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.

Continuer la lecture →