Land- atmosphere exchange of elemental mercury : new insights using a novel relaxed eddy accumulation and enclosure techniques

Anthropogenic activities, such as mining and burning of fossil fuels, have significantly increased the emissions of mercury (Hg) to the atmosphere, and the subsequent deposition onto global ecosystems. To restrain Hg emissions and reduce its accumulation in biota and human exposure, the UN’s legally binding Minamata Convention was signed by 128 countries. To estimate the potential of different ecosystems as sinks or sources for atmospheric Hg, reliable quantification of land-atmosphere exchange of gaseous elemental Hg (GEM) is crucial. Despite extensive efforts to quantify GEM exchange and to characterize controls, large uncertainty remains due to the complexity of bi-directional GEM flux, model parameterization, and the application of different measurement techniques. The majority of flux studies were temporally biased toward summer and daytime. More than 60% of these measurements have been conducted over Hg-enriched sites and limited to small-scale studies using enclosure techniques. The main goal of the thesis was to identify the role of boreal peatlands as net sinks or sources of Hg by calculating the first annual Hg budget including continuous measurements of peatland-atmosphere exchange of GEM. Peatlands are major mediators for the high levels of Hg in freshwater fish in Europe and North America, because the peatlands provide favorable conditions for the formation of bioavailable and highly toxic methylmercury. In high latitude regions almost all freshwater fish have Hg concentrations exceeding European limits for good chemical status (0.02 mg Hg kg-1 fish muscle, Chalmers et al., 2011, Åkerblom et al., 2014). To test the hypothesis that enough Hg evades from peat to the atmosphere to play a significant role in Hg removal, we developed a relaxed eddy accumulation (REA) system for long-term and large-scale GEM flux monitoring. The first objective was to test the system over an urban site and a boreal peatland at different heights with contrasting surface and turbulence characteristics. In addition, we aimed to inter-compare REA with dynamic flux chambers (DFCs) during a concurrent measurement campaign. DFCs represent the far most common GEM flux measurement technique mainly because they are relatively simple to use and cheaper than micrometeorological methods, while also being suitable for short-term and small-scale flux measurements. As a result they provide an efficient method to resolve confounding influences on GEM flux over a boreal peatland and to test whether GEM emission from contaminated properties constitutes a health risk for residents caused by chronic inhalation of Hg vapor. The novel REA design features two inlets and two pairs of gold cartridges for continuous sampling of GEM in both updrafts and downdrafts for subsequent measurement on a single Hg detector. We tested the system for two weeks in the center of Basel, Switzerland, and for a period of three weeks during snowmelt above the nutrient poor, minerogenic Degerö Stormyr peatland, located about 50 km NW of Umeå, Sweden. Both environments were identified as net sources of GEM to the atmosphere, with average emission rates of 3 and 15 ng m-2 h-1, respectively. The tests revealed that our REA system reduced major uncertainties caused by the sequential sampling in previous single detector designs. Continuous and autonomous measurements were facilitated by regular monitoring of detector drift and recovery rates using a GEM reference gas and a Hg zero-air generator. Despite the very low GEM concentration difference between updraft and downdraft (0.13 ng m-3) at Degerö Stormyr, the results indicate that REA is feasible for measurements that are close to the surface over snow and/or short vegetation. In a longer deployment we continuously monitored the GEM flux at Degerö Stormyr over a period of one year. The annual Hg mass balance was dominated by net GEM emission (10.2 µg m-2) due to substantial evasion between May and October. The annual wet bulk deposition was 3.9 µg m-2. The annual discharge export of Hg from the peatland area (1.9 km2) amounted to 1.3 µg m-2. The GEM evasion rate, a factor of eight higher than runoff Hg export, results most likely from recent declines in atmospheric Hg concentrations (Amos et al., 2015) that have turned the peatland from a net sink into a source of atmospheric Hg. This is consistent with the Hg concentration gradients in the superficial peat which decline from a Hg concentration peak at about 30 cm depth (110 ng g-1, corresponding to Hg emission peaks during the 1950s) towards the surface (23 ng g-1). Under the assumptions that environmental conditions remain stable and that catchment runoff is dominated by Hg from the uppermost peat layers, it will take around 80 years to deplete the entire pool of legacy Hg in the uppermost 34 cm to a background concentration level of 20 ng g-1. We suggest that the strong Hg evasion demonstrated in this study means that open boreal peatlands and thus downstream ecosystems may recover more rapidly from past atmospheric Hg deposition than previously assumed. The method comparison study investigating differences between a Teflon® PFA DFC (TDFC), a new type DFC (NDFC) and REA was conducted over four days in July 2014. This revealed that the variability in GEM flux increased in the following order: TDFC < NDFC < REA. The average ± SD fluxes were 0.7 ± 1.3 ng m-2 h-1, 1.9 ± 3.8 ng m-2 h-1 and 2 ± 24 ng m-2 h-1, respectively. Compared to conventional chamber designs the NDFC is able to account for the effect of wind and yielded cumulative flux values similar to the turbulent fluxes measured by REA (< 2% difference). This result indicates the potential of the NDFC to bridge the gap between turbulent and enclosure-based flux measurements. While the REA flux was rather variable within a day, alternate DFC measurements revealed a distinct diel pattern with highest GEM emission in the early afternoon. Spatial heterogeneity in peatland surface characteristics introduced by total Hg concentrations in the uppermost 34 cm (48 - 67 ng g-1), vascular plant cover (18 - 60%), water table level (4 - 18 cm) or dissolved gaseous Hg concentrations (20 - 82 pg L-1) did not appear to significantly influence GEM flux. We conclude that for short-term mechanistic studies DFCs are the preferred tool while the NDFC is suitable for quantitative flux estimations over short vegetation. The comparison of peatland-atmosphere exchange of GEM from 16 experimental plots determined using a shaded polycarbonate DFC revealed significantly lower flux rates, occasionally indicating Hg uptake, from plots subjected to sulfur additions at rates of 20 kg ha-1 yr-1. These deposition rates were typical during the 1980s in southern Sweden which are approximately seven times faster than contemporary deposition rates in northern Sweden. Enhanced nitrogen deposition and greenhouse treatment had no significant effect on GEM fluxes. The suppressed GEM evasion from the sulfur-treated plots was most likely related to Hg binding to S in organic matter, making Hg less susceptible to evasion, and more prone to transport in runoff at the start of the S additions 15 years earlier. The thesis was completed with shaded NDFC flux measurements over industrially polluted properties in Switzerland. Topsoil (0 - 10 cm) THg concentrations from 27 measurement plots at nine properties ranged from 0.2 to 390 µg g-1. We found that atmospheric GEM concentrations at 1 m height over the parcels were up to 14 times higher than northern hemispheric background concentrations (~1.5 ng m-3), however, they did not appear to reach harmful levels. The parcel averaged fluxes ranged from 38 to 1258 ng m-2 h-1 and were clearly driven by total Hg concentrations in the soil (r2 = 0.77, p < 0.01). GEM emission from the entire area of 8.6 km2 was estimated to 4.5 kg yr-1. This accounts for 0.5% of the total Hg emission in Switzerland, as estimated by emission inventories (BAFU, 2015). It is emphasized that GEM evasion dominates the flux during the growing season over the studied peatland and that elevated sulfur concentrations in the peat also influence flux magnitudes. Spatial heterogeneity in peat characteristics did not explain the variations in flux. The all-season REA measurements identified peatlands as sources of GEM to the atmosphere. Release of Hg that accumulated earlier in the uppermost peat layers may continue for the next half century. This implies that Hg contamination to aquatic ecosystems and food webs will decrease in parts of Europe and North America with substantial areas covered by peatlands. The variation may be even greater between sites located in different climate zones. A combination of long-term GEM flux measurements, Hg tracer and Hg isotope experiments are necessary to further elucidate the complex biogeochemical cycle of Hg in peatlands, especially to detect potential peak flux events, identify mechanisms of Hg reduction in the soils and to pinpoint pathways of GEM transport from soils to the atmosphere

Eddy covariance flux measurements of gaseous elemental mercury over a grassland

Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg-0) are important to improve our understanding of global Hg cycling and, ultimately, human and wildlife Hg exposure. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg-0 flux estimates. It currently remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg-0. Here, we show a detailed validation of direct Hg-0 flux measurements based on the eddy covariance technique (Eddy Mercury) using a Lumex RA-915 AM mercury monitor. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m(-2) h(-1) (maximum) with a 50% cutoff at 0.074 ng m(-2) h(-1). We present eddy covariance NEE measurements of Hg-0 over a low-Hg soil (41-75 ng Hg g(-1) in the topsoil, referring to a depth of 0-10 cm), conducted in summer 2018 at a managed grassland at the Swiss FluxNet site in Chamau, Switzerland (CH-Cha). The statistical estimate of the Hg-0 flux detection limit under outdoor conditions at the site was 5.9 ng m(-2) h(-1') (50% cutoff). We measured a net summertime emission over a period of 34 d with a median Hg-0 flux of 2.5 ng m(-2) h(-1) (with a -0.6 to 7.4 ng m(-2) h(-1) range between the 25th and 75th percentiles). We observed a distinct diel cycle with higher median daytime fluxes (8.4 ng m(-2) h(-1)) than night-time fluxes (1.0 ng m(-2) h(-1)). Drought stress during the measurement campaign in summer 2018 induced partial stomata closure of vegetation. Partial stomata closure led to a midday depression in CO2 uptake, which did not recover during the afternoon. The median CO2 flux was only 24% of the median CO2 flux measured during the same period in the previous year (2017). We suggest that partial stomata closure also dampened Hg-0 uptake by vegetation, resulting in a NEE of Hg-0 that was dominated by soil emission. Finally, we provide suggestions to further improve the precision and handling of the "Eddy Mercury" system in order to assure its suitability for long-term NEE measurements of Hg-0 over natural background surfaces with low soil Hg concentrations (< 100 ng g(-1)). With these improvements, Eddy Mercury has the potential to be integrated into global networks of micrometeorological tower sites (FluxNet) and to provide the long-term observations on terrestrial atmosphere Hg-0 exchange necessary to validate regional and global mercury models

Preparation of nano-gypsum from anhydrite nanoparticles: Strongly increased Vickers hardness and formation of calcium sulfate nano-needles

The preparation of calcium sulfate by flame synthesis resulted in the continuous production of anhydrite nanoparticles of 20-50nm size. After compaction and hardening by the addition of water, the anhydrite nanoparticles reacted to nano-gypsum which was confirmed by X-ray diffraction, diffuse reflectance IR spectroscopy and thermal analysis. Mechanical properties were investigated in terms of Vickers hardness and revealed an up to three times higher hardness of nano-gypsum if compared to conventional micron-sized construction material. The improved mechanical properties of nano-gypsum could in part be due to the presence of calcium sulfate nano-needles in the nano-gypsum as showed by electron microscop

A bottom-up quantification of foliar mercury uptake fluxes across Europe

The exchange of gaseous elemental mercury, Hg(0), between the atmosphere and terrestrial surfaces remains poorly understood mainly due to difficulties in measuring net Hg(0) fluxes on the ecosystem scale. Emerging evidence suggests foliar uptake of atmospheric Hg(0) to be a major deposition pathway to terrestrial surfaces. Here, we present a bottom-up approach to calculate Hg(0) uptake fluxes to aboveground foliage by combining foliar Hg uptake rates normalized to leaf area with species-specific leaf area indices. This bottom-up approach incorporates systematic variations in crown height and needle age. We analyzed Hg content in 583 foliage samples from six tree species at 10 European forested research sites along a latitudinal gradient from Switzerland to northern Finland over the course of the 2018 growing season. Foliar Hg concentrations increased over time in all six tree species at all sites. We found that foliar Hg uptake rates normalized to leaf area were highest at the top of the tree crown. Foliar Hg uptake rates decreased with needle age of multiyear-old conifers (spruce and pine). Average species-specific foliar Hg uptake fluxes during the 2018 growing season were 18 ± 3 µg Hg m−2 for beech, 26 ± 5 µg Hg m−2 for oak, 4 ± 1 µg Hg m−2 for pine and 11 ± 1 µg Hg m−2 for spruce. For comparison, the average Hg(II) wet deposition flux measured at 5 of the 10 research sites during the same period was 2.3 ± 0.3 µg Hg m−2, which was 4 times lower than the site-averaged foliar uptake flux of 10 ± 3 µg Hg m−2. Scaling up site-specific foliar uptake rates to the forested area of Europe resulted in a total foliar Hg uptake flux of approximately 20 ± 3 Mg during the 2018 growing season. Considering that the same flux applies to the global land area of temperate forests, we estimate a foliar Hg uptake flux of 108 ± 18 Mg. Our data indicate that foliar Hg uptake is a major deposition pathway to terrestrial surfaces in Europe. The bottom-up approach provides a promising method to quantify foliar Hg uptake fluxes on an ecosystem scale

Response of the topological surface state to surface disorder in TlBiSe2_2

Through a combination of experimental techniques we show that the topmost layer of the topo- logical insulator TlBiSe$_2$ as prepared by cleavage is formed by irregularly shaped Tl islands at cryogenic temperatures and by mobile Tl atoms at room temperature. No trivial surface states are observed in photoemission at low temperatures, which suggests that these islands can not be re- garded as a clear surface termination. The topological surface state is, however, clearly resolved in photoemission experiments. This is interpreted as a direct evidence of its topological self-protection and shows the robust nature of the Dirac cone like surface state. Our results can also help explain the apparent mass acquisition in S-doped TlBiSe$_2$.Comment: 16 pages, 5 figure

A local formulation of lattice QCD without unphysical fermion zero modes

The problem of unphysical zero modes in lattice QCD with Wilson fermions can be solved in a clean way by including a mass term proportional to i \psibar \gamma_5 \tau^3 \psi in the standard lattice theory with Nf=2 mass degenerate Wilson quarks. We argue that up to cutoff effects, this lattice theory is equivalent to standard lattice QCD, for suitable choices of the mass parameters and with a natural re-interpretation of observables. On-shell O(a) improvement can be implemented in a straightforward way.Comment: LATTICE99(Theoretical Developments), 6 pages Latex using espcrc2.sty, to appear in the conference proceedings of Lattice '99, Pisa, Ital

Evaluation of the Interprofessional Education Day 2019

Interprofessional education (IPE) means that students from different professions learn with, from and about each other. In 2019, an interprofessional education day (IPE day) was held in the canton of Zurich with 68 students and eight lecturers over eight lessons with the aim of improving interprofessional competencies. Students from six health care disciplines and PhD students with different professional backgrounds had to work together in groups on two cases with standardised patients. A pre-post online survey was conducted to evaluate the IPE day. It included self-assessment using items from the Zürcher InterProfessionelle AusbildungsStation (ZIPAS ®) competency framework and the Interprofessional Collaborative Competency Attainment Survey (ICCAS) as well as open-ended questions about the IPE day. ZIPAS ® competency framework and ICCAS were evaluated quantitatively, while the open-ended questions were evaluated qualitatively. There were statistically significant improvements in most of the subscales of the ZIPAS ® competency framework but only in one third of the ICCAS subscales. In addition, the qualitative analysis of the statements showed improvements in collaboration in particular, as well as positive statements on the exchange with students from other professions, whereby many students attributed great importance to the topic of interprofessionality and have already focused their attention on the future and their everyday lives. The IPE day could be a good method to improve the collaboration and communication with students from other professions in the health sector. Keywords - Interprofessional Education DayMixed Methods Studyinterprofessional educationInterprofessional Collaboration = Interprofessionelle Ausbildung bzw. Lehre und Zusammenarbeit gewinnen im Gesundheitswesen zunehmend an Bedeutung. Bei der interprofessionellen Lehre (IPL, engl. Interprofessional Education [IPE]) handelt es sich um das «mit-, von- und übereinander» Lernen verschiedener Professionen oder Studierender dieser (Centre for the Advancement of Interprofessional Education [CAIPE], 2016, S. 1). Ziel der IPL ist, dass die Auszubildenden unter anderem Aufgaben, Kompetenzen und Verantwortung der anderen Berufsgruppen kennenlernen und weitere Kompetenzen erwerben, die für die interprofessionelle Zusammenarbeit unabdingbar sind (Barr, 1998). Bei der Planung von interprofessionellen Ausbildungsprogrammen gibt es verschiedene Aspekte zu berücksichtigen, die Oandasan und Reeves (2005) in drei Ebenen einteilen. Auf der «Mikroebene» werden der Einfluss vorgefertigter Ansichten und die Entwicklung der Teilnehmenden zu Gesundheitsfachleuten beschrieben. Die «Mesoebene» beinhaltet Organisation und Planung sowie die Unterstützung einflussreicher institutioneller Personen. Auf der «Makroebene» wird der Politik und verschiedenen Institutionen eine wichtige Rolle beigemessen. IPL kann einen positiven Effekt auf verschiedenen Ebenen bewirken und so das Gesundheitssystem beeinflussen. So zeigten sich in der Studie von Nagge et al. (2017) durch IPL Verbesserungen in der Zusammenarbeit und im Rollenverständnis. Auch kann eine Wertschätzung gegenüber anderen Professionen gefördert werden (Singer et al., 2018). In der Studie von Strasser et al. (2008) konnte durch ihre Intervention ein gewisser positiver Einfluss auf ein Patienten-Outcome gezeigt werden. Im Review von Reeves et al. (2013), welcher letztere Studie inkludiert hat, weisen die Autoren darauf hin, dass die Ergebnisse aufgrund der großen Heterogenität der eingeschlossenen Studien keine allgemeinen Aussagen erlauben. In der Schweiz gibt es Bestrebungen, die interprofessionelle Zusammenarbeit durch gemeinsame Ausbildungsangebote, darunter die Zürcher InterProfessionelle AusbildungsStation (ZIPAS®; Ulrich et al., 2019), zu verbessern. Solche Angebote sind jedoch oft singulär und (noch) nicht fest in den Curricula verankert. Zudem sind Studierende der Gesundheits- und Medizinalberufe meist institutionell und örtlich voneinander getrennt. Im Kanton Zürich beispielsweise bietet die Zürcher Hochschule für Angewandte Wissenschaften (ZHAW) die Studiengänge «Ergotherapie», «Hebamme», «Pflege» und «Physiotherapie» an. Dagegen studiert man Humanmedizin an der Universität Zürich (UZH) und Pharmazie an der Eidgenössischen Technischen Hochschule (ETH). Die ETH bietet zudem neu Humanmedizin auf Bachelor-Stufe an. Zwischen den Studiengängen der Universitäten und Fachhochschulen gibt es bisher nur wenig gemeinsame Lehrveranstaltungen, da vielfach die entsprechenden Strukturen und Prozesse (z. B. Flexibilität der einzelnen Curricula) fehlen. Die Institutionen ZHAW und UZH haben am 12. Oktober 2019 erstmalig den Interprofessionellen Ausbildungstag (IPE-Tag) durchgeführt, mit der Zielsetzung, das gegenseitige Rollenverständnis von Studierenden verschiedener Fachrichtungen im Gesundheitswesen zu verbessern und interprofessionelle Kompetenzen zu vermitteln bzw. zu vertiefen. Das Ziel dieser Untersuchung war es, den IPE-Tag inklusive der Erwartungen, positiven Aspekte und Verbesserungsvorschläge seitens der Studierenden zu evaluieren und den Kompetenzerwerb der Studierenden zu messen

Recent advances in understanding and measurement of mercury in the environment: Terrestrial Hg cycling

This review documents recent advances in terrestrial mercury cycling. Terrestrial mercury (Hg) research has matured in some areas, and is developing rapidly in others. We summarize the state of the science circa 2010 as a starting point, and then present the advances during the last decade in three areas: land use, sulfate deposition, and climate change. The advances are presented in the framework of three Hg "gateways" to the terrestrial environment: inputs from the atmosphere, uptake in food, and run off with surface water. Among the most notable advances:The Arctic has emerged as a hotbed of Hg cycling, with high stream fluxes and large stores of Hg poised for release from permafrost with rapid high-latitude warming.The bi-directional exchange of Hg between the atmosphere and terrestrial surfaces is better understood, thanks largely to interpretation from Hg isotopes; the latest estimates place land surface Hg re-emission lower than previously thought.Artisanal gold mining is now thought responsible for over half the global stream flux of Hg.There is evidence that decreasing inputs ofHg to ecosystems may bring recovery sooner than expected, despite large ecosystem stores of legacy Hg.Freshly deposited Hg is more likely than stored Hg to methylate and be incorporated in rice.Topography and hydrological connectivity have emerged as master variables for explaining the disparate response of THg and MeHg to forest harvest and other land disturbance.These and other advances reported here are of value in evaluating the effectiveness of theMinamata Convention on reducing environmental Hg exposure to humans and wildlife. (C) 2020 The Authors. Published by Elsevier B.V