YSI ADV6600 - Manual (Page 187)

ADV6600
Y S I Environmental
Page 177
Appendix E. Chlorophyll Measurements
This section is designed to help the user attain the maximum possible benefit from the YSI 6025
chlorophyll system by supplementing the discussions of chlorophyll provided in other sections of
this manual. It does not deal with specific instructions for operation of the sondes at the level
presented elsewhere in the manual.
What is the YSI 6025 chlorophyll probe designed to measure?
The YSI sensor is designed to estimate the phytoplankton content of environmental water.
Phytoplankton concentrations can be useful in predicting detrimental algal blooms and,
indirectly, in determining nutrient loading in environmental applications. The
phytoplankton content is estimated by detecting the fluorescence from the chlorophyll in
these species in vivo, i.e., without disrupting the living cells. Note, however, that the
sensor directly measures the fluorescence of all species in the water sample that occurs
when they are irradiated with blue light (centered at about 470 nm). Usually most of the
fluorescence is due to the chlorophyll in the phytoplankton, but it is important to remember
that any compounds which are present in the water sample (either in chemical or biological
form), and fluoresce under the optical constraints of the sensor, will contribute to the
readings.
What level of accuracy can be expected in my chlorophyll determinations with the YSI 6025?
YSI feels that the user will attain about the same accuracy with the YSI 6025 as with other
commercial fluorometers that are designed to carry out in vivo determinations of
environmental chlorophyll. As for all measurements of this type, the accuracy will be less
than that attained if the user collects water samples and analyzes them in the laboratory by
disrupting cells and quantifying by spectrophotometric or HPLC analysis of the extracted
molecular chlorophyll as described in Standard Methods. The relative accuracy of the in
vivo measurement will be completely dependent on which method of calibration the user
employs. No matter what calibration technique is used, however, the readings from the
YSI 6025 should approximately track the chlorophyll trends in the environmental water
being analyzed. For example, if the user deploys the sensor and acquires readings over
time at a standard sampling interval (e.g., every 15 minutes), the changes in the chlorophyll
data will usually reflect increases or decreases in the phytoplankton content at the site over
a long period of time. If the user makes horizontal or vertical profiling spot readings in the
same body of water, then the sensor output will usually indicate the presence of more or
less phytoplankton at the various sampling sites. The figure below shows the tracking of
the chlorophyll content at various sites by both the YSI 6025 and a good quality single
parameter commercial fluorometer.