Introduction to Lake Surveys
Basic Water Quality Assessment
Unit 3 Module 8
Part B Field Profiles
Objectives
Students will be able to:
 identify, utilize, calibrate and troubleshoot probes used for measuring
temperature.
 identify, utilize, calibrate and troubleshoot probes used for measuring
dissolved oxygen.
 interpret information gathered by temperature and dissolved oxygen
probes.
 identify examples of error from data gathered from field probes.
 identify, utilize, calibrate and troubleshoot probes used for measuring
electrical conductivity (EC25).
 estimate total dissolved solid (TDS) concentrations in lakes
 identify, utilize, calibrate and troubleshoot probes used for measuring pH.
 explain how to effectively use a secchi disk to determine water clarity.
 interpret secchi disk data to evaluate water clarity trends in a lake.
 explain how to effectively use a transparency tube to determine water
clarity.
 identify, utilize, calibrate and troubleshoot probes used for measuring
turbidity.
 relate the importance of light to lake profiles and chlorophyll production.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s2
Basic water quality assessment
 These slides focus on learning
basic field techniques used by
limnologists:
 Morphometry - estimating
critical lake basin
measurements
 Field profiles - physical and
chemical parameters
measured from top to
bottom of the water column
 Sampling – collecting water,
sediments, and aquatic
organisms
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s3
Physical and chemical profiles
 Goal:
Insert how
a wonderful
image that captures the joy
 Learn
to collect
of measuring physical and chemical profiles
basic water quality
data using common
field instrumentation
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s4
Physical and chemical field profiles
 Field profiles
 Sensors
 Temperature
 Dissolved oxygen
 pH
 Specific conductivity
 Transparency
 Secchi, turbidity
 Chlorophyll probes
 Light profiles
 Profiling guidelines/examples/helpful hints
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s5
Physical and chemical field profiles
 Topics covered:
 Definition - why it’s important (quick review)
 Units of measure - data reporting
 Probe types - calibration, storage, cleaning
 Where and how often should profiles be
measured?
 Troubleshooting and QA (what can go wrong and
how to avoid or correct it)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s6
Field profiles-temperature
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s7
Temperature – importance and reporting
 Temperature regulates the rate of many
biological and chemical processes within the
lake.
 Units are degrees Celsius (oC) or Fahrenheit
(oF)
 Reported to nearest 0.5 oC
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s8
Temperature probes
 Types of probes
 Liquid-in-glass: not very practical for lake
temperature profiles unless the lake is really shallow
or your arms are really long. Absolutely NO mercury
(Hg) thermometers, existing Hg thermometers
should be turned in at your state water quality
agency.
 Thermistor: based on measuring changes in
electrical resistance of a semi-conductor with
increasing temperature.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s9
Temperature probes
Some probe examples:
Temp probe
Temp probe
www.onset.com
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s10
Temperature probes
 Temperature is always measured concurrently
with oxygen, pH, and conductivity because all
of these parameters are temperature
dependent.
 Most sensors have built-in temperature
compensation.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s11
Temperature - calibration
 Calibration
 Compare against a NIST-certified (National
Institute of Standards and Technology)
thermometer at 3 temperatures; 0, 25 and 40 oC
 The thermometer should read within ± 0.2 oC of
the NIST thermometer
 Typically you cannot adjust to calibrate but check
the instrument manual. It is a good idea to check
it at 0oC in a slurry of ice-water and at room
temperature if a calibrated (NIST) thermometer
is not available.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s12
Temperature - calibration
 Common errors
 Temperature is pretty fool-proof and thermistors
generally last for > 10 yrs
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s13
Temperature - troubleshooting
Symptom
Possible cause and corrective action
Liquid-in-glass thermometer
doesn’t read accurately
liquid separated
Thermistor doesn’t read
accurately
dirty sensor
weak batteries
Erratic thermistor readings
Bad or dirty connection at meter or
sensor
Break in the cables
Weak batteries
Thermistor slow to stabilize
Dirty sensor
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s14
Temperature- field example
Example: Grindstone
Lake- Summer
DO
 Temp gradient sharpest
T
from 5-6 meters
 Conclusion: sample
every meter to ~ 10m to
characterize the
thermocline; then
sample at 2 or even 5 m
intervals to save time
without losing much
information
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s15
Dissolved oxygen (DO)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s16
DO – importance and reporting
 Oxygen is produced during photosynthesis
and consumed during respiration and
decomposition.
 Generally < 3 mg/L is stressful to aquatic life.
 Units of measurement are:
 Concentration: mg/L = ppm; concentrations range 0.0 to
20 mg/L
 % saturation – used to determine if water is fully
saturated with oxygen at a particular temperature
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s17
DO – techniques
 Probe types and measurement techniques:
 Winkler titration
 Amperometric (polarographic) method, most
commonly used
http://www.lumcon.edu/education/StudentDatabase/gallery.asp
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s18
DO – techniques
 Winkler titration
 Water is collected with Van Dorn or Kemmerer
samplers then placed in special glass bottles
with pointed stoppers to exclude air bubbles
(syringes may be used also).
 Winkler “wet chem” titration is very accurate if
done correctly.
 Still done by researchers; kits are available to
simplify titrations (e.g., Hach Co., LaMotte Co.,
and others).
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s19
DO – techniques
 How do you do a
Winkler titration?
 On the web at:
(http://www.lamotte.com/W
EB-SITE/ENV/HOMEENV.HTM)
 And appendix 1
http://io.uwinnipeg.ca/~simmons/ysesp/images/mvc-002f.jpg
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s20
DO – probes
 Most common sensor is the temperature
compensated polarographic membrane-type
(amperometric)
 Temperature sensitive (but virtually all are
compensated).
 The probes actually consume O2 as they work so
measurements require moving water using either
a built-in stirrer (typical in multiparameter sondes
and BOD probes) or “hand jiggling” during the
measurement.
 in situ sensors are prone to fouling by
algal/bacterial slimes and by silt in streams.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s21
DO – probes
Gold
cathode
KCl –
electrolyte
bridge
Silver
anode
Silver
anode
Gold
cathode
http://www.netl.doe.gov/publications/proceedings/00/app-rvr00/3-1.PDF
Hydrolab
Developed by: E. Ruzycki and R. Axler
YSI
Updated: Dec 2, 2003
U3-m8b-s22
DO Probes - “older” polarographic sensors
O-ring seals the membrane over
the gold cathode ring
Chamber surrounding silver filled
with saturated KCl
Protective guard
Rubber diaphragm for pressure compensation
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s23
DO probes and meters
 The WOW RUSS’s use either Hydrolab or YSI
multiprobe datasounds, but there are many others
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s24
DO probes – The WOW RUSS multiprobes
 The Russ Unit multiprobe sondes
pH reference
DO
pH
pH
EC
DO
EC
turbidity
Turbidity
(with wiper)
Ion specific
electrodes
YSI 6800 series
Developed by: E. Ruzycki and R. Axler
Hydrolab
Updated: Dec 2, 2003
U3-m8b-s25
DO - calibration
Most common calibration for field or lab is
saturated air method:
1. Equilibrate sensor in sealed cup with wet
2.
3.
4.
5.
6.
toweling
Blot membrane if water droplets are present
Assume 100% O2 saturation
Correct for barometric pressure (usually just the
elevation effect)
Correct for salinity in estuaries
Make sure you are using a temperature
compensated probe
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s26
DO - calibration
If low DOs are expected, a zero DO solution can
be made by:
1. Sparging (bubble) water with an airstone fed by a tank of
N2, Ar or He; or
2. An excess of sodium sulfite and a trace of cobalt chloride
to a sample
 Be aware that if a water sample makes you wretch from
H2S smell (rotten egg gas), it must have zero DO. A
good way to check your meter. You can use the
measured “offset” value to correct your higher DO
values.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s27
DO zero offset calibration
SHAGAWA LAKE RUSS SITE. Manual profile taken 9/06/01 09:20 hrs
(http://wow.nrri.umn.edu/wow/data/other/shag_manual.xls)
Field Notes
Observers:emr, jrh, cat, jmr
Instrument - YSI 85
air calibration
Weatherair temp: 21 oC (70 F)
hazy overcast
wind S 10 mph
secchi - 1.2 m
bottom water -10 and 12 m
samples had H2S odor
bottom - 12.5 m
Z
(m)
0
1
2
3
4
5
6
7
8
9
10
11
12
Developed by: E. Ruzycki and R. Axler
T
(oC)
21.1
21.1
21.1
21.0
21.0
21.0
21.0
20.6
20.4
19.5
17.0
137
13.1
DO
(mg/L)
9.1
9.0
9.0
9.0
8.8
8.8
8.8
7.4
6.9
1.9
0.2
0.3
0.3
DO
(% sat)
102%
101%
101%
101%
99%
99%
99%
83%
77%
21%
2%
2%
3%
Updated: Dec 2, 2003
EC25
(uS/cm)
82
82
82
82
82
82
82
82
83
92
134
166
196
U3-m8b-s28
DO field measurements – precautions
• Winkler method:
• When sampling, avoid contact with air and
agitation, and keep out of direct sunlight.
• Exposure to sunlight, and temperature and
pressure changes will affect O2 content
http://www.epa.gov/owow/estuaries/monitor/c
hptr09.html
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s29
DO field measurements – precautions
• Teflon membrane sensors
• bubbles, wrinkles and pinholes –replace (diagnostic:
slow response or gradual increase with depth when not
expected)
• bottom muck from lowering into bottom sediments –
shake in lake
• siltation & bioslime growth in continuous in situ monitors
– clean/replace
• The rubber pressure diaphragm can become brittle and
crack – replace (diagnostic: DO may seem to increase
with depth when not expected)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s30
DO field measurements – precautions
Teflon membrane sensors (cont):
 Anode tarnished – silver turns black from sulfide
poisoning; see instrument manual
 Cathode tarnished – buff gold ring w/ blotter paper or if
necessary 600 grit emery paper
 Change membrane monthly
 DO % saturation exceeds 100% = Supersaturation: see
next slide
USGS DO meter troubleshooting table (appendix 2)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s31
DO field measurements – supersaturation
 Supersaturation -
possible causes:
temperature
DO %
saturation
 Photosynthesis
 High pressure
>100% sat ?
injection below
dams
 Air/Water
equilibration
(potential error)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s32
DO Field profiles – supersaturation
 Here’s the raw profile data from Medicine Lake
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s33
DO field sensors – cleaning & calibrating
A nice clean Hydrolab sonde-before…
YSI calibration
a month of periphyton
growth
Hydrolab
calibration
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s34
DO field sensors – membrane installation
1. Fill reservoir with
saturated KCl solution
then stretch a new
membrane on to the
probe
2. Stretch the O-ring
on avoiding touching
the top of the
membrane with your
fingers
3. Trim off the excess
membrane. Invert the
probe and check for
air bubbles.
4. If bubbles or wrinkles are present, guess what? You get to do it all over again !
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s35
DO field sensors – membrane installation
 Note – if you get really good you can use this
two-handed, no knees technique
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s36
DO field measurements – helpful tips
 Replace the membrane at
least monthly.
 Change the membrane
the day before you need it
and let it sit “on” in a
bucket of water overnight
to stabilize (called
“polarization”).
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s37
DO field measurements – helpful tips
 Avoid prolonged periods in anoxic, high H2S
water – most manuals state that this can
poison the sensor although some of us have
never experienced this.
 This is very important for continuously deployed data
logging sensors. Don’t “park” it in anoxic zones for
extended periods.
 If in doubt, check the sensor in surface water – it should
rise within a few minutes from zero to >80% saturation.
 If your multi-sensor probe is equipped with a
stirrer or circulator make sure it is turned on.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s38
DO field measurements – helpful tips
 Equilibration time is
critical - it takes longer,
the steeper the O2
gradient. It may take >5
minutes at the oxycline
(where it drops abruptly
to near zero).
 Make sure the line is
taut and vertical !! The
data is worthless if you
report the wrong depth
because of
trigonometry.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s39
DO field measurements – helpful tips
 Never leave your DO
meter sitting outside,
uncovered for 3
years. It voids the
warranty.
 Lower the cable +
probe into the water,
not the meter box,
even if the cable is
too short to reach
bottom.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s40
DO field measurements – error example
 Shagawa lake, May 2002 : DO profiles “seemed” funky
during this period.
 Here’s the table of data for May 11, see how the DO values
are up and down with depth but temp and EC are uniform?
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s41
DO field measurements – error example
 To the right is an
example of the color
mapper and line plot set
for DO data from
Shagawa Lake.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s42
DO field measurements – error example
 Here’s the QA/QC manual profile that we trust
from May 7, 2002.
EC @ 25 C
Lake
Date
depth (m) temp C
Shagawa 5/7/02 9:44
0.0
6.2
1.0
5.7
2.0
5.5
3.0
5.4
4.0
5.4
5.0
5.4
6.0
5.4
7.0
5.4
8.0
5.3
9.0
5.3
10.0
5.3
11.0
5.3
11.5
5.3
Developed by: E. Ruzycki and R. Axler
uS/cm
Updated: Dec 2, 2003
DO (mg/L) DO (% Sat)
82
11.3
90.8
82
11.3
90.4
83
11.4
89.9
83
11.3
89.6
83
11.2
88.6
84
11.1
88.2
84
11.1
88.1
84
11.1
87.5
84
11.1
87.5
84
11.0
87.0
84
11.0
86.7
84
11.0
86.8
84
10.9
86.1
U3-m8b-s43
DO field measurements – error example
 The WOW DxT tool doesn’t really help much unless you
look carefully at those low DO vertical bars on 5/10 and
5/11 from 9-14 m depth. Are they real?
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s44
Specific electrical conductivity = EC25
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s45
EC25 - importance
 Cheap, easy way to characterize the total
dissolved salt concentration of a water sample.
 For tracing water masses and defining mixing
zones.
 Groundwater plumes
 Stream flowing into another stream or into a lake
or reservoir
 For characterizing density stratified layers in a
lake.
 Lots of data examples from WOW lakes
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s46
EC25 – units and reporting
 Principle of measurement
 A small voltage is applied between 2 parallel
metal rod shaped electrodes, usually 1 cm apart.
 Measured current flow is proportional to the
dissolved ion content of the water.
 If the sensor is temperature compensated to
25oC, EC is called “specific” EC (EC25)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s47
EC25 – units
 What in the world are
MicroSiemens per centimeter (µS/cm)?
 Units for EC and EC25 are mS/cm or μS/cm
@25oC. The WOW site reports it as EC @25oC
(in μS/cm).
 Usually report to 2 or 3 significant figures (to + ~
1-5 μS/cm).
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s48
EC 25 – probe visuals
 YSI 33-field conductivity
meter (with metered,
weighted cable).
1 cm
thermistor
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s49
EC 25 – probes
Temperature
probe
Conductivity
bridge
Conductivity
and temperature probe
Hydrolab (Surveyor II)
Developed by: E. Ruzycki and R. Axler
YSI 6820
Updated: Dec 2, 2003
U3-m8b-s50
EC 25 – calibration
KCl is the typical standard
Standard concentrations
should approximate field
values
Dry solid KCl at 105oC for
1 hr, cool, then weigh
Dilute volumetrically to 1L
with lab grade deionized
water (<0.1 uS/cm)
Note- table values are in
mS/cm = milliSiemens/cm.
(1000 uS/cm = 1 mS/cm)
Developed by: E. Ruzycki and R. Axler
KCl Molar
Concentratio
n
KCl
g/L
EC25 (mS/cm)
0.5
37.28
58.64
0.2
14.92
24.82
0.1
7.46
12.90
0.05
3.728
6.668
0.02
1.492
2.76
0.01
0.746
1.413
0.005
0.3728
0.718
0.002
0.1492
0.292
0.001
0.0746
0.147
0.0005
0.0373
0.074
Updated: Dec 2, 2003
U3-m8b-s51
EC 25 – field example
 When a reasonably
productive lake such as
Shagawa stratifies in the
summer there will
typically be an increase
in EC25 with depth.
 This is mostly due to the
buildup of carbonic acid
(H2CO3) and
bicarbonate (HCO3-)
from bacterial
decomposition of
organic matter.
Developed by: E. Ruzycki and R. Axler
Hypolimnetic
EC25 increase
Updated: Dec 2, 2003
U3-m8b-s52
EC 25 – field example
 Electrical conductivity is
a good parameter for
showing how the mixed
epilimnion differs from
the hypolimnion.
 Example - Ice Lake, MN
 Its profile in midsummer in
stratified Ice Lake shows
the buildup of salts below
the thermocline.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s53
EC25 – troubleshooting
Some common errors include:
 Not immersing the entire probe in the sample
 Forgetting to report as specific conductivity: i.e.
reporting values without temperature correction.
 To re-calculating non-temperature corrected reading
use:
Cm
C25 
1  0.0191(t m  25)
Where, C25 = corrected conductivity value adjusted to 25 oC
Cm = actual conductivity measured before correction; and
tm = water temperature at time of Cm measurement.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s54
EC25 - troubleshooting
Symptom
Possible cause and corrective action
Will not calibrate to standards
use fresh standards
Electrodes dirty
Air trapped in conductivity sensor
Weak batteries
Temperature compensation incorrect
Sensor constant incorrect
Erratic instrument readings
Loose or defective connections
Broken cables
Air trapped in conductivity sensor
Rapid changes in water temperature
Broken sensor
Instrument requires frequent
calibration
Temperature compensator not working-measure
conductivity of a solution. Place solution in a water
bath and raise solution temperature to about 20oC.
Measure conductivity again
Allowing sufficient time for temperature of
conductivity sensor to equilibrate to temperature of
solution. If the two values differ by 5% or more,
replace the conductivity sensor
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s55
EC25 and total dissolved solids (TDS)
 TDS concentration of a water sample can be
estimated by multiplying its normalized EC
(EC25) by a factor of between 0.5 and 1.0 for
natural waters, depending upon the type of
dissolved solids.
 A widely accepted value to use for a ballpark
“guestimate” is 0.67.
TDS (ppm)  EC @ 25oC (S/cm) x 0.67
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s56
Examples of EC25 and TDS concentrations
Divide Lake
Lake Superior
Lake Tahoe
Grindstone Lake
Ice Lake
Lake Independence
Lake Mead
Atlantic Ocean
Great Salt Lake
Dead Sea
EC25 (µS/cm)
TDS (mg/L)
10
4.6
97
63
92
64
95
65
110
79
316
213
850
640
43,000
35,000
158,000
230,000
?
~330,000
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s57
EC25 and total dissolved solids (TDS)
 How much salt is there in a body of water?
 Below is a representation of what is dissolved in
a liter of water from the previous examples.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s58
pH
Image courtesy of USGS at http://www.usgs.gov/
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s59
pH – importance in aquatic systems
 The pH of a sample of water is a measure of the
concentration of hydrogen ions.
 pH determines the solubility and biological
availability of chemical constituents such as
nutrients (phosphorus, nitrogen, and carbon)
and heavy metals (lead, copper, cadmium, etc.).
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s60
pH - reporting
 pH can be measured electrometrically or
colorimetrically (pH paper) BUT ONLY the
former technique is approved by the EPA and
USGS for natural waters.
 The electrometric method uses a hydrogen ion
electrode.
 pH meters require extensive care in handling
and operation.
 Report to the nearest 0.1 standard pH unit
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s61
pH – probes
 Field probe types:
 Combination probes (e.g.YSI)
 Less expensive; more rugged design
 Less precise
 Shorter life because reference solution cannot be
replenished
 Separate reading and reference electrodes (e.g.,
Hydrolab)
 Costs more
 More precise; faster response time
 Allows user maintenance; Teflon junction and electrolyte
can be replaced
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s62
pH – probes
 Or, alternatively, a
bench or hand-held
meter and probe can
be used in a fresh
subsample if you
don’t have a field
meter with a pH
probe.
Image courtesy of USGS at http://www.usgs.gov/
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s63
pH – submersible probes
YSI 556
pH
electrode
pH
electrode
pH electrode
pH
reference
and Teflon
junction
Hydrolab
MiniSonde
YSI 6820
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s64
pH - calibration
 Calibration
 Two point calibration
 Use pH 7.0 and either pH 4 or 10 for the second
point depending on the anticipated sample pH.
 pH is temperature dependent; most meters
compensate for the temperature effect (not as
strong an effect as for EC)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s65
pH - calibration
 Buffers/standards
 pH measurements are only as accurate as the
buffers used for calibration.
 Discard buffers after their expiration dates.
 Be careful not to contaminate stock solutions
with used buffer, rinse water or with a different
buffer.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s66
pH – probe maintenance
 Gel-filled electrodes:
 do not require filling but cannot be left in dilute
water for extended periods (KCl solution leaches
out over time).
 Store in tap or lake water for short periods of
time and KCl solution or old pH 4 buffer for
longer periods of time.
 DO NOT STORE PROBE DRY.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s67
pH – probe maintenance
 Liquid-filled electrodes:
 replace junction and electrolyte per
manufacturers instructions.
 Tap water is OK for longer term storage but
electrolyte must be replaced before use.
 DO NOT STORE PROBE DRY.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s68
pH – field example
Lake Independence, MN
 pH in a stratified
eutrophic lake will often:
 decrease in the
hypolimnion due to
build-up of CO2 from
organic matter
decomposition.
 increase near the
surface due to the
removal of CO2 from the
water by algal
photosynthesis.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s69
pH – field example data table
 Lake Independence, MN July 7, 1999
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s70
pH – troubleshooting
 Common error
 Probes will often calibrate fine in strong ionic
strength buffers but will not read accurately in
lower ionic strength surface waters. If you
suspect this is the case, use low ionic strength
buffers.
 Electrode cleaning
 Rinse with deionized water after each use
 Rejuvenation procedures vary with probe type.
You must refer to the manufacturer’s guidelines.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s71
Symptom
Possible cause and corrective action
Instrument will not
calibrate full-scale
Buffers may be contaminated or old
Faulty electrode
Weak batteries-
Slow response time
For liquid-filled electrodes
 Weak filling solution-change filling solution
 No filling solution-add fresh solution
 Dirty tip-clean with soap solution. Do not scratch electrode tip.
 Chemical deposits-place electrode in a 0.1 M HCL solution for about 30
minutes
 Clogged or partially clogged junction-unclog by placing electrode in 0.1 M KCl
solution for about 90 minutes.
 Water is cold or of low ionic strength-longer equilibration time is needed Weak batteries-replace
For gel-filled electrodes
 Dirty bulb-rinse with deionized water
 Clogged junction-liquefy gel by placing electrode into warm (~60oC) water for
one minute or less.
Erratic readings
Loose or defective connections
Broken or defective cable
Static charge
Loose battery connection
Air bubbles in the electrode bulb
Weak batteries
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s72
Water clarity (transparency)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s73
Water clarity (transparency)
 Water clarity (transparency) is used routinely
as an indicator of the condition and
productivity of lakes.
 Three common methods of measuring clarity
are discussed:
 Secchi depth: lakes, deep rivers, estuaries
 Turbidity and transparency tube:
- streams, ponds/wetlands, coastal zones
 Light meters (radiometers): lakes, deep rivers,
estuaries
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s74
Water clarity - Secchi disk
 A powerful tool in detecting
long-term trends in lakes
because it is cheap, easy to
use and usually linked to
algal growth, nutrient levels
or sediment inflows.
Where are their PFD’s ?
www.pca.state.mn.us/water/clmp.html#what
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s75
Secchi disk – Angelo Secchi
 The Secchi disk originated
with Fr. Pietro Angelo
Secchi (pye'trO än'jAlO
sek'kE), a renown Italian
astrophysicist and scientific
advisor to the Pope.
 At the request of the Papal
Navy, Secchi measured the
clarity of water in the
Mediterranean Sea in April
of l865 using white disks.
Angelo Secchi (1818-1878)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s76
Other noteworthy Secchi’s …
4.Fettuccine com funghi secchi
1. Walmir Secchi Latin Dance Center
2. Olive oil
3. What configuration of the corona leads to a Coronal Mass Ejection ?
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s77
Secchi depth
 Equipment
 A secchi disk and
metered rope or chain
 Black and white or all
white? What size?
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s78
Secchi depth
 Method
 Measurements should be made as near to
midday as possible (10AM - 3 PM when sunny
and calm is optimal)
 Try to lower it in the shade of the boat
 Slowly lower the disk into the water until it
disappears and note the depth
 Lower the disk a little further, then slowly raise
until the disk reappears and note the depth
again.
 Average the two readings and record
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s79
Secchi trend analysis example
U. of Arizona GLOBE Project -http://www.hwr.arizona.edu/globe/
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s80
Mean annual Secchi data
Is there a true
trend over time
?
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s81
Monthly Secchi trends
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s82
Monthly Secci
Significant
Secchi
trends
trends
http://www.cee.vt.edu/program_areas/environmental/teach/smprimer/secchi/secchi.html
 How many secchi depth
measurements are needed to
detect a significant trend ?
 Depends on the lake
 Minnesota study (MPCA):
 > 4 readings (i.e. at least monthly
from Jun-Sep) for 8 -10 yrs for
statistically significant trend (20%
change) at the 10% level of
confidence.
 Means there is a 10 % chance of
identifying a trend that doesn't exist.
Yoyo secchi
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s83
Secchi long-term trends- Lake Tahoe
 Visibility has decreased by over 35 feet in the last 40
years.
 Secchi depth is directly related to the amount of
suspended matter, both organic (largely algal growth)
and inorganic.
 http://trg.ucdavis.edu/research/response.html
•http://minerals.usgs.gov/west/reno/gallery.html
www.development.ucdavis.edu/tahoe/trg_update_apr_99
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s84
Lake Tahoe – eutrophication story
Data courtesy of C.R. Goldman and J.E. Reuter, Tahoe Research Group, U. of California-Davis,
http://www.news.ucdavis.edu/tahoetv/
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s85
Tahoe Secchi –
- models
models
The thousand $$ version
http://www.development.ucdavis.edu/tahoe/trg_update_sept_98
The million $$ version
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s86
Field replication
secchi
flow
http://voyager.snc.edu/.../pictures/
secchi/pages/015.html
dissolved O2 / temperature
Developed by: E. Ruzycki and R. Axler
in situ
Updated: Dec 2, 2003
U3-m8b-s87
Water clarity – transparency tubes
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s88
Water clarity – transparency tubes
 Used in streams, ponds,
wetlands, and some
coastal zones
 Analogous to Secchi
depth in lakes: a measure
of the dissolved and
particulate material in the
water
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s89
Water clarity – transparency tubes
 Useful for shallow water
or fast moving streams
bodies where a Secchi
would still be visible on
the bottom
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s90
Water clarity – transparency tubes
 Best for clearwater bodies of
http://www.forestry-suppliers.com/
water (not stained with
dissolved organic compounds
from bogs) but not too clear
water
 It is a good measure of turbidity
and suspended sediment
(TSS)
 Used in many volunteer stream
monitoring programs
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s91
Water clarity – transparency tubes
 How does Turbidity relate to TSS ?
 A general rule of thumb:
 1 mgTSS/L ~ 1.0 - 1.5 NTU’s of turbidity
 BUT – Turbidity scattering depends on particle size
so this is only a rough approximation
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s92
Water clarity – turbidity
 Turbidity measures the
scattering effect
suspended particles
have on light
 inorganics like clay and
silt
 organic material, both
fine and colored
 plankton and other
microscopic organisms
Even small amounts of wave action can erode
exposed lakeshore sediments, in this case a
minepit lake from northeastern Minnesota.
Guess the mineral mined here.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s93
Turbidity
 Field turbidity measurements are made with
 turbidimeters (bench meter for discrete samples)
 Submersible turbidity sensors (Note - USGS
currently considers this a qualitative method)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s94
Turbidity
 Turbidimeters -
Nephelometric optics
 nephelometric turbidity
estimated by the
scattering effect
suspended particles
have on light
 detector is at 90o from
the light source
http://www.bradwoods.org/eagles/turbidity.htm
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s95
Turbidity – units and reporting
 Nephelometric Turbidity Units (NTU)
 standards are formazin or other certified
material
 JTU’s are from an “older” technology in which
a candle flame was viewed through a tube of
water
 1 NTU = 1 JTU (Jackson Turbidity Unit)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s96
Turbidity – formazin units
 Formazin is most commonly the standard for
turbidity
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s97
Turbidity – clay example
 Here’s a sample containing clay particles with
corresponding NTUs
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s98
Turbidity – meters and probes
 Bench and portable instruments and kits vs
Submersible Turbidimeters
YSI 6820 with
unwiped
turbidity
YSI wiping
turbidity
Hydrolab
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s99
Turbidity - methods
 Comparability of different methods:
 With the proliferation of automated in situ
turbidity sensors there is concern about the
comparability of measurements taken using very
different optical geometries, light sources and
light sensors.
 The US Geological Survey and US
Environmental Protection Agency are currently
(August 2002) developing testing procedures for
a field comparison of a number of instruments
produced by different manufacturers.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s100
Turbidity - calibration
 Turbidity free water = zero (0 NTU) standard
 USGS recommends filtering either sample water
or deionized water through a 0.2 um or smaller
filter to remove particles
 WOW uses deionized water that is degassed by
sparging (bubbling) with helium to minimize air
bubbles that give false turbidity readings
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s101
Turbidity – standards
 Standards range depends on anticipated
sample values:
 Lakes - typically 0-20 NTU
 Streams and wetlands - 0-20, 0-50 or 0-100 NTU
 2 non-zero standards typically adequate
(response is linear)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s102
Turbidity - standards
 Types of standards
 Formazin particles (either from a “recipe” or
purchase a certified, concentrated stock solution
(usually 4000 NTU)
 other materials - polystyrene
 need to worry about storage limits - primary
stock of 400 NTU’s lasts < 1 month when
refrigerated. Dilute working standards from
intermediate stock solution daily.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s103
Turbidity – standards
Source
Concentrations
Hach Company
Suggested holding times
2 to 20 NTU
Prepare daily
20 to 40 NTU
Prepare monthly
Standard Methods
All dilutions
Prepare daily
EPA
All dilutions
Prepare weekly
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s104
Light
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s105
Light – importance in aquatic systems
 Primary production (PPr; photosynthesis)
 Euphotic (photic) zone = layer where there is a
positive net daily PPr
 from surface to depth where irradiance ~0.51% of surface light
 stratum of net O2 production & CO2 -fixation
during the day
 Aphotic zone = bottom of photic zone to lake
bottom
 too little light for photosynthesis
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s106
Light – importance in aquatic systems
 Plant germination (macrophytes)
 Navigation, predation, breeding behavior, prey
refugia
 Heat (see Module 3 and WOW Lake Ecology
Primer)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s107
Light profiles – radiometry
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s108
Light profiles – attenuation
I(z) = I(0) * [ e-kz ]
Ln I(z) = -nz + Ln I(0)
The semi-log plot of Light vs depth
will linearize exponential attenuation
light vs depth plot
Light (% surface)
0
40
20
60
80
Ln light Intensity
100
0.00
0
10
4.00
6.00
8.00
0
A
A
5
B
15
Depth (m)
Depth (m)
5
2.00
B
10
15
20
20
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s109
Light – definitions
 Io = the irradiance at the water surface
 Iz = the irradiance at any depth z
 Z sd = Secchi depth
 Euphotic zone = layer where there is a positive
net daily primary productivity
 Aphotic zone = bottom of photic zone to lake
bottom
I(z) = I(0) * [ e-kz ]
or Ln I(z) = -nz + Ln I(0)
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s110
Light reference charts
http://www.intl-light.com/handbook/
http://www.physicsclassroom.com/
http://www.physicsclassroom.com/
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s111
Light – relationship to Secchi depth
 light at Zsd is about 10% I0
 n (in m-1) ~ 1.7/ Zsd
 euphotic zone = maximum
depth at which algae and
macrophytes can grow.
 Usually where light is
0.5%–1% of surface light
 euphotic zone = 2 - 3 times
the Secchi depth
http://www.dnr.state.wi.us/org/water/wm/np
s/waterquality.htm
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s112
Light energy distribution
Scattered ~5-20%
WATER
Reflected ~5-6%
(also called albedo)
Absorbed ~75%
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s113
Chlorophyll
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s114
Chlorophyll - importance
 Measuring chlorophyll-a
is a long-accepted
method for estimating
the amount of algae in
lakes.
 Chlorophyll-a is the
green pigment that is
responsible for a plant's
ability to convert sunlight
into the chemical energy
needed to fix CO2 into
carbohydrates.
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s115
Chlorophyll – probes
 In-situ (in-lake) chlorophyll probes are
relatively new and are becoming increasingly
popular for lake monitoring.
 But are they Quantitative, Semi-quantitative or
Qualitative?
FLUORESCENCE  CHLOROPHYLL a
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s116
Chlorophyll – probes
 Probes currently cannot replace the traditional
filtered and extracted chlorophyll a techniques
for a number of reasons:
 Physiological effects: fluorescence per unit
chlorophyll a concentration can change based
on algal physiology.
 Ambient light and temperature also affect in situ
fluorescence readings.
 The light history of the algal cells will affect their
fluorescence
 Temperature correction is also necessary
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s117
Chlorophyll – probes
SCUFA chlorophyll
sensor
Fluorescence
probe with wiper
Hydrolab Minisonde with
Turner-Designs SCUFA
YSI 6820
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s118
Appendices
Unit 3 Module 8
Part B Field Profiles
Appendix 1
Image from Wasington State DEP
http://www.ecy.wa.gov
BACK
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s120
Appendix 2
DO meter
Troubleshooting
chart
BACK
Developed by: E. Ruzycki and R. Axler
Updated: Dec 2, 2003
U3-m8b-s121