A Turner Designs Product Update
Effects Of Turbidity On In Vivo Chlorophyll Fluorescence

Turbidity can have two primary effects on chlorophyll readings:

1. It may increase blank due to increased light scatter.
2. It may reduce the fluorescence reading due to light absorption.

The extent to which turbidity affects fluorescence depends upon the turbidity level, its variability, and the composition of compounds creating the turbid environment. Slight, consistent turbidity levels will have a minimal effect upon in vivo chlorophyll levels. High and variable turbidity levels can introduce significant errors.

Method

To determine and correct for turbidity effects on in vivo chlorophyll readings, you need 3 pieces of information.

1. in vivo chlorophyll data
2. Turbidity data
3. Extracted chlorophyll values of grab samples, which correspond to the in vivo and turbidity data

While taking field measurements, collect periodic grab samples for extracted chlorophyll a analysis (5-10 or more if preferred). If sampling over dramatically different environments (example: freshwater river Þ estuary Þ coastal shelf), you should collect a set of grab samples for each different environment. Extract and measure the chlorophyll from each of your grab samples. With this data, perform a multiple regression, modeling the in vivo chlorophyll data and turbidity data (independent variables) to the extracted chlorophyll data (dependant variable). This can be performed with any number of different statistical or spreadsheet programs.

Calculation

To correct and convert your in vivo chlorophyll data into actual chlorophyll data, create the following equation from the results of your multiple regression:

y =m_xx + m_zz + b

Where:

y = corrected chlorophyll value
m_x = coefficient (slope) for in vivo chl
m_z = coefficient (slope) for turbidity
b = y intercept

Use your turbidity and in vivo chlorophyll data to calculate the actual chlorophyll concentration for the rest of your data.

Field Instrumentation

Turner Designs offers the SCUFA^®™ and Aquafluor™. Both are dual channel fluorometers with dedicated in vivo chlorophyll and turbidity channels, enabling the user to easily collect the appropriate data for the turbidity correction.