10:45 AM - 12:15 PM
[AHW18-P21] Environmental transition of Anenuma Lake deciphered from the fluorescent properties of sediment organic matter
Keywords:environmental transition, eutrophic lake, fluorescence analysis, lake sediment, organic matter
Soils transported by rivers from the watershed and the debris/remains of plankton and coastal vegetation growing in the lake are deposited on the bottom and turn into lake sediment. Organic matter in sediment (SOM) varies in its quality, reflecting its origin and the diagenetic processes. As such, qualitative information on the SOM is useful in better understanding of the lake environment through elucidating the origin and the diagenetic processes of SOM. Since the sediment of eutrophic lake is deeply involved in eutrophication, it is important to better understand its nature. In addition, a better understanding of the changes in the lake environment would be helpful in improving water quality in the future.
Lake Anenuma, located in eastern Aomori Prefecture, was selected as the study site. Anenuma is a hypertrophic freshwater lake, and its water quality has deteriorated significantly. Columnar sediments were collected at the center of the lake to a depth of 3.4 m using a gravity corer in 2019, and sliced into 4-cm-thick slices. Alkaline-extractable organic matter was extracted from the sediment slices, and its quality was evaluated based on its fluorescent properties. Fluorescence analysis has high sample throughput and can detect differences in organic matter quality with high sensitivity. The fluorescent properties were evaluated using a combination of three-dimensional fluorescence spectrometry (EEM) and statistical analysis using the 10-component PARAFAC model established by the authors.
In this presentation, we show transitions in the lake environment over a period of ca. 1000 years, including large runoff due to extreme weather events, morphological changes, and eutrophication of the Lake Anenuma, using the following three indices.
(1) C1/C3 ratio: a proxy indicator for the relative contribution of low marsh soils and Ando soils. C1 (Exmax/Emmax=<260, 445nm/510nm) has been found to be abundant in soil humic acid with low humification degree, and the C3 (Exmax/Emmax=265, >470nm/>550nm) has been found to be abundant in highly humified soil humic acid from Ando soils.
(2) C5 intensity: a proxy indicator for the amount of terrestrial-derived organic matter entering a river from a terrestrial area. C5 (Exmax/Emmax=<260nm/444nm) has been found to be abundant in terrestrial fulvic acid undergone photolysis or intensive oxidative degradation.
(3) The C10 intensity: a proxy indicator for plankton productivity in the lake. The C10 (Exmax/Emmax=275nm/340nm) is protein-like substance. Protein is a major component of plankton, including cyanobacteria, the main species of blue-green algae.
Lake Anenuma, located in eastern Aomori Prefecture, was selected as the study site. Anenuma is a hypertrophic freshwater lake, and its water quality has deteriorated significantly. Columnar sediments were collected at the center of the lake to a depth of 3.4 m using a gravity corer in 2019, and sliced into 4-cm-thick slices. Alkaline-extractable organic matter was extracted from the sediment slices, and its quality was evaluated based on its fluorescent properties. Fluorescence analysis has high sample throughput and can detect differences in organic matter quality with high sensitivity. The fluorescent properties were evaluated using a combination of three-dimensional fluorescence spectrometry (EEM) and statistical analysis using the 10-component PARAFAC model established by the authors.
In this presentation, we show transitions in the lake environment over a period of ca. 1000 years, including large runoff due to extreme weather events, morphological changes, and eutrophication of the Lake Anenuma, using the following three indices.
(1) C1/C3 ratio: a proxy indicator for the relative contribution of low marsh soils and Ando soils. C1 (Exmax/Emmax=<260, 445nm/510nm) has been found to be abundant in soil humic acid with low humification degree, and the C3 (Exmax/Emmax=265, >470nm/>550nm) has been found to be abundant in highly humified soil humic acid from Ando soils.
(2) C5 intensity: a proxy indicator for the amount of terrestrial-derived organic matter entering a river from a terrestrial area. C5 (Exmax/Emmax=<260nm/444nm) has been found to be abundant in terrestrial fulvic acid undergone photolysis or intensive oxidative degradation.
(3) The C10 intensity: a proxy indicator for plankton productivity in the lake. The C10 (Exmax/Emmax=275nm/340nm) is protein-like substance. Protein is a major component of plankton, including cyanobacteria, the main species of blue-green algae.