Halogens in pore water of peat bogs – the role of peat decomposition and dissolved organic matter

Abstract

Abstract.Halogens are strongly enriched in peat and peatlands and such they are one of their largest active terrestrial reservoir. The enrichment of halogens in peat is mainly attributed to the formation of organohalogens and climatically controlled humification processes. However, little is known about release of halogens from the peat substrate and the distribution of halogens in the peat pore water. In this study we have investigated the distribution of chlorine, bromine and iodine in pore water of three pristine peat bogs located in the Magellanic Moorlands, southern Chile. Peat pore waters were collected using a sipping technique, which allows in situ sampling down to a depth greater than 6 m. Halogens and halogen species in pore water were determined by ion-chromatography (IC) (chlorine) and IC-ICP-MS (bromine and iodine). Results show that halogen concentrations in pore water are 15-30 times higher than in rainwater. Mean concentrations of chlorine, bromine and iodine in pore water were 7-15 mg l −1 , 56-123 µg l −1 , and 10-20 µg l −1 , which correspond to mean proportions of 10-15%, 1-2.3% and 0.5-2.2% of total concentrations in peat, respectively. Organobromine and organoiodine were the predominant species in pore waters, whereas chlorine in pore water was mostly chloride. Advection and diffusion of halogens were found to be generally low and halogen concentrations appear to reflect release from the peat substrate. Release of bromine and iodine from peat depend on the degree of peat degradation, whereas this relationship is weak for chlorine. Relatively higher release of bromine and iodine was observed in less degraded peat sections, where the release of dissolved organic carbon (DOC) was also the most intensive. It has been concluded that the release of halogenated dissolved organic matter (DOM) is the predominant mechanism of iodine and bromine release from peat.

Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

“…Generally, concentrations at the PBr2 site, with the highest humification index, were also low. Concentrations positively correlated with C/N ratios (r = 0.712, p < 0.05), as described in the study of Biester et al (2006) before for this site. Highest DOC concentrations occurred at the SkyII site, with lowest humification index.…”

“…A negative relation of DOM concentrations with the degree of peat decomposition has been reported (Kalbitz and Geyer, 2002;Biester et al, 2006). Generally, concentrations at the PBr2 site, with the highest humification index, were also low.…”

“…Beer et al, 2008;Kalbitz et al, 1999;Cocozza et al, 2003). More decomposed peat was further reported to release less DOC than undecomposed peat (Biester et al, 2006;Kalbitz and Geyer, 2002). Thus, an inverse relation of the peat degree of decomposition and DOC concentrations may be expected, although the DOC quality and thus degradability may also change.…”

“…Mean annual temperature is about 6.5 • C (Schneider et al, 2003). We derived relative differences in spray input by mean bromide concentrations in the solid peat, as bromide is a major constituent of sea spray and better retained in the peat than chloride (Biester et al, 2006). Highest precipitation occurs at the SkyI site (∼1500 mm yr −1 ).…”

Natural Niche for Organohalide-Respiring Chloroflexi

“…Natural organobromine is ubiquitous in marine sediments and appears to be degraded during the breakdown of organic matter as part of a biogeochemical bromine cycle (27). Reducing conditions are believed to promote reductive debromination of natural organobromine in the sedimentary environment (4,6,33). Indeed, the hypothesis that bacteria indigenous to…”