How to Make a Pond

On a Monday morning in August 1883, a volcano erupted on the Pacific island of Krakatau, smothering its flora and fauna under a blanket of sulfurous ash more than 100 feet thick in some places. Krakatau had been literally sterilized; what remained of the island was about as dead as a place on this earth can get. By the following year, however, visiting naturalists began to observe the return of life to the island, starting with a couple of spiders and blades of grass. By 1886, 34 plant species were counted, including blue-green algae, mosses and some ferns; by 1897, there were 61. A few years later, the island was once again enveloped in life.

I thought about Krakatau in the spring as I watched life colonize my new pond—determinedly, improbably, astonishingly. Five months before, there had been only a raw, sterile-looking crater out here in the woods behind my house, a kind of scaled-down, concave Krakatau. It, too, had had its origins in violence, which often seems to attend the birth of ponds made by animals like us. My own began with the howl of chain saws, the screech of a chipper big enough to devour trees thick as thighs, and then the gut-tightening roar of heavy earth-moving machinery. For two days in October, my house shook, as a mammoth front-end loader, working together with a bulldozer in a kind of rough, elephantine dance, plunged its toothed bucket into the earth’s surface, tearing first through the thin, living skin of black humus and then deep into progressively lighter layers of subsoil to a depth of 12 feet, where life is all but undetectable. When they were done, Al and Ken and their machines had rendered this landscape almost unrecognizable; it was as though the revisionary work of a glacier had been compressed into the space of 16 hours.

Or perhaps more accurately, as if the blast effects of a bomb dropped on my backyard had been drawn out over two days. For what I now gazed out on was a deep, reddish-brown gash in the earth’s crust that looked as though it might never heal. I felt abashed by the destructiveness of the process, and no small uncertainty. It was hard to imagine that this hole, packed with sterile clay, would ever fill with water, much less come to support life. As a gardener, I’m ordinarily not too shy about making changes in the land, but by the time the excavators had herded their steel beasts off the property, I wondered if this time I might have gone too far.

What had ever incited me to this terrestrial revolution? I suspect that, sooner or later, all gardeners wish for water in their gardens. A garden is a world in miniature, hospitable in the extreme, and one that lacks water—if only a small pool or a fountain, or even the mere implication of water that a weeping willow can convey—will always feel incomplete. As for this particular landscape, its genius loci seemed to demand something more ambitious than a pool or fountain. I live on an obstreperous piece of land, a hillside so rocky and restless that all of its half-dozen tenants over the past two and a half centuries seem to have shared the urge to somehow moderate it, clearing small meadows wherever the slope seemed tolerable and carving habitable terraces for the house and its outbuildings, as well as for the garden. Though none of us would be likely to think of it in these terms, we’ve all been laboring to improve the feng-shui of this place, which a geomancer would say suffers from an excess of yang land forms. Part of the reason I dug a pond was to establish one tranquil, perfectly level plane on the property, a caesura in the midst of so much roiling ground. Water in vast quantities slides and tumbles through here each spring, every molecule seemingly in a great hurry to find its way to the Housatonic River, two miles to the west. I hoped with my pond merely to make it pause a while.

As it turned out, I was the one forced to pause, at least for a season. For though my pond now overflows its spillway, at this time last year I was watching its surface sink as steadily and perceptibly as coffee through a filter. By August, a little rowboat I’d bought in an incomprehensible act of hubris sat beached on the lip of an empty sump. As I walked the hillside, squinting to picture the flow of imaginary ground water over it, straining to think like water, it became clear that there were more direct routes to the river than through my pond site. Several acres of the watershed descended through a meadow and into a gully that passed a few dozen feet to the south of my pond, on its way to a culvert that took it across a road and into a marsh. I called my excavator, imploring him to come back with his smallest bulldozer and reroute the gully into the pond. Al got around to it in late October. In November, over two days of biblical-quality rainfall, the pond filled completely.

And with the water came life, all in the space of a few busy spring weeks. Early in March, even before the ice had entirely cleared, chartreuse algae gathered into cirrus clouds and began to drift through the cold water. One evening toward the end of the month, the digital love song of spring peepers issued from the pond for the first time; it hasn’t let up since, and in April their high-pitched chorus was joined by the twanging of green frogs and the bass notes of bulls. From the sound of it, an awful lot of frog sex was being had in my pond, the proof coming in the form of the clear jellies studded with black eggs that began appearing along the shore in May. That same month, water striders, fish spiders and whirligig beetles began plying the pond’s surface, while back swimmers and water boatmen worked its depths, cruising for meals of insect larvae and plankton. By then, aquatic grasses bearded the pond’s shoreline and emergent weeds pierced the surface in the shallows, providing a convenient mooring for the egg sacs of dragonflies and legions of other egg layers I don’t yet know by name. Already the once-sterile pond bottom was cloaked with a thick brown layer of burping, excrementitious decay.

Life has enveloped my pond in a process so swift and amazing as to make me understand how people could have clung to a belief in spontaneous generation well into the last century. Many of these newly arrived species live in freshwater ponds and nowhere else. So how in the world did they find their way to my pond, this isolated and all-but-dead hole in the ground, this backyard Krakatau? How am I to account for the appearance out of thin air of these frogs and algae, those wingless water striders and that thicket of submarine flora? A 17th-century scientist named van Helmont once offered a formula for making mice out of old underwear; I could as easily offer one for making frogs and algae with a front-end loader and two days of rain.

According to E. O. Wilson, the first pioneers to make landfall in Krakatau were what scientists call “aeolian plankton”—the seeds, spores, eggs and insects that are borne constantly on the wind, sometimes for hundreds of miles. No doubt my pond has been visited by the local aeolian plankton, which in these parts might carry algae spores, diatoms and the seedy shrapnel of exploded cattails, as well as any aquatic spider who chanced to raise her thread of silk to the air in a pond upwind of here. Then there are the waterfowl, who carry on their feet and in their gut exotic cargoes of seed and egg and spore. On March 9, a pair of mallards skidded in for a look-see; my cat quickly persuaded them to move on, but who knows what hitchhikers they let off before scrambling back into the air? Chances are, fish eggs are already incubating among the reeds.

Henry David Thoreau, whose own research helped disabuse his contemporaries of the common belief that oak trees could spontaneously generate in the ashes of burned-down pine forests (he demonstrated how acorns buried by squirrels accounted for that particular miracle), once described in his journal a visit to the site of a pond he had surveyed in Sleepy Hollow cemetery. The pond had been dug only the year before, and Thoreau marveled at the speed with which it had been colonized by aquatic plants—at the flowering of so much new life hard by so much death. “You will no sooner have got your pond dug,” he wrote, “than nature will begin to stock it.”

And not just stock it, either, but choreograph it too, for each of the myriad life forms taking up residence in my pond this spring seems to have instantly assumed its proper role in an intricate dance of predator and prey, parasite and host, everybody climbing smartly aboard the food chain. The frogs have found their meal of diving water beetles, the beetles are chubby with tadpoles, the tadpoles have had their fill of water fleas and rotifers who in turn have fattened up on the single-celled diatoms that get by on little more than carbon dioxide, nitrogen and phosphorus (washed in by rain) and the rays of springtime sunlight. To the frogs, taking in the show from the pond’s edge, the whole thing must seem like a pretty marvelous contraption for the creation of frog flesh. The arrival of raptors and snakes will overthrow this frogocentrism soon enough, however.

Already the pond has divided and subdivided itself into distinct neighborhoods, each of them populated with its own cast of supremely well-adapted characters. Even a zone as unpromising as the surface film of the pond has found its denizens, has its own codes and customs and ecological address: scientists call it the “neuston.” The surface in June looked like Long Island Sound from the air, with water striders and whirligig beetles zooming here and about like pleasure boats, inscribing the water with their distinctive wakes as they dart among islands of algae and a flotsam of tree pollen, catkins and leaves. My own favorite member of the neuston is the water strider, an improbable bug who lives his whole life in two dimensions. Water striders step blithely across the water on a cushion of waxy, air-filled leg hair, their footprints dimpling the surface of the pond as if it were a mattress, extra firm, and not just molecules of H2 O. (Some people call them Jesus bugs.) To a water strider, the pond’s surface film is dwelling, cafeteria and telephone rolled into one. They dine on any insect larvae that chance to float up to it from below, or fall on it from above—worlds that must seem as foreign and inhospitable to a water strider as the atmosphere on Mars. (When a stiff wind flakes the water surface, pulling a strider under, the bug will drown if he can’t quickly clamber back up on top.) The male also uses the surface film as a medium of communication, pulsing it with waves of one frequency to attract females, another to ward off rivals.

So how, in the absence of some pond-scum highway, did these filmbound bugs ever get here in the first place? According to the current theory, when a given population of water striders grows too large for its habitat, individuals possessing wings somehow start being born; these pioneers strike out for new ponds, there to spawn generations of normal, wingless water striders. When it comes to stocking a new pond, whether it is man-made, beaver-dammed or glaciated, nature is endlessly inventive.

By early June, the pond seemed to be doing well, aside from a minor infestation of aquatic weeds and filamentous algae: unsightly perhaps, but tolerable, at least to a novice pond-maker happy now to let nature take its course. I have to admit, I felt pretty pleased with myself to have had a hand in the making of this thriving new ecosystem, now pulsing with so much life. There’s something very hopeful in this, today even more than in Thoreau’s time. For we seem to have lost our confidence (and for good reason) that the actions we take in nature can ever redound to the good of nature—that even the violence of our chain saws and bulldozers sometimes might actually contribute to the diversity and sheer abundance of life in a place, to its very ecological health. “Improving nature” was once a phrase people uttered without self-consciousness. A great deal of damage has been done under that banner, it is true, yet it’s worth keeping in mind there has been some good done, too. I’m thinking of all the hedgerows and gardens and ponds people have made, all those vibrant edge communities where life seems to flourish with a variety and intensity unmatched in the wilderness or in an old-growth forest. You could say these ecosystems are in some sense artificial, but what difference does that make to the complex communities of plants and animals that have taken to calling them home?

Certainly my pond is proving to be extremely popular with the local wildlife. After one early spring snow, I identified the tracks of nearly a dozen different species tattooing its banks, including fox, wild turkeys, deer, raccoons, woodchucks and various species of birds. In no time, my pond has become part and parcel of the local landscape, been added to the itineraries of foragers and imprinted on the mental maps of migrating birds. When I recently brought a jar of its water to Ted Davis, a local biology teacher who had offered to show me around its planktonic realm, I asked him if he knew of any way to distinguish a sample of water from a man-made pond from one made by beavers or glaciers. He thought about it a while, scratched his chin and then said it was probably impossible. It seems to be the consensus of the rotifers, copepods, diatoms, tribonemas, oscillatorias and flagellates he introduced me to—this vast society of strange beings passing in boisterous silence beneath his microscope’s eye—that pond water is pond water.

Davis did say, however, that a man-made pond, unlike some others, won’t remain a pond for very long. My youthful ecosystem is highly unstable, he explained, and unless I intervene to stop it, the natural aging process will eventually see to it that my pond reverts back to something resembling the forest I’d cut down to dig it. A visiting naturalist, a pond man with the local Audubon chapter, seconded Ted Davis’s discouraging words: “The day a pond is dug,” he told me, “is the day it begins to die.” This is when I began to wonder, for the second time, if maybe I wasn’t cut out for this pond-making business after all. My brand-new ecosystem was doomed already?

So it seems. As algae and weeds grow and die and settle to the bottom, the water becomes progressively shallower; as more light and nutrients reach the bottom, the growth of algae and weeds redoubles, accelerating the process of sedimentation until finally the plants on the shoreline can gain a toehold and finish off the job. Marching in steadily from the edge, a foot or two each summer, the sedges and rushes and water willows will colonize the rich, rising bottom until there is no open water left. Before long, my pond is a swamp, then a wet spot in a meadow, and finally a forest. The whole community of organisms that seemed so eager to take up residence in my pond this spring turns out to be programmed for self-destruction.

The time had come to stop admiring the vibrant new ecosystem I’d helped establish, and get to work defending it—raking out the algae, yanking the more insidious of the shoreline weeds and devising some way to stanch the runoff of nutrients into the pond. Because it turns out that infestation of weeds and algae is not just a blemish in my eye—it’s the beginning of the end. So I’m considering things like stocking the pond with triploid grass carp, a sterile herbivore that will supposedly devour the weeds. I might also plant cattails along the bank where the water flows in, to filter out the nutrients and silt. It’s true that either of these moves could set in motion a whole new dance of ecological consequences, very possibly raising new problems: the carp, if introduced in excessive numbers, could eat so many weeds as to deprive the pond of the oxygen it needs; the cattails could prove invasive. But I’m coming to see that, in the long term, doing nothing is no more realistic an option in the pond than it is in the garden. Maintenance has become an obligation, unless I’m prepared to let the forest conquer the pond. This is something the dimmest beavers know, but somehow I overlooked it, naively assuming that, the digging done, I could step back and let my pond pretty much take care of itself. Not so. Digging this hole, I took on a certain responsibility, implicated myself for better or worse in the life and death of a pond. No longer a spectator standing on the shore, I’m now in deep.

 
 
Michael Pollan