Background concentrations of mercury in Australian freshwater sediments : the effect of catchment characteristics on mercury deposition

Waterways in the Southern Hemisphere, including on the Australian continent, are facing increasing levels of mercury contamination due to industrialization, agricultural intensification, energy production, urbanization, and mining. Mercury contamination undermines the use of waterways as a source of potable water and also has a deleterious effect on aquatic organisms. When developing management strategies to reduce mercury levels in waterways, it is crucial to set appropriate targets for the mitigation of these contaminated waterways.These mitigation targets could be (1) trigger values or default guideline values provided by water and sediment quality guidelines or (2) background (pre-industrialization) levels of mercury in waterways or sediments. The aims of this study were to (1) quantify the differences between existing environmental guideline values for mercury in freshwater lakes and background mercury concentrations and (2) determine the key factors affecting the spatial differences in background mercury concentrations in freshwater lake systems in Australia. Mercury concentrations were measured in background sediments from 21 lakes in Australia. These data indicate that background mercury concentrations in lake sediments can vary significantly across the continent and are up to nine times lower than current sediment quality guidelines in Australia and New Zealand. This indicates that if waterway managers are aiming to restore systems to ‘pre-industrialization’ mercury levels, it is highly important to quantify the site-specific background mercury concentration. Organic matter and precipitation were the main factors correlating with background mercury concentrations in lake sediments. We also found that the geology of the lake catchment correlates to the background mercury concentration of lake sediments.The highest mercury background concentrations were found in lakes in igneous mafic intrusive regions and the lowest in areas underlain by regolith. Taking into account these findings, we provide a preliminary map of predicted background mercury sediment concentrations across Australia that could be used by waterway managers for determining management targets. Copyright: © 2020 The Author(s). **Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Peter Gell” is provided in this record*

Background concentrations of mercury in Australian freshwater sediments: the role of catchment’s physico-chemical parameters on mercury deposition

Waterways in the Australian continent are facing increasing levels of mercury contamination due to industrialisation, agricultural intensification, energy production, urbanisation and mining. Mercury contamination undermines the use of waterways as a source of potable water and also has a deleterious effect on aquatic organisms. When developing management strategies to reduce mercury levels in waterways, it is crucial to set appropriate targets for mitigation of these contaminated waterways. These mitigation targets could be (1) trigger values or default guideline values provided by water and sediment quality guidelines or (2) background (pre-industrialisation) levels of mercury in the waterway. The aims of this study were to: (1) quantify the differences between existing environmental guideline values for mercury in aquatic systems, and background mercury concentrations, and (2) determine key factors affecting the spatial differences in background mercury concentrations in freshwater lake systems in Australia. Mercury concentrations were measured in background sediments from 21 lakes in Australia. Organic matter and precipitation were the main factors to explain mercury concentrations in sediments of lakes. These data indicate that background mercury concentrations in lake sediments can vary significantly across the continent, and the background concentrations are up to nine times lower than current sediment quality guidelines in Australia and New Zealand. This indicates that if waterway managers are aiming to restore systems to ‘pre-industrialisation’ mercury levels, it is highly important to quantify the site-specific background mercury concentration. We found that the geology of the lake catchment correlates to the background mercury concentration of lake sediments, with the highest mercury background levels being identified in lakes in igneous mafic intrusive regions and the lowest in areas underlain by regolith. Taking into account these findings, we provide a preliminary map of predicted background mercury sediment concentrations across Australia that could be used by waterway managers for determining management targets

Development of the data-driven models for accessing the impact of design variables on heavy metal removal in constructed wetlands

Constructed wetlands are a type of green infrastructure commonly used for urban stormwater treatment. Previous studies have shown that the various design characteristics have an influence on the outflow heavy metal concentrations. In this study, we develop a Bayesian linear mixed model (BLMM) and a Bayesian linear regression model (BLRM) to predict the outflow concentrations of heavy metals (Cd, Cu, Pb and Zn) using an inflow concentration (Cin) and five design variables, namely media type, constructed wetland type (CWT), hydraulic retention time, presence of a sedimentation pond (SedP) and wetland-to-catchment area ratio (Ratio). The results show that the BLMM had much better performance, with the mean Nash–Sutcliffe efficiency between 0.51 (Pb) and 0.75 (Cu) in calibration and between 0.28 (Pb) and 0.71 (Zn) in validation. The inflow concentration was found to have significant impacts on the outflow concentration of all heavy metals, while the impacts of other variables on the wetland performance varied across metals, e.g., CWT and SedP showed a positive correlation to Cd and Cu, whereas media and Ratio were negatively correlated with Pb and Zn. Results also show that the 100-fold calibration and validation was superior in identifying the key influential factors

Energy Resolution Performance of the CMS Electromagnetic Calorimeter

The energy resolution performance of the CMS lead tungstate crystal electromagnetic calorimeter is presented. Measurements were made with an electron beam using a fully equipped supermodule of the calorimeter barrel. Results are given both for electrons incident on the centre of crystals and for electrons distributed uniformly over the calorimeter surface. The electron energy is reconstructed in matrices of 3 times 3 or 5 times 5 crystals centred on the crystal containing the maximum energy. Corrections for variations in the shower containment are applied in the case of uniform incidence. The resolution measured is consistent with the design goals

Using sediment cores to reconstruct historical pollution records: digging up the Yarra's dirty past

Despite the increasing threat of flooding due to climate change, there is limited understanding of the level of contamination of flood deposits, and their risk to humans and the environment. It is expected that sediment cores can provide a better understanding of the contaminants deposited by floods, because sediment cores can preserve both the pollution and flood histories of aquatic systems. This PhD thesis aims to use sediment cores to identify pollutant levels (heavy metal concentrations) in sediments deposited by past fluvial floods. The Yarra River, which flows through a metropolitan area (Melbourne) in South-East Australia is used as a case study, and contaminant levels within fluvial flood deposits during the 20th century are identified in sediment cores from two floodplain lakes (billabongs). First, overall pollution trends within the Yarra River billabongs are explored. It is found that current sediment quality trigger values used in Australia do not reflect background heavy metal concentrations in the Yarra River billabongs. This highlights the need to use sediment cores to identify the background conditions of aquatic systems, when developing environmental management targets, instead of relying on generic trigger values. Also, urban stormwater from purely residential catchments appears to result in heavy metal pollution of aquatic systems. Although the installation of a stormwater treatment wetland has coincided with a slight decrease in heavy metal levels within one of the billabongs, background levels have not been restored. Second, two methods for identifying discrete flood deposits within sediment cores are presented. One method utilises the elemental composition of sediments, a flood proxy not previously sufficiently explored, to identify flood layers. The historical flood records reconstructed using billabong sediment cores can be used to infer that flooding frequency of the Yarra River has decreased through the 20th century. These reconstructed records were checked using measured flow data An uncertainty framework for using sediment cores to obtain historical pollution records is also presented. The greatest source of uncertainty is the assumption that all metals entering the aquatic system are deposited on the sediment bed. Observations during a 12-month field monitoring period indicate that whilst there may be a discrepancy between the total mass of metal inputs and total mass of metals deposited on the bed sediment, they vary throughout the year in a similar manner. These results suggest that sediment core heavy metal profiles are indicative of historical pollution trends in the aquatic system. The thesis also demonstrates how high resolution historical pollution and hydrologic trends, both reconstructed using sediment cores, can be used together to determine the pollution sources of aquatic systems. This shows that the main source of pollution in billabongs can vary greatly even if these billabongs are close to each other spatially. Whilst one billabong had higher heavy metal concentrations in flood-deposited sediments, the other had higher concentrations in sediments that were not deposited by floods. Cumulative distribution functions of heavy metal concentrations (lead and zinc) in sediments deposited by Yarra River floods at the two billabongs over the 20th century are also presented. These functions could be used to help predict the contaminant deposition by future floods of the Yarra River at the two billabongs. The methods presented in this thesis can be applied to other river catchments to better understand their sources of contamination; in particular, the importance of flooding in the deposition of contaminants in floodplains and billabongs. Furthermore, having these data of heavy metal concentrations in flood deposits will better equip us for the future, enabling us to better understand the risks associated with fluvial floods, and the management strategies that are required

Development of the data-driven models for accessing the impact of design variables on heavy metal removal in constructed wetlands

AbstractConstructed wetlands are a type of green infrastructure commonly used for urban stormwater treatment. Previous studies have shown that the various design characteristics have an influence on the outflow heavy metal concentrations. In this study, we develop a Bayesian linear mixed model (BLMM) and a Bayesian linear regression model (BLRM) to predict the outflow concentrations of heavy metals (Cd, Cu, Pb and Zn) using an inflow concentration (Cin) and five design variables, namely media type, constructed wetland type (CWT), hydraulic retention time, presence of a sedimentation pond (SedP) and wetland-to-catchment area ratio (Ratio). The results show that the BLMM had much better performance, with the mean Nash–Sutcliffe efficiency between 0.51 (Pb) and 0.75 (Cu) in calibration and between 0.28 (Pb) and 0.71 (Zn) in validation. The inflow concentration was found to have significant impacts on the outflow concentration of all heavy metals, while the impacts of other variables on the wetland performance varied across metals, e.g., CWT and SedP showed a positive correlation to Cd and Cu, whereas media and Ratio were negatively correlated with Pb and Zn. Results also show that the 100-fold calibration and validation was superior in identifying the key influential factors.</jats:p

Stormwater biofilters as barriers against Campylobacter jejuni, Cryptosporidium Oocysts and adenoviruses; results from a laboratory trial

Biofilters are a widely used stormwater treatment technology. However; other than some evidence regarding non-pathogenic indicator microorganisms; there are significant knowledge gaps in the capacity of stormwater biofilters to remove actual pathogens and how this removal is impacted by biofilter design elements and operational conditions. In this study; we explored the capacity of stormwater biofilters to remove three reference pathogens (Campylobacter spp.; adenovirus and Cryptosporidium oocysts) and compared these to commonly used indicator microorganisms (E. coli; FRNA coliphages and Clostridium perfringens). Two different biofilter designs; each having a submerged zone (SZ); were tested under extended dry weather periods (up to 4 weeks) and different event volumes (the equivalent of 1-2 pore volumes) in a laboratory trial. These systems were able to consistently reduce the concentrations of all tested reference pathogens (average log reduction in Campylobacter spp. = 0.7; adenovirus = 1.0 and Cryptosporidium oocysts = 1.7) and two of the indicators (average log reduction in E. coli = 1.2 and C. perfringens = 2.1). However; none of the tested indicators consistently mimicked the removal performance of their corresponding reference pathogens after extended dry weather periods and during larger simulated storm events. This indicates that the behaviour of these pathogens in stormwater biofilters are not adequately represented by their corresponding indicator microorganisms and that to optimise biofilter designs for pathogen removal it is critical to further study pathogen removal processes in these systems.</p

Using sediment cores to establish targets for the remediation of aquatic environments

When assigning site-specific restoration targets for deteriorating aquatic systems, it is necessary to have an understanding of the undisturbed or background state of the system. However, the sitespecific characteristics of aquatic systems prior to disturbance are mostly unknown, due to the lack of historical water and sediment quality data. This study aims to introduce a method for filling this gap in our understanding, using dated sediment cores from the beds of aquatic environments. We used Bolin Billabong, a floodplain lake of the Yarra River (South-East Australia), as a case study to demonstrate the application of this method. We identified the concentrations of aluminium, cadmium, chromium, copper, iron, lead, manganese, nickel, tin and zinc at 8 cm intervals through the sediment core. This showed that aluminium, chromium, copper, iron, lead, nickel, tin and zinc concentrations in Bolin Billabong sediments significantly increased after European settlement in the river catchment in the mid-19th century. The differences between current Australian sediment quality guidelines trigger values and the background metal concentrations in Bolin Billabong sediments underscore the value of using locally relevant background toxicant concentrations when setting water and sediment quality targets.</p