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

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.