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PhD defence N.J. Speetjens

20 March 2024 11:45 - 13:15

Arteries of a Changing Arctic: Small Rivers on a Global Scale

This thesis explores the intensification of the freshwater cycle under ongoing climate change through the lens of a specific landscape type: The ice-wedge polygon tundra. Permafrost degradation plays an important role in the shifting arctic biogeochemical cycle and large uncertainties exist regarding arctic land-ocean fluxes. The manuscript focuses on three investigations: 1. Local scale study: The study examines an Arctic lowland watershed in a permafrost degradation zone near the Arctic Ocean shoreline. The findings reveal differences in soil porewater DOM properties and DOC concentrations between different thermal layers and landforms, impacting hydrology and biogeochemical fluxes. Lateral fluxes of dissolved organic matter (DOM) from soil to streams are influenced by polygon type and drainage patterns. 2. Global scale inventory: The thesis highlights the lack of focus on smaller arctic river systems in scientific literature when upscaling lateral fluxes to the pan-Arctic scale. We present a comprehensive circum-arctic catchment database, which contains over 140 climatic, physiographic, and environmental variables. This database allows for the identification of catchments draining into the Arctic Ocean and their associated characteristics. Notably, smaller catchments in the northernmost regions, underlain by continuous permafrost and featuring substantial permafrost-specific terrain types, are found to be more vulnerable to temperature increases and are crucial in lateral carbon fluxes. 3. Modeling lateral fluxes: The thesis proposes a conceptual hydrological-biogeochemical model for ice-wedge polygon terrain to simulate runoff and DOC flux. The model indicates increased lateral flux in catchments transitioning from low-centered to high-centered polygon-dominated landscapes due to increased drainage and subsequent DOC export. The research emphasizes the importance of studying lateral biogeochemical fluxes from permafrost landscapes and the challenges in quantifying these fluxes. It suggests the need for improved field studies, data collection, and the development of scalable models to better predict and understand the impacts of permafrost thaw and climate change on Arctic ecosystems and the global carbon budget.

More information on the thesis


PhD defence by N.J. Speetjens

PhD Faculty of Science


  • dr. J.E. Vonk
  • dr. S.S.N. Veraverbeke
  • dr. W.R. Berghuijs

The PhD defence can also be followed online.

About PhD defence N.J. Speetjens

Starting date

  • 20 March 2024


  • 11:45 - 13:15


  • Auditorium, Hoofdgebouw


  • De Boelelaan 1105
  • 1081 HV Amsterdam

Follow the defence online

Go to livestream
Niek Jesse Speetjens