Although the best choice would be to not destroy our environment to begin with, it comes too late for the vernal pool. Vernal pools are seasonally flooded pockets of wetland that serve as breeding grounds for both obligate and facultative species. Most salamanders, toads and tree frogs rely on these seasonal pools for breeding because of the freedom they offer from predatory fish. Unfortunately, estimates are that >90% of all these habitats have been destroyed. Whatever small attempt we suburbanites make is worthwhile.
The Eastern part refers to pools found in woodlands east of the Rockies, vernal pools typical of Californai are a world unto themselves.
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Step 1: What We'll Need
A shallow wide container, ie. A cement mixing tub, a child's wading pool, etc. I chose a cement mixing tub based on longevity, I've used them for at least five years for hydroponics with no UV degradation.
Some small pavers
Step 2: Find a Place
Start by locating a shady place for your pool, vernal pools are heterotrophic with the leaf mould feeding the ecosystem, shade also moderates temperature swings.
Lay out your container and sprinkle flour around it to mark where to dig. Excavated until the container sits in the hole just a little proud of the ground level, we want to avoid runoff from the lawn (with it's associated contaminates) from entering the pool. Level the pool in the hole and backfill with soil, firm the soil around the container being sure to keep an eye on the level.
Setting up the pool
Use the pavers to build steps out of the pool, we aren't building a toad trap here, and without the steps they won't be able to get out either as adults or juveniles. Now sprinkle an inch thick layer of leaf mould on the bottom, if you can collect this legally from a known pool, great, if not, just from under a tree is fine. Don't worry if it floats it will sink after a few days.
Step 3: Dress It Up
Here's the treasure I found, as I was digging the hole I found these rocks buried there by a prior owner and used them to border the pool. My wife, the landscape designer said Oh, that's, umm, nice ;-).
If you absolutely must add plants, go ahead but locate the pool in a spot where it gets 6+ hours of sun a day or the plants won't do well. Eventually ground covers will be planted around the pool.
Step 4: Maintainance
Once a month, throw in part of a mosquito dunk. They are very specific to dipterans and won't affect the ecosystem unduly.
If you live where it freezes allow the pool to dry up during the late summer and refill with spring melt, in the south the pool can be kept filled year round.
Be sure to keep leaves from filling the pool completely and most importantly NEVER ADD FISH.
Step 5: In Conclusion
Adding a small fish free pool to the average suburban yard will do precious little to mitigate the impact of suburban sprawl, but if you're already a part of the problem, it offers a small means to increase the biodiversity of your backyard and a respite for those animals displaced from their traditional breeding grounds.
Finally here's a few pictures of creatures that have frequented one of my backyard vernal ponds.