Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Biogeosciences Discuss., 8, 7525–7550, 2011 Biogeosciences www.biogeosciences-discuss.net/8/7525/2011/ Discussions BGD doi:10.5194/bgd-8-7525-2011 8, 7525–7550, 2011 © Author(s) 2011. CC Attribution 3.0 License. Organohalogens This discussion paper is/has been under review for the journal Biogeosciences (BG). from saline Please refer to the corresponding final paper in BG if available. environments K. Kotte et al. Organohalogen emission from saline environments – spatial extrapolation Title Page using remote sensing as most promising Abstract Introduction tool Conclusions References Tables Figures K. Kotte1, F. Low¨ 2, S. G. Huber1, I. Mulder1, and H. F. Scholer¨ 1 J I 1Institute of Earth Sciences, University of Heidelberg, 69120 Heidelberg, Germany 2Department of Remote Sensing, Institute of Geography, University of Wurzburg,¨ J I 97074 Wurzburg,¨ Germany Back Close Received: 1 July 2011 – Accepted: 14 July 2011 – Published: 28 July 2011 Full Screen / Esc Correspondence to: K. Kotte ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. Printer-friendly Version Interactive Discussion 7525 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract BGD Due to their negative water budget most recent semi-/arid regions are characterized by vast evaporates (salt lakes and salty soils). We recently identified those hyper-saline 8, 7525–7550, 2011 environments as additional sources for a multitude of volatile halogenated organohalo- 5 gens (VOX). These compounds affect the ozone layer of the stratosphere and play Organohalogens a key role in the production of aerosols. A remote sensing based analysis was per- from saline formed in the southern Aral Sea basin, providing information of main soil types as well environments as their extent and spatial and temporal evolution. VOX production has determined in dry and moist soil samples for 24 h. Several C1- and C2 organohalogens, including K. Kotte et al. 10 chloromethane and bromomethane, have been found in hyper-saline topsoil profiles. The range of naturally produced organohalogens includes dichloroethene. For the 15 000 km2 ranging research area in the southern Aralkum desert a daily production of Title Page up to 23 t dichloroethene has been calculated using MODIS time series and supervised Abstract Introduction image classification. The applied setup reproduces a short-term change in climatic 15 conditions starting from dried-out saline soil, instantly humidified during rain events or Conclusions References flooding. VOX emission from dry fallen Aral Sea sediments will further increase since Tables Figures the area of salt affected soils is expected to increase in future. Opportunities, limits and requirements of satellite based rapid change detection and salt classification are discussed. J I J I 20 1 Introduction Back Close Organic compounds containing halogens – especially chlorine – have been considered for a long time to be of industrial origin only, and it was assumed that humans could eas- Full Screen / Esc ily control the production and emission of these compounds in case they would cause a threat for life on Earth. Recent environmental problems such as stratospheric ozone Printer-friendly Version 25 destruction and the increasing pollution of the biosphere through volatile organohalo- Interactive Discussion gens (VOX) are considered to have a large impact on the well-being of mankind. VOX are effectively linked to atmospheric chemistry cycles, leading to potentially significant 7526 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | feedbacks on cloud formation, Earth’s albedo and eventually the regional and global climate. BGD Since the middle of the 70’s it became clear that some reactive organohalogens are 8, 7525–7550, 2011 purposefully produced by nature e.g. in soils and sediments of hyper-saline salt lakes 5 (Winterton, 2000; Gribble, 2010; Scholer¨ and Keppler, 2003; Weissflog et al., 2005). To date, the natural production of more than 4714 different organohalogens is known, Organohalogens involving biogeochemical, biochemical and microbial processes (Gribble, 2010). This from saline includes de-novo producers like fungi, halophilic bacteria and archaea, plants, animals, environments and insects. K. Kotte et al. 10 In addition to volatile alkyl halides and polar organohalogens such as haloacetates, there is evidence that even semi-volatile organohalogens can be naturally formed from humic substances through abiotic geochemical processes. For instance nature’s pro- Title Page duction of chloromethane (5–6 Mt) exceeds the anthropogenic production (50 Kt) by a factor of 100 (WMO, 2007). Abstract Introduction 15 While anthropogenic organohalogen pollution is certainly an important issue and the ban of some compounds as stipulated in international treaties have to be carefully con- Conclusions References trolled, it is high time to commence with a comprehensive study of the natural release Tables Figures of organohalogen species, in particular to the lower atmosphere and the terrestrial environment. The importance of very short-lived halogenated substances (VSLS) for J I 20 the budget of stratospheric bromine was emphasized by WMO (2007). Many of these VSLS are of natural origin. J I Relevant data on the quantity and variety of low molecular weight organohalogens Back Close in the terrestrial environment are limited. This compartment receives significant fluxes of inorganic halides via the deposition of sea salt aerosols and from combustion pro- Full Screen / Esc 25 cesses, and in addition from weathering processes of rocks. Due to the lower con- centrations of halides in soil (except for peaty and saline soils) natural halogenation Printer-friendly Version processes in the terrestrial environment have been assumed to be a VOX source of mi- nor importance. However, there is evidence that natural halogenation is a widespread Interactive Discussion phenomenon in some terrestrial environments. 7527 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | There have been a number of studies that have dealt with the release of organohalo- gens from coastal marshes and other wetlands, where halogenation was suggested BGD to depend on fungal and bacterial activity (e.g. von Glasow and Crutzen, 2007). Be- 8, 7525–7550, 2011 sides biotic formation of organohalogens there is also increasing evidence of an abiotic 5 formation in soils involving humic substances and iron (Keppler et al., 2000, 2004; Hu- ber et al., 2009). Although the exact mechanisms leading to the abiotic formation of Organohalogens organohalogens, e.g. the potential role of radicals and reactive humic and Fe species from saline are still not fully understood. environments There is a number of studies that tried to come up with budgets for longer-lived halo- K. Kotte et al. 10 carbons, mainly of interest for stratospheric chemistry, including emissions from peat- lands (e.g. Dimmer et al., 2001), wetlands (Varner et al., 1999), salt marshes (Rhew et al., 2000), and terrestrial vegetation (Yokouchi et al., 2000, 2002; Hamilton et al., Title Page 2003). It is not clear if further polyhalogenated C1-organohalogens such as CH2Cl2, CHCl3, and CCl4 or even C2-organohalogens such as tri- and tetrachloroethene are Abstract Introduction 15 formed during the decomposition of dead organic matter in soil. Research has so far mainly focussed on regions polluted by humans and on coastal Conclusions References areas. Thus the global source strengths of organohalogens from soils and vegetation Tables Figures are poorly constrained. Keppler et al. (2005) highlighted the need for a better quantifi- cation of long-lived halomethanes such as CH3Cl and CH3Br from recently discovered, J I 20 additional natural terrestrial sources. For example, Wishkerman et al. (2008) eluci- dated the reaction of plant pectin with bromide forming CH3Br. This appears abiotically J I at ambient temperatures with the observed emission to doubled with every 5 ◦C rise. Back Close Elevated concentrations of CH3Br and CHCl3 have been proven for hyper-saline sedi- ments of southern Russian and Kalmykian salt lakes (Weissflog et al., 2005). These re- Full Screen / Esc 25 sults have important implications for the VOX release from vegetation and soils located in regions that are particularly affected by climate change (i.e. heat waves and drought). Printer-friendly Version However, the global source strength still remains uncertain. The main driver behind the mentioned biogeochemical VOX production can be attributed to pH-level, salt content, Interactive Discussion salt composition (halide, sulfate, carbonate) as well as soil humidity, respectively soil 7528 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | water content, and organic content. Some VOX or their metabolic degradation products exhibit a phytotoxic potential, BGD where infected plants show increased plant transpiration, early senescence, decreased 8, 7525–7550, 2011 plant growth and overall lower plant vitality. Especially in combination with drought 5 stress episodes and soil salting this can accelerate desertification. Thus, the emission and deposition of VOX to and from the atmosphere can strongly Organohalogens influence the functioning of terrestrial ecosystems (e.g. Lange et al., 2004). from saline Beside the intensified public discussion on the trustability of climate models