Turbidity and Chlorophyll
Lecture 3
YSI (Yellow Springs Inc)
https://www.ysi.com/ysi/Products
YSI sensors
HACH - Hydrolab
http://www.hydrolab.com/sondes.asp
Some Hydrolab sensors
Turbidity
http://en.wikipedia.org/wiki/Turbidity
• Measure of suspended particles in water – can
include inorganic (sediments) as well as organic
(bacteria, plankton).
• High turbidity reduces light transmission (by both
absorption and scattering), i.e. larger light
attenuation coefficient (K).
• Can measure with secchi disk (secchi depth, cm)
• Can measure by weight (total suspended solids
(TSS, mg/L)
• Can measure with turbidimeter = nephelometer
(NTU)
NTU
• Nephelometric Turbidity Units (NTU)
Nephelometer comes from the Greek word for cloud, nephos,
dete
ctor
mirror
A more popular term for this instrument in water quality testing is a turbidimeter.
However, there can be differences between models of turbidimeters, depending upon
the arrangement (geometry) of the source beam and the detector. A nephelometric
turbidimeter always monitors light reflected off the particles and not attenuation due to
cloudiness. In the United States environmental monitoring the turbidity standard unit is
called Nephelometric Turbidity Units (NTU)
http://en.wikipedia.org/wiki/Nephelometer
Turbidity standards
• Formazine based (carcinogenic) – typically
4000NTU stock diluted. Need to test
against NIST standards. Precipitates
unless stirred constantly.
• AMCO beads – non-toxic. Long shelf life.
More expensive. Slightly different
scattering properties.
http://www.amcoclear.com/products/water.s
tandards.php
Some NTU numbers
•
•
•
•
•
DI or RO water (approx 0 NTU)
Tapwater (<0.3NTU)
Surface waters clear (<5NTU)
Surface waters visibly turbid (10-50NTU)
Silted waters from erosion (up to 1000NTU)
• Problems for fish/organisms (>50-100NTU)
• Protect benthic seagrasses (<5-10NTU)
Light Limitation is the Principal
Determinant of SAV Distribution
Water Quality drives light limitation
TSS
• Secchi depth (m) or attenuation coefficient
(Kd) in 1/m
• Light-limitation depends on water quality
• Light is absorbed (a) and scattered (b) by
water+TSS+color+chl a
• From mathematical models of light
absorption and scattering a direct link
between water quality and light available to
SAV can be calculated.
U.S. Coastal States Water-Quality Criteria for Turbidity
Patrick Biber - Univ. of North Carolina, Chapel Hill
Best
Numerical Exceed Exceed
Year Criterion+ 25NTU1 5NTU2
Region
State
Criteria for saltwaters (surface WQ standards)
NE
Connecticut
not to exceed natural origin, use BMPs (FW <5NTU over backgrnd)
1997
NE
Delaware
<10NTU above background natural turbidity
1999
NE
Maine
no turbidity criteria
2000
NE
Massachussetts
free from turbidity that aesthetically objectionable or impair any use
1993
NE
New Hampshire
<10NTU above background natural turbidity
NE
Rhode Island
<5NTU above background (SA), <10NTU above background (SB, SC)
CEN
Maryland
not exceed 50NTU monthly avg, not exceed 150NTU point msr
CEN
New Jersey
CEN
+10
-15
5
1999
+10
-15
5
1997
+5
-20
0
1995?
50
25
45
<10NTU 30 day avg, <30 NTU point msr
2002
10
-15
5
New York
no increase that will cause substantial visible contrast to natural conditions
1999
CEN
Virginia
no turbidity criteria
1997
SE
Florida
<29NTU above background natural turbidity
1996
+29
-4
24
SE
Georgia
free from turbidity that results in a substantial visual contrast due to man-made activity
2000
SE
North Carolina
not exceed 25NTU, if natural background >25 NTU no increase over background permitted
1996
25
0
20
SE
South Carolina
not exceed 25NTU provided existing uses maintained
1976?
25
0
20
GOM
Alabama
<50NTU above background natural turbidity
2002?
+50
25
45
GOM
Louisiana
estuarine lakes, bays, bayous <50NTU
2000
50
25
45
GOM
Mississippi
<50NTU above background turbidity beyond a 750ft mixing zone at time of discharge
1995
+50
25
45
GOM
Texas
no substantial and persistent changes from ambient conditions
1997
PAC
Alaska
not exceed 25NTU, not increased Ksecchi by more than 10%
2003
25
0
20
PAC
California
Wastewater to oceans = 75NTU 30 day avg, 100NTU 7 day avg, max 225NTU point msr
1990
75
50
70
PAC
Oregon
<10% cum increase relative to upstrm control location, except in emergency/construction w BMPs
2001
PAC
Washington
<5NTU above background when <50NTU, <10% above background otherwise (AA, A); <10NTU above
background when <50NTU, <20% above background otherwise (B, C)
1997
+5
-20
0
HA
Hawaii
Estuaries and embayments = geom mean <1.5NTU, 90% of time <3NTU, 98% ot time <5NTU
1992?
1.5
-23.5
-3.5
NAT
FEDERAL
no turbidity criteria
NB: Hawaii only state that has turbidity criteria that appear to be fully protective of seagrasses to depths >1m
+
Numerical criterion based on background of 0 NTU
1,2
Turbidity levels associated with minimum light requirements for seagrass at 1m depth in 1. North Carolina and 2. Chesapeake Bay
Calibration
• Always check expiration dates. Make
Formazin solutions fresh EACH time –
check against a standard in turbidimeter
before use.
• Always check 0 NTU first (DI water)
• Always use a standard higher than max
value expected (e.g. 10 NTU or 100 NTU)
• ALWAYS check for AIR BUBBLES – this
is the major source of error or bad data.
Chlorophyll Fluorescence
• Derived from light NOT used for
photosynthesis.
• A proxy for phytoplankton concentration (=
abundance of cells)
• Affected by amount of photosynthesis
happening as well as cell density.
• Can vary widely over the course of a day
FOR THE SAME AMOUNT OF CELLS!!!
Photosynthesis
Chloroplast
Chlorophyll Excitation
• Each quantum of light absorbed by a
chlorophyll molecule rises an electron from
the ground state to an excited state.
Light reaction – Z scheme
http://www.steve.gb.com/science/photosynthesis.html
http://www.geosciences.unl.edu/~dbennett/physiology.html
Photosynthesis
3%
Light Energy “Usage”
Light Rct and Fluorescence
IN VIVO - LIVING CELLS:
• Not all light is used for photosynthesis, i.e.
for electron transport in the light reaction.
• Depending in species, conditions,
physiological state, some or most of light
is converted to fluorescence (measurable)
or heat (“not” measurable)
IN VITRO – chl extracted with acetone:
• None of the above matters – fluorescence
is directly proportional to chl concentration
METHODS – chl extraction
• EPA standard method 445 (fluorometric) or ESS150
(spectrophotometer) are for phytoplankton.
• Grind sample in solvent (90% acetone) in dark and
keep cold (chl is easily destroyed!)
• Allow to extract overnite in fridge (40C)
• Centrifuge or filter to remove “particles”
• Read Abs or Flr on machine.
• [Acidify with HCL – read phaeophytin and used in
calculations]
• [Other solvents include methanol,
dimethylformamide (DMF), fluorocarbon ionic
surfactant Zonyl FSA, etc.]
Turner TD700 fluorometer
• Sensitive – use for low concentrations
(very faint green color). Best for
phytoplankton.
• Configuring the Turner Designs Model TD-700 Fluorometer for
Method 445.0
• Your fluorometer should be equipped with the following Turner
Designs optical filter kit (or equivalent):
• Optical Kit: PN: 7000-961
Excitation filter: 10-050R color specification 5-60
Emission filter: 10-051R color specification 2-64
Lamp: 10-045 Daylight White Lamp
• http://www.turnerdesigns.com/t2/doc/appnotes/998_6000.html
Turner TD700 fluorometer
• Sensitive – use for low concentrations
(very faint green color). Best for
phytoplankton.
• Configuring the Turner Designs Model TD-700 Fluorometer for
Method 445.0
• Your fluorometer should be equipped with the following Turner
Designs optical filter kit (or equivalent):
• Optical Kit: PN: 7000-961
Excitation filter: 10-050R color specification 5-60
Emission filter: 10-051R color specification 2-64
Lamp: 10-045 Daylight White Lamp
• http://www.turnerdesigns.com/t2/doc/appnotes/998_6000.html
THEREFORE
• In water quality monitoring chl fluorescence is a
RELATIVE indicator of change in phytoplankton
population abundance.
• IT IS NEVER AN ABSOLUTE MEASURE!
• The only “absolute” measure is to take a water
sample, filter to concentrate, extract with
solvent (e.g. 90% acetone), determine sample
chl concentration and back-calculate to in-water
chl concentration after correcting for volume
filtered.
Another note
• Usually chl samples are frozen after filtering,
and run weeks or months later.
• THIS MAY BE A PROBLEM?
• A recent study in Long Island showed about a
30% decrease in extracted chl concentration of
samples frozen longer than 2 weeks compared
to the SAME samples if extracted immediately.
• NUTRIENT MANAGEMENT STRATEGIES
ARE BASED LARGELY ON CHL NUMBERS…
Lab
• Check turbidity standards.
• Calibrate NTU+ sensor and read water
samples.
• Optical sensor maintenance.
• Test chl flr sensor with fluorophore