will be a series of articles for people who
want to obtain the best possible results from their fluorometer. For
example, you may have wondered what causes the variations in your
fluorometer readings when you know your sample concentration has not
changed.
The articles will cover: how to optimize your fluorometer
installation; understanding how instrument specifications can affect
readings; the impact of non-controllable variables such as
environmental considerations; and other factors that can influence
the accuracy and repeatability of your measurements.
This first article is for engineers monitoring chlorophyll a, in
a continuous flow mode, using a fluorometer such as the Turner
Designs AlgaeWatch.
Plumbing Kit Accessories Improve Measurement Repeatability
Two factors that can cause chlorophyll measurements to "drift"
with time result from 1) build up of biofouling organisms (bacteria,
algae, etc.) in the flow cell of the fluorometer and 2) air bubbles
resulting from intermittent flow of sample water through the flow
cell. To reduce these effects on measurement repeatability, Turner
Designs offers two plumbing Kits for use with the AlgaeWatch: an
Inlet Kit, see Photo 1, and an Outlet Kit shown in Photo 2. The
Inlet Kit is designed to address the problems of debris in the water
affecting the measurement of the amount of chlorophyll present.
The basket strainer should be cleaned regularly depending on: the
water conditions, and the efficiency of any earlier filtering that
has been done before the pump in the system. (The basket strainer
is conventional, and provides easy access to all parts for convenient
cleaning).
The next component in the Inlet Kit is the Flow Switch
with its electrical connection to the AlgaeWatch. For optimal
measurements, the sample stream should be between 0.5 and 1.25 gpm.
The purpose of the Flow Switch is to send a signal to the
fluorometer if the sample stream flow falls below 0.5 gpm. (To
prevent control valve chatter, or unnecessary relay action, the
fluorometer needs to see the "no-flow" signal for more than 5
minutes before turning on the alarm flag on the display).
The third component is a Pressure Gauge calibrated to read up to
100 psi, the maximum specified pressure for the sample cell.
The Outlet Kit has a 3-Way Valve. Purpose of this valve is to
make it easy to collect a sample of the water being measured for
extraction purposes. (Extraction is a process for obtaining pure
chlorophyll that can be measured very precisely, and then correlated
to the fluorometer readings of chlorophyll in the water).
Summary
The inlet plumbing kit is used to "condition" the inlet water to
the sample cell to extend the time interval between cleaning the
flow cell, and to ensure there is a consistent flow of water. These
steps will reduce the "drift" in fluorometer readings from biofouling
effects, and/or inadequate water flow in the sample cell. Next month's
article will describe a recommended procedure for cleaning the flow
cell as part of your regularly scheduled maintenance routine. Further
information on the AlgaeWatch Plumbing Kit is available here.
Turner Designs announces that, effective immediately, it
has added online sales for its Aquafluor line of fluorometers and
accessories to its website.
Jim McCormick, our Tech Support Manager, has been with Turner
Designs for over 15 years and has extensive experience with our entire
line of instruments.
The Water Resources Division of the United States
Geological Survey in Menlo Park, CA are using chlorophyll fluorometers
in San Francisco Bay to provide critical data that is being used as
part of the Plankton Dynamics Project. Fluorescence is a known proxy
for phytoplankton biomass - the USGS utilizes moored fluorometers
in San Francisco Bay and the Sacramento-San Joaquin Delta combined
with underway and laboratory fluorometers to determine the abundance
and productivity of planktonic microalgae in order to define and quantify
some important processes:
One, soon to be two, permanently moored SCUFAs at the
Dumbarton Bridge, South San Francisco Bay. Surface and bottom high
frequency sampling - helping us understand not only total biomass
of phytoplankton, but information on how blooms develop and exactly
when they develop. They are presently working on radio-telemetering
this data so that we can access it real time on the web. 
