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Linking distributed hydrological processes with ecosystem vegetation dynamics and carbon cycling: Modelling studies in a subarctic catchment of northern Sweden

Tang, Jing LU (2014)
Abstract (Swedish)
Popular Abstract in Chinese

北极和亚北极地区对全球气候变化影响尤为重要。目前,北极地区正面临着变暖速度高于全球平均的现状。全球大约有50%的土壤碳储存在高纬度地区的土壤里,这些土壤碳主要分布于冻土层和泥炭层中。冻土层的解冻会使原先被冻结的土壤碳加速分解,产生温室气体,从而对全球变暖形成一个强烈的正反馈。与此同时,气温的增加可能会很大程度地影响植被在这些地区的生长和分布。动态生态系统模型是一种非常强大的工具,被用来研究气候变化对生态系统的影响,并且可以量化生态系统对大气的反馈信息。然而这些模型通常只关注大气、地表植被和土壤之间的水和碳的纵向转移,从而忽略了其在模型空间单元中的横向移动。这样可能会导致模型对于水和碳平衡的计算不够准确和全面,尤其在气候敏感的高纬度极地地区,这种偏差可能会更大。

本论文旨在解决动态生态系统模型中的这个局限性问题。基于目前最先进的动态生态系统模型LPJ-GUESS,我们利用和结合空间地形指数实现了模拟水和碳(主要是土壤溶解性有机碳)在空间单元中的相互作用。文中所提出来的建模方法和算法被应用到坐落于亚北极地区,瑞典北部的Stordalen流域,以探索模型新方法对估算水文和生态过程的潜在影响。在整个应用过程中,我们采用了大量的观测数据集来进行模型评估。

... (More)
Popular Abstract in Chinese

北极和亚北极地区对全球气候变化影响尤为重要。目前,北极地区正面临着变暖速度高于全球平均的现状。全球大约有50%的土壤碳储存在高纬度地区的土壤里,这些土壤碳主要分布于冻土层和泥炭层中。冻土层的解冻会使原先被冻结的土壤碳加速分解,产生温室气体,从而对全球变暖形成一个强烈的正反馈。与此同时,气温的增加可能会很大程度地影响植被在这些地区的生长和分布。动态生态系统模型是一种非常强大的工具,被用来研究气候变化对生态系统的影响,并且可以量化生态系统对大气的反馈信息。然而这些模型通常只关注大气、地表植被和土壤之间的水和碳的纵向转移,从而忽略了其在模型空间单元中的横向移动。这样可能会导致模型对于水和碳平衡的计算不够准确和全面,尤其在气候敏感的高纬度极地地区,这种偏差可能会更大。

本论文旨在解决动态生态系统模型中的这个局限性问题。基于目前最先进的动态生态系统模型LPJ-GUESS,我们利用和结合空间地形指数实现了模拟水和碳(主要是土壤溶解性有机碳)在空间单元中的相互作用。文中所提出来的建模方法和算法被应用到坐落于亚北极地区,瑞典北部的Stordalen流域,以探索模型新方法对估算水文和生态过程的潜在影响。在整个应用过程中,我们采用了大量的观测数据集来进行模型评估。

我们提出了一种基于网格单元对网格单元的分布式水文(DH)方法来动态模拟流域内的水流。我们进一步比较了不同的流量路径算法对于模拟水文和生态过程的影响。结果表明,当我们在Stordalen流域内使用结合了分布式水文方法的模型时,该模型对于径流估算的精度比以往有所提高。同时实验结果也表明了流量路径算法的选择会对研究区域内水通量和碳通量的估算产生重大的影响。基于以上结果,我们(在高空间分辨率下)利用该模型对流域内的碳预算有了一个更为完整的估算。我们发现,Stordalen流域现在是一个碳汇,并且在不久的将来有可能成为一个更大的碳汇。然而这一预测结果非常地依赖于空气中二氧化碳浓度的增加对流域内植被固碳能力的影响,同时还受流域内泥炭地里甲烷的排放量的影响。除此之外,该模型进一步扩展了对土壤水中的溶解性有机碳(DOC)的含量及其空间横向传输的动态模拟。模拟的输出表明,土壤中DOC的动态变化主要受DOC 的产生量和矿化作用的影响,潮湿的沼泽泥炭地在现在和将来都会是土壤DOC输出的热点区域。

总而言之,本论文展示了在LPJ-GUESS模型中加入用以描述水流的地形指数的可行性,同时证明了在高纬度地区模拟碳动态变化时对于水文条件的空间异质性的考量的重要性。此外,本论文还说明了在高空间分辨率下,综合考虑垂直和水平碳通量可以提供更准确和更完整的碳预算的估计,也可以动态地模拟不同的碳成分在应对气候变化时产生的不同结果。



Popular Abstract in Swedish

De arktiska och subarktiska regionerna är av särskild betydelse för den globala klimatförändringen, och genomgår nu en klimatuppvärmning som är högre än genomsnittshöjningen på jorden. Omkring 50 % av världens markkol är lagrat i nordliga jordar (på höga latituder), och där främst i permafrost- och torvjordar. Upptiningen av permafrost påskyndar nedbrytningen, och därmed frigöring, av tidigare fryst markkol, vilket förväntas ha kraftiga effekter på den globala uppvärmningen. Samtidigt kan en ökad lufttemperatur påtagligt påverka tillväxt och utbredning av vegetation i dessa regioner. Dynamiska ekosystemmodeller är effektiva verktyg för att studera klimatförändringars påverkan på ekosystemprocesser, inklusive kvantifiering av återkopplingar från olika ekosystem till atmosfären. Dessa modeller fokuserar emellertid främst på det vertikala utbytet av kol och vatten mellan atmosfär, landyta, vegetation och mark. Därför tar de i allmänhet inte hänsyn till de horisontella vatten- och kolflödena som förekommer mellan de modellerade rumsliga enheterna (jmf gridceller i en rasterkarta eller pixlar i en bild). Denna förenkling kan leda till en ofullständig uppskattning av vatten- och kolbudgetar, och då i synnerhet för de klimatkänsliga regionerna på de höga latituderna.

Denna avhandling syftar till att reducera ovan nämnda begränsningar genom att implementera rumsliga topografiska index i den dynamiska ekosystemmodellen LPJ-GUESS, samt att inkorporera interaktioner mellan vatten och kol (huvudsakligen löst organiskt kol, DOC) över ytan (mellan gridcellerna i kartan). De modeller som utvecklats inom denna studie har implementerats i det subarktiska Stordalens avrinningsområde, beläget i norra Sverige. Där har modellernas eventuella inverkan på hydrologiska och ekologiska simuleringar analyserats och dokumenterats. För utvärdering av modellerna har omfattande observationsdata använts.

Vidare föreslås en distribuerad hydrologisk (DH) metod för att dynamiskt simulera vattentransport från cell till cell inom Stordalens avrinningsområde, och jämförande studier av de hydrologiska och ekologiska effekterna beroende på olika algoritmer för modellering av vattenflöden har genomförts. Resultaten visar att den föreslagna DH-metoden kan modellera avrinningen i Stordalens avrinningsområde bättre än tidigare föreslagna metoder. Vidare kan det konstateras att valet av flödesalgoritm har en stor inverkan på modelleringen av vatten- och kolflöden i regionen. Den utvecklade metoden användes även för att utföra en fullständig uppskattning av kolbudgeten i avrinningsområdet. I denna delstudie kom det fram att upptagningsområdet idag är en kolsänka, och att det inom en snar framtid sannolikt kommer att bli en ännu starkare sänka. Detta förlopp är emellertid starkt beroende av framtida atmosfäriska CO2-koncentrationer och metanutsläpp från torvmarkerna. Den sista delen av avhandlingen behandlar ytterligare utveckling av modellen för att dynamiskt kunna modellera DOC i markvatten, samt den laterala (horisontella) transporten av DOC i landskapet. Resultaten visar att produktion och mineralisering av DOC i stor utsträckning bidrar till DOC-flöden, samt att våta torvmarker är och kommer att vara hetfläckar (även kallade hotspots) för DOC-export.

Sammanfattningsvis visar denna avhandling möjligheterna att implementera topografiska index och vattenflöden (lateralt och vertikalt) i LPJ-GUESS. Den demonstrerar också vikten av att ta hänsyn till rumslig heterogenitet i hydrologiska förhållanden vid modellering av koldynamik på höga latituder. Avhandlingsarbetet har gjort det möjligt att genom integrering av vertikala och laterala kolflöden vid höga rumsliga upplösningar noggrannare skatta en fullständig kolbudget, samt att dynamiskt simulera vilken påverkan klimatförändringarna har på olika kolkomponenter. (Less)
Abstract
The Arctic and Subarctic regions are of particular importance to the global climate change and are now experiencing a climate warming that is higher than the global average. Around 50% of the global soil carbon is stored in high latitude soils, especially in permafrost and peatland soils. Permafrost thawing, speeding up the decomposition of previously frozen soil carbon, is expected to result in strongly positive feedbacks to global warming. Meanwhile, increased air temperature may strongly impact vegetation growth and distributions in this region. Dynamic ecosystem models are powerful tools to study climate change influences on ecosystem processes and also to quantify ecosystem feedbacks to the atmosphere. However, these models often... (More)
The Arctic and Subarctic regions are of particular importance to the global climate change and are now experiencing a climate warming that is higher than the global average. Around 50% of the global soil carbon is stored in high latitude soils, especially in permafrost and peatland soils. Permafrost thawing, speeding up the decomposition of previously frozen soil carbon, is expected to result in strongly positive feedbacks to global warming. Meanwhile, increased air temperature may strongly impact vegetation growth and distributions in this region. Dynamic ecosystem models are powerful tools to study climate change influences on ecosystem processes and also to quantify ecosystem feedbacks to the atmosphere. However, these models often focus on the vertical transfer of carbon and water between the atmosphere, the land surface vegetation and soils. Therefore, they generally do not consider the horizontal water and soluble carbon flows between the modelled spatial units (grid cells), which could result in an incomplete estimation of water and carbon budgets, especially for climatically sensitive high latitude regions.

In this thesis, we aim to overcome this limitation by implementing spatial topographical indices into a state-of-the-art dynamic ecosystem model, LPJ-GUESS, and to incorporate water and carbon (mainly dissolved organic carbon, DOC) interactions between the grid cells. Modelling approaches and algorithms developed in this thesis were applied to study the subarctic Stordalen catchment, located in northern Sweden, and to explore the potential influence on the model’s hydrological and ecological estimations. Extensive sets of observation data were used for model evaluation throughout.

We proposed a distributed hydrological (DH) approach to dynamically simulate water flow from cell to cell within the catchment and compared the hydrological and ecological impacts resulting from different flow routing algorithms. The results indicate an improved accuracy of runoff estimation when using the proposed DH scheme in the Stordalen catchment. They also show that the choice of flow algorithm can have strong impacts on water and carbon flux estimations in this region. Furthermore, a complete estimation of the catchment carbon budget was assessed using our developed model. We found that the catchment is a carbon sink at present and could become a stronger sink in the near future, a result which is, however, very dependent on future atmospheric CO2 concentrations and methane (CH4) emissions from the peatlands. Additionally, the model was further extended to dynamically model soil water DOC and the lateral transport of DOC across the landscape. The modelled outputs suggest that DOC production and mineralization largely contribute to DOC fluxes and that wet fen peatland is and will be a hotspot for DOC export.

In conclusion, this thesis demonstrates the feasibility of implementing topographical indices into LPJ-GUESS to describe water flows, and the importance of considering spatial heterogeneity in hydrological conditions when modelling carbon dynamics at high latitudes. Furthermore, the integration of vertical and horizontal carbon fluxes at high spatial resolutions can be used to provide more accurate estimations of a complete carbon budget and can dynamically simulate the fate of different carbon components in response to climate change. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr. Blyth, Eleanor, Centre for Ecology & Hydrology, Wallingford, United Kingdom
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Carbon cycling, Water cycling, Hydrological modelling, Ecosystem modelling, Subarctic ecosystems, Climate change
pages
187 pages
publisher
Department of Physical Geography and Ecosystem Science, Lund University
defense location
Världen auditorium, Geocentrum I, Sölvegatan 10, 223 62, Lund Sweden
defense date
2014-12-16 13:00
ISBN
978-91-85793-44-0
project
MERGE
language
English
LU publication?
yes
id
fe2584d3-7192-4155-93af-b3ae67b27009 (old id 4778923)
date added to LUP
2014-11-24 12:12:33
date last changed
2016-09-19 08:45:05
@phdthesis{fe2584d3-7192-4155-93af-b3ae67b27009,
  abstract     = {The Arctic and Subarctic regions are of particular importance to the global climate change and are now experiencing a climate warming that is higher than the global average. Around 50% of the global soil carbon is stored in high latitude soils, especially in permafrost and peatland soils. Permafrost thawing, speeding up the decomposition of previously frozen soil carbon, is expected to result in strongly positive feedbacks to global warming. Meanwhile, increased air temperature may strongly impact vegetation growth and distributions in this region. Dynamic ecosystem models are powerful tools to study climate change influences on ecosystem processes and also to quantify ecosystem feedbacks to the atmosphere. However, these models often focus on the vertical transfer of carbon and water between the atmosphere, the land surface vegetation and soils. Therefore, they generally do not consider the horizontal water and soluble carbon flows between the modelled spatial units (grid cells), which could result in an incomplete estimation of water and carbon budgets, especially for climatically sensitive high latitude regions. <br/><br>
In this thesis, we aim to overcome this limitation by implementing spatial topographical indices into a state-of-the-art dynamic ecosystem model, LPJ-GUESS, and to incorporate water and carbon (mainly dissolved organic carbon, DOC) interactions between the grid cells. Modelling approaches and algorithms developed in this thesis were applied to study the subarctic Stordalen catchment, located in northern Sweden, and to explore the potential influence on the model’s hydrological and ecological estimations. Extensive sets of observation data were used for model evaluation throughout. <br/><br>
We proposed a distributed hydrological (DH) approach to dynamically simulate water flow from cell to cell within the catchment and compared the hydrological and ecological impacts resulting from different flow routing algorithms. The results indicate an improved accuracy of runoff estimation when using the proposed DH scheme in the Stordalen catchment. They also show that the choice of flow algorithm can have strong impacts on water and carbon flux estimations in this region. Furthermore, a complete estimation of the catchment carbon budget was assessed using our developed model. We found that the catchment is a carbon sink at present and could become a stronger sink in the near future, a result which is, however, very dependent on future atmospheric CO2 concentrations and methane (CH4) emissions from the peatlands. Additionally, the model was further extended to dynamically model soil water DOC and the lateral transport of DOC across the landscape. The modelled outputs suggest that DOC production and mineralization largely contribute to DOC fluxes and that wet fen peatland is and will be a hotspot for DOC export. <br/><br>
In conclusion, this thesis demonstrates the feasibility of implementing topographical indices into LPJ-GUESS to describe water flows, and the importance of considering spatial heterogeneity in hydrological conditions when modelling carbon dynamics at high latitudes. Furthermore, the integration of vertical and horizontal carbon fluxes at high spatial resolutions can be used to provide more accurate estimations of a complete carbon budget and can dynamically simulate the fate of different carbon components in response to climate change.},
  author       = {Tang, Jing},
  isbn         = {978-91-85793-44-0},
  keyword      = {Carbon cycling,Water cycling,Hydrological modelling,Ecosystem modelling,Subarctic ecosystems,Climate change},
  language     = {eng},
  pages        = {187},
  publisher    = {Department of Physical Geography and Ecosystem Science, Lund University},
  school       = {Lund University},
  title        = {Linking distributed hydrological processes with ecosystem vegetation dynamics and carbon cycling: Modelling studies in a subarctic catchment of northern Sweden},
  year         = {2014},
}