Water Chemistry…… What does it all mean?

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Water ChemistryWhat does it all mean?

• Eric Starkey
• Upper Columbia Basin Network, Moscow ID

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Overview

• Basic Parameters
• What do they show?
• How do they vary over time?
• Why are these parameters important?
• Calibration
• Why is frequent calibration necessary?
• What is the process?
• How is it done?

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Overview

• Water chemistry sampling equipment
• Grab sample/test kit
• Multi-parameter handheld unit (YSI 556)
• Multi-parameter sonde (HACH Hydrolab)
• Methods of sampling water (temporal and spatial)
• Point sample
• Continuous
• Transect
• Vertical profile

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Basic Parameters

• Temperature
• Effects many other parameters
• Increased temperature decreased D.O. bad news
  for aquatic organisms!
• Upper lethal for trout 77-78 F (25-25.5 C)
• pH differs slightly according to temperature
• Indicates along with other parameters
• Degree of stream shading
• Input of ground water/dewatering
• Thermal pollution
• Habitat suitability for aquatic organisms

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Basic Parameters

• Temperature Variability
• 24hour, Seasonal (Example from Nez Perce National
  Historical Park Lapwai Creek)

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Basic Parameters

• Dissolved Oxygen (mg/L)
• Likely the most important parameter to consider
  relative to aquatic life!
• Responds to temperature, barometric pressure,
  salinity, productivity, decomposition, pollutants
• Indicates along with other parameters
• Levels of eutrophication, productivity,
  decomposition
• Excessively high water temperature

Ideal D.O. 5 mg/L
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Basic Parameters

• Dissolved Oxygen Variability
• 24hour, Seasonal (Example from Nez Perce National
  Historical Park Lapwai Creek)

Why does DO increase each afternoon?
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Basic Parameters

• Specific Conductance (µS/cm)
• Measure of the electrical conductance of water,
  translates to the amount of dissolved
  constituents
• Increased Sp. Cond. increased salinity
• Decreased Sp. Cond. decreased salinity
• Many natural processes can change Sp. Cond.
• Temperature - Geology - Name Another?
• Might also be an indication of
• Industrial Pollutants

Typical for this area 150-300 µS/cm
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Basic Parameters

• Specific Conductance Variability
• 24hour, Seasonal (Example from Nez Perce National
  Historical Park Lapwai Creek)

Noon
Noon
Why the increase each night?
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Basic Parameters

• pH (Units)
• Measure of the acidity or basicity of a solution
• activity of dissolved hydrogen ions (H)
• Responds to productivity, as CO2 ? pH ?
• Influences
• The effects of pollutants on aquatic organisms
• Efficiency of gills
• Indicates along with other parameters
• Eutrophication
• Other forms of pollution

Ideal pH 6.0 9.5
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Basic Parameters

• pH Variability
• 24hour, Seasonal (Example from Nez Perce National
  Historical Park Lapwai Creek)

Midnight
Noon
Why does pH increase each afternoon?
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Upland Drivers of Water Chemistry

• Temperature stream shading/upland vegetation
  (sagebrush vs. forested), surface flow (parking
  lots vs grassland)
• Dissolved Oxygen fertilizer input, stream
  shading, organic input (leaves,
  etc.)/decomposition
• Specific Conductance geology, rainfall
• pH stream shading, temperature, geology

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Quality Control

• Always use the sensor guard
• The cleaner the better!
• Rinse sensors with distilled water after use
• Make sure not to damage the D.O. membrane or pH
  sensor when cleaning
• Never store the sensors in lake water or
  distilled water
• Store with ¼ inch of pH 4 standard solution
• CALIBRATE prior to use! (especially if the
  instrument has not been used for several days)

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Units

• Best units for data collection
• Temperature C
• Specific Conductance µS/cm
• pH Units
• Dissolved Oxygen mg/L
• Also Saturation
• Why?
• Comparability
• Consistency

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Calibration
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Calibration

• Why?
• Calibration Drift electronic or sensor drift
• Fouling biological growth or sediment on
  sensors
• Quality Control
• How often?
• Prior to use if the instrument has
• been unused for more than a few
• days
• Every week if used consistently

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Calibration

• YSI 556 handheld meter
• Temperature, Specific Conductance, pH, Dissolved
  Oxygen
• Section 6. pg. 37-55 of user manual
• Calibration materials
• Distilled water
• Calibration cup
• Paper towels
• Calibration standards
• pH 7 and pH10
• 1412 µS/cm
• Distilled water

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Temperature

• No Calibration ?
• Double check with thermometer (should be within
  0.5 C)

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Conductivity

• Rinse with D.I. water
• Dry with paper towel (be careful not to damage
  the pH bulb and D.O. membrane)
• Rinse with standard solution
• Discard standard solution
• Go to the calibration screen for Specific
  Conductance
• Fill calibration cup with enough solution to
  cover sensor
• Enter the standard value
• Calibrate

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Dissolved Oxygen

• As oxygen crosses the membrane, it is consumed in
  a chemical reaction which generates a small
  electrical current between the electrodes
• The current measured is directly proportional to
  the amount of oxygen in the water sample
• Must be kept moving in order to get a correct
  reading
• Determine barometric pressure
• Local weather station (mbar, corrected to sea
  level)
• Convert to mmHg
• Convert from barometric pressure at seal level to
  pressure at altitude BP BP-2.5(Aft/100)

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Dissolved Oxygen

• Rinse with D.I. water
• Dry with paper towel (be careful not to damage
  the pH bulb and D.O. membrane)
• Add 1/8th inch of water to calibration cup
• Place cap on cup but do not tighten
• Wait 10-15 minutes for air in cup to saturate
  with water
• Enter barometric pressure
• Calibrate

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pH

• Measures hydrogen ion concentration
• Requires a 2-point calibration at pH 7 and 10
• Rinse with D.I. water
• Dry with paper towel (be careful not to damage
  the pH bulb and D.O. membrane)
• Rinse with pH 7 / discard
• Add pH 7 standard
• Enter temperature corrected pH value
• Calibrate
• Repeat steps 3-6 with pH 10

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Storage

• Short Term Storage (lt 1month)
• Add ¼ inch of pH 4 standard to calibration cup
• Disconnect sensor cable from unit
• Remove all sand etc. from case and cable
• Long term storage (gt1 month)
• Store as above and remove batteries
• Replace D.O. cap/electrolyte when used again

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Questions?