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Fluorescence spectroscopy of sedimentary pore-water humic substances: a simple tool for retrospective analysis of lake ecosystems |
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| Authors: | Aina Leeben Annika Mikomägi Viia Lepane Tiiu Alliksaar |
| Institution: | 1. Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117, Rannu, Tartumaa, Estonia 2. Institute of Mathematics and Natural Sciences, Tallinn University, Narva mnt. 25, 10120, Tallinn, Estonia 3. Institute of Ecology, Tallinn University, Uus-Sadama 5, 10120, Tallinn, Estonia 4. Department of Chemistry, Faculty of Science, Tallinn University of Technology, Akadeemia tee 15, 12618, Tallinn, Estonia 5. Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086, Tallinn, Estonia |
| Abstract: | PurposeThe feasibility of applying the method of single-scan fluorescence emission spectra of humic substances (HSs) without chemical pretreatments of sediment pore-water samples was tested to ascertain the past productivity and sources of organic matter of lakes.Materials and methodsSediment samples were collected from ten Estonian lakes (located between 57°36′ and 59°25′N and 22°12′ and 26°59′E) covering all levels of the trophic scale. The height (fluorescence intensity), location (fluorescence maximum) and shape (fluorescence index, the ratio of intensities at the emission wavelengths 450 and 500 nm) of the fluorescence emission spectrum at an excitation of 340 nm were under consideration.Results and discussionPore-water humic substances (pwHSs) from sediments of eutrophic lakes had generally a high fluorescence intensity and fluorescence index and their fluorescence maximum was located at shorter wavelengths. Characteristic features of pwHSs from oligotrophic lakes were low fluorescence intensity, emission of maximum fluorescence at shorter wavelengths and high fluorescence index values. Pore-water humic substances from sediments of dystrophic lakes were characterized by a low fluorescence intensity and fluorescence index and their spectral peak was shifted to longer wavelengths. The study also demonstrated that a shift in the peak location of pwHSs fluorescence was accompanied with a change in the C/N ratios of sedimentary organic matter, and the alteration in the fluorescence index of pwHSs was synchronous with the changes in their molecular weight.ConclusionsThe obtained results suggest that fluorescence spectroscopy of pwHSs without using chemical pretreatments has a great potential in the reconstruction of past lake conditions. |
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