Particulate-phase mercury emissions from biomass burning and impact on resulting deposition: a modelling assessment.

Mercury (Hg) emissions from biomass burning (BB) are an important source of atmospheric Hg and a major factor driving the interannual variation of Hg concentrations in the troposphere. The greatest fraction of Hg from BB is released in the form of elemental Hg(Hg(g)0) . However, little is known about the fraction of Hg bound to particulate matter (HgP) released from BB, and the factors controlling this fraction are also uncertain. In light of the aims of the Minamata Convention to reduce intentional Hg use and emissions from anthropogenic activities, the relative importance of Hg emissions from BB will have an increasing impact on Hg deposition fluxes. Hg speciation is one of the most important factors determining the redistribution of Hg in the atmosphere and the geographical distribution of Hg deposition. Using the latest version of the Global Fire Emissions Database (GFEDv4.1s) and the global Hg chemistry transport model, ECHMERIT, the impact of Hg speciation in BB emissions, and the factors which influence speciation, on Hg deposition have been investigated for the year 2013. The role of other uncertainties related to physical and chemical atmospheric processes involving Hg and the influence of model parametrisations were also investigated, since their interactions with Hg speciation are complex. The comparison with atmospheric HgP concentrations observed at two remote sites, Amsterdam Island (AMD) and Manaus (MAN), in the Amazon showed a significant improvement when considering a fraction of HgP from BB. The set of sensitivity runs also showed how the quantity and geographical distribution of HgP emitted from BB has a limited impact on a global scale, although the inclusion of increasing fractions HgP does limit Hg(g)0 availability to the global atmospheric pool. This reduces the fraction of Hg from BB which deposits to the world's oceans from 71 to 62 %. The impact locally is, however, significant on northern boreal and tropical forests, where fires are frequent, uncontrolled and lead to notable Hg inputs to local ecosystems. In the light of ongoing climatic changes this effect could be potentially be exacerbated in the future.

Atmospheric mercury concentrations observed at ground-based monitoring sites globally distributed in the framework of the GMOS network.

Long-term monitoring of data of ambient mercury (Hg) on a global scale to assess its emission, transport, atmospheric chemistry, and deposition processes is vital to understanding the impact of Hg pollution on the environment. The Global Mercury Observation System (GMOS) project was funded by the European Commission (http://www.gmos.eu) and started in November 2010 with the overall goal to develop a coordinated global observing system to monitor Hg on a global scale, including a large network of ground-based monitoring stations, ad hoc periodic oceanographic cruises and measurement flights in the lower and upper troposphere as well as in the lower stratosphere. To date, more than 40 ground-based monitoring sites constitute the global network covering many regions where little to no observational data were available before GMOS. This work presents atmospheric Hg concentrations recorded worldwide in the framework of the GMOS project (2010-2015), analyzing Hg measurement results in terms of temporal trends, seasonality and comparability within the network. Major findings highlighted in this paper include a clear gradient of Hg concentrations between the Northern and Southern hemispheres, confirming that the gradient observed is mostly driven by local and regional sources, which can be anthropogenic, natural or a combination of both.

Data quality through a web-based QA/QC system: implementation for atmospheric mercury data from the global mercury observation system.

The overall goal of the on-going Global Mercury Observation System (GMOS) project is to develop a coordinated global monitoring network for mercury, including ground-based, high altitude and sea level stations. In order to ensure data reliability and comparability, a significant effort has been made to implement a centralized system, which is designed to quality assure and quality control atmospheric mercury datasets. This system, GMOS-Data Quality Management (G-DQM), uses a web-based approach with real-time adaptive monitoring procedures aimed at preventing the production of poor-quality data. G-DQM is plugged on a cyberinfrastructure and deployed as a service. Atmospheric mercury datasets, produced during the first-three years of the GMOS project, are used as the input to demonstrate the application of the G-DQM and how it identifies a number of key issues concerning data quality. The major issues influencing data quality are presented and discussed for the GMOS stations under study. Atmospheric mercury data collected at the Longobucco (Italy) station is used as a detailed case study.

Atmospheric mercury footprints of nations.

The Minamata Convention was established to protect humans and the natural environment from the adverse effects of mercury emissions. A cogent assessment of mercury emissions is required to help implement the Minamata Convention. Here, we use an environmentally extended multi-regional input-output model to calculate atmospheric mercury footprints of nations based on upstream production (meaning direct emissions from the production activities of a nation), downstream production (meaning both direct and indirect emissions caused by the production activities of a nation), and consumption (meaning both direct and indirect emissions caused by final consumption of goods and services in a nation). Results show that nations function differently within global supply chains. Developed nations usually have larger consumption-based emissions than up- and downstream production-based emissions. India, South Korea, and Taiwan have larger downstream production-based emissions than their upstream production- and consumption-based emissions. Developed nations (e.g., United States, Japan, and Germany) are in part responsible for mercury emissions of developing nations (e.g., China, India, and Indonesia). Our findings indicate that global mercury abatement should focus on multiple stages of global supply chains. We propose three initiatives for global mercury abatement, comprising the establishment of mercury control technologies of upstream producers, productivity improvement of downstream producers, and behavior optimization of final consumers.

Mercury in the Mediterranean. Part 2: processes and mass balance.

Mass balance of contaminants can provide useful information on the processes that influence their concentrations in various environmental compartments. The most important sources, sinks and the equilibrium or non-equilibrium state of the contaminant in individual environmental compartments can also be identified. Using the latest mercury speciation data, the results of numerical models and the results of recent studies on mercury transport and transformation processes in the marine environment, we have re-evaluated the total mercury (HgT) mass balance in the Mediterranean Sea. New calculations have been performed employing three distinct marine layers: the surface layer, the thermocline and the deep sea. New transport mechanisms, deep water formation and density-driven sinking and upwelling, were included in the mass balance calculations. The most recent data have even enabled the calculation of an approximate methylmercury (MeHg) mass balance. HgT is well balanced in the entire Mediterranean, and the discrepancies between inputs and outputs in individual layers do not exceed 20 %. The MeHg balance shows larger discrepancies between gains and losses due to measurement uncertainties and gaps in our knowledge of Hg species transformation processes. Nonetheless, the main sources and sinks of HgT (deposition and evasion) and MeHg (fluxes from sediment, outflow through the Gibraltar Strait) are in accordance with previous studies on mercury in the Mediterranean Basin. Mercury in the Mediterranean fish harvest is the second largest MeHg sink; about 300 kg of this toxic substance is consumed annually with sea food.

Contribution of contaminated sites to the global mercury budget.

Global mercury emission inventories include anthropogenic emissions, contributing via current use or presence of mercury in a variety of products and processes, as well as natural source emissions. These inventories neglect the contribution of areas contaminated with mercury from historical accumulation, which surround mines or production plants associated with mercury production or use. Although recent studies have shown that releases of mercury from these historical sites can be significant, a database of the global distribution of mercury contaminated sites does not exist, nor are there means of scaling up such releases to estimate fluxes on a regional and global basis. Therefore, here we estimated for the first time the contribution of mercury releases from contaminated sites to the global mercury budget. A geo-referenced database was built, comprising over 3000 mercury contaminated sites associated with mercury mining, precious metal processing, non-ferrous metal production and various polluted industrial sites. In the assessment, mercury releases from these sites to both the atmosphere as well as the hydrosphere were considered based on data available for selected case studies, their number, the reported extent of contamination and geographical location. Annual average global emissions of mercury from identified contaminated sites amount to 198 (137-260) Mgyr(-1). Of that, 82 (70-95)Mgyr(-1) contribute to atmospheric releases, while 116 (67-165) Mgyr(-1) is estimated to be transported away from these sites by hydrological processes. Although these estimates are associated with large uncertainties, our current understanding of mercury releases from contaminated sites indicates that these releases can also be of paramount importance on the global perspective. This is especially important as it is known that these sites represent a long-term source of releases if not managed properly. Therefore, the information presented here is needed by governments and NGO's in order to re-focus resources in making decisions regarding mitigation and remediation strategies on a global level.

Stochastic analysis to assess the spatial distribution of groundwater nitrate concentrations in the Po catchment (Italy).

A large database including temporal trends of physical, ecological and socio-economic data was developed within the EUROCAT project. The aim was to estimate the nutrient fluxes for different socio-economic scenarios at catchment and coastal zone level of the Po catchment (Northern Italy) with reference to the Water Quality Objectives reported in the Water Framework Directive (WFD 2000/60/CE) and also in Italian legislation. Emission data derived from different sources at national, regional and local levels are referred to point and non-point sources. While non-point (diffuse) sources are simply integrated into the nutrient flux model, point sources are irregularly distributed. Intensive farming activity in the Po valley is one of the main Pressure factors Driving groundwater pollution in the catchment, therefore understanding the spatial variability of groundwater nitrate concentrations is a critical issue to be considered in developing a Water Quality Management Plan. In order to use the scattered point source data as input in our biogeochemical and transport models, it was necessary to predict their values and associated uncertainty at unsampled locations. This study reports the spatial distribution and uncertainty of groundwater nitrate concentration at a test site of the Po watershed using a probabilistic approach. Our approach was based on geostatistical sequential Gaussian simulation used to yield a series of stochastic images characterized by equally probable spatial distributions of the nitrate concentration across the area. Post-processing of many simulations allowed the mapping of contaminated and uncontaminated areas and provided a model for the uncertainty in the spatial distribution of nitrate concentrations.

Response of a mature Pinus laricio plantation to a three-year restriction of water supply: structural and functional acclimation to drought.

The response of mature forest stands to a reduction in water availability has received little attention. In particular, the extent to which a short-term reduction in gas exchange can be alleviated in the long-term by acclimation processes is not well understood. We studied the impact of a severe reduction in water availability on the water relations and growth of 35-year-old Pinus laricio Poiret. trees in a replicated experiment. Sapwood and needle increments, soil and tree water status, stand transpiration, xylem embolism and plant hydraulic architecture were monitored over a 3-year period in control and drought-treated plots. Needle length was reduced in drought-treated trees by 30, 19 and 29%, and sapwood increments by 50, 27 and 24% over the 3 years. Drought did not result in tree mortality or in extensive xylem embolism or foliage dieback. On the contrary, a conservative water-use strategy was observed, because minimum leaf water potentials did not differ between treatments or over the season. Plant hydraulic resistance was also unaffected by restricted water availability. Stand transpiration was strongly reduced by drought treatment over the summer, but not during the winter, despite significant differences in leaf area between control and drought-treated trees, implying higher transpiration rates per unit leaf area in the droughted plants. This suggests that water transport capacity, rather than the amount of leaf area, controlled stand transpiration, which is at variance with expectations based on experiments with seedlings and short-term experiments with mature trees.