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

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

Digging up the dirty past: evidence for stormwater's contribution to pollution of an urban floodplain lake

Negative effects of urbanisation on the health of aquatic environments are well recognised; but more data are needed for an accurate assessment of the particular effects of residential development on the health of aquatic systems. This study explores the relationship between residential growth and increasing pollution, by analysing temporal trends of chemical fluxes into Willsmere Billabong-an urban floodplain lake of the Yarra River in South-East Australia. Sediment cores were extracted to reveal depositions over three centuries (∼1700-2012). The cores were sub-sampled at high resolution and analysed for heavy metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs). Pollutant concentrations in the sediments appear to have been significantly affected by residential development in the local catchment. Normalised concentration profiles show these effects to be exacerbated from the mid-20th century, after a stormwater drain was installed in the billabong. The study suggests that urban stormwater management techniques are critical for the protection of aquatic systems incorporated into residential zones.</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

Stormwater management impacts of small urbanising towns: The necessity of investigating the ‘devil in the detail’

In many parts of the world, small towns are experiencing high levels of population growth and development. However, there is little understanding of how urban growth in these regional towns will impact urban runoff. We used the case study of Wangaratta, located in South-East Australia, between 2006 and 2016, to investigate land cover changes and their impacts on urban runoff discharge. Detailed spatio-temporal analysis (including neighbourhood composition analysis and supervised classification of aerial imagery) identified that population, land use and land cover changes in Wangaratta, although subtle, were mostly driven by residential growth in the outskirts of the town, where there were large increases in impervious surface area. Overall, the urban growth was minimal. However, in spite of these small changes, a sub-catchment only SWMM model showed that the increase in impervious surface area nevertheless resulted in a statistically significant increase in total runoff across the town. Particularly, this increase was most pronounced for frequent and shorter storms. The analysis of urban development pattern changes coupled with urban hydrological modelling indicated that land cover changes in regional towns, especially when analysed in detail, may result in hydrological changes in the urban region (likely to be exacerbated in coming years by changing climate) and that adaptation efforts will need to adopt a variety of approaches in both existing and growth zones. Our findings highlight the necessity of detailed fine-scale analyses in small towns as even subtle changes will have substantial future implications and robust planning and adaptation decisions are even more important when compared to larger cities due to the greater economic constraints that small towns face and their important relationship with the surrounding hinterlands. © 2020 The AuthorsISSN:0048-9697ISSN:1879-102

Enhancing Escherichia coli removal in stormwater biofilters with a submerged zone:balancing the impact of vegetation, filter media and extended dry weather periods

Stormwater biofilters have shown promising yet variable removal of faecal microorganisms. The effects of vegetation, filter media and extended drying on the removal of Escherichia coli are investigated in the current study. Semi-synthetic stormwater was applied to 25 biofilters representing five different design configurations, all of which contained a submerged zone (SZ). The influence of extended dry periods on E. coli removal depended on the presence/absence of vegetation. Uptake of SZ water by plants with extensive roots during the dry periods lead to deterioration of the subsequent outflow water quality compared to unvegetated biofilters. Without a significant loss of SZ volume, a loamy sand biofilter planted with either Carex appressa or Leptospermum continentale can achieve a higher removal performance than an unvegetated washed sand biofilter. However, in warmer climates that experience long dry weather periods, and inability to control SZ volumes, un-vegetated columns may result in lower effluent E. coli concentrations.</p