new church life: jan uary/february 2016
oxygen on the planet. Although most of us have never heard of them, their
loss would be even more devastating (I’m told) than that of all the rain forest.
There are hundreds of thousands of species of them, all different, but they
fall into two basic categories: so called “benthic” or bottom-dwelling diatoms,
which are generally shaped like a feather and so are called “pennate”; and
“planktonic” or floating diatoms, which tend to be round, at least seen from
one angle, and are therefore called “centric.”
Sherri devoted a lot of time to studying diatoms in the Chesapeake Bay. She
found that they tell a very precise story year by year about ecological conditions
in the distant past. And what she found was that for thousands of years there
was a stable balance in the bay; the bottom was covered in hundreds of species
of diatoms that happily coexisted and thrived through their diversity; there
was plenty of sunlight for all, streaming through the clear water.
Then in the 18th century the human land use inadvertently drove up the
levels of nitrogen and phosphorous in the water, with the result that one of two
species of planktonic or floating, centric diatoms became dominant. In what is
rather kindly called a “bloom,” these floating diatoms reproduced wildly and
upset the balance in the bay; they hogged the sunlight, killing all the benthic
diatoms at the bottom; then ran out of silica and nutrients, died, sank to the
bottom, and in the course of rotting, sucked all of the remaining oxygen out
of areas of the bay, creating what is called “anoxia,” or lack of oxygen, which
affects everything in the food chain. It is not an irreversible condition but an
extremely dire one nonetheless.
To Sherri I think the contrast between the heavenliness of a stable,
longstanding condition of diversity, evenness and balance, and a deadness
because just one species on land changed the land use, and just one or two
others in the water became devastatingly dominant as a result, was highly
instructive and attention-getting.
And what about evenness? Even non-scientists know that diversity is
important for a rich, vibrant ecosystem, but not as many of us are aware that
it is not just the number of different species present, but how evenly they are
distributed that matters. In formulas used by scientists to determine diversity,
the evenness of each species is part of the equation. Having a hundred or even
a thousand different species in a given environment does not supply much
stability or balance if just one of those species hogs 75 percent of the space and
controls 95 percent of the nutrients.
Is this an issue among humans as well? Do humans sometimes want to
exercise their will on each other and dictate how others should be? Do some
take more than their fair share? It seems we sometimes do!
I say this at the outset because understanding how crucial diversity,
evenness and balance were to Sherri helps us understand the choices she made
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