Observations of iodine speciation and cycling in the hydrosphere

Iodine is an important element in oceanic, atmospheric, and terrestrial systems. Firstly, radical reactions in the troposphere can lead to significant ozone depletion, and secondly, nucleation of gaseous iodine molecules can produce new aerosol formation events, presenting possible direct and indirect natural cooling effects on climate. In the terrestrial environment iodine is a vital micronutrient for all mammals, with a lack of iodine intake leading to several debilitating disorders such as goiter and cretinism. The aim of this study was to investigate iodine systematics, and particularly speciation, in the atmosphere (aerosols, rain, and snow) and terrestrial hydrosphere (lakes) in order to gain a better understanding of how iodine moves between and within each environmental compartment. A subsidiary aim was to develop an inexpensive, but sensitive and accurate method for iodine quantification in soils and sediments using conventional analytical equipment. Rain and snow samples were taken from both northern (Germany, Switzerland, Ireland, Greenland) and southern (Australia, New Zealand, Chile) hemispheres whereas aerosols were obtained from Mace Head, Ireland using cascade (5 stages) and PM 2.5 impactors. Iodine cycling in lakes was investigated in the Mummelsee, a small headwater lake in the Black Forest. Speciation measurements were conducted by coupling an ion chromatograph to an ICP-MS and the organic fraction calculated as total iodine minus the inorganic species iodide and iodate. Organically bound iodine was the most abundant fraction in the atmospheric aqueous phase, despite the fact that iodine oxides are currently thought to be the theoretical sink species. Aerosols from Mace Head, Ireland, contained a median of 50 pmol m-3 total iodine, with more than 90 % being associated with organic matter. Iodide was the next most abundant species (median 5 %) with iodate being the least abundant (median 0.8 %). Similar results were found in the precipitation samples from northern and southern hemispheres, with organic iodine composing over half of the total iodine, and in the snow from Greenland up to 88 %; although in general the organic fraction was lower in precipitation than in aerosols. Up to 5 unidentified peaks, representing iodine species in addition to iodide and iodate, were observed in aerosol and precipitation chromatograms, providing direct evidence for organic iodine compounds in aerosols and precipitation. While these species remain unidentified, they are thought to be anionic and relatively small (i.e. low molecular weight). It is suggested that these compounds and iodide form during (photolytic) decomposition of organo-I of high molecular weight, the organic material possibly stemming from the ocean surface microlayer. It was also found that orographically induced precipitation significantly effects iodine concentrations in snow, with iodine levels decreasing exponentially with altitude over a transect in the Black Forest; indeed, more than halving (38 to 13 nmol l-1) over an altitude change of 840 m and horizontal distance of only 5 km. It is suggested that orographic affects may be more important than lateral distance from the ocean in determining iodine levels in continental precipitation. Once precipitation enters terrestrial ecosystems it may interact with soils, rocks, and biota. Iodine levels in the Mummelsee were very similar to rain and snow, averaging 15.2 ± 2.4 nmol l-1, suggesting at very little iodine input from the catchment geology. Iodine in the lake and the spring inflow was dominantly associated with organic matter with, on average, 85 ± 7 % organically bound. However, inorganic iodine cycling in the lake was also important, and displayed pronounced redox chemistry, with both iodide release from the sediments and iodate reduction in the hypolimnion during anoxic stratified conditions. The iodide flux (up to 10.1 nmol m-2 d-1) back into the water column is probably due to the decomposition of detritus in the top few centimeters of the sediments. In contrast to the hypolimnion, iodide was removed from the epilimnion during the summer and autumn months, whereas iodate levels increased slightly over the same time period, suggesting at the importance of biological reactions. This was supported by a sediment core that contained high iodine concentrations, averaging 92 μmol kg-1 total iodine, and a significant correlation with organic carbon (p<0.001). The analytical method entailed combusting sediment or soil samples in the oven of an AOX apparatus at 1000 oC and trapping the vapours in Milli-Q water. The solution was then analysed for iodine by a kinetic UV/Vis photospectrometry whereby iodide quantitatively catalyses the oxidation of As3+ and reduction of chromophoric Ce4+. The method was shown to be sensitive (detection limit 49 ng at 95 % confidence) and precise with relative standard deviations less than 5%. In conclusion, while this work has shown that organic matter plays a very important role in the hydrosphere, particularly in regards to iodine cycling, considerably more work needs to be conducted on themes such as identifying the organic iodine species, how is the iodine bound to the organic material and what is the role of organisms in the formation of organic iodine. With the current interest in iodine chemistry it is hoped that these and many other pressing questions will be answered in the near future

Quantifizierung lokaler Grundwassereintritte in die Spree und deren Bedeutung für die Verockerungsproblematik in der Laustiz

Local groundwater inflow is an unknown but central component for the precipitation and accumulation of iron in the Spree River, Lusatia. In this study, the natural tracer radon was used to map and quantify local groundwater inflows into the Spree and Kleine Spree rivers in the Lusatian lignite mining district. During two measurement campaigns, the total groundwater inflow for a 20 km long reach of the Kleine Spree and a 34 km long reach of the Spree ranged between ~3,000 and ~7,000 m³ d⁻¹ (Kleine Spree) and between ~20,000 and ~38,000 m³ d⁻¹ (Spree). Particularly high groundwater inflow was identified (up to 70% of total inflow) along the Spreewitzer Rinne, a local aquifer consisting of excavated mining materials. Along these river reaches, large amounts of dissolved iron are entering the rivers with inflowing groundwater. Using the measured iron and sulphate loadings, we calculated that up to 120 tons/day of iron (oxy)-hydroxide was retained in the combined Spree and Klein Spree catchments

Quantifizierung lokaler Grundwassereintritte in die Spree und deren Bedeutung für die Verockerungsproblematik in der Laustiz

Eine unbekannte, schwer zu bestimmende aber zentrale Komponente in der Verockerungs-Problematik der Spree ist der lokale Grundwasserzufluss. Als Teil dieser Studie wurden mithilfe des natürlichen Tracers Radon (222Rn) die lokalen Grundwasserzuflüsse in die Spree und Kleine Spree im Lausitzer Braunkohlerevier bestimmt. Der gesamte Grundwasserzufluss, für das 20 km lange Teilstück der Kleinen Spree und den 34 km langen Abschnitt der Spree, variierte je nach Messkampagne zwischen ~3.000 und ~7.000 m3 d−1 (Kleine Spree) sowie ~20.000 und ~38.000 m3 d−1 (Spree). Entlang der Spreewitzer Rinne, einem vom Tagebauabraum geprägten Aquifer, wurden Flussabschnitte mit besonders hohem, präferenziellem Grundwassereintritt identifiziert (bis zu 70 % des gesamten Zustromes). Für diese Bereiche gelangen große Mengen an gelöstem Eisen aus dem Grundwasser in die Fließgewässer. Basierend auf gemessenen lokalen Eisen- und Sulfatfrachten in beiden Fließgewässern, wurde für das Einzugsgebiet die Menge an zurückgehaltenem Eisen quantifiziert. Für das gesamte untersuchte Einzugsgebiet der Spree liegt die Menge an zurückgehaltenem Eisen durch die Eisenhydroxid-Bildung bei bis zu 120 Tonnen/Tag.Universität Bayreuth (3145)Mapping and quantifying groundwater inflow to the Spree River (Lusatia) and its role in Fe precipitation and coating of the river be

Why productive lakes are larger mercury sedimentary sinks than oligotrophic brown water lakes

Mercury accumulation in lake sediments is a widespread environmental problem due to the biomagnification of Hg in the aquatic food chain. Soil Hg concentrations, catchment vegetation, erosion, and lake productivity are major factors controlling the accumulation of Hg in lakes. However, their influence on the Hg mass balance in lakes with different catchment characteristics and trophic state is poorly understood. In this multilake study, we decipher the effects of catchment vegetation (coniferous vs. deciduous forest), soil Hg content, and trophic state on Hg sedimentation at six lakes in Germany. We investigated Hg concentrations in leaves, soils, and the lake's water phase. Soils under coniferous stands show slightly higher Hg concentrations than under deciduous forest. Hg concentrations in the water phase were higher in the oligotrophic brown water lakes (8.1 ± 5.6 ng L−1 vs. 3.0 ± 1.9 ng L−1). Lower Hg concentrations in sediment trap material indicate dilution by algae organic matter in the mesotrophic lakes (0.12–0.17 μg g−1 vs. 0.57–0.89 μg g−1). However, Hg accumulation rates in sediment traps were up to 14‐fold higher in the mesotrophic lakes (113–443 μg m−2 yr−1) than in the brown water lakes (32–144 μg m−2 yr−1), which could not be explained by higher Hg fluxes to the productive lakes. Hg mass balance calculation reveals that water phase Hg scavenging by algae is the major reason for the intense Hg export to the sediments of productive lakes which makes them significantly larger sedimentary sinks than oligotrophic brown water lakes.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165