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Chlorine Transport in a Small Catchment
Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.ORCID iD: 0000-0002-6471-143X
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [sv]

De senaste decenniernas forskning har påvisat att en omfattande bildning och nedbrytning av klororganiska föreningar sker i mark. Bildning av sådana föreningar sker genom att klorid binds in i organiskt material. Denna naturliga bildning har rönt uppmärksamhet dels för att många klorerade ämnen är giftiga och dels för man tidigare trott att alla klororganiska ämnen uteslutande kommer från mänsklig verksamhet. Huvudmålet för föreliggande avhandling var att (i) uppskatta transporten av klorerade föreningar i nederbörd och avrinningsvatten, (ii) diskutera de klorerade föreningarnas ursprung med utgångspunkt från hur deras förekomst varierar i avrinningsvatten, (iii) undersöka hur transporten av klorid (salt) påverkas av olika faktorer och (iv) studera hur frisättningen av flyktiga klorerade föreningar från mark påverkas av kväve.

Avhandlingen bygger på en klorbudget som konstruerats utifrån fältstudier som genomförts i ett litet skogsbeklätt avrinningsområde i sydöstra Sverige. Dessutom har laboratoriestudier genomförts med jord som inhämtats från samma område. Resultaten visar att lagret av klor i marken är betydligt större än flödena och att det främst består av organiska ämnen medan flödet domineras av klorid (salt). Detta tyder på att en stor del av kloriden deltar i en biogeokemisk cykel vilket strider mot gängse uppfattning att klorid rör sig opåverkat genom mark. Hypotesen är att de översta marklagren fungerar som en sänka för klorid genom att omvandlas till organiskt bundet klor. De djupare jordlagren fungerar däremot som en kloridkälla genom att det klorerade organiska materialet transporterats med regnvatten från de ytligare till de djupare liggande lagren för att så småningom brytas ner, varvid klorid frisätts. Ovan beskrivna hypotes stöds av laboratoriestudierna där man kunnat notera att det sker såväl en fastläggning som en frisättning av klorid i mark. Resultaten från avhandlingen tillsammans med resultat från tidigare studier tyder på att en stor del av den klorid som finns i avrinningsvatten kommer från förmultnande organiskt material och att klorid med andra ord inte följer regnvattnets väg genom marken, vilket man tidigare trott. Studierna tyder alltså på att klorid till viss del ”gör en omväg” med en tidsfördröjning på troligen åtskilliga upp till hundratals år. Vidare tyder studierna på att flyktiga klorerade föreningar som kloroform och tetraklormetan bildas i mark och att tillsats av kväve orsakar en minskning av kloroform och en ökning av tetraklormetan.

Avhandlingen visar tydligt att det är nödvändigt att rikta uppmärksamhet mot klors biogeokemi i mark och då inte minst mot de processer som påverkar transporten av klor från de övre marklagren till grundvatten och ytvatten om vi ska öka förståelsen av hur klorerade ämnen som tillförts naturen genom mänskliga aktiviteter beter sig.

Abstract [en]

It is generally known that chlorine compounds are ubiquitous in the environment. In recent years, researchers have concluded that chlorine is part of a biogeochemical cycle in soil involving an interaction between chloride (Clin) and organic-matter-bound chlorine (Clorg). Even though there is indisputable evidence that Clorg is formed naturally, there are actually few simultaneous field measurements of Clorg and Clin. Previously stipulated conclusions with respect to underlying processes and transport estimates have thus been deduced from rather few concentration measurements. It is well known that the chemical composition in soil and runoff water varies widely over time and in space. The main objective of the thesis is to investigate the on-site variation of Clin, Clorg and VOCls in runoff water in order to (i) construct a chlorine budget on a catchment scale to visualize the relative contribution of Clin, Clorg, and VOCls; (ii) more reliably estimate how and why the concentrations of Clin, Clorg, and VOCls in runoff water vary; and (iii) analyze the influence of various environmental variables on the transport.

The present thesis highlights the on-site variation and fluxes of Clin, Clorg, and VOCls in a small forested catchment in southeast Sweden. Field flux data collected during a twoyear period and a constructed overall chlorine budget were evaluated. The results show that the storage is dominated by Clorg whereas the transport is dominated by Clin and that the storage is far much larger than the transport. Still, input and output is nearly in balance for all investigated chlorine species. It is interesting to note that these observations resemble observations made for carbon, nitrogen and sulphur; i.e. a large storage, small transport, complex biogeochemical cycling processes at hand but still close to steady state conditions with respect to output-input balances. It appears as if topsoil acts as a sink for Clin, while deeper soil acts as a source of Clin. In addition, the results of the thesis suggest that on-site variation depend on seasonal variations. These variations are to some extent caused by water discharge, but also by water residence time, internal chlorination/dechlorination of organic matter, and different soil water origins. Furthermore, both a net retention and a net release of Clin were observed in laboratory studies. The study indicates that simultaneous retention and release of Clin takes place in soil, which probably has an impact on the Clin import and export fluxes. Finally, the results show for the first time that tetrachloromethane can be emitted from laboratory incubated soil, and that soil nitrogen concentrations has quite different effects on the emission rates of chloroform and tetrachloromethane.

The results of the thesis, considered together with results of previous research, suggest that the turnover of chlorine in soils is extensive and potentially important for chlorine cycling in general, which must be taken into account if one wishes to increase the understanding of the cycling of anthropogenic chlorine compounds in the environment.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2006. , 56 + papers 1-5 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 352
Keyword [en]
catchment, chloride, chlorine, chloroform, organic chlorine, runoff water, soil, VOCls
Keyword [sv]
avrinningsområde, avrinningsvatten, flyktiga klorerade föreningar klor, klorid, kloroform, organiskt klor, mark
National Category
Oceanography, Hydrology, Water Resources
Identifiers
URN: urn:nbn:se:liu:diva-6316ISBN: 91-85523-85-2 (print)OAI: oai:DiVA.org:liu-6316DiVA: diva2:21758
Public defence
2006-05-12, K3, Kåkenhus, Campus, Norrköping, Norrköping, 10:15 (English)
Opponent
Supervisors
Note

On the day of the public defence the status of article IV was: Accepted.

Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2017-01-12Bibliographically approved
List of papers
1. The role of organic matter bound chlorine in the chlorine cycle: a case study of the Stubbetorp catchment, Sweden
Open this publication in new window or tab >>The role of organic matter bound chlorine in the chlorine cycle: a case study of the Stubbetorp catchment, Sweden
Show others...
2005 (English)In: Biogeochemistry, ISSN 0168-2563, Vol. 75, no 2, 241-269 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this study is to construct a balanced chlorine budget for a small forested catchment, focusing on the interaction between chloride (Clinorg) and organic-matter-bound chlorine (Clorg). Data from the actual catchment are combined with secondary data from other sites to elucidate more clearly which parts of the cycle are fairly well known and which are more or less unknown. The budget calculations show that the principal input and output fluxes of Cl in the catchment are inorganic but that the main pool is Clorg in the soil. In addition, the budget calculations suggest that a considerable portion of Clinorg in soil is transformed to Clorg and subsequently leached to deeper soil layers, that net mineralization of Clorg takes place in soil, preferably in deeper soil layers, and that degrading organic matter is a major source of Clinorg in runoff. The loss of Clorg through runoff is small to negligible in relation to other fluxes. It appears as if dry deposition of Clinorg is at risk of being underestimated if Clinorg is assumed to be conservative in soil. The pool of organic-matter-bound chlorine in soil is considerably larger than the annual flux of chloride through the system. The estimates suggest that the amount of Clorg in the upper 40 cm of the soil at the investigated site is approximately twice as large as the Clinorg. Furthermore, the amount of Clorg biomass is small in relation to the occurrence of Clorg in soil. Finally, the estimates indicate that the transport of volatile Clorg from the soil to the atmosphere may influence the chlorine cycle.

Keyword
Biogeochemistry, Chloride, Cycling, Organic chlorine
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-13819 (URN)10.1007/s10533-004-7259-9 (DOI)
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2013-12-17
2. Chlorine transport in a small catchment in southeast Sweden during two years
Open this publication in new window or tab >>Chlorine transport in a small catchment in southeast Sweden during two years
2007 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 82, no 2, 181-199 p.Article in journal (Refereed) Published
Abstract [en]

Previous studies have revealed that chlorine participates in a complex biogeochemical cycle in soil, which suggests that the transport of chloride through catchments may also be influenced. The present study is based on field observations of organic carbon, chloride (Clin), and chlorinated organic carbon (Clorg) in precipitation, soil, and runoff over a 2-year period from a small, forested catchment in southeast Sweden. The study reveals that (1) the soil pool is dominated by Clorg, (2) the input via wet deposition and output of Clin via runoff is 30 times smaller than the total storage of chlorine (Clin + Clorg) in soil, and (3) the transport is dominated by Clin. The organic matter that entered the outlet of the catchment was more chlorinated in the autumn than during the rest of the year, and rain events taking place in low-flow periods had a greater influence on TOC, Clorg, and Clin than did rain events taking place in high-flow periods. The seasonal pattern in combination with the low-flow versus high-flow pattern and previous findings of increasing chlorine-to-carbon ratios with soil depth suggests that the chlorine-to-carbon ratio variation in the leached organic matter is due that water preferentially comes from deeper layers in low-flow conditions. This study provides well-founded estimates of Clorg and Clin storage and fluxes for the studied catchment; however, the processes underlying the observed seasonal Clorg variations and transportation processes need further study.

Keyword
Catchment, chloride, chlorine, organic chlorine, soil, water, watershed
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-38911 (URN)10.1007/s10533-006-9062-2 (DOI)46101 (Local ID)46101 (Archive number)46101 (OAI)
Note

The previous status of this article was Manuscript.

Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13Bibliographically approved
3. Chloroform in runoff water: a two-year study in a small catchment in southeast Sweden
Open this publication in new window or tab >>Chloroform in runoff water: a two-year study in a small catchment in southeast Sweden
2007 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 82, no 2, 139-151 p.Article in journal (Refereed) Published
Abstract [en]

Chloroform concentrations were observed and input and output fluxes estimated over a 2-yr period in a small coniferous catchment (0.22 km2) in southeast Sweden. Water discharge was measured daily, and runoff water was sampled bi-weekly for chloroform analysis. An approximate chloroform budget was calculated, which indicated that the annual output of 6 μg m−2 yr−1 was approximately six times higher than the input, inferring an internal source of chloroform in the catchment. To the best of our knowledge, neither flux estimates nor mass balances have previously been made for chloroform on a catchment scale, nor have data regarding natural runoff variation with time been gathered. Concentrations of chloroform in runoff were found to be generally high during wet periods, such as spring, but also peaked during summer rain events. The observed pattern suggests that chloroform is formed in surface soil layers and transported to the outlet under high-flow conditions and during dry-period rain events; it is lost through degradation or evaporation during drier periods due to longer soil water residence times. The data suggest that the variation among replicates increases with concentration; this emphasizes the need to know what the degree of on-site variation is, so one can collect a sufficient number of replicates to permit detection of spatial or temporal changes.

Keyword
Biogeochemistry, Catchment, Chloroform, Water, VOCl
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-13821 (URN)10.1007/s10533-006-9059-x (DOI)
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2017-12-13Bibliographically approved
4. Chloride retention and release in a boreal forest soil: effects of soil water residence time and nitrogen and chloride loads
Open this publication in new window or tab >>Chloride retention and release in a boreal forest soil: effects of soil water residence time and nitrogen and chloride loads
Show others...
2006 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 40, no 9, 2977-2982 p.Article in journal (Refereed) Published
Abstract [en]

The common assumption that chloride (Cl-) is conservative in soils and can be used as a groundwater tracer is currently being questioned, and an increasing number of studies indicate that Cl- can be retained in soils. We performed lysimeter experiments with soil from a coniferous forest in southeast Sweden to determine whether pore water residence time and nitrogen and Cl- loads affected Cl- retention. Over the first 42 days there was a net retention of Cl- with retention rates averaging 3.1 mg Cl- m-2 d-1 (68% of the added Cl- retained over 42 days). Thereafter, a net release of Cl- at similar rates was observed for the remaining experimental period (85 d). Longer soil water residence time and higher Cl- load gave higher initial retention and subsequent release rates than shorter residence time and lower Cl- load did. Nitrogen load did not affect Cl transformation rates. This study indicates that simultaneous retention and release of Cl- can occur in soils, and that rates may be considerable relative to the load. The retention of Cl- observed was probably due to chlorination of soil organic matter or ion exchange. The cause of the shift between net retention and net release is unclear, but we hypothesize that the presence of O2 or the presence of microbially available organic matter regulates Cl- retention and release rates.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13822 (URN)10.1021/es0523237 (DOI)
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2017-12-13Bibliographically approved
5. Influence of nitrogen on the release of volatile organochlorines from coniferous forest soil: a laboratory study
Open this publication in new window or tab >>Influence of nitrogen on the release of volatile organochlorines from coniferous forest soil: a laboratory study
Manuscript (Other academic)
Identifiers
urn:nbn:se:liu:diva-13823 (URN)
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2010-01-13

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