I need to construct Piper diagrams using historical water quality data, but don't have carbonate/bicarbonate concentrations... Please advise if it's possible.
What are you really doing ? History matching or temporal/spatial variation in water quality or quality transformation through different catchment ? What about the geological terrain ? If the laboratory analysis of your samples (water) has not revealed the presence of either carbonate or bicarbonate then suffice to state that they are not present or below detectable limits. However, if carbonate or bicarbonate tests were omitted while carrying out the analysis, you can use the results of calcium hardness and titrimetry.
I'm looking at the quality of irrigation water abstracted from two different river systems by initially comparing historical data form the South African Department of Water Affairs. Unfortunately, I understand that carbonate/bicarbonate concentrations were never quantitatively measured... Which is why I'm facing this problem... Do you perhaps have a formula/reference? Many thanks!
Do you data for water hardness obtained as calcium carbonate ?
Piper diagram is one of the oldest tool for the classification of water. Mainly Na, K, Ca Mg as cations and Cl, SO4 and HCO3 are used for making the diagram. All the ions are presented in equivalent part per millions ( epm ). If HCO3 data is not available it can be deduced from the chemical analysis data. Thus piper diagram can be prepared.
The relevant concept is Alkalinity, measured by acidimetry and Gran titration. It can be expressed first as the sum of concentrations of bases times the number of protons each base can accept minus the concentration of proton, secondly as the algebraic difference between concentrations of cations conjugate from strong bases minus the concentrations of anions conjugate from strong acids. If it was not measured, you can assess Alkalinity as: Alk. = [Na+] + [K+] + 2[Ca2+] + 2[Mg2+] - [Cl-] - 2[SO42-] - [NO3-].
From Alkalinity and pH, you can compute equilibrating pCO2. See Stumm and Morgan, Aquatic chemistry (1970) and more recent augmented editions, and my publication, in french.
Thank you all for the answers. Total Alkalinity was measured, which makes it easier to now determine HCO3 and CO3... Many thanks!
Hi Gerhard,
The link below is one of the most accurate method to calculate what you want. Currently, I am using this method for working out alkalinity and other species in the samples.
Good luck
http://or.water.usgs.gov/alk/methods.html
if we didn't measure alkalinity, how should we calculate bicarbonate ? please suggested again if I missed some information above
HCO3 and CO3 can not be calculated from TDS , EC and pH data of water sample.
You can calculate carbonate/bicarbonate concentrations since you mentioned that in addition to TDS/pH/EC you have results for major ions. Do ionic balance for your water samples? Assume that the ion balance error is zero. EC will help you to check the anions and cations concentrations. From the balance you will get the bicarbonate value. Use the pH value to estimate carbonate from bicarbonate. See an online ion balance calculator if you need the calculation assistance http://www.lenntech.com/calculators/accuracy/accuracy-water-analysis.htm.
Hi Gerhard, the answer for your question is" yes" it is possible to calculate the Carbonate /Bi- Carbonate concentration in the TDS. Obviously it want be a simple step answer. You have to do multiple steps and bit of mathematical adjustment to get the correct answer. Use the following arguments and you can work out the answer yourself.
At fix temperature and pH.
1. You will find this on your soil sample first
2. In the TDS (Total dissolved solids) find the breakdown sulphate, chloride and carbonate/bi-Carbonate.
3. Try to establish from standard solubility what proportion can exist in water (Na, K,Cal and Al etc)
4. Solubility index of each Cations will tell you which one can exists in what ratio
5. You can use games theory or other probability model to refine this.
6. Keep it in mind there other factors that do affect solubility but you will work that out any way. You can always use the reaction models against pH and temperature and work out possible concentrations as well. I am sure you will be able to work it out from here.
This question is related to water.
Purpose is to prepare piper diagram.
major ions, TDS, EC and pH data availabl.
HCO3 and CO3 data not availabl.
As to prepare piper diagram HCO3 and CO3 are essential component. Which is deducted even in epm level.
preparation of this Diagram used for very specific/ diagnosed purpose. Further study mostly related to this.
Therefore, it is better to avoid shortcut please.
Well,
accurate to some extent(approximately), accuracy: 95%
according to the ionic balance where, anions(meq/l)= cations (meq/l)
using the following from anions and cations (meq/l)
Na+ K + Ca + Mg = Cl + SO4 +(Alkalinity or (HCO3+CO3)
Sincerely