Friday, March 27, 2009

The Life of the Pond!

Our book today is The Life of the Pond by a wise and able man named William Amos about that single most charming of all natural phenomena: the pond.

Some of that charm surely derives from the fact that ponds are viable little worlds unto themselves, featuring all the topographical variation of full biospheres, only compressed into a space you can easily walk around. A typical pond features land-life, shore-life, and water-life, and with a good pair of waders or a light flat-bottomed boat, you can tour in an hour different zones that exist to some extent independently of each other.

The most familiar of these areas for the casual pond-observer is the littoral zone, the shore of any pond. The appearance of this zone can vary enormously from pond to pond, depending on how rich the water is in life. Warmer, shallower ponds are usually eutrophic, meaning they're rich in oxygen, nitrogen, potassium, phosphorus, and nitrogen compounds - so their littoral zones are choked with plants, and their water is murky with plankton. Colder and deeper ponds tend to be oligotrophic, with clear water and little or no littoral growth.

The big zone that comprises the bulk of the rest of any pond is the limnetic, which is basically the open water and deep-bottom away from shore. Here your larger predators like snapping turtles and pickerel or bullhead will patrol, and this is where eagles and hawks will do their fishing if they're so inclined.

Both the littoral and the limnetic zones - as well as the other pond-areas, like the water's surface and the muck at the bottom - are entirely ruled by the seasons, which affect a pond more strongly than they do less self-contained ecosystems. And all of these zones have one thing in common that gives ponds their unique appeal: they change visibly over time.

As Amos points out, the pond is one of the only ecosystems whose entire life-cycle can be watched by a reasonably long-lived human being. Ponds are amazingly fertile (their equivalents almost certainly spawned the first life on Earth) - they start attracting organisms almost immediately upon formation (even large rain puddles sometimes do this). Within a few years, all their zones are fully inhabited. Within a decade or two, the extension of the littoral vegetation and the silting of the bottom begin to shrink the limnetic zone. A decade or so after that, such an overgrown pond can be entirely silted up - you can walk over what you once needed a boat to cross. And a decade after that, you can watch this rich-soiled meadow begin to host young trees.

Which isn't to say all ponds are so temporary - it really depends on the specific nature of your pond. And that 'your pond' is the key to another part of the pond's charm: how personal they are. You don't just observe a pond - you adopt one. People who see no intrinsic interest in ponds (and you know who you are) are always people who have no direct daily access to one - the rest of us are hooked over and over again, because once you first adopt a pond, you keep doing it in every new place you live. As Amos observes:

When you begin to study ponds, it is best to choose one small body of water and learn all you can about it. Such a concentrated approach is far better than skipping from pond to pond, stopping to look only at what is obvious, and never staying long enough to understand the complex community each one harbors.

And these communities are deceptively vast! Amos again, on a typical specimen:

The pond itself is less than an acre in extent and is no more than five feet deep in the center, yet it harbors a concentration of life far exceeding that of any lake and rivaling that of a tropical coral reef. A few miles away there is another pond about the same size; yet the plants and animals that it contains are different from those in this pond. No two ponds are exactly the same.

There are roughly two million ponds in the continental United States alone, comprising some 2.5 million acres of water - that's a lot of ponds, and yet the majority of the people I know have either never had the opportunity or never taken the time to get to know a pond well. In order to do that, you have to experience the pond the way it should be experienced: leisurely, minutely, daily, and in all seasons - so of course pond-watching is an excellent adjunct to dog-walking. I've known many ponds, in the company of many, many beagles (or, lately, in the company of a) a pointer who wants to kill-and-transport every water bird she sees, and b) a basset hound who wants to make herself sexually available to every water bird she sees)(sigh).

My first pond is long since gone, but that's the nature of most ponds, especially eutrophic ones where the profusion of growing thing speeds along the change. My pond now is another kettle of fish altogether - literally! It's the mighty Jamaica Pond, a kettle pond left behind by receding glaciers. Jamaica Pond is very much of the oligotrophic persuasion: its waters are clear and cool - and deep, down to 50 feet, the deepest pond-water in Massachusetts - and they're artificially stocked with fish every season (not to mention having two large dog-hating swans trucked in every spring).

But Jamaica Pond is the big show - I have a backup pond, as it were, that I visit virtually every day. It's a tiny fraction of Jamaica Pond's size (much more suitable for increasingly-reluctant basset-waddling), and it's committedly eutrophic, teeming with littoral life. And it's intensely, gloriously seasonal - it often freezes solid in winter, and summer droughts can leave it looking a little dry. But as Spring slowly approaches, it begins to tremble. The ground is softening, and the organisms who've been sleeping in the earth since last autumn are beginning to stir. Raccoons are regular visitors to this little postage stamp, as is some kind of water-rat or vole (as is the case with all the best visitors, I never actually see them), and soon there will be a riot of birds.

A pond of such minuscule size and lush growth is doomed to a short life - but it's a beautiful life, and I'm glad I'm there to see it. I strongly encourage everybody to find a pond of their own (even if other people know about it, you'll see it differently - it'll still be yours) and do likewise. You'll be amazed how quickly - and how wonderfully - it can put the rest of your life in perspective.


jgracey said...

I read this book in High School, it and others in the series help cement my ideals for what I was going to do as a profession and I did fulfill them. I have a copy of these books in my own library and my son is now glancing the pages. We purchased property, and constructed a pond, and it is so neat to see the evolution over time. We chronicle it photographically, and it is amazing to notice the difference.

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Micro-habitat like that there aren't in any place. If you look a pond water in a microscopy. You will see a lot of organisms