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Dissolved organic matter dynamics across terrestrial and aquatic systems: sources, chemistry and microbial processing

Geert Hensgens dissertation cover
Thesis defense
Geert Hensgens will defend his PhD thesis.

Abstract

The movement of DOM from terrestrial to aquatic systems is a globally significant flux affecting both carbon sequestration and CO2 emissions. Here, DOM dynamics were investigated in terrestrial and aquatic systems within the context of this carbon flux. The overall aim was to investigate the source and chemistry of DOM and determine how chemistry is affected by microbial processing of DOM. 

In the boreal forest, understory vegetation produced more than 80 %, with the species V. myrtillus contributing more than 50 % of litter derived DOM at the forest stand level. Litter reactivity was linked to greater chemical changes in the DOM produced at different decay stages. High reactive species (V. myrtillus, birch, alder) initially produced DOM with a higher lability rich in oxidized phenolic compounds, indicating lignin degradation of the source litter. As the DOM was microbially processed the similarity between litter species increased as oxygenated phenolic compounds from high reactive litter leachates were degraded and stable aliphatic secondary microbial compounds created. 

Of the DOM extracted from podzols roughly a third consisted of aged (1000 yr) labile carbon as indicated by depleted 14C concentrations in Keeling plot intercepts. This fraction cannot be readily detected by bulk radiocarbon measurements without further incubation of the DOM. As such, the mobilization of aged carbon might have gone on undetected. This has important implications for e.g. predicting the future carbon balance of the boreal forest. 

Severe drought resulted in strongly decreased CDOM concentrations of lakes as a result of hydrological disconnection. This effect was more pronounced in large lakes. During normal conditions, temperature was a positive driver of CDOM in lakes. Drought systematically weakened the regulation of CDOM by the surrounding area. Furthermore, microbial processing of DOM in lakes with little terrestrial influence show that CDOM is systematically microbially produced while at the same time DOM is degraded. The strength of CDOM production is dependent on CDOM concentrations in these lakes. 

Combined these results highlight that future DOM regulation might change unexpectedly as temperatures rise, drought becomes more prevalent, understory vegetation composition changes and precipitation and runoff patterns will become more variable. 

Chairman

Lars Harrie, Professor, Department of Physical Geography and Ecosystem Science, Lund University

Opponent

Karsten Kalbitz, Professor, Technical University Dresden

Opponent

Karsten Kalbitz, Professor, Technical University Dresden

Committee

  • Magdalena Zofia Bieroza, Swedish University of Agricultural Sciences
  • Jeffrey Hawkes, docent under evaluation, Uppsala University
  • Per Persson, Professor, Centre for Environmental and Climate Research, Lund University

Suppleant

Anne Birgitte Nielsen, Senior Lecturer, Department of Geology, Lund University

Supervisor

Martin Berggren, Senior Lecturer, Department of Physical Geography and Ecosystem Science, Lund University

Online defense

The defense will be done using Zoom. Use the following link to join:
https://lu-se.zoom.us/j/62869983605?pwd=NytRUUVrRmVFeUZvTVkzYlVWSUpEdz09

Webinar ID: 628 6998 3605
Passcode: 51961

Time: 
3 December 2020 10:00 to 13:00
Location: 
Room "Pangea" (room number 229), Sölvegatan 12, Geocentre II, Lund
Contact: 
geert.hensgens [at] nateko.lu.se

About the event

Time: 
3 December 2020 10:00 to 13:00
Location: 
Room "Pangea" (room number 229), Sölvegatan 12, Geocentre II, Lund
Contact: 
geert.hensgens [at] nateko.lu.se

Department of Physical Geography and Ecosystem Science
Lund University
Sölvegatan 12
S-223 62 Lund
Sweden

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