permaculture

[KAKerby@aol.com]

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
_______________________________________________
permaculture  mailing list
permaculture@lists.ibiblio.org
subscribe/unsubscribe|user  config|list  info:
http://lists.ibiblio.org/mailman/listinfo/permaculture
message  archives:  https://lists.ibiblio.org/sympa/arc/permaculture/
Google  message archive search:
site: lists.ibiblio.org/pipermail/permaculture  [searchstring]
Avant Geared   http://www.avantgeared.com