Xylem 6-Series Multiparameter - Manual (Page 269)

Principles of Operation Section 5
YSI Incorporated Environmental Monitoring Systems Manual 5-31
experiments indicate that a suspension of phytoplankton measured with a YSI 6025 sensor will have
chlorophyll interference characterized by a factor of about 0.10 µg/L Rhodamine WT per ug/L of
chlorophyll. For example, the chlorophyll content of the water must be above 30 ug/L chlorophyll to
produce an apparent Rhodamine WT reading equal to 3 µg/L. In water with a high algal content, the user
may wish to use the independently-determined chlorophyll value and the above compensation factor to
correct measured Rhodamine values using, for example, a spreadsheet.
5.16 PHYCOCYANIN-CONTAINING BLUE-GREEN
ALGAE
Introduction
Blue-green algae (BGA), also known as cyanobacteria, are common forms of photosynthetic bacteria
present in most freshwater and marine environments. BGA contain a unique set of accessory pigments of
the phycobiliprotein family that serve a variety of roles for the organism. The primary phycobilin pigments
are phycocyanin (PC) and phycoerythrin (PE) and both happen to have strong fluorescent signatures that do
not interfere significantly with the fluorescence of the chlorophylls. This allows for the in vivo detection of
cyanobacteria with minimal interference from other groups of algae. BGA with the PC phycobilin
pigment can be found in both fresh and brackish water environments while BGA with the PE phycobilin
pigment is usually found only in brackish or marine environments.
The monitoring of BGA is of growing interest in a number of research and monitoring fields and of
particular interest is the monitoring of BGA as a public health risk in freshwater and estuarine areas. As
the rates of eutrophication accelerate due to human impacts on aquatic ecosystems, algal blooms are
becoming a more common problem. In the case of BGA blooms, some species can produce toxins
generally referred to as cyanotoxins that can cause health risks to humans and animals. The real-time
monitoring of BGA through fluorometry can serve as an early warning system for potentially hazardous
conditions. In addition to potential toxin production, BGA blooms can also result in water with an
unpleasant appearance, and in the case of drinking water, an unpleasant taste and odor. These problems
adversely affect water quality and diminish the water's recreational utility. Also of concern are high cell
concentrations causing an increase in filter run times in drinking water plants. Thus, monitoring the BGA
population and distribution in lakes, reservoirs and estuarine areas is extremely important for basic
research, resource protection, and public health and safety.
The YSI 6131 sensor, when used in conjunction with YSI 6-series multiparameter sondes, is designed to
detect and monitor the presence of PC-containing BGA in order to eliminate, or at least reduce, their public
health risks and their general effects on drinking water purification.
The determination of BGA as an indicator of water quality has historically been carried out using either (a)
extraction of BGA samples followed by analysis of the extracts by fluorometry, HPLC, or a combination of
the two techniques or (b) the automated or manual counting of actual BGA cells in the known volume of
sample water. While accurate, these types of analytical techniques usually are done as part of a “spot
sampling” protocol and almost never yield continuous data with regard to BGA content. The methods are
time-consuming and usually require an experienced, efficient analyst to generate consistently accurate and
reproducible results. Most importantly, the methods do not lend themselves readily to continuous
monitoring of PC-containing BGA, since the analysis of a collection of samples taken at reasonable time
intervals, e.g., every hour, would be extremely tedious.
YSI has developed the YSI 6131 sensor for the determination of PC-containing BGA in spot sampling and
continuous monitoring applications. It is based on an alternative method for the measurement of BGA
which overcomes the disadvantages of discrete laboratory methods outlined above, albeit with the potential
loss of accuracy. In this procedure, PC-containing BGA are measured in vivo, i.e., without either
disrupting the cells as in the laboratory extractive analysis procedure or using cell counting techniques as