As discussed in the introduction, water quality sampling is merely a snapshot in time. To get the most meaning out of this lab it is better to analyze samples over time, or from different sources.
Step 1. Sample Collection
Samples can be either collected prior to starting this lab, or as part of the lab. When collecting samples students should take detailed notes of the conditions at the time of sampling (weather conditions, temperature, condition of river, etc.) A map should be drawn to show the location of each sample site.
Properly label and document each sample bottle. Sample bottles should be thoroughly cleaned prior to sampling, and then rinsed three times with stream water prior to sample collection. You should wear gloves at all times during sample collection so you do not contaminate your samples. Use a special dissolved oxygen bottle if possible for the DO samples (included in the Hach kit).
Step 2. Analytical Procedure
Once samples have been collected it is important to analyze them as soon as feasibly possible. If samples can not be analyzed the same day they should be placed in a refrigerator. Dissolved oxygen samples are the most susceptible to changes over time, and should be analyzed with 8 hours of being preserved with sulfamic acid.
Step 3. Evaluation of Results
Keep track of your data! As the activity is replicated over time it gets more and more interesting. Just as you would only draw limited conclusions from one photograph - so do you need more water quality "snapshots" to evaluate your stream.
It often makes sense for groups of students to evaluate different parameters, share their results with other groups, and then write a summary report of their findings. If old reports are available they too can be used in the summary report to evaluate changes over time.
Data can also be shared with
other schools through BASIN
or contact the City of Boulder Water Resources Educator at 413-7365.
Alkalinity, hardness, and dissolved oxygen can be determined by titration. This can be accomplished with the a simple kit (i.e. what is found in the BVSD Pond Trunk or by checking at the City of Boulder Hach kit) or by doing a full blown chemical titration.
Natural water usually has a a pH value from 6-9.
Drinking water regulations for nitrate are 10 mg/L
Ammonia toxicity to fish is dependent on pH, temperature, and alkalinity. Generally, concentrations above 2.0 mg/L are toxic to fish.
The EPA recommends that phosphate concentrations do not exceed 0.05 mg/L for streams entering lakes or reservoirs, and 0.1 mg/L for streams that do not discharge into lakes or reservoirs.
As a laboratory exercise, analyzing environmental samples often has a much greater impact than doing a titration of a known acid. Students get to be real scientists, collecting samples, performing the analytical work, and interpreting their results. The chemistry is slightly more complex (so to speak) because hardness, alkalinity, and dissolved oxygen use metal-ligand complexes as the mechanism by which an observed color change occurs. However, the more complex chemistry can be greatly simplified in terms of what is explained to your students They follow the procedures, titrate drop by drop, and look for a definitive color change that gives them a direct correlation on the amount of:
- carbonate and bicarbonate
ions (clear to gray pink)
The procedures have been laid out very carefully by the RiverWatch program. If you are not a member of RiverWatch you can still perform the tests by checking out the Pond Kit from BVSD, or by checking out one of the Hach kits from the City of Boulder. Or you can do the experiments as long as you have the following equipment and materials.
sodium thiosulfate (0.025 N)
Making standard solutions.
It is important to have a standard solutions made up to verify water quality results. The following methods are recommended for each test.
Alkalinity - Dissolve 1.324 grams of Na2CO3 in a small amount of deionized water in a 100 mL volumetric flask. Add up to the 100 mL mark with DI water to make a stock solution of 12500 mg/L CaCO3. Take 1 mL of this stock solution and dilute it up to 50 mL to make a standard concentration of 250 mg/L CaCO3.
Hardness - Dissolve 2.947 grams of Ca(NO3)2 · 4H20 in a 100 mL volumetric flask and add DI water to the 100 mL mark to make a stock solution of 12500 mg/L CaCO3. Take 1 mL of this solution and dilute it up to 50 mL with DI water to make a standard concentration of 250 mg/L CaCO3.
Dissolved Oxygen - not easily possible to make a standard concentration
Nitrate - dissolve 2.003 grams of KNO3 with DI water in a 100 mL volumetric flask and add DI water to the 100 mL mark to make a stock solution of 12500 mg/L N as NO3. Take 1 mL of this solution and dilute it up to 50 mL to make a stock solution of 250 mg/L N as NO3. Take another 1 mL of this solution and dilute to 50 mL to make a standard concentration of 5 mg/L.
Phosphate - dissolve 2.158 grams of Na3PO4 in a 100 mL volumetric flask and add up DI water to the 100 mL mark to make a stock solution of 12500 mg/L P as PO4. Take 1 mL of this and dilute up to 50 mL to make a stock solution of 250 mg/L P as PO4. Take 1 mL of this solution and dilute up to 50 mL to make a stock solution of 5 mg/L P as PO4. Take 1 mL of this solution and dilute up to 50 mL to make a standard concentration of 0.1 mg/L P as PO4.