The sediment fluorescence–trophic level relationship: using water-extractable organic matter to assess past lake water quality in New Zealand

ABSTRACT

Lake sediments are the physical remnants of past allochthonous and autochthonous carbon and mineral inputs and therefore have the potential to illuminate both past terrestrial carbon cycling and within-lake biological productivity. However, there are currently no robust, rapid, and inexpensive methods to chemically characterise the organic matter (OM) components in lake sediments, which limits their utility for reconstructing past soil carbon export trends or trophic status. This study explores the use of 3D excitation–emission matrix (EEM) fluorescence spectroscopy of water extractable dissolved organic matter (WEDOM) from lake sediments as a method for reconstructing past soil dissolved organic matter (DOM) export and past lake water quality. Using contemporary lake sediments from 11 New Zealand lakes, we demonstrate that both overall WEDOM fluorescence and protein-like fluorescence intensity are strong functions of trophic status across lakes. We also demonstrate that protein-like fluorescence is a function of sedimentary total nitrogen concentrations in palaeo-sediments from a pristine, high-altitude lake (Adelaide Tarn). This approach has applications in the evaluation of the trophic status of infrequently monitored lakes and in palaeolimnology.

KEYWORDS:

• Dissolved organic matter (DOM); Fourier transform infrared spectroscopy (FTIRS)
• 3D excitation emission matrices (EEMs)
• fluorescence
• water quality
• eutrophication
• trophic level
• climate change

Acknowledgements

We thank Dr Carsten Meyer-Jacob (Paleoecological Environmental Assessment and Research Laboratory, Queen’s University Canada/ Department of Ecology and Environmental Science, University of Umeå) for PLSR modelling of FTIRS-TOC data.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was made possible by Marsden Fund Grant UOW1403 and public research funding from the Government of New Zealand via contract C05X1702 to GNS Science. AH was also supported by a Rutherford Discovery Fellowship award [grant number RDF-UOW1601]. Collection of Adelaide Tarn samples was funded by Marsden Fund Grant GNS1001: Bacterial geo-thermometer: A new, precise indicator of climate change. MJV was also supported by the Ministry of Business, Innovation and Employment, New Zealand (Programme: ‘Our Lake’s Health; Past, Present and Future’; grant number C05X1707).