Assessing fluorescent DOM with spectral in situ sensors: from multi-channel to matrix- approaches
Institute for Chemistry and Biology of the Marine Environment –University Oldenburg, Germany
Dissolved organic matter (DOM) is a key parameter in aquatic biogeochemical processes. Part of the DOM pool exhibits optical properties, namely absorption and fluorescence. The latter is frequently utilized in laboratory measurements of fluorescent dissolved organic matter (FDOM) excitation-emission-matrices (EEM). We present the design and field application of a novel EEM sensor system applicable in situ, the ‘Kallemeter’. Observations are based on a field campaign, starting in Norwegian coastal waters entering the Trondheimsfjord. Comparison against a commercial single channel FDOM sensor and a recently developed multi-channel fluorometer (MatrixFlu-UV) exhibited a good correspondence of the different methods and the ability to resolve gradients and dynamics along the transect. Additional laboratory EEM measurements and subsequent PARAFC analysis revealed three dominant components. Both the EEM sensor system and the MatrixFlu-UV were able to detect the two main humic-like substances, but were limited towards the Tryptophan-like substances. Multi-channel FDOM sensors are capable to resolve rapid changes and processes based on the assessment of spectral properties. Their combination with upcoming spectrally resolved in situ EEM sensors will enhance our capacities in observing biogeochemical process in the marine environment.
Characterisation and classification of fluorescent dissolved organic matter in water: Current challenges and future directions
Khan M.G. Mostofa, Zihuan Fu, M. Mohinuzzaman, Longlong Li, Xinyu Lao, Yijun Liu, and Cong-Qiang Liu
Institute of Surface-Earth System Science, Tianjin University, 92 Weijin Road, Tianjin 300072, China.
Corresponding author: Email address: firstname.lastname@example.org
Three-dimensional fluorescence (excitation-emission matrix, EEM) spectroscopy (EEMS) coupled with parallel factor (PARAFAC), EEM-PARAFAC modelling has been extensively applied to identify the sources of fluorescent dissolved organic matter (FDOM) and their biogeochemical processes. But much research did not follow the same method on three key challenges: selective EEM data analysis, calibration of EEM data and classification of fluorescent components, which present challenges to the widespread application of EEM-PARAFAC studies. Based on the evidence, this study suggests that (1) selective EEM data analysis could be performed on each characteristic sample, not all EEM data together, in order to determine the biogeochemical facts and their mechanisms of action on the respective ecosystem; (2) detection of FDOM using EEM-PARAFAC analysis could be performed only on raw EEM data, not on the Raman Unit (RU) calibration data; and (3) classification of fluorescent components could be denoted commonly.
Continuer la lecture
For those who are interested in PARAFAC, below is the update I promised on the new tools discussed in my presentation.
(1) The drEEM toolbox, providing extended tools for visualisation and validation of models is now available at http://www.models.life.ku.dk/drEEM
(2) The OpenFluor database, for quantitatively comparing NOM-PARAFAC components, will be available as soon as possible at www.OpenFluor.org. If you have published PARAFAC models that you would like to add to the database at the pre-release stage, please drop me a line. I will email instructions. Models submitted before Nov. 15 will be available for matching as soon as the website goes live. Once the website is live, you can go to www.OpenFluor.org and follow the instructions there to upload models directly.
Pictures of the WOMS13 event
on July 2013
Quantification of natural organic matter: caveats and needs
1 Institute F.-A. Forel, Université de Genève, 10 route de Suisse, CH-1290 Versoix, Switzerland
2 SCHEMA, Rue Principale 92, L-6990 Rameldange, Luxembourg
Natural organic matter (NOM) plays an important role in many environmentally-relevant processes. NOM includes many different types of compounds, not all of which behave similarly. Much effort has gone into characterising some fractions of NOM (e.g., humic substances) in the different environmental compartments, in finding tracers to ascertain their origin, etc. –sometimes by using extremely sophisticated techniques–, but no comparable effort has been put into developing quantification techniques. As a result, field studies have often limited themselves to measuring only total (TOC) or dissolved (DOC) organic carbon or some surrogate parameter.
Quantification of NOM fractions in waters is not straightforward. Any analytical method measures a property of an analyte (or its reaction product) but the operationally defined nature of some NOM categories, together with the concomitant elusive and non-constant composition and structure of some of these substances, makes it difficult to find such an intrinsic property for them. Moreover, results have to be expressed as a function of the response of a standard, which is perceived as unsatisfactory by some users and, more importantly, remains largely misunderstood by many.
Four different cases will be discussed:
carbohydrates (or “when not all sugar is glucose”),
TEP (a completely operational category),
‘humics’ (the most difficult case?).
The importance of being able to quantify different types of NOM will be discussed in three different fields: thermodynamic modelling of trace element speciation (and implications for their use in ecotoxicology models such as BLM), understanding the fate of natural colloids and nanoparticles in freshwaters, studying long-term trends of NOM concentrations in relation to global climatic change.
International Training Workshop on Organic Matter Characterization Using Spectroscopic Techniques
19-21 May 2010
UNIVERSITY OF GRANADA, SPAIN
The meeting was opened to scientist interested in the characterization of dissolved organic matter in marine and inland waters using spectroscopic techniques.