Saturday, June 15, 2013

Garden Pond a Study in Ecology

One of the best things we have done in the garden in years is add a pond. We have actually been working in this direction for about five years. Originally, we removed a tree. Then we removed the stump, and were left with a large hole in the ground. We decided to make it larger rather than fill it up, and eventually we wound up with a pond.

Watching our pond develop its own little ecosystem has been both fun and instructive. We began in February, as soon as the weather began giving us a few warm, bright days, by adding a commercial bacterial starter culture to seed the pond with beneficial bacteria. This technique is much like adding a bacterial product to your compost, or putting nitrogen-fixing bacteria into a row with bean seeds. You are giving Nature a head start on ecosystem development. Left to its own devices, the pond will acquire these essential micro-organisms. They will drift in on air currents, on the feet and feathers of birds and on the bodies of insects that happen to visit the pond. Adding the commercial product simply speeds up this process.

Within a week, the pond became cloudy, teeming with microscopic life. Besides the added bacteria, the water was full of microscopic algae that tinted everything greenish brown. During the first month, the water was alternately cloudy and clear, as vast numbers of organisms grew and died, each subtly altering the water conditions and contributing to the pond's ecology.

By the end of March, we had added some marginal plants. Marsh marigold (Caltha palustris) was the first flowering plant to go into the new pond. Our plant came originally from a friend in Michigan, and it has lived in various ponds and containers for almost 25 years. Next we added Iris virginica, the native blue flag. Our plants are tetraploid ones, originally from Barry Glick at Sunshine Farm and Gardens. During early spring, we added several other species that like wet feet, including cinnamon and royal ferns (Osmunda cinnamonea, and O. regalis), dwarf cattail (Typha minima), blue moneywort (Lindernia grandiflora) and four-leaf-clover (Marsilea quadrifolia).

This week, we added our first water lily, Nymphaea aquatica 'Charley's Choice.' This cultivar remains under three feet in diameter, making it a good choice for a small pond such as ours. The pink and white blossoms open during the daylight hours.

We have also added fish. While we would prefer to have native Tennessee fishes in the pond, it is illegal to maintain native fish species in captivity without a permit, so we have opted for goldfish and livebearers from Aquarium Knoxville, our local pond supply store. The goldfish is a Shubunkin type, bred for coloration that shows up well when the fish is observed from above. We have only one spcecimen, whom we have named "Ichiban." With 1200 gallons of water, the pond can support only a limited number of fish. Because goldfish can reproduce prodigiously after a couple of years in the pond, we decided to keep only one. If we added more and happened to end up with a pair, we would need to periodically net out many hundreds of offspring. Finding a home for unwanted fishes is even harder than trying to place a litter of kittens. And unfortunately, there is no way to determine the gender of small goldfish. Ichiban, therefore, will remain celibate.

To help Ichiban with mosquito control (the primary purpose of having pond fish in the first place) we added a couple of dozen small mixed livebearers from Aquarium. They sell these to feed larger fish, and they are therefore quite cheap. Further, they will bear offspring about every three weeks, ensuring a continuously growing population all season long. Livebearers are also not winter hardy in Tennessee's climate, sparing us the need to cull them at season's end.

While it is true that the decisions Jerry and I make regarding the pond's inhabitants have an effect on its development, many of its most interesting denizens arrived on their own. Certainly this was the case with the micro-organisms that were not in the bottle of bacterial starter. In terms of diversity of species, one look with a microscope will reveal that this part of the pond's ecology is the hands-down leader. Next came the insects. Even while the nights were still a bit frosty, midges arrived in hordes, and their aquatic larvae were soon teeming on the bottom of the pond, hiding themselves in little tubes they construct from debris. Next to show up were the water striders, accomplished hunters who sit delicately poised on the surface to await another insect's misfortune. As soon as anything alive falls into the water, the striders head for it, hoping to make a meal of a struggling fly or moth. A little later, backswimmers arrived. They also hunt for prey at the water surface, but with a different strategy. The backswimmer lies upside down (hence the name) just beneath the surface, rather than floating supported by surface tension. This appears to confer the advantage of speed, as the backswimmers can move faster than water striders can. The last insect arrivals have been the elegant dragonflies and damselflies. The blue dasher (Pachydiplax longipennis) has been the most common species so far. Males spend most of their time defending territories from each other, awaiting the arrival of a female with which to mate. I have observed the females depositing eggs within a few moments after a mating flight. Dragonfly larvae are aquatic predators, while adults hunt other insects on the wing. We have seen a damselfly, probably an Enallagma species, together with two other dragonflies, one is a member of the darner family, the other is a common whitetail, Plathemis lydia. The latter is unmistakable, with its powder white abdomen and boldly marked wings. Both of these dragonflies have been occasional visitors, whereas the dashers seem to have taken up residence.

We also have at least two species of frogs. One is the common leopard frog. We also have a smaller chorus frog and possibly a tree frog species. All the frogs found the pond on their own, possibly moving from one of the small creeks that surround the base of our ridge.

Within only a few months, our pond has gone from being a hole in the ground to a thriving community that never fails to provide entertainment and insight.

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