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  • From: KAKerby@aol.com
  • To: permaculture@lists.ibiblio.org
  • Subject: Re: [permaculture] pc aquaponics
  • Date: Mon, 8 Oct 2012 14:29:24 -0400 (EDT)

It's not a single study. It's a working rule of thumb that as you plan
out how many plants you want, there's a fair amount of literature on how
much
irrigation water you'd need to carry them in conventional agriculture.
Yet roughly 1/10 of that would be how much water you'd need stored in an
aquaponics system. Also keep in mind that different aquaponics systems
feature
drastically different volumes of water, again in part to serve whatever
goals are at work. Some use the aquaponics water storage as a heat sink to
help regulate thermal swings during the day, such that solar gain heats the
water during the day and the water radiates that heat at night. Heaters,
in that instance, would only be needed for extended cloudy periods. Also,
since that water leave the system only through evaporation, rather than any
form of percolation and/or runoff, it's a much, much lower number than
in-soil irrigation needs. Comparing the size of that "water bill" to what
would be needed for irrigation to conventional row crops, that's where you
see
dramatic water savings.

Granted, not everyone uses conventional irrigation for conventional single
row crops. Amongst the market farmers I know, many have at least begun
the move away from single-row setups towards wider beds and/or mulching. We
use drip irrigation and soaker-hose irrigation here for heavily mulched
beds. But even with that, our water usage for our in-soil crops is heavier
than it would be for the aquaponics, because we must keep adding water to
the
beds. With the aquaponics, we already have high humidity and we don't get
a lot of evaporation.

As for the heated water issue, that varies dramatically according to
location, system design, species of fish used, etc. Tilapia are frequently
listed as "the" fish, first and foremost because they can tolerate lower
dissolved oxygen rates than other fish. But a variety of other species have
been
used successfully in aquaponics, including decidedly cold-water-favoring
fish such as goldfish and trout. Perch and a few others that I can't
remember now have also been used. So no, there is no inherent need to heat
the
water just because it's aquaponics. The individual criteria of the system
and its particular environment will drive that decision. Granted, some
folks will gleefully pump a lot of heat into a system because that's what
they
want. But don't mistake that for being a requirement for the approach in
general. It's not.
Kathryn Kerby
frogchorusfarm.com
Snohomish, WA


In a message dated 10/8/2012 11:12:15 A.M. Pacific Daylight Time,
Josh@SDSustainable.org writes:

Can someone point me to the study that everyone seems to use in stating
that aquaponics uses 1/10th water that soil beds do? I want to know what
their assumptions are. I have had many people state this fact and then when
I look at their systems, they use reverse osmosis water, which can waste
up
to 10 gallons for every gallon produced. Some then spend tons of energy
heating the water to 80 degrees to raise tilapia and other warm water fish.
Huge embodied energy that consumes huge volumes of water on the energy side
of things. Yet depending on the type of soil growing you do, factors can
completely change the amount of water used such as a mulched vs unmulched
bed. So any help finding this study about the water savings of aquaponics
would be great.

Josh Robinson

--
Josh Robinson
Director
San Diego Sustainable Living Institute <http://www.sdsustainable.org>
619-884-7749
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