbon thus reducing greenhouse gases, they provide habitat for wildlife and assist in the recovery of rare and declining species, and they provide numerous education and recreational opportunities.
Just What is a Vernal Pond?
Vernal ponds, named for the relationship to the vernal or spring equinox, periodically dry up thus never contain fish. This drying up occurs annually; however, most vernal ponds will dry up during late summer and early fall as temperatures climb and frequent rainfall ceases. Because of the firm soil bed underneath and their ability to hold water, heavy rains may fill them at any time of the year even after they have dried up. It is the temporary aspect of these small wetlands that make them so valuable to the fauna that inhabit them. This wet-dry cycle prevents fish from becoming established, thus allowing critical breeding habitat for amphibians, crustaceans, and insects whom are permitted to function and fulfill their role in our ecosystems.
The key to designing and constructing a successful vernal pond is that it not only holds water but that it also dries up once in a while. In general, ninety (90) or more consecutive days of water are needed over the winter and spring months to allow insect and amphibian larvae to develop. A shallow wetland with a limited watershed, constructed in a sunny location is likely to dry up every year and may not provide enough time for salamander and frog larvae to develop. However, a deep wetland with a large watershed, placed in a shady location may never go dry. It is the balancing act of these core components that prove pivotal when designing and constructing these temporary water features.
A key principle that is often repeated by practitioners in the permaculture world is to be amongst your land, actively observing it for a period of 1-2 years before planning any permanent, land or structural features. This period of observation allows ample time to experience multiple weather events, seasonality, and plant phenology. Immediately after purchasing our farm in Marengo, we experienced a 100-year flood event in early spring and a 200-year event during the summer that completely washed out our roadway just before the newly constructed bridge that crossed Whiskey Run. This bridge, and the surrounding land I feel certain were studied, designed and performed by professional architects and development companies contracted by the county of Crawford. This, however, is just one example showing that despite man’s best efforts, in the end, Mother Nature will ALWAYS win!
By observing these events early on, it forced us to pump the brakes and slow our role a bit as our first inclination when we took possession was to immediately begin improving the area that runs alongside the creek. Fortunately, since that first year, we haven’t experienced any further catastrophic rain events (knocking on wood), but with the ever-changing climate, we are now thinking more rational and know that these events will unfortunately become more normal in the coming years.
Ecology & Wildlife Supported
In North America, approximately one-half of all frog and one-third of all salamander species rely on seasonal/temporary wetlands for their development. Wood frog (Lithobates sylvaticus), Spotted salamander (Ambystoma maculatum), and Eastern Spadefoot toad (Scaphiopus holbrookii) larvae are just a few of the amphibians that can successfully mature and emerge from these fishless habitats. In addition, vernal ponds are less likely to contain saprolegnia, a fungus that is detrimental to frog, toad, and salamander eggs and is frequently present in permanent ponds. Vernal ponds also have low numbers of Eastern newts (Notophthalmus viridescens) who prey heavily on other amphibian eggs and larvae.
Waterfowl species such as the Wood duck (Aix sponsa) and Mallards (Anas platyrhynchos) use vernal ponds extensively during their migration, consuming insects, crustaceans, and seeds that inhabit these spaces and are within close proximity. Shorebirds, like the Spotted Sandpiper (Actitis macularius) and Lesser Yellowlegs (Tringa flavipes), search out and feed on exposed mud flats that are created as water levels drop.
Additionally, reptiles such as the Eastern Box turtle (Terrapene carolina carolina) and the Eastern Garter snake (Thamnophis sirtalis sirtalis) also use vernal ponds as feeding stations as they navigate from one area to another. Numerous bat species use vernal ponds as a source of water and feed on the insects that fly over.
Mosquito, Moscato
Concerns about increased mosquito populations are valid when considering setting up a vernal pond but allow me to ease those concerns.
Yes, mosquito larvae may be present in vernal ponds, developing from egg to adult in less than a week’s time during warmer months. Have no fear though! Salamander, dragonfly, and damselfly larvae, along with many other predatory insects species such as the Water strider (Aquarius remiges) and Backswimmer (Notonectidae), all consume large quantities of developing mosquito larvae.
Adult dragonflies and multiple species of swallows patrol the sky just above the water line during the daytime, preying heavily on the adult mosquitoes that dare make an appearance. Bats frequent these same areas during the night, feeding on mosquitoes and other flying insects. With this type of balanced system, one rarely encounters adult mosquitoes near vernal ponds as their populations are kept in check by the vast array of species that utilize them as a source of food.
You have taken the time to plan. You designed and executed your vernal pond perfectly. Now all that is left to do is to pop the cork on your favorite bottle of aged and fermented grapes, pour yourself a glass, sit back and revel in what you have created!