Assessing fluorescent DOM with spectral in situ sensors: from multi-channel to matrix- approaches

by

Oliver Zielinski

Institute for Chemistry and Biology of the Marine Environment –University Oldenburg, Germany

Abstract :
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.

10h

Characterisation and classification of fluorescent dissolved organic matter in water: Current challenges and future directions

by

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: mostofa@tju.edu.cn

Abstract

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.

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Quantification of natural organic matter: caveats and needs

M. Filella^1,2

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”),

• thiols,

• 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.

The WOMS13

The Gala Diner

Organisation team

IHSS – Day