Spectral fingerprinting for specific algal groups on sediments in situ: a new sensor

Currently it is still extremely difficult to adequately sample populations of microalgae on sediments for large-scale biomass determination. We have now devised a prototype of a new benthic sensor (BenthoFluor) for the quantitative and qualitative assessment of microphytobenthos populations in situ. This sensor enables a high spatial and temporal resolution and a rapid evaluation of the community structure and distribution. These determinations are based on the concept that five spectral excitation ranges can be used to differentiate groups of microalgae, in situ, within a few seconds. In addition, because sediments contain a lot of yellow substances, which can affect the fluorescence and optical differentiation of the algae, the device was equipped with a UV-LED for yellow substances correction. The device was calibrated against HPLC with cultures and tested in the field. Our real-time approach can be used to monitor algal assemblage composition on sediments and is an ideal tool for investigations on the large-scale spatial and temporal variation of algal populations in sediments. Apart from the differentiation of algal populations, the BenthoFluor allows instantaneous monitoring of the chlorophyll concentrations and determination of which algae are responsible for this on the uppermost surface of sediments in the field and in experimental set-ups

Differentiation of Spectral Groups of Algae with Compute-Based Analysis of Fluorescence Excitation Spectra

Members of the same division of algae have a similar pigment composition. This results in typical fluorescence excitation spectra with emission wavelength between 680 nm and 720 nm. It is, therefore, possible to assign algal classes to distinct spectral groups of algae. In order to measure a meaningful fluorescence excitation spectrum five light-emitting diodes were chosen and built into a new instrument. Their emission wavelengths fit the absorption wavelength of the pigments phycocyanin, phycoerythrin, fucoxanthin, peridinin and chlorophylls, respectively. Spectra of different algae from four spectral groups (blue-green algae)(cyanobacteria), green algae, browns and cryptophyta (Cryptomonas) were recorded. An average fluorescence spectrum per Chlorophyll a concentration in a sample of water for each spectral group of algae resulted. This allows the calculation of the chlorophyll a concentration and the distribution of four different spectral groups of algae from an excitation spectrum. Results of in-vivo and in-situ measurements are shown. The application of a submersible probe is discussed

Fluorometric depth-profiling of chlorophyll corrected for yellow substances

The 'spectral groups' of algae (green, blue, brown, mixed) are each characterized by a specific composition of photosynthetic pigments, particularly relevant are: Chl a, phycocyanobilin, phycoerythrobilin, fucoxanthin, peridinin and, consequently, by a specific excitation spectrum of the Chl fluorescence. This was used in earlier approaches to determine the amount of chlorophyll and the algal group composition of phytoplankton. Yellow substances (coloured dissolved organic matter) may interfere with the measurement because of overlap in the excitation spectra with phytoplankton. In a new approach, built into a submersible instrument, we correct for the influence of yellow substances on the chlorophyll fluorescence. The newly-developed probe is a submersible fluorometer which measures the emission intensity at six characteristic wavelength ranges employing pulsed light-emitting diodes. The submersible probe transfers all data on-line to a computer or stores them in the probe (fluorescence data plus the simultaneously measured water pressure for depth determination). The six-point excitation spectra are deconvoluted on the basis of norm spectra which have been obtained by analysis of several species of each spectral group. The usage of an ultra violet (UV)-ecxitation source (370 nm LED) enables the differentiation between algal fluorescence and fluorescence of yellow substance

In situ profiles of phytoplankton : algal composition and biomass determined fluorometrically

A new methodology enabling rapid evaluation of the phytoplankton community structure and distribution with high spatial and temporal resolution in situ is introduced. This is based on the concept that four 'spectral groups' of phytoplankton (green, blue, brown, mixed) are each characterised by specific photosynthetic pigment compositions and, consequently, by specific excitation spectra of chlorophyll-fluorescence. We have developed a submersible fluorometer which measures the emission intensity for excitation in five characteristic wavelength ranges employing pulsed light-emitting diodes (LED’s). These five spectral excitation ranges can be used to differentiate the four spectral groups of microalgae in situ within a few seconds. In examples of depth profiles of phytoplankton populations in a eutrophic lake we also show a significant correlation of deconvoluted fluorescence profiles to corresponding biovolume

Method and instrumentation for the determination of benthic algae.

A new benthic sensor for the differentiation of algal groups in mixed microphytobenthos populations in situ with high spatial and temporal resolution has been developed. The differentiation is based on the concept that five spectral excitation ranges can be used to determine groups of microalgae in situ within a few seconds. As sediments contain a lot of yellow substances, which can effect the optical differentiation of the algae, the device is additionally equipped with a correcting UV-LED for yellow substances. Results from the differentiation on microphytobenthos populations and their migrating behaviour in the field and in mesocosm experiments are compared with algal biomass and pigment estimations. The usefulness of this non-retrospect approach is discussed critically in view of its potential role for ground truth investigations on the large-scale spatial and temporal variation of algal populations in sediments