Turbidity and chlorophyll
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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.

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Ysi yellow springs inc
YSI (Yellow Springs Inc)

https://www.ysi.com/ysi/Products



Hach hydrolab
HACH - Hydrolab

http://www.hydrolab.com/sondes.asp



Turbidity
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,

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 Statesenvironmental monitoring the turbidity standard unit is called Nephelometric Turbidity Units (NTU)

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


Turbidity standards
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
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)


  • 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

Light Limitation is the Principal Determinant of SAV Distribution Water Quality drives light limitation


Calibration
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
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!!!




Chlorophyll excitation
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




Light rct and fluorescence
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
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
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 fluorometer1
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
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
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


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