Photo-chemical reactivity of dissolved organic carbon in subarctic lakes from northern Sweden
(2020) In Student thesis series INES NGEM01 20182Dept of Physical Geography and Ecosystem Science
- Abstract (Swedish)
- Dissolved organic matter (DOM) is the major absorber of sunlight in most natural waters and a critical component of the carbon cycle in aquatic systems. The photochemical decomposition of DOM can have a significant impact on the landscape-atmosphere carbon exchange. However, little is known about how changing characteristics of DOM due to water browning (allochthonous inputs of DOM from terrestrial sources) affect the photochemical processing of the DOM. A shift from in situ self-produced (autochthonous) DOM to allochthonous DOM in clear tundra lakes may imply changes in the optical characteristics and thus photo-reactivity of the DOM. In this study, I measured the absorption of ultraviolet (UV) light and subsequent CO2 emissions resulting... (More)
- Dissolved organic matter (DOM) is the major absorber of sunlight in most natural waters and a critical component of the carbon cycle in aquatic systems. The photochemical decomposition of DOM can have a significant impact on the landscape-atmosphere carbon exchange. However, little is known about how changing characteristics of DOM due to water browning (allochthonous inputs of DOM from terrestrial sources) affect the photochemical processing of the DOM. A shift from in situ self-produced (autochthonous) DOM to allochthonous DOM in clear tundra lakes may imply changes in the optical characteristics and thus photo-reactivity of the DOM. In this study, I measured the absorption of ultraviolet (UV) light and subsequent CO2 emissions resulting from the photochemical DOM decay in 148 subarctic lakes from northern Sweden exposed to artificial sunlight, to assess how increasing chromophoric dissolved organic matter CDOM (browning) may affect the photo mineralization processes. In parallel the chemical composition of the DOM was assessed using fluorescence excitation-emission matrix analysis. The study lakes are situated along an environmental gradient in the subarctic Abisko region, ranging from brown-water lakes connected with some small mires to tundra clear-water lakes. The main objective of this study was to see how increasing CDOM due to increasing terrestrial inputs to the lakes affects the photochemical DOM mineralization. As expected the photo decay rates were positively correlated to the CDOM in absolute values. However, the photo decay per unit of absorbed light energy did not increase with increasing CDOM, but rather showed a weak decreasing trend (R2 = 0.07), which indicates that browning may lead to less photochemically induced CO2 emissions from lakes at any given level of UV light energy absorption. The percentage of lost dissolved organic carbon through photo-mineralization was significantly negatively correlated to the CDOM as well. Fluorescence analyses helped explain these patterns, as humic-like fluorescent DOM of presumable terrestrial origin was generally not more photo-reactive than other types of DOM. The results suggest that even though increasing inputs of terrestrial humic substances (browner water) means higher abundance of photo degradable materials, it would not mean that the CO2 emissions increase in lakes where browning limits the ability of light to penetrate deeper water. (Less)
- Popular Abstract
- The photochemical decomposition of the dissolved organic matter DOM can have a significant impact on the landscape-atmosphere carbon exchange. However, little is known about how changing characteristics of DOM due to water browning (allochthonous inputs of DOM from terrestrial sources) affect the photochemical processing of the DOM. A shift from in situ self-produced (autochthonous) DOM to allochthonous DOM in clear tundra lakes may imply changes in the optical characteristics and thus photo-reactivity of the DOM. In this study, I measured the absorption of ultraviolet (UV) light and subsequent CO2 emissions resulting from the photochemical DOM decay in a set of subarctic lakes situated in northern Sweden exposed to artificial sunlight, to... (More)
- The photochemical decomposition of the dissolved organic matter DOM can have a significant impact on the landscape-atmosphere carbon exchange. However, little is known about how changing characteristics of DOM due to water browning (allochthonous inputs of DOM from terrestrial sources) affect the photochemical processing of the DOM. A shift from in situ self-produced (autochthonous) DOM to allochthonous DOM in clear tundra lakes may imply changes in the optical characteristics and thus photo-reactivity of the DOM. In this study, I measured the absorption of ultraviolet (UV) light and subsequent CO2 emissions resulting from the photochemical DOM decay in a set of subarctic lakes situated in northern Sweden exposed to artificial sunlight, to assess how increasing chromophoric dissolved organic matter CDOM may affect the photo mineralization processes. In parallel the chemical composition of the DOM was assessed using fluorescence excitation-emission matrix analysis. The main objective of this study was to see how increasing CDOM due to increasing terrestrial inputs to the lakes affects the photochemical DOM mineralization. As expected the photo decay rates were positively correlated to the CDOM in absolute values. However, the photo decay per unit of absorbed light energy did not increase with increasing CDOM, but rather showed a weak decreasing trend (R2 = 0.07), which indicates that browning may lead to less photochemically induced CO2 emissions from lakes at any given level of UV light energy absorption. The percentage of lost dissolved organic carbon through photo-mineralization was significantly negatively correlated to the CDOM as well. Fluorescence analyses helped explain these patterns, as humic-like fluorescent DOM of presumable terrestrial origin was generally not more photo-reactive than other types of DOM. The results suggest that even though increasing inputs of terrestrial humic substances means higher abundance of photo degradable materials, it would not mean that the CO2 emissions increase in lakes where browning limits the ability of light to penetrate deeper water. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9017941
- author
- Younes, Hani LU
- supervisor
- organization
- course
- NGEM01 20182
- year
- 2020
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Photo-reactivity, DOM, subarctic lakes, EEM-PARAFAC. Brownification
- publication/series
- Student thesis series INES
- report number
- 502
- language
- English
- additional info
- External supervisors: François Guillemette, Department of environmental sciences, Université du Québec à Trois-Rivières, and
Cristian Gudasz, Department of Ecology and Environmental Sciences, Umeå University - id
- 9017941
- date added to LUP
- 2020-06-17 12:28:56
- date last changed
- 2024-04-11 09:23:01
@misc{9017941,
abstract = {{Dissolved organic matter (DOM) is the major absorber of sunlight in most natural waters and a critical component of the carbon cycle in aquatic systems. The photochemical decomposition of DOM can have a significant impact on the landscape-atmosphere carbon exchange. However, little is known about how changing characteristics of DOM due to water browning (allochthonous inputs of DOM from terrestrial sources) affect the photochemical processing of the DOM. A shift from in situ self-produced (autochthonous) DOM to allochthonous DOM in clear tundra lakes may imply changes in the optical characteristics and thus photo-reactivity of the DOM. In this study, I measured the absorption of ultraviolet (UV) light and subsequent CO2 emissions resulting from the photochemical DOM decay in 148 subarctic lakes from northern Sweden exposed to artificial sunlight, to assess how increasing chromophoric dissolved organic matter CDOM (browning) may affect the photo mineralization processes. In parallel the chemical composition of the DOM was assessed using fluorescence excitation-emission matrix analysis. The study lakes are situated along an environmental gradient in the subarctic Abisko region, ranging from brown-water lakes connected with some small mires to tundra clear-water lakes. The main objective of this study was to see how increasing CDOM due to increasing terrestrial inputs to the lakes affects the photochemical DOM mineralization. As expected the photo decay rates were positively correlated to the CDOM in absolute values. However, the photo decay per unit of absorbed light energy did not increase with increasing CDOM, but rather showed a weak decreasing trend (R2 = 0.07), which indicates that browning may lead to less photochemically induced CO2 emissions from lakes at any given level of UV light energy absorption. The percentage of lost dissolved organic carbon through photo-mineralization was significantly negatively correlated to the CDOM as well. Fluorescence analyses helped explain these patterns, as humic-like fluorescent DOM of presumable terrestrial origin was generally not more photo-reactive than other types of DOM. The results suggest that even though increasing inputs of terrestrial humic substances (browner water) means higher abundance of photo degradable materials, it would not mean that the CO2 emissions increase in lakes where browning limits the ability of light to penetrate deeper water.}},
author = {{Younes, Hani}},
language = {{eng}},
note = {{Student Paper}},
series = {{Student thesis series INES}},
title = {{Photo-chemical reactivity of dissolved organic carbon in subarctic lakes from northern Sweden}},
year = {{2020}},
}