Advanced

Peatland dynamics in response to past and potential future climate change : A regional modelling approach

Chaudhary, Nitin LU (2017)
Abstract (Swedish)
En majoritet av de nordliga torvmarkerna utvecklades under holocen som ett resultat av en positiv massbalans mellan nettoprimärproduktion och heterotrofa nedbrytningshastigheter. Sedan dess har de lagrat stora mängder kol i terrestra ekosystem. En betydande del av dessa områden sammanfaller också med regioner med underliggande permafrost och uppvisar olika ackumulationsmönster av torv. Således, för att kunna förutse och förstå den långsiktiga utvecklingen av kollagret i torvmark i Arktiska områden, är det nödvändigt att använda mekanistiska framställningar av både torvmark och permafrost i modellering. I den här avhandlingen beskrivs en ny dynamisk flerskiktsimplementering av torvmarker och permafrostdynamik i den individ- och... (More)
En majoritet av de nordliga torvmarkerna utvecklades under holocen som ett resultat av en positiv massbalans mellan nettoprimärproduktion och heterotrofa nedbrytningshastigheter. Sedan dess har de lagrat stora mängder kol i terrestra ekosystem. En betydande del av dessa områden sammanfaller också med regioner med underliggande permafrost och uppvisar olika ackumulationsmönster av torv. Således, för att kunna förutse och förstå den långsiktiga utvecklingen av kollagret i torvmark i Arktiska områden, är det nödvändigt att använda mekanistiska framställningar av både torvmark och permafrost i modellering. I den här avhandlingen beskrivs en ny dynamisk flerskiktsimplementering av torvmarker och permafrostdynamik i den individ- och patchbaserade dynamiska vegetations- och ekosystemmodellen LPJ-GUESS. Syftet med studierna i avhandlingen är att förbättra förståelsen av de processer som påverkar långsiktig torvackumulering och dess inre dynamik samt att inkludera hur dessa system påverkas av småskalig heterogenitet, vegetationsdynamik och interaktion med underliggande permafrost. En enkel tvådimensionell mikrotopografisk modell har också tagits fram för att undersöka etablerade hypoteser rörande stabilitet, beteende och transformation av dessa mikrostrukturer och effekter av denna småskaliga heterogenitet på kopplad dynamisk vegetation, hydrologi och torvackumulering. LPJ-GUESS kalibrerades och validerades med data från en myr i Stordalen i norra Sverige och utvärderades med data från flera platser i Skandinavien och Mer Bleue i Kanada. Modellen tillämpades sedan på regional nivå för att förbättra kunskapen om kolinlagringshastigheter för olika rums- och tidsupplösningar samt för att demonstrera potentiella följder av nuvarande uppvärmning på dessa klimatkänsliga ekosystem. Båda modellerna som utvecklades i den här avhandlingen fungerade tillfredsställande vid jämförelser med experimentella data.

LPJ-GUESS är tämligen robust på att beskriva torvackumulering och permafrostdynamik med rimliga vegetations- och hydrologiska förhållanden för tids- och rumsupplösningar för olika klimatgradienter. Simuleringarna förbättrade vår kunskap om hur torvmarken utvecklades i det förflutna men också hur det utvecklas idag och kan komma att utvecklas i framtiden. Det visade sig att myren i Stordalen kommer att fortsätta att ackumulera kol de kommande årtionderna men senare kommer att övergå till en kolkälla. Det visade sig också att permafrostfria regioner som förutses erhålla reducerad mängd av nederbörd kan komma att förlora en signifikant mängd kol i framtiden till följd av minskad markfukt, medan torvmark med underliggande permafrost kan öka kolinlagringen på grund av en initial ökning i markfukt till följd av permafrostupptining, vilket undertrycker nedbrytning och förhöjer växtproduktion. Våra modelleringsresultat antyder även att torvmark kan uppvisa olika beteende med alternativ sammansättning och strukturell dynamik beroende på initiala topografiska- och klimatologiska förhållanden, växtegenskaperna och det kommer i allmänhet att bli en utmaning att inkludera dem i nuvarande ESM:s. Dock så är LPJ-GUESS redo att användas i ESM:s i sin nuvarande form där den kan hantera problem relaterade till biogeokemiska och biofysikaliska återkopplingar till klimatförändringar i Arktis och globalt.

(Less)
Abstract
The majority of the northern peatlands developed during the Holocene as a result of a positive mass balance between net primary productivity (NPP) and heterotrophic decomposition rates. Over that time they have sequestered a huge amount of carbon in terrestrial ecosystems. A significant proportion of these areas also coincides with areas underlain with permafrost and shows a diverse range of peat accumulation patterns. Thus, for predicting and understanding the long-term evolution of peatland carbon stocks across the pan-Arctic, mechanistic representations of both peatland and permafrost dynamics are needed in the modelling framework. In this thesis, a novel implementation of dynamic multi-layer peatland and permafrost dynamics in the... (More)
The majority of the northern peatlands developed during the Holocene as a result of a positive mass balance between net primary productivity (NPP) and heterotrophic decomposition rates. Over that time they have sequestered a huge amount of carbon in terrestrial ecosystems. A significant proportion of these areas also coincides with areas underlain with permafrost and shows a diverse range of peat accumulation patterns. Thus, for predicting and understanding the long-term evolution of peatland carbon stocks across the pan-Arctic, mechanistic representations of both peatland and permafrost dynamics are needed in the modelling framework. In this thesis, a novel implementation of dynamic multi-layer peatland and permafrost dynamics in the individual- and patch- based dynamic vegetation and ecosystem model (LPJ-GUESS) is described. The major emphasis of this work goes into enhancing the current understanding of the processes involved in the long-term peat accumulation and its internal dynamics, including how these systems are influenced by small-scale heterogeneity, vegetation dynamics and interactions with underlying permafrost. A simple two-dimensional microtopographical (2-DMT) model was also developed to address the established hypotheses concerning stability, behaviour and transformation of these microstructures and the effects of this small-scale heterogeneity on the coupled dynamics of vegetation, hydrology and peat accumulation. LPJ-GUESS was calibrated and validated using data from a mire in Stordalen, northern Sweden, and evaluated using data from multiple sites in Scandinavia and from Mer Bleue, Canada. It was subsequently applied across the pan-Arctic to advance the existing knowledge on carbon accumulation rates at different spatial and temporal scales, and also to demonstrate the potential implications of current warming on these climate sensitive ecosystems. Both of the models developed in this thesis performed satisfactorily when confronted with experimental data.

LPJ-GUESS is quite robust in capturing peat accumulation and permafrost dynamics including reasonable vegetation and hydrological conditions at temporal and spatial scales across various climate gradients. The simulations improved our knowledge of peatland functioning in the past, present and future. It was found that Stordalen mire will continue to accumulate carbon in the coming decades but later will turn into a carbon source. It was also found that permafrost-free regions that are predicted to experience reduced rates of precipitation may lose significant amount of carbon in the future due to reductions in soil moisture. Conversely, peatlands currently underlain with permafrost could gain carbon due to an initial increase in soil moisture as a result of permafrost thawing. My modelling results also suggest that peatlands can show diverse range of behaviour with alternative compositional and structural dynamics depending on the initial topographical, climatic conditions, and plant characteristics, therefore, it will be challenging to represent such dynamics in current Earth System Models (ESMs). With the inclusion of aforementioned processes, LPJ-GUESS has now become quite robust. The resultant model can now be coupled with ESM where it can address issues related to peatland-mediated biogeochemical and biophysical feedbacks to climate change in the Arctic and globally.
(Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr. Williams, Mathew, Global Change Research Institute, University of Edinburgh, United Kingdom
organization
publishing date
type
Thesis
publication status
published
subject
keywords
PEATLANDS, PERMAFROST, Carbon accumulation, Microtopography, LPJ-GUESS, Earth system models
pages
227 pages
publisher
Lund University, Faculty of Science, Department of Physical Geography and Ecosystem Science
defense location
Lecture hall “Världen”, Geocentre I, Sölvegatan 10, Lund
defense date
2017-04-21 13:00
ISBN
978-91-85793-80-8
978-91-85793-79-2
language
English
LU publication?
yes
id
adfb11ee-7719-4337-9d03-4ccd03fbbef5
date added to LUP
2017-04-04 18:06:52
date last changed
2017-04-12 15:57:16
@phdthesis{adfb11ee-7719-4337-9d03-4ccd03fbbef5,
  abstract     = {The majority of the northern peatlands developed during the Holocene as a result of a positive mass balance between net primary productivity (NPP) and heterotrophic decomposition rates. Over that time they have sequestered a huge amount of carbon in terrestrial ecosystems. A significant proportion of these areas also coincides with areas underlain with permafrost and shows a diverse range of peat accumulation patterns. Thus, for predicting and understanding the long-term evolution of peatland carbon stocks across the pan-Arctic, mechanistic representations of both peatland and permafrost dynamics are needed in the modelling framework. In this thesis, a novel implementation of dynamic multi-layer peatland and permafrost dynamics in the individual- and patch- based dynamic vegetation and ecosystem model (LPJ-GUESS) is described. The major emphasis of this work goes into enhancing the current understanding of the processes involved in the long-term peat accumulation and its internal dynamics, including how these systems are influenced by small-scale heterogeneity, vegetation dynamics and interactions with underlying permafrost. A simple two-dimensional microtopographical (2-DMT) model was also developed to address the established hypotheses concerning stability, behaviour and transformation of these microstructures and the effects of this small-scale heterogeneity on the coupled dynamics of vegetation, hydrology and peat accumulation. LPJ-GUESS was calibrated and validated using data from a mire in Stordalen, northern Sweden, and evaluated using data from multiple sites in Scandinavia and from Mer Bleue, Canada. It was subsequently applied across the pan-Arctic to advance the existing knowledge on carbon accumulation rates at different spatial and temporal scales, and also to demonstrate the potential implications of current warming on these climate sensitive ecosystems. Both of the models developed in this thesis performed satisfactorily when confronted with experimental data.<br/><br/>LPJ-GUESS is quite robust in capturing peat accumulation and permafrost dynamics including reasonable vegetation and hydrological conditions at temporal and spatial scales across various climate gradients. The simulations improved our knowledge of peatland functioning in the past, present and future. It was found that Stordalen mire will continue to accumulate carbon in the coming decades but later will turn into a carbon source. It was also found that permafrost-free regions that are predicted to experience reduced rates of precipitation may lose significant amount of carbon in the future due to reductions in soil moisture. Conversely, peatlands currently underlain with permafrost could gain carbon due to an initial increase in soil moisture as a result of permafrost thawing. My modelling results also suggest that peatlands can show diverse range of behaviour with alternative compositional and structural dynamics depending on the initial topographical, climatic conditions, and plant characteristics, therefore, it will be challenging to represent such dynamics in current Earth System Models (ESMs). With the inclusion of aforementioned processes, LPJ-GUESS has now become quite robust. The resultant model can now be coupled with ESM where it can address issues related to peatland-mediated biogeochemical and biophysical feedbacks to climate change in the Arctic and globally.<br/>},
  author       = {Chaudhary, Nitin},
  isbn         = {978-91-85793-80-8},
  keyword      = {PEATLANDS,PERMAFROST,Carbon accumulation,Microtopography,LPJ-GUESS,Earth system models},
  language     = {eng},
  pages        = {227},
  publisher    = {Lund University, Faculty of Science, Department of Physical Geography and Ecosystem Science},
  school       = {Lund University},
  title        = {Peatland dynamics in response to past and potential future climate change : A regional modelling approach},
  year         = {2017},
}