Vernal Pool

​by Gerald Rowan

Credit - Western PA Conservancy

​It was one of those rare days that happen in the changing of the seasons. The temperature was in the fifties, the sun spring warm on the skin, and the air had a lingering chill left over from a particularly hard winter. In late April, the sun was noticeably high above the horizon and brilliant in a clear blue sky. A cloudless sky—the product of a Canadian high pressure dome that had warmed a few degrees on its way south.
 
I walked a trail along Jordan Creek, in Lehigh County—a broad, flat creek still full of snowmelt. Ahead of me, a young couple walked with a black lab, clearly the family pet. They were absorbed in the day, playing with their dog, and enjoying each other. They would throw a stick ahead of them and the lab would run to retrieve it.  
 
One of their throws was directed to and landed in a small vernal pool near the trail. The lab enthusiastically bounced down the trail and leaped into the air, landing in the small pool. The lab landing in the small vernal pool set off an explosion of a pair of mallards attempting to flee what they perceived as sudden death. The dog paddled around in the pool for a time, attempting to grip the stick that was thrown. The dog climbed out of the pool, shook himself vigorously, and ran back to the couple, with the stick in his mouth.
 
All innocent enough? Not quite. The pool contained thousands of frog and toad eggs just beginning to hatch. The pair of mallards had a nest in the tall grasses and bulrushes growing along the bank of the small pool. No foul, no harm? I walked to the pool to see. In either entering or leaving the pool, the dog had charged through the ducks’ nest, destroying 3 of the clutch of 7 eggs laid there.
 
The dog probably killed a number of small tadpoles or smashed tadpole eggs laid there. This was a typical vernal pool. A shallow depression filled with spring meltwater, and an environment necessary for frogs and toads to reproduce. They instinctually seek out these quiet pools—places that, since they dry out in the late spring and summer, don’t harbor any predators that might eat either their eggs or hatching tadpoles.
 
Still no foul, no harm? In thrashing around in the small pool, the lab stirred up a cloud of mud and silt. He climbed out of the pool, shook himself, and ran off down the trail hoping to get his stick tossed again. As the pool settled, a film of silt settled over the unhatched eggs. The forming tadpoles would normally draw oxygen from the water in the pool. The silt would choke them, causing a high mortality rate.
 
A stick thrown innocently enough had caused a microcatastrophe. The mallards would not return to the nest due to the destroyed eggs. The smell would surely attract raccoons or coyotes that night. They may or may not build a new nest this season. Hundreds and hundreds of frogs or toads would die in their egg cases without a chance—smothered by the fine silt that had settled over them.
 
I’m not faulting the couple who were walking their dog. I’m certainly not faulting their dog. The fault lies in not having an intimate understanding of nature. That same walk several weeks later would have had no adverse impact on the toads, frogs, or ducks. The mother mallard would have led her ducklings to the safety of the stream shortly after they were hatched. The tadpoles would have absorbed their tails, grown legs and lungs, and hopped away to the protection of some damp glade. Untold thousands of insects that would have been eaten by the young frogs and would have become part of the food chain. Some of those frogs and toads would have been food for wading birds, raccoons, and coyotes. Yet others would have wintered over to lay eggs the next spring in the same vernal pool they had hatched from. Fewer hikers on that trail would have had the annoyance of mosquito bites.
 
Understanding is important for several reasons. Knowing on a number of different levels allows for an enjoyment on a number of levels. Knowing nature generates a respect for nature and its complexity. Knowing nature allows a hiker to be in sync with nature. Knowing also increases the enjoyment of nature.
 
I grew up loving the woods and trails—everything about nature. This love has given me a strong desire to protect the environment. The challenge is how to spread this love and concern to others. It is my conclusion that the best way to protect wild Pennsylvania is to get people to love it. The more that people experience nature personally and understand it more fully, the more deeply they will come to love it. Nature operates as an interactive, interdependent system. There is an awe that settles over the hiker when he or she gets tuned into the system. There is a spirituality to be experienced in nature understood on this level.