| 1. |
- Bastviken, David, et al.
(författare)
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Chloride retention and release in a boreal forest soil: effects of soil water residence time and nitrogen and chloride loads
- 2006
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 40:9, s. 2977-2982
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Bastviken, David, et al.
(författare)
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Chloride retention in forest soil by microbial uptake and by natural chlorination of organic matter
- 2007
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Ingår i: Geochimica Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 71:13, s. 3182-3192
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic chlorine (i.e. chloride; Cl-in) is generally considered inert in soil and is often used as a tracer of soil and ground water movements. However, recent studies indicate that substantial retention or release of Cl-in can occur in soil, but the rates and processes responsible under different environmental conditions are largely unknown. We performed Cl-36 tracer experiments which indicated that short-term microbial uptake and release of Cl-in, in combination with more long-term natural formation of chlorinated organic matter (Cl-org), caused Cl-in imbalances in coniferous forest soil. Extensive microbial uptake and release of Cl-in occurred over short time scales, and were probably associated with changes in environmental conditions. Up to 24% of the initially available Clin within pore water was retained by microbial uptake within a week in our experiments, but most of this Cl-in, was released to the pore water again within a month, probably associated with decreasing microbial populations. The natural formation of Clorg resulted in a net immobilization of 4% of the initial pore water Clin over four months. If this rate is representative for the area where soil was collected, Clorg formation would correspond to a conversion of 25% of the yearly wet deposition of Cl-in. The study illustrates the potential of two Clin retaining processes in addition to those previously addressed elsewhere (e.g. uptake of chloride by vegetation). Hence, several processes operating at different time scales and with different regulation mechanisms can cause Clin imbalances in soil. Altogether, the results of the present study (1) provide evidence that Cl-in cannot be assumed to be inert in soil, (2) show that microbial exchange can regulate pore water Cl-in, concentrations and (3) confirm the controversial idea of substantial natural chlorination of soil organic matter.
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| 3. |
- Bastviken, David, et al.
(författare)
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Chlorine cycling and fates of 36Cl in terrestrial environments
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Chlorine-36 (36Cl), a radioisotope of chlorine (Cl) with a half-life of 301,000 years, is present in some types of nuclear waste and is disposed in repositories for radioactive waste. As the release of 36Cl from such repositories to the near surface environment has to be taken into account it is of interest to predict possible fates of 36Cl under various conditions as a part of the safety assessments of repositories for radioactive waste. This report aims to summarize the state of the art knowledge on Cl cycling in terrestrial environments. The view on Cl cycling in terrestrial environments is changing due to recent research and it is clear that the chloride ion (Cl–) is more reactive than previously believed. We group the major findings in three categories below according to the amount of data in support of the findings.From the result presented in this report it is evident that:There is an ubiquitous and extensive natural chlorination of organic matter in terrestrial ecosystems.The abundance of naturally formed chlorinated organic compounds (Clorg) frequently exceeds the abundance of Cl–, particularly in soils. Thereby Clorg in many cases dominates the total Cl pool.This has important implications for Cl transport. When reaching surface soils Cl– will not be a suitable tracer of water and will instead enter other Cl pools (Clorg and biomass) that prolong residence times in the system.Cl– dominates import and export from terrestrial ecosystems while Clorg and biomass Cl can dominate the standing stock Cl within terrestrial ecosystems.Both Cl and Clorg pools have to be considered separately in future monitoring programs addressing Cl cycling.Further, there are also indications (in need of confirmation by additional studies) that:There is a rapid and large uptake of Cl– by organisms and an accumulation in green plant parts. A surprisingly large proportion of total catchment Cl (up to 60%) can be found in the terrestrial biomass.Emissions of total volatile organohalogens could be a significant export pathway of Cl from the systems.Some of the Clorg may be very persistent and resist degradation better than average organic matter. This may lead to selective preservation of some Clorg (with associated low bioavailability).There is a production of Clorg in tissues of e.g. plants and animals and Cl can accumulate aschlorinated fatty acids in organisms.Most other nevertheless important aspects are largely unknown due to lack of data. Key unknowns include:The development over time of major Cl pools and fluxes. As long as such data is lacking we cannot assess net changes over time.How the precesses behind chlorination, dechlorination and transport patterns in terrestrial systems are regulated and affected by environmental factors.The ecological roles of the chlorine cycling in general.The ecological role of the microbial chlorination in particular.The chlorine cycling in aquatic environments – including Cl– and Clorg pools in sediment and water, are largely missing.Given the limited present information available, and particularly the lack of data with a temporal dimension and the lack of process understanding, predictive models are challenging. We also summarize currently available methods to study Cl in the environment.
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| 4. |
- Bastviken, David, 1971-, et al.
(författare)
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Temperature sensitivity indicates enzyme controlled chlorination of soil organic matter
- 2009
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:10, s. 3569-3573
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Tidskriftsartikel (refereegranskat)abstract
- Old assumptions that chloride is inert and that most chlorinated organic matter in soils is anthropogenic have been challenged by findings of naturally formed organochlorines. Such natural chlorination has been recognized for several decades, but there are still very few measurements of chlorination rates or estimates of the quantitative importance of terrestrial chlorine transformations. While much is known about the formation of specific compounds, bulk chlorination remains poorly understood in terms of mechanisms and effects of environmental factors. We quantified bulk chlorination rates in coniferous forest soil using 36Cl-chloride in tracer experiments at different temperatures and with and without molecular oxygen (O2). Chlorination was enhanced by the presence of O2 and had a temperature optimum at 20 °C. Minimum rates were found at high temperatures (50 °C) or under anoxic conditions. The results indicate (1) that most of the chlorination between 4 and 40 °C was biotic and driven by O2 dependent enzymes, and (2) that there is also slower background chlorination occurring under anoxic conditions at 20 °C and under oxic conditions at 50 °C. Hence, while oxic and biotic chlorination clearly dominated, chlorination by other processes including possible abiotic reactions was also detected.
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| 5. |
- Bastviken, David, et al.
(författare)
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Temperature Sensitivity Indicates That Chlorination of Organic Matter in Forest Soil Is Primarily Biotic
- 2009
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:10, s. 3569-3573
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Tidskriftsartikel (refereegranskat)abstract
- Old assumptions that chloride is inert and that most chlorinated organic matter in soils is anthropogenic have been challenged by findings of naturally formed organochlorines. Such natural chlorination has been recognized for several decades, but there are still very few measurements of chlorination rates or estimates of the quantitative importance of terrestrial chlorine transformations. While much is known about the formation of specific compounds, bulk chlorination remains poorly understood in terms of mechanisms and effects of environmental factors. We quantified bulk chlorination rates in coniferous forest soil using Cl-36-chloride in tracer experiments at different temperatures and with and without molecular oxygen (O-2). Chlorination was enhanced by the presence of O-2 and had a temperature optimum at 20 degrees C. Minimum rates were found at high temperatures (50 degrees C) or under anoxic conditions. The results indicate (1) that most of the chlorination between 4 and 40 degrees C was biotic and driven by O-2 dependent enzymes, and (2) that there is also slower background chlorination occurring under anoxic conditions at 20 degrees C and under oxic conditions at 50 degrees C. Hence, while oxic and biotic chlorination clearly dominated, chlorination by other processes including possible abiotic reactions was also detected.
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| 6. |
- Gustavsson, Malin, et al.
(författare)
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Organic Matter Chlorination Rates in Different Boreal Soils: The Role of Soil Organic Matter Content
- 2012
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Ingår i: Environmental Science and Technology. - : American Chemical Society. - 0013-936X .- 1520-5851. ; 46:3, s. 1504-1510
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Tidskriftsartikel (refereegranskat)abstract
- Transformation of chloride (Cl-) to organic chlorine (Cl-org) occurs naturally in soil but it is poorly understood how and why transformation rates vary among environments. There are still few measurements of chlorination rates in soils, even though formation of Cl-org has been known for two decades. In the present study, we compare organic matter (OM) chlorination rates, measured by Cl-36 tracer experiments, in soils from eleven different locations (coniferous forest soils, pasture soils and agricultural soils) and discuss how various environmental factors effect chlorination. Chlorination rates were highest in the forest soils and strong correlations were seen with environmental variables such as soil OM content and Cl- concentration. Data presented support the hypothesis that OM levels give the framework for the soil chlorine cycling and that chlorination in more organic soils over time leads to a larger Cl-org pool and in turn to a high internal supply of Cl- upon dechlorination. This provides unexpected indications that pore water Cl- levels may be controlled by supply from dechlorination processes and can explain why soil Cl- locally can be more closely related to soil OM content and the amount organically bound chlorine than to Cl- deposition.
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| 7. |
- Johansson, Emma, et al.
(författare)
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Organic and chlorine in Swedish spruce forest soil : Influence of nitrogen
- 2001
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 101:3-4, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations of organic and inorganic chlorine were estimated in samples collected in forest soils in the southern part of Sweden, and changes were observed after the addition of nitrogen in incubated samples. All of the investigated samples contained both inorganic and organic chlorine, and the concentration of organic chlorine was 2-4 times larger than that of inorganic chlorine. The results suggest that the amount of organic chlorine in mature spruce forest soils with a moderate chloride deposition in the temperate region is larger than the amount of inorganic chlorine. The results of the nitrogen incubation indicate that addition of ammonium nitrate causes a net decrease in the concentration of organic chlorine and a net increase in chloride concentration. The observed change appears to mainly be a result of a dechlorination of the organic matter present in the water leachable fraction. © 2001 Elsevier Science B.V.
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| 8. |
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| 9. |
- Svensson, Teresia, 1975-, et al.
(författare)
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Chlorine cycling and the fate of Cl in terrestrial environments
- 2021
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Ingår i: Environmental Science and Pollution Research. - : Springer. - 0944-1344 .- 1614-7499. ; 28:7, s. 7691-7709
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Tidskriftsartikel (refereegranskat)abstract
- Chlorine (Cl) in the terrestrial environment is of interest from multiple perspectives, including the use of chloride as a tracer forwater flow and contaminant transport, organochlorine pollutants, Cl cycling, radioactive waste (radioecology; 36Cl is of largeconcern) and plant science (Cl as essential element for living plants).During the past decades, there has been a rapid developmenttowards improved understanding of the terrestrial Cl cycle. There is a ubiquitous and extensive natural chlorination of organicmatter in terrestrial ecosystems where naturally formed chlorinated organic compounds (Clorg) in soil frequently exceed theabundance of chloride. Chloride dominates import and export from terrestrial ecosystems while soil Clorg and biomass Cl candominate the standing stock Cl. This has important implications for Cl transport, as chloride will enter the Cl pools resulting inprolonged residence times. Clearly, these pools must be considered separately in future monitoring programs addressing Clcycling. Moreover, there are indications that (1) large amounts of Cl can accumulate in biomass, in some cases representing themain Cl pool; (2) emissions of volatile organic chlorines could be a significant export pathway of Cl and (3) that there is aproduction of Clorg in tissues of, e.g. plants and animals and that Cl can accumulate as, e.g. chlorinated fatty acids in organisms.Yet, data focusing on ecosystem perspectives and combined spatiotemporal variability regarding various Cl pools are still scarce,and the processes and ecological roles of the extensive biological Cl cycling are still poorly understood.
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| 10. |
- Svensson, Teresia, 1975-, et al.
(författare)
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Chlorine transport in a small catchment in southeast Sweden during two years
- 2007
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 82:2, s. 181-199
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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