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

• 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)

http://en.wikipedia.org/wiki/Turbidity

NTU• Nephelometric Turbidity Units (NTU)

http://en.wikipedia.org/wiki/Nephelometer

detector

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)

Nephelometer comes from the Greek word for cloud, nephos,

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.standards.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

• 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.

TSS

U.S. Coastal States Water-Quality Criteria for TurbidityPatrick Biber - Univ. of North Carolina, Chapel Hill

Region State Criteria for saltwaters (surface WQ standards) Year

Best Numerical Criterion+

Exceed 25NTU1

Exceed 5NTU2

NE Connecticut not to exceed natural origin, use BMPs (FW <5NTU over backgrnd) 1997

NE Delaware <10NTU above background natural turbidity 1999 +10 -15 5

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 1999 +10 -15 5

NE Rhode Island <5NTU above background (SA), <10NTU above background (SB, SC) 1997 +5 -20 0

CEN Maryland not exceed 50NTU monthly avg, not exceed 150NTU point msr 1995? 50 25 45

CEN New Jersey <10NTU 30 day avg, <30 NTU point msr 2002 10 -15 5

CEN 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 FluorescenceIN 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: 7000-961Excitation filter: 10-050R color specification 5-60Emission filter: 10-051R color specification 2-64Lamp: 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: 7000-961Excitation filter: 10-050R color specification 5-60Emission filter: 10-051R color specification 2-64Lamp: 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