Date: 2 December 1998
From: John Gorst <john@gorst.demon.co.uk>
To: BRINE-L@UGA.CC.UGA.EDU
QUESTION:
As an A-level course work experiment (pre-university qualification here in the UK), we are going to investigate the effects of CO2 concentration and temperature on brine shrimps.
We are going to find the rate at which they beat their legs (or something like that!) as an indication of their respiratory rate (can brine shrimps 'breath' in more deeply?).
The idea I guess is that CO2 concentration and temperature are meant to put the brine shrimp under stress. The CO2 will make them breath faster as they have to try harder to get rid of CO2 from their bodies...eventually it will become too much and they will die.
The way we will investigate CO2 concentration effects, is that we will use saturated carbonated water (i.e. tonic/soda water). We will then water this down to get the different concentrations. My main concern is that this will seriously effect the pH of the water (i.e. make it more acidic), therefore we will be looking at the effect of CO2 concentration AND pH on the brine shrimps. Are brine shrimps seriously affected by pH, what are their operating ranges (although I do not know what type of brine shrimp we are using yet).
The other thing is that when we do the temperature experiments (varying the temp. for all the different CO2 concentrations), some of the CO2 will 'leave' the water as CO2 solubility is inversely proportional to temp. Therefore when comparing two different temperatures which are meant to be at the same CO2 concentration... they will in fact be at different concentrations. Does anyone know if this is a big factor or is CO2 solubility of CO2 quite high at CO2 temperatures (i.e. 40 degrees) as we are only going to use 40% saturated solution (at room temp.)?
Also does anyone have any web links to any info on the anatomy of the brine shrimp...some good biological detail that I can use to reach a conclusion?
John Gorst
john@gorst.demon.co.uk
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COMMENTS 1:
Use of carbonated water will definitely decrease the pH of the system.
You have actually bitten off a rather difficult question. The concentration of carbon dioxide in water is linked to the concentration of bicarbonate and carbonate by a series of linked equilibria. It isn't possible to change the CO2 concentration without affecting the concentration of the other linked components.
It is also somewhat difficult to measure the CO2 concentration in water directly. Test methods for CO2 concentration that work in freshwater don't work in seawater, because the pKa values for the various acids in that system vary quite a bit as the salinity of the solution is increased. They are also sensitive to the magnesium concentration in the solution.
If you wanted to use brines at near seawater ionic rations, you could use a program developed by the CO2 group at Brookhaven to calculated the carbon dioxide concentration, given the carbonate alkalinity and pH of the solution.
http://cdiac.esd.ornl.gov/oceans/co2rprt.html
Please be aware, though, that this program was written for use with a seawater matrix, and the values that it calculates will not be correct for a brine of arbitrary composition. I also think that the program has an upper limit for the salinity that it will accept.
Perhaps someone else knows of programs that will enable the calculation of pCO2 in a brine of arbitrary composition. If so, I'd be interested to hear about them.
Craig Bingman
<cbingman@netcom.com>