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Re: relevance of natural ecosystems for tanks

On Mon, 11 Feb 2002, Doug wrote:

> As I was hiking in the woods yesterday, it occurred to me that a major
> difference between our tanks and the natural systems where ecosystem studies
> are conducted is not just scale, but the linkage to the terrestrial
> ecosystem.  Many aquatic ecosystems will be phosphate limited in part
> because nitrogen species run off from the land much more easily than the
> relatively immobile (in soils) phosphate.  Perhaps this is stating the
> obvious, but one of the major differences between tanks and aquatic systems
> is the source of nutrients (fish food+fertilizer vs leachate).

Here's a few other differences to keep in mind:

a) Most freshwater bodies are small and are (as you know) pretty much
inseparable from the terrestrial system around them.  In many cases
detritus and soil washed into an unpolluted stream or pond is a bigger
source of food and plant nutrients than is leachate.  In addition to
regular detritus (seeds, leaf mold, twigs and so on) there are insects and
other small terrestrial animals falling into the water and water fowl and
larger animals leaving their wastes in the water.

b) In many -- especially smaller -- aquatic ecosystems insects and insect
larvae are often the dominant grazers and sometimes are the dominant
predators.  Certainly they're a vital part of food web.

c) In most freshwater ecosystems the water is very murky.  If it isn't
clouded by detritus or suspended sediments then it is colored by organic

d) Freshwater ecosystems are frequently very energetic and subject to
large and rapid variations in every condition, including temperature, pH,
turbidity, and current. The principle exception to that is below the level
of wave action in large lakes.

e) Water in a natural freshwater system -- even in larger lakes -- is
constantly moving between divergent environments; it may be in open water
and full sunlight one day, shaded in shallow reeds in another, deep within
dark lake depths at yet another.

Compare that to our planted aquariums. Diana Walstad's ecologically
principled aquariums have clear water with relatively calm currents and a
very limited biodiversity.  They offer but two environments (soil and
water) and a setting that is very unnaturally stable.  Water changes once
every 6 months?  A natural stand of plants would see different water every
few minutes!

A more high tech tank may be run with more water changes and might (with a
darkened sump and filter) offer more physical diversity, but biodiversty
would still be low and all conditions would be closely controlled.  Don't
even think of murky water, sinking detritus or suspended sediments!  
Maybe adding fertilizers is a reasonable simulation of a deer or tapir
peeing in the water.  Maybe not.

There's really very little similarity between our aquariums and natural
systems, and almost nothing from ecology that can be projected into our
aquariums.  Observations from nature may give valuable clues about the
physiology of some plants. Otherwise, information from the natural setting
where a particular plant thrives is of little value because we almost
never offer plants conditions that are anything like their natural

The natural environment in which our aquatic plants grow is no more
relevant to most of our planted aquariums than the natural environment of
wild squash is relevant to how you should grow zucchini in your garden.

Roger Miller