Niek Jesse Speetjens - Academia.edu (original) (raw)

Papers by Niek Jesse Speetjens

Research paper thumbnail of Microbial growth in a warming Arctic: Exploring controls and temperature responses in permafrost soils

Research paper thumbnail of Distribution Patterns of Pahs and Pcbs in Ice-Wedge Polygon Soils of a Canadian Coastal Tundra Catchment

Research paper thumbnail of Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

Research paper thumbnail of The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

Frontiers in Earth Science, Mar 24, 2021

Research paper thumbnail of Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Landscape-related ground ice variability on the Yukon coastal plain inferred from computed tomography and potential implications on lateral permafrost carbon release

Warming in the Arctic causes strong environmental changes with permafrost degradation being among... more Warming in the Arctic causes strong environmental changes with permafrost degradation being among the most striking effects. Active layer deepening and permafrost erosion can result in the mobilization and lateral transport of organic carbon (OC), which potentially alters carbon cycles in the Arctic substantially. Although the understanding of ground ice contents and permafrost OC release is improving, still little is known of permafrost OC release rates, lateral transport pathways and its driving mechanisms on a landscape scale. In this study we investigate ground ice characteristics and OC composition of the most dominant landscape units of the Yukon coastal plain. In total, 12 permafrost cores were taken from moraine, lacustrine, fluvial and glaciofluvial deposits with a SIPRE corer. Ground ice and sediment contents were analysed using computed tomography and k-means classification. Active layer and upper permafrost were subsampled to analyse OC contents and isotopes of bulk material and a leaching-incubation experiment was conducted with active layer and permafrost sediments to assess potential dissolved OC export and degradation rates. Preliminary results show that ground ice contents vary significantly between landscape units. Ground ice contents in permafrost average 72.4 vol.-% with highest contents in moraines (78.3 vol.-%) and lowest contents in fluvial deposits (53.2 vol.-%). We expect highest dissolved OC leaching and loss rates from permafrost in contrast to active layer and from fluvial and lacustrine deposits, as they simply contain more OC. Yet, lateral OC transport is more likely for landscapes with a topographic gradient such as ground ice-rich moraines. We conclude that due to the high ground ice contents on the Yukon coastal plain, substantial changes of the permafrost landscape will occur under current warming trends. This will include subsidence, abrupt erosion, changes in hydrology and OC degradation processes, which will differ between landscape units

Research paper thumbnail of High resolution mapping shows differences in soil carbon and nitrogen stocks in areas of varying landscape history in Canadian lowland tundra

Research paper thumbnail of Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

Research paper thumbnail of Small watersheds may play a disproportionate role in arctic land-ocean fluxes

Research paper thumbnail of Permafrost soil organic matter (de)composition in times of global warming

The Arctic warms four times faster than the global average, resulting in widespread permafrost th... more The Arctic warms four times faster than the global average, resulting in widespread permafrost thaw. Organic matter that was stored in permanently frozen soil for up to millennia now becomes available to microbial decomposition. Warming might also alter microbial community composition and physiology and thus change the decomposition potential of soils. Our current knowledge about permafrost soil organic matter (SOM) composition and decomposition is limited, particularly in regard to the heterogeneity of permafrost landscapes, thus hampering our ability to predict possible permafrost soil feedbacks to climate change. The objective of this study was to characterize SOM and microbial community composition of the active layer and the upper permanently frozen soil from permafrost-affected polygonal lowland tundra.We collected more than 80 soil samples from four different soil layers (organic, mineral, cryoturbated, permanently frozen) from three developmental stages of ice-wedge polygons...

Research paper thumbnail of The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Subjecting permafrost microorganisms to short-term warming

EPIC3AGU Fall Meeting, Online, 2020-12-01-2020-12-17, Dec 9, 2020

Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in ... more Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in the wake of climate change, outpacing the global rate of temperature increases. The risk of thawing permafrost soils raises concerns about a positive feedback process being mediated by increased microbial activity that does not acclimate over time freeing greenhouse gases. However, the mechanistic understanding of the controls on microbial carbon cycling upon warming is still vague. In the following study we investigate microbial growth and soil organic matter decomposition in different soil horizons of the active layer and upper permafrost, covering different polygonal landscape units in two small catchments at the Canadian Yukon Coast. 81 soil samples were subjected to a short-term warming experiment under controlled temperature (4 °C and 14 °C) and moisture conditions. Microbial respiration was measured weekly whereas microbial biomass and physiological parameters were determined at the end of the incubation period and used to assess temperature responses. Microbial growth was estimated by measuring the incorporation of 18O from labelled water into DNA and used to calculate CUE. Microbial biomass was determined via chloroform fumigation. Potential activities of extracellular enzymes were measured using microplate fluorometric assays. Microbial biomass carbon was not affected by warming except for permafrost layers where it either increased or decreased depending on the examined catchment. Microbial respiration strongly responded to warming following the pattern organic layers > upper frozen permafrost > cryoturbated material > mineral layers. Mass specific growth and extracellular enzymatic activities were also enhanced with short-term warming in all soil horizons. This led to rather variable CUE being unaffected in mineral and cryoturbated layers whereas we could observe a minor reduction in organic and permafrost layers where the response of respiration outpaced the one of microbial growth. Our results are not indicative for any physiological acclimatization of permafrost microbes when subjected to 8 weeks of experimental warming and hence support the current concern for potential prolonged carbon losses from warming tundra soils. This work is part of the EU H2020 project “Nunataryuk”

Research paper thumbnail of Spatial variability shapes microbial communities of permafrost soils and their reaction to warming

Research paper thumbnail of Persistent organic pollutants distribution of small coastal catchments at the Canadian Beaufort coast

Research paper thumbnail of Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

Frontiers in Earth Science, 2021

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in... more Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (Sr: 0.63 ± 0.02 and SUVA254: 1.65 ± 0.06 L mg C−1 m−1 & Sr: 0.68 ± 0.01 and SUVA254: 1.17 ±...

Research paper thumbnail of Landscape-driven carbon export from small coastal permafrost watersheds

Research paper thumbnail of How do microorganisms from permafrost soils respond to short-term warming?

Research paper thumbnail of Late Quaternary palaeoenvironmental records from a glacially and permafrost affected island in the Canadian Arctic (Herschel Island, Yukon Coastal Plain)

Research paper thumbnail of Microbial growth in a warming Arctic: Exploring controls and temperature responses in permafrost soils

Research paper thumbnail of Distribution Patterns of Pahs and Pcbs in Ice-Wedge Polygon Soils of a Canadian Coastal Tundra Catchment

Research paper thumbnail of Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

Research paper thumbnail of The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

Frontiers in Earth Science, Mar 24, 2021

Research paper thumbnail of Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Landscape-related ground ice variability on the Yukon coastal plain inferred from computed tomography and potential implications on lateral permafrost carbon release

Warming in the Arctic causes strong environmental changes with permafrost degradation being among... more Warming in the Arctic causes strong environmental changes with permafrost degradation being among the most striking effects. Active layer deepening and permafrost erosion can result in the mobilization and lateral transport of organic carbon (OC), which potentially alters carbon cycles in the Arctic substantially. Although the understanding of ground ice contents and permafrost OC release is improving, still little is known of permafrost OC release rates, lateral transport pathways and its driving mechanisms on a landscape scale. In this study we investigate ground ice characteristics and OC composition of the most dominant landscape units of the Yukon coastal plain. In total, 12 permafrost cores were taken from moraine, lacustrine, fluvial and glaciofluvial deposits with a SIPRE corer. Ground ice and sediment contents were analysed using computed tomography and k-means classification. Active layer and upper permafrost were subsampled to analyse OC contents and isotopes of bulk material and a leaching-incubation experiment was conducted with active layer and permafrost sediments to assess potential dissolved OC export and degradation rates. Preliminary results show that ground ice contents vary significantly between landscape units. Ground ice contents in permafrost average 72.4 vol.-% with highest contents in moraines (78.3 vol.-%) and lowest contents in fluvial deposits (53.2 vol.-%). We expect highest dissolved OC leaching and loss rates from permafrost in contrast to active layer and from fluvial and lacustrine deposits, as they simply contain more OC. Yet, lateral OC transport is more likely for landscapes with a topographic gradient such as ground ice-rich moraines. We conclude that due to the high ground ice contents on the Yukon coastal plain, substantial changes of the permafrost landscape will occur under current warming trends. This will include subsidence, abrupt erosion, changes in hydrology and OC degradation processes, which will differ between landscape units

Research paper thumbnail of High resolution mapping shows differences in soil carbon and nitrogen stocks in areas of varying landscape history in Canadian lowland tundra

Research paper thumbnail of Degradation of Ice-Wedge Polygons Leads to Increased Fluxes of Water and Doc

Research paper thumbnail of Small watersheds may play a disproportionate role in arctic land-ocean fluxes

Research paper thumbnail of Permafrost soil organic matter (de)composition in times of global warming

The Arctic warms four times faster than the global average, resulting in widespread permafrost th... more The Arctic warms four times faster than the global average, resulting in widespread permafrost thaw. Organic matter that was stored in permanently frozen soil for up to millennia now becomes available to microbial decomposition. Warming might also alter microbial community composition and physiology and thus change the decomposition potential of soils. Our current knowledge about permafrost soil organic matter (SOM) composition and decomposition is limited, particularly in regard to the heterogeneity of permafrost landscapes, thus hampering our ability to predict possible permafrost soil feedbacks to climate change. The objective of this study was to characterize SOM and microbial community composition of the active layer and the upper permanently frozen soil from permafrost-affected polygonal lowland tundra.We collected more than 80 soil samples from four different soil layers (organic, mineral, cryoturbated, permanently frozen) from three developmental stages of ice-wedge polygons...

Research paper thumbnail of The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Supplementary material to "The Pan-Arctic Catchment Database (ARCADE)

Research paper thumbnail of Subjecting permafrost microorganisms to short-term warming

EPIC3AGU Fall Meeting, Online, 2020-12-01-2020-12-17, Dec 9, 2020

Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in ... more Arctic environments are a prime example for ecosystems facing manifold vast and rapid changes in the wake of climate change, outpacing the global rate of temperature increases. The risk of thawing permafrost soils raises concerns about a positive feedback process being mediated by increased microbial activity that does not acclimate over time freeing greenhouse gases. However, the mechanistic understanding of the controls on microbial carbon cycling upon warming is still vague. In the following study we investigate microbial growth and soil organic matter decomposition in different soil horizons of the active layer and upper permafrost, covering different polygonal landscape units in two small catchments at the Canadian Yukon Coast. 81 soil samples were subjected to a short-term warming experiment under controlled temperature (4 °C and 14 °C) and moisture conditions. Microbial respiration was measured weekly whereas microbial biomass and physiological parameters were determined at the end of the incubation period and used to assess temperature responses. Microbial growth was estimated by measuring the incorporation of 18O from labelled water into DNA and used to calculate CUE. Microbial biomass was determined via chloroform fumigation. Potential activities of extracellular enzymes were measured using microplate fluorometric assays. Microbial biomass carbon was not affected by warming except for permafrost layers where it either increased or decreased depending on the examined catchment. Microbial respiration strongly responded to warming following the pattern organic layers > upper frozen permafrost > cryoturbated material > mineral layers. Mass specific growth and extracellular enzymatic activities were also enhanced with short-term warming in all soil horizons. This led to rather variable CUE being unaffected in mineral and cryoturbated layers whereas we could observe a minor reduction in organic and permafrost layers where the response of respiration outpaced the one of microbial growth. Our results are not indicative for any physiological acclimatization of permafrost microbes when subjected to 8 weeks of experimental warming and hence support the current concern for potential prolonged carbon losses from warming tundra soils. This work is part of the EU H2020 project “Nunataryuk”

Research paper thumbnail of Spatial variability shapes microbial communities of permafrost soils and their reaction to warming

Research paper thumbnail of Persistent organic pollutants distribution of small coastal catchments at the Canadian Beaufort coast

Research paper thumbnail of Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

Frontiers in Earth Science, 2021

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in... more Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (Sr: 0.63 ± 0.02 and SUVA254: 1.65 ± 0.06 L mg C−1 m−1 & Sr: 0.68 ± 0.01 and SUVA254: 1.17 ±...

Research paper thumbnail of Landscape-driven carbon export from small coastal permafrost watersheds

Research paper thumbnail of How do microorganisms from permafrost soils respond to short-term warming?

Research paper thumbnail of Late Quaternary palaeoenvironmental records from a glacially and permafrost affected island in the Canadian Arctic (Herschel Island, Yukon Coastal Plain)