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Experimental Evidence of Large Changes in Terrestrial Chlorine Cycling Following Altered Tree Species Composition
Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
Andra, France.
EDF, France.
INRA Centre Nancy, France.
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2015 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 8, 4921-4928 p.Article in journal (Refereed) Published
Abstract [en]

Organochlorine molecules (Cl-org) are surprisingly abundant in soils and frequently exceed chloride (Cl-) levels. Despite the widespread abundance of Cl-org and the common ability of microorganisms to produce Cl-org, we lack fundamental knowledge about how overall chlorine cycling is regulated in forested ecosystems. Here we present data from a long-term reforestation experiment where native forest was cleared and replaced with five different tree species. Our results show that the abundance and residence times of Cl- and Cl-org after 30 years were highly dependent on which tree species were planted on the nearby plots. Average Cl- and Cl-org content in soil humus were higher, at experimental plots with coniferous trees than in those with deciduous trees. Plots with Norway spruce had the highest net accumulation of Cl- and Cl-org over the experiment period, and showed a 10 and 4 times higher Cl- and Cl-org storage (kg ha(-1)) in the biomass, respectively, and 7 and 9 times higher storage of Cl- and Cl-org in the soil humus layer, compared to plots with oak. The results can explain why local soil chlorine levels are frequently independent of atmospheric deposition, and provide opportunities for improved modeling of chlorine distribution and cycling in terrestrial ecosystems.

Place, publisher, year, edition, pages
American Chemical Society , 2015. Vol. 49, no 8, 4921-4928 p.
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:liu:diva-118871DOI: 10.1021/acs.est.5b00137ISI: 000353610300017PubMedID: 25811074OAI: diva2:817361

Funding Agencies|EDF, France; French national radioactive waste management agency (Andra), France; Linkoping University, Sweden; "Fonds National de la Recherche Scientifique" (FNRS) of Belgium

Available from: 2015-06-05 Created: 2015-06-04 Last updated: 2016-04-01
In thesis
1. Chlorine Cycling in Terrestrial Environments
Open this publication in new window or tab >>Chlorine Cycling in Terrestrial Environments
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Klorets kretslopp i terrestra miljöer
Abstract [en]

Chlorinated organic compounds (Clorg) are produced naturally in soil. Formation and degradation of Clorg affect the chlorine (Cl) cycling in terrestrial environments and chlorine can be retained or released from soil. Cl is known to have the same behaviour as radioactive chlorine-36 (36Cl), a long-lived radioisotope with a half-life of 300,000 years. 36Cl attracts interest because of its presence in radioactive waste, making 36Cl a potential risk for humans and animals due to possible biological uptake. This thesis studies the distribution and cycling of chloride (Cl) and Clorg in terrestrial environments by using laboratory controlled soil incubation studies and a forest field study. The results show higher amounts of Cl and Clorg and higher chlorination rates in coniferous forest soils than in pasture and agricultural soils. Tree species is the most important factor regulating Cl and Clorg levels, whereas geographical location, atmospheric deposition, and soil type are less important. The root zone was the most active site of the chlorination process. Moreover, this thesis confirms that bulk Clorg dechlorination rates are similar to, or higher than, chlorination rates and that there are at least two major Clorg pools, one being dechlorinated quickly and one remarkably slower. While chlorination rates were negatively influenced by nitrogen additions, dechlorination rates, seem unaffected by nitrogen. The results implicate that Cl cycling is highly active in soils and Cl and Clorg levels result from a dynamic equilibrium between chlorination and dechlorination. Influence of tree species and the rapid and slow cycling of some Cl pools, are critical to consider in studies of Cl in terrestrial environments. This information can be used to better understand Cl in risk-assessment modelling including inorganic and organic 36Cl.

Abstract [sv]

Klorerade organiska föreningar (Clorg) bildas naturligt i mark och påverkar klorets kretslopp genom att de stannar kvar längre i marken. Detta stabila klor anses ha samma egenskaper som klor-36, som är en långlivad radioisotop med en halveringstid på 300 000 år. Klor-36 förekommer i olika typer av radioaktivt avfall och om klor-36 sprids i naturen finns det en potentiell risk för människor och djur genom biologiskt upptag. Syftet i denna avhandling är att öka kunskapen om fördelningen och cirkulationen av klorid (Cl-) och Clorg i terrestra miljöer med hjälp av studier i laboratoriemiljö samt en fältstudie i skogsmiljö. Resultaten visar att bildningshastigheten av Clorg är högst i barrskogsjord och rotzonen tycks vara en aktiv plats. Det finns också en större mängd Cl- och Clorg i barrskogsjordar än i betesmark och jordbruksmark. Den mest betydande faktorn som styr halterna av Cl- och Clorg är trädsort, medan geografiskt läge, atmosfäriskt nedfall, och jordmån är av mindre betydelse. Bildning och nedbrytning av Clorg sker med liknande hastigheter, men det tycks finnas två förråd av Clorg i jorden varav ett bryts ner snabbt och ett mer långsamt. Bildningshastigheten av Clorg är lägre i jordar med höga halter av kväve medan nedbrytningshastigheterna inte påverkas av kväve.

Slutsatsen från studiernas resultat är att klor i hög grad är aktivt i mark och att Cl- och Clorg halterna bestäms av en dynamisk jämvikt mellan bildning och nedbrytning av Clorg. I studier av klor i terrestra miljöer bör trädsorters inverkan och nedbrytning av olika klorförråd beaktas då det kan ge varierande uppehållstider av Cl- och Clorg i mark. Denna information är viktig vid riskbedömningar av hur radioaktivt klor kan spridas och cirkulera vid en eventuell kärnkraftsolycka.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 62 p.
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 672
Chloride, organic chlorine, chlorination, dechlorination, 36Cl, risk assessment modelling, Klorid, organiskt klor, klorering, deklorering, klor-36, riskmodellering
National Category
Soil Science Environmental Sciences related to Agriculture and Land-use Agricultural Science Forest Science Ecology
urn:nbn:se:liu:diva-125913 (URN)10.3384/diss.diva-125913 (DOI)978-91-7685-813-4 (Print) (ISBN)
Public defence
2016-04-15, TEMCAS, Hus T, Campus Valla, Linköping, 10:15 (English)
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2016-03-09Bibliographically approved

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