Water Quality

Hydrology Investigation

Workstations on Water

Objectives:

Students will be able to select a specific site where the hydrology measurements (water temperature, pH, dissolved oxygen, alkalinity, electrical conductivity, and nitrate) will be taken.

Students will collect and analyze samples taken from Willowbrook creek-Students will choose the same location of Willowbrook creek-this is called the sampling site.

Students will complete and turn in the data collection sheets to every test completed.

water temperature

dissolved oxygen

alkalinity

electrical conductivity

nitrate

Workstation: Water Collection

Materials:

4-L bucket with a strong rope attached securely to the handle
paper towels
sampling container(can be anything clean with a lid)

Description:

Students will go to Willowbrook creek and collect water for one week to be analyzed in the lab through workstations

Sampling Techniques:

Holding onto the rope, lower the bucket into the water and allow it to fill partially with water.
Once some water enters the bucket, retrieve the bucket and swirl the water around to clean out the bucket. Discard this water and repeat the procedure once more. Do not use distilled water to rinse the bucket as this will change the sampling results. Likewise never let the sampling bucket be used for cleaning or other purposes since this will also affect the sampling results.
The sampling site should be a location where the creek is flowing slightly.

Bottling Technique

Using masking tape make a label for your sampling container including your name, date, and time.
Rise the bottle and cap with sample water.
Fill the bottle completely and place the top on the bottle
Seal the top to the container with masking tape Note: Tape serves as a label, and an indicator of whether the container has been opened. Tape should NOT be in contact with the water sample itself.
Store these samples in a refrigerator at about 4° C until they can be tested.
Once the seal is broken, do the temperature test first, then pH test , then the tests for salinity or electrical conductivity, alkalinity, and nitrate. Ideally, once opened, all the measurements should be performed during the same lab session

Internet resource: http://archive.globe.gov/sda-bin/wt/ghp/TG+L(en)+P(hydrology/CollectingWater)

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Workstation: Temperature

Materials:

Alcohol-filled thermometer
A clock or watch
Enough string to lower the thermometer into the water
Rubber band

Description:

In this workstation students will be taking the temperature of water samples from a one week period. The temperature of the water sample is needed for the dissolved oxygen and pH measurements.

How to take the temperature:

Tie one end of a piece of string securely to the end of the thermometer and the other end to a rubber band. Slip the rubber band around the wrist so that the thermometer is not lost if it is accidentally dropped in the water.
Hold the end of the thermometer (opposite the bulb) and shake it several times to remove any air in the enclosed liquid. Note the temperature reading.
Immerse the thermometer to a depth of 10 cm in the sample water for three to five minutes.
Raise the thermometer only as much as is necessary to read the temperature. Quickly note the temperature reading. If the air temperature is significantly different from the water temperature or it is a windy day, the thermometer reading may change rapidly after it is removed from the water; try to take the reading while the bulb of the thermometer is still in the water. Lower the thermometer for another minute or until it stabilizes. Read it again. If the temperature is unchanged, proceed.
Record this temperature along with the date and time on the Hydrology Investigation Data Work Sheet.
Take the average of the temperatures measured by the student groups. If all measured values are within 1.0o C of the average, record the average temperature on the data sheet. Otherwise, repeat the measurement

Internet resource:http://archive.globe.gov/sda-bin/wt/ghp/TG+L(en)+UP(hydrology/Contents)

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Workstation: pH

Materials: water samples, vernier pH probe, laptop with loggerpro and Labpro interface

Description:

In this workstation students will record the pH from the collected water samples using the pH electrode. Students will learn pH and its measurements, calibration techniques,and how temperature affects pH.

How to take pH:

Rinse the electrode and the surrounding area with distilled water using the squeeze bottle. Blot the area dry with a soft tissue.
Fill a clean, dry 100 ml beaker to the 50 ml line with the water to be tested.
Immerse the electrode in the water. Be sure that the entire electrode is immersed, but avoid immersing it any further than necessary.
Stir once and then let the display value stabilize.
Once the display value is stable, read the pH value and record it in the Hydrology Investigation Data Work Sheet.
Repeat steps 1 through 5 for another sample as a quality control check. The two pH values should agree to within 0.2 which is the accuracy of this technique.
Rinse the probe with distilled water, blot it dry with soft tissue, replace the cap on the probe, and turn the instrument off.
Take the average of pH values measured by the student groups. If there is a wide scatter in results, discuss the procedure and the potential sources of error with the students, but do not report a value. Repeat the protocol if possible to produce a reportable measurement.
Note: pH pen or meter readings may not be accurate if your water sample has a conductivity below 100 microSiemens/cm (pH pens and meters do not function properly below this level).

Internet resource:http://archive.globe.gov/sda-bin/wt/ghp/TG+L(en)+P(hydrology/WaterTemperature)

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Workstation: Dissolved Oxygen

Materials: water samples, vernier DO probe, laptop with loggerpro and Labpro interface

Description:

In this workstation students will measure the amount of oxygen dissolved in the water sample. Dissolved oxygen is closely related to survival of plant and animal life in all bodies of water. It is affected by natural processes and by human activities.

Calibration and Quality Control

Rinse a 250 ml bottle twice with distilled water. Measure 100 ml of distilled water with a graduated cylinder.

Pour this water into the 250 ml bottle. Put the lid on tightly and shake it vigorously for 5 minutes.

Uncap the bottle and take the temperature of the water. Be sure the tip of the thermometer does not touch the bottom or sides of the bottle. Wait 1 minute before reading the temperature.

Record the temperature on the Hydrology Investigation Data Work Sheet.

Follow directions to measure dissolved oxygen.

On the data sheet, record the value as mg/L DO for the distilled-water standard. The mg/L DO found using the shaken standard must be within 0.4 mg/L of the expected value for a shaken (thus saturated with oxygen) distilled water sample. To find the expected value for a saturated DO distilled water sample:

Look up the temperature of your standard in Table HYD-P-1.

Look at the corresponding solubility of oxygen (mg/L) and record it on the Calibration Data Work Sheet.
Example: a standard temperature of 22o C has a corresponding DO solubility of 8.7 mg/L.

Look at the Calibration Value in Table HYD-P-2 corresponding to your elevation in meters and record it on the Calibration Data Work Sheet.
Example: An elevation of 1,544 meters has a corresponding saturation calibration value of 0.83.

Multiply the solubility of oxygen found in Step 2 by the calibration found in Step 3.
Example: At an altitude of 1,544 meters and a temperature of 22o C, you multiply (8.74 mg/L) x (0.83) = 7.25.

This value (7.25 in the example) is your expected value for a shaken distilled water standard.

Compare this value to the value for DO that you found when you tested your shaken, distilled water standard. If the value is not within 0.4 mg/L (LaMotte kit) or 1 mg/L (Hach kit), try the measurement again on the distilled water. If it is still off, but by less than 1 mg/L, record the DO value on the Calibration Investigation Data Work Sheet.

If you get a difference of more than 1 mg/L, report the value you get and replace the chemicals in your test kit before making more measurements. Recalibrate when you get fresh chemicals.

How to Measure Dissolved Oxygen:

Rinse the sampling bottle and hands with sample water three times. Rinse vial three times in distilled water.
Replace the cap on the bottle.
Submerge the bottle in sample water and remove the cap. Allow the container to fill.
Tap the bottle to release air bubbles.
While the bottle is submerged, replace the cap. Remove the capped bottle from the water.
Check to ensure that no bubbles are present in the bottle. If bubbles are found, repeat the sampling process.
Record your results on the data sheet.

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Workstation:Alkalinity

Materials:

Alkalinity Test Kit (See Toolkit)
Baking soda (sodium bicarbonate)
Distilled water bottle
Distilled water
500 ml beaker
100 ml graduated cylinder
500 ml graduated cylinder
Stirring rod
Data sheets
Sample bottle
Latex gloves/safety goggles
Balance

Description:

Students will measure and record the alkalinity of collected water samples over a one week period.

Measuring Alkalinity:

Calibration and Quality Control -Preparing the Baking Soda Standard
Using your balance, weigh out 1.9 g baking soda and add it to your 500 ml graduated cylinder. Make sure to transfer all of the baking soda to the cylinder.
Fill the 500 ml graduated cylinder to the 500 ml mark with distilled water.
Pour this solution into the 500 ml beaker, and stir it with a stirring rod to make sure all of the baking soda has dissolved.
Pour 15 ml from the beaker into the 100 ml graduated cylinder.
Rinse the 500 ml graduated cylinder with distilled water first. Pour the 15 ml of your baking soda solution into the 500 ml graduated cylinder.
Fill the 500 ml graduated cylinder to the 500 ml mark with distilled water.
The solution in your 500 ml graduated cylinder is your standard.
The true alkalinity of this baking soda standard is 68 mg/L as CaCO3. The true value for distilled water is usually below 14 mg/L.

Quality Control Procedure
Do the alkalinity protocol below using the baking soda standard instead of your water sample.
Record the alkalinity value in mg/L as CaCO3 on the Calibration Data Work Sheet.
If the baking soda standard is off by more than the mg/L equivalent of one drop or one gradation of the titrator for your alkalinity kit, prepare a new baking soda standard making sure your weights and dilutions are accurate. If you are still off by more than the mg/L equivalent of one drop or one gradation of the titrator for your alkalinity kit, you may need to get new reagents for your kit.

How to Measure Alkalinity
If your alkalinity kit has both a low range protocol and a high range protocol, use the low range protocol unless your water sample has an alkalinity greater than about 125 mg/L as CaCO3. This will enable you to make more precise measurements.

Follow the manufacturer's instructions. The kits are based on the technique of adding a color indicator to the sample and then adding an acid titrant dropwise until a color change is observed.
Record the total alkalinity in mg/L as CaCO3 on the Hydrology Investigation Data Work Sheet.
Take the average of the alkalinity values measured by the student groups. If the recorded values are all within the equivalent in mg/L of one drop or one gradation of the titrator for your test kit of the average, If you have more than three groups and there is one outlier (a value far different from the rest) discard that value and calculate the average of the other values. If they are now all within the equivalent in mg/L of one drop or one gradation of the titrator for your test kit of this new average, report this new average to the data sheet. If there is a wide scatter (more than the equivalent of one drop or one gradation of the titrator) in results, discuss the procedure and the potential sources of error with the students. Repeat the protocol to produce a reportable measurement.

Internet Resource:http://archive.globe.gov/sda-bin/wt/ghp/TG+L(en)+P(hydrology/Alkalinity)
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Workstation: Electrical Conductivity

Background
Conductivity is measured in microSiemens/centimeter (µs/cm). A microSiemen is the same as a micromho.

Conductivity of a water sample is a measure of its ability to carry an electric current. The more impurities (total dissolved solids) in water, the greater its electrical conductivity. By measuring the conductivity of a water sample, the amount of total dissolved solids in the sample can be determined. To convert the electrical conductivity (microSiemens/cm) of a water sample to the concentration of total dissolved solids (ppm) in the sample, the conductivity must be multiplied by a factor of between 0.54 and 0.96 for natural waters. The value of this factor depends upon the type of dissolved solids. A widely accepted value to use when you are not determining the type of dissolved solids is 0.67.

TDS (PPM) = Conductivity (microSiemens/cm) x 0.67

Materials: vernier conductivity probe, loggerpro, Labpro interface

Description:

Temperature Compensation Check
Conductivity measurements are affected by the water sample temperature. Your meter should be temperature compensated to give a conductivity reading equivalent to a temperature of 25° C.

Rinse the electrode with distilled water and blot it dry.
Fill a clean, dry, 100 ml beaker with water to be tested.
Immerse the electrode in the water sample.
Gently stir the sample for a few seconds, then allow the display value to stabilize.
Read the display value and record its value on the Hydrology Investigation Data Work Sheet.
Take the average of the electrical conductivity values measured by the student groups. If the recorded values are all within 40 microSiemens/cm of the average, record the average. If you have more than three groups and there is one outlier (a value far different from the rest), discard that value and calculate the average of the other values.

Internet source: http://archive.globe.gov/sda-bin/wt/ghp/tg+L(en)+P(hydrology/Conductivity)

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Workstation: Nitrogen

Materials:

50 mL beaker or flask
Nitrate Test Kit (if you have salt or brackish water, be sure to
use an appropriate test kit)
100 ml graduated cylinder
500 ml graduated cylinder
3 500-ml bottles or jars
Distilled water

Overview
Measuring nitrate levels in water is an important step in the determination of water quality.
Nitrogen exists in water in numerous forms, two of which are nitrate (NO3) and nitrite (NO2). Of these forms, nitrate is usually the most important. Nitrite can be found in suboxic waters. Nitrate is an essential nutrient for growth of algae and other aquatic plants, and can be present at high levels due to inputs from a variety of sources. Nitrate is very difficult to measure directly, so it is reduced to nitrite and the resulting nitrite concentration is measured. The measurement gives the combined concentration of nitrite (if present) and nitrate concentrations. Because we are interested in the nitrate measurement, background levels of nitrite also have to be measured. Nitrate measurements are reported as nitrate nitrogen (mg/L). Nitrite measurements are reported as nitrite nitrogen (mg/L).

Measuring Nitrate:

Quality Control Procedure

Dilute the 100 mg/L standard to make a 2 mg/L standard. Use this standard to test the accuracy of the nitrate kit. Measure out 10 ml of the 100 mg/L standard nitrate solution using the 100 ml graduated cylinder. Pour this into the 500 ml flask or beaker. Measure out 490 ml of distilled water in the 500 ml graduated cylinder and add to 500 ml bottle or jar. Label with masking tape (include date). Carefully swirl the solution to mix the standard.
Follow the directions in the Protocol section to measure the standard. Where it says "sample water" this is where you use the standard that you made.
Record the value of the standard after testing on the Hydrology Investigation Data Work Sheet.
If the nitrate standard is off by more than 1 mg/L, prepare new dilutions and repeat the measurement. If still off, make a new stock solution and repeat the procedure.

How to Measure Nitrate Nitrogen

Rinse the sample tubes in the kit at least 3 times with sample water before starting the measurement.
Nitrate nitrogen plus nitrite nitrogen: Follow the manufacturer's nitrate instructions in the kit. The kits are based on the technique of adding a reagent that reacts with nitrate to form nitrite. The nitrite reacts with a second reagent to form a color. The intensity of the color is proportional to the amount of nitrate in the sample. The concentration is determined by comparing the sample color, after addition of reagents, to a color comparator included in the kit. If the kit calls for shaking the sample, be sure to shake for the specified period of time. Failure to follow the times specified in the directions will result in inaccurate measurements.
Have at least 3 students in the group read the color comparator. Record the nitrate concentration for each student group on the Hydrology Investigation Data Work Sheet. (Note: Hold the comparator up to a light source such as a window, the sky or a lamp. Do not hold it up to the sun.)
Take the average of the three readings. If the recorded values are all within 1 mg/L of the average, record the average on the Hydrology Investigation Data Work Sheet. (Note: do not reread if more than 5 minutes has elapsed.)
Nitrite nitrogen: Follow the manufacturer's instructions for nitrite. It is the same procedure, except the reagent to reduce nitrate to nitrite is not used.
Repeat steps 3 and 4 to obtain nitrite values.
Note: Test results should be reported as mg/L nitrate nitrogen (NO3- N; the same units as your standards), and not as mg/L nitrate (NO3).
For general information: To convert mg/L nitrate to mg/L nitrate nitrogen divide by 4.4, the ratio of their molecular weights. For example: 44 mg/L NO3 is equivalent to 10 mg/L NO3-N. To convert mg/L nitrite to mg/L nitrite nitrogen divide by 3.3, the ratio of their molecular weights.

Internet source:http://archive.globe.gov/sda-bin/wt/ghp/TG+L(en)+P(hydrology/Nitrate)

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