fluorescence can be used to estimate the concentration of algae and to track
developments in the algal population, e.g. as early warning system for algal blooms.
The central pigment responsible for photosynthesis is chlorophyll. However, as this
is widely present in most photosynthetic organisms, the measurement of chlorophyll
alone does only allow for monitoring total algal concentrations, but not classification. As some algae use auxiliary pigments next to chlorophyll A for the collection of
photons, using multiple light sources to selectively excite the specific pigments,
differentiation between classes becomes possible [21]. An example is the use of red
light for the detection of the pigment phycocyanin that is present in cyanobacteria,
which are a major cause for toxic algal blooms. Alternatively, the red fluorescence
of the accessory pigment phycoerythrin is used to monitor some salt water
cyanobacteria. The more advanced instruments attempt to distinguish between
cyanobacteria, green algae and diatoms using spectral curve fitting methods [21],
although adaptation of the calibration to the algae that are predominant in the waters
analysed is often necessary.
It should be noted that in situ measurement of algal pigments does not provide
quantitative information about cell concentrations or biovolumes, as signals strongly
depend on the algae present, their physiological state and environmental factors such
as brightness of the sunlight.
5.2.2 Dissolved Organic Matter
All natural waters as well as drinking waters contain natural organic matter (NOM).
Common NOM compounds include proteins, polysaccharides and humic substances, which originate primarily from the breakdown products of plant material.
Although NOM does not pose a risk to human health on its own, some NOM
compounds are known to react with chlorine and chloramines to produce disinfection by-products (DBPs), some of which are carcinogenic and genotoxic. Monitoring
the NOM levels in source waters is used to optimise water treatment and minimise
DBP formation. In particular in surface waters with highly fluctuating compositions,
e.g. strong seasonal influences, or high sensitivity to runoff during heavy rainfall,
monitoring NOM is critical for water treatment performance.
NOM is also receiving attention in research related to climate change, with a
particular focus on the release of NOM from boreal forests [22]. In this work, NOM
levels and composition are used as indicators for changes in the biochemical cycles
and mobilisation of organic matter (e.g. from permafrost) as a result global warming.
Furthermore, changes in NOM may require adaptation of the water treatment
systems to ensure continued supply of safe drinking water.
Monitoring of NOM is focusing on detection of humic and fulvic acids, both
groups of substances with an aromatic character. Due to this aromatic character they
are easily detected using fluorescence. This parameter is referred to as fluorescent
dissolved organic matter (FDOM) and typically measured using fixed excitationemission pair filter spectrometer devices. More detailed characterisation can be
Spectroscopic Methods for Online Water Quality Monitoring
301
developments in the algal population, e.g. as early warning system for algal blooms.
The central pigment responsible for photosynthesis is chlorophyll. However, as this
is widely present in most photosynthetic organisms, the measurement of chlorophyll
alone does only allow for monitoring total algal concentrations, but not classification. As some algae use auxiliary pigments next to chlorophyll A for the collection of
photons, using multiple light sources to selectively excite the specific pigments,
differentiation between classes becomes possible [21]. An example is the use of red
light for the detection of the pigment phycocyanin that is present in cyanobacteria,
which are a major cause for toxic algal blooms. Alternatively, the red fluorescence
of the accessory pigment phycoerythrin is used to monitor some salt water
cyanobacteria. The more advanced instruments attempt to distinguish between
cyanobacteria, green algae and diatoms using spectral curve fitting methods [21],
although adaptation of the calibration to the algae that are predominant in the waters
analysed is often necessary.
It should be noted that in situ measurement of algal pigments does not provide
quantitative information about cell concentrations or biovolumes, as signals strongly
depend on the algae present, their physiological state and environmental factors such
as brightness of the sunlight.
5.2.2 Dissolved Organic Matter
All natural waters as well as drinking waters contain natural organic matter (NOM).
Common NOM compounds include proteins, polysaccharides and humic substances, which originate primarily from the breakdown products of plant material.
Although NOM does not pose a risk to human health on its own, some NOM
compounds are known to react with chlorine and chloramines to produce disinfection by-products (DBPs), some of which are carcinogenic and genotoxic. Monitoring
the NOM levels in source waters is used to optimise water treatment and minimise
DBP formation. In particular in surface waters with highly fluctuating compositions,
e.g. strong seasonal influences, or high sensitivity to runoff during heavy rainfall,
monitoring NOM is critical for water treatment performance.
NOM is also receiving attention in research related to climate change, with a
particular focus on the release of NOM from boreal forests [22]. In this work, NOM
levels and composition are used as indicators for changes in the biochemical cycles
and mobilisation of organic matter (e.g. from permafrost) as a result global warming.
Furthermore, changes in NOM may require adaptation of the water treatment
systems to ensure continued supply of safe drinking water.
Monitoring of NOM is focusing on detection of humic and fulvic acids, both
groups of substances with an aromatic character. Due to this aromatic character they
are easily detected using fluorescence. This parameter is referred to as fluorescent
dissolved organic matter (FDOM) and typically measured using fixed excitationemission pair filter spectrometer devices. More detailed characterisation can be
Spectroscopic Methods for Online Water Quality Monitoring
301