Advanced

Reactive dissolved organic carbon dynamics in a changing environment : Experimental evidence from soil and water

Panneer Selvam, Balathandayuthabani LU (2016)
Abstract (Swedish)
Löst organiskt kol (DOC) är den huvudsakliga formen av organiskt kol i vattenekosystem. Biologisk och fotokemisk nedbrytning av löst organiskt kol (DOC) är viktiga orsaker till utsläpp av växthusgaser från akvatiska ekosystem. Enligt studier vid olika platser på norra halvklotet så kan pågående klimatförändringar orsaka både ökningar och minskningar i total DOC-export från mark till vatten. Det finns dock kunskapsbrist om effekterna av förändrade miljöförhållanden på DOC-reaktivitet (bio- och fotonedbrytningspotentialer). Därför syftade avhandlingen till att kombinera empiriska och experimentella metoder för att bestämma dynamiken i DOC-reaktivitet orsakad av förändringar i viktiga miljöparametrar kopplade till markfrostförhållanden och... (More)
Löst organiskt kol (DOC) är den huvudsakliga formen av organiskt kol i vattenekosystem. Biologisk och fotokemisk nedbrytning av löst organiskt kol (DOC) är viktiga orsaker till utsläpp av växthusgaser från akvatiska ekosystem. Enligt studier vid olika platser på norra halvklotet så kan pågående klimatförändringar orsaka både ökningar och minskningar i total DOC-export från mark till vatten. Det finns dock kunskapsbrist om effekterna av förändrade miljöförhållanden på DOC-reaktivitet (bio- och fotonedbrytningspotentialer). Därför syftade avhandlingen till att kombinera empiriska och experimentella metoder för att bestämma dynamiken i DOC-reaktivitet orsakad av förändringar i viktiga miljöparametrar kopplade till markfrostförhållanden och hydrologi. Jag samlade prover från olika delar av den boreala regionen för att utföra laboratorienedbrytningsexperiment och analysera DOC-nedbrytningspotentialer i förhållande till miljövariabler och intrinsiska (inneboende) egenskaper hos DOC.
I en boreal region med säsongstjäle så minskade DOC-bioreaktivitet med reduktioner av tjälens utbredning och varaktighet, medan fotoreaktiviten var oförändrad. Dock så uppvisade DOC från experimentellt upptinat permafrosttorv i subarktiska områden högre bio- och fotoreaktivitet än DOC från aktiva torvlager ovanför permafrosten. Marktyp och skillnader i intrinsiska DOC-egenskaper kunde förklara dessa skillnader i DOC-reaktivitet. I ytvattens så var biologisk nedbrytning den dominerande mekanismen för DOC-nedbrytning i bruna sjöar, medan fotonedbrytning spelade en relativt större roll i klara vatten. Fotoreaktivitet per enhet ljusabsorption var hög både vid både sura och alkaliska förhållanden, medan lägre fotoreaktivitet uppvisades vid intermediärt pH, troligen på grund av effekterna av DOC-protoneringstillstånd på fotoreaktivitet. Således orsakade pH-förändring längs sötvattenskontinueet en extrinsisk kontroll av fotoreaktivitet på landskapsnivå.
Sammanfattningsvis visar resultaten att klimatuppvärmning minskar exporten av bio-reaktivt DOC i en boreal skog, men det ökar sannolikt exporten av bio- och fotoreaktivt DOC i torvmark med tinande permafrost. I ett fuktigare klimat med kortare vattenuppehållstider så kan vattnet bli brunare och en förskjutning ske i den relativa betydelsen av fotonedbrytning respektive biologisk nedbrytning, medan redan bruna sjöar förblir bruna och dominerade av biologisk nedbrytning. Vidare så kan förlusten av fotoreaktivt DOC under transport i sötvattensnätverket uppvägas av förändringar i extrinsiska variabler såsom pH.
(Less)
Abstract
Dissolved organic carbon (DOC) is the major form of organic carbon in aquatic ecosystems. Biological and photochemical degradation of DOC are major causes of greenhouse gas emissions from aquatic ecosystems. In response to current changes in climate, studies at different northern-hemisphere locations have shown both increases and decreases in total DOC export from land to water. However, there is lack of knowledge on the effect of changing environmental conditions on bio- and photo-degradation potentials. Therefore, this thesis aimed to combine empirical and experimental methods to determine the dynamics of DOC reactivity in response to key environmental parameters related to soil frost conditions and hydrology. I collected samples from... (More)
Dissolved organic carbon (DOC) is the major form of organic carbon in aquatic ecosystems. Biological and photochemical degradation of DOC are major causes of greenhouse gas emissions from aquatic ecosystems. In response to current changes in climate, studies at different northern-hemisphere locations have shown both increases and decreases in total DOC export from land to water. However, there is lack of knowledge on the effect of changing environmental conditions on bio- and photo-degradation potentials. Therefore, this thesis aimed to combine empirical and experimental methods to determine the dynamics of DOC reactivity in response to key environmental parameters related to soil frost conditions and hydrology. I collected samples from the boreal region to carry out laboratory degradation experiments and to analyze the DOC degradation potentials in relation to environmental variables and intrinsic properties of the DOC.

In a boreal forest region that has seasonal soil frost, the DOC bio-reactivity decreased with experimental reductions in the extent and duration of soil frost, while photo-reactivity remained constant. However, DOC from experimentally thawed permafrost peat in the subarctic north showed higher bio- and photo-degradation potentials than the DOC from active peat layers above the permafrost. The nature of the soil and intrinsic DOC properties explained these patterns in soil DOC reactivity. In the surface water network, bio-degradation was the dominant DOC degradation mechanism in brow-water lakes, while photo-degradation played a relatively larger role in clearer waters. The surface water photo-reactivity per unit of light absorption was high at both acidic and at alkaline conditions, while lower at intermediate pH, probably due to effects of the protonation state of DOC on photo-reactivity. Therefore, pH change along the aquatic network caused extrinsic control on the photo-reactivity at the landscape scale.

In conclusion the results show that climate warming decreases the export of bio-reactive DOC in a boreal forest, but it likely increases the export of bio- and photo-reactive DOC in a permafrost peatland. In a wetter climate with shorter residence times, clear waters may experience browning and relative shift from photo-degradation to bio-degradation, while already brown lakes will remain brown and dominated by bio-degradation. Furthermore, the loss of photo reactive DOC during transport in aquatic network may be counter balanced by the changes in extrinsic variables such as pH.
(Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Roulet, Nigel, McGill University, Canada
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Dissolved organic carbon, DOC, Photodegradation, Biodegradation, DOC reactivity
pages
164 pages
publisher
Lund University, Faculty of Science, Department of Physical Geography and Ecosystem Science
defense location
Geocentre I, lecture hall “Världen”, Sölvegatan 10, Lund
defense date
2016-10-14 10:00
ISBN
978-91-85793-59-4
language
English
LU publication?
yes
id
24c68fe9-546b-4ac1-a4ba-e0448ab6afdb
date added to LUP
2016-09-21 17:12:54
date last changed
2016-10-14 12:53:01
@misc{24c68fe9-546b-4ac1-a4ba-e0448ab6afdb,
  abstract     = {Dissolved organic carbon (DOC) is the major form of organic carbon in aquatic ecosystems. Biological and photochemical degradation of DOC are major causes of greenhouse gas emissions from aquatic ecosystems. In response to current changes in climate, studies at different northern-hemisphere locations have shown both increases and decreases in total DOC export from land to water. However, there is lack of knowledge on the effect of changing environmental conditions on bio- and photo-degradation potentials. Therefore, this thesis aimed to combine empirical and experimental methods to determine the dynamics of DOC reactivity in response to key environmental parameters related to soil frost conditions and hydrology. I collected samples from the boreal region to carry out laboratory degradation experiments and to analyze the DOC degradation potentials in relation to environmental variables and intrinsic properties of the DOC.<br/><br/>In a boreal forest region that has seasonal soil frost, the DOC bio-reactivity decreased with experimental reductions in the extent and duration of soil frost, while photo-reactivity remained constant. However, DOC from experimentally thawed permafrost peat in the subarctic north showed higher bio- and photo-degradation potentials than the DOC from active peat layers above the permafrost. The nature of the soil and intrinsic DOC properties explained these patterns in soil DOC reactivity. In the surface water network, bio-degradation was the dominant DOC degradation mechanism in brow-water lakes, while photo-degradation played a relatively larger role in clearer waters. The surface water photo-reactivity per unit of light absorption was high at both acidic and at alkaline conditions, while lower at intermediate pH, probably due to effects of the protonation state of DOC on photo-reactivity. Therefore, pH change along the aquatic network caused extrinsic control on the photo-reactivity at the landscape scale.<br/><br/>In conclusion the results show that climate warming decreases the export of bio-reactive DOC in a boreal forest, but it likely increases the export of bio- and photo-reactive DOC in a permafrost peatland. In a wetter climate with shorter residence times, clear waters may experience browning and relative shift from photo-degradation to bio-degradation, while already brown lakes will remain brown and dominated by bio-degradation. Furthermore, the loss of photo reactive DOC during transport in aquatic network may be counter balanced by the changes in extrinsic variables such as pH.<br/>},
  author       = {Panneer Selvam, Balathandayuthabani},
  isbn         = {978-91-85793-59-4 },
  keyword      = {Dissolved organic carbon,DOC,Photodegradation,Biodegradation,DOC reactivity},
  language     = {eng},
  pages        = {164},
  publisher    = {ARRAY(0xa662958)},
  title        = {Reactive dissolved organic carbon dynamics in a changing environment : Experimental evidence from soil and water},
  year         = {2016},
}