YSI ADV6600 - Manual (Page 191)

Appendix E. Chlorophyll Measurements
ADV6600
Y S I Environmental
Page 181
analytical procedure has begun. Some users prefer to filter the sample in the field and keep
the filter pads on ice in the dark during transport.
My environmental sites have a lot of visible floating algae, but my YSI 6025 chlorophyll sensor
shows very low readings. What is causing this paradox?
The YSI 6025 is not designed to measure macroscopic algal or plant material that floats on
the surface. Rather it measures the fluorescence from the microscopic phytoplankton that
is suspended below the surface of the water. It is fairly common to see mats of floating
algae on environmental water that has low subsurface phytoplankton concentrations.
What sort of “noise” level is expected for unattended monitoring studies?
All environmental water is somewhat heterogeneous with regard to phytoplankton content
and this factor will cause some noise or jumpiness in long term monitoring studies for
chlorophyll. The extent of the noise will be dependent on the your site. The data from a
typical 36-day deployment at a YSI test site (lake in southwestern Ohio) is shown in the
figure below as a reference.
Note, however, that you may observe less or more noise at your site with no compromise in
sensor performance. Occasional spikes during a monitoring study are normal and usually
simply indicate the transient passage of a large phytoplankton particle over the optical face
during the time of sampling.