Riparian buffers: Disrupting the transport of E. coli from rural catchments to streams.

High levels of E. coli and associated faecal microbes in waterways as a result of agricultural and residential land use can pose environmental, human health, and economic risks. This study aims to understand the impacts of land use, climatic variables, and riparian buffers on in-stream E. coli concentrations. Flow, temperature, and E. coli were monitored during three sampling campaigns within eleven independent catchments. These catchments have varying land use and extents of riparian buffer coverage. Results showed that catchments with predominantly agricultural and residential land uses (average = 349.7 MPN/100 mL) had higher E. coli concentrations than predominantly forested catchments (average = 111.8 MPN/100 mL). However, there were no statistically significant differences in E. coli concentrations between the agricultural and residential land uses. Riparian buffers appear to reduce E. coli concentrations in streams, as indicated by significant negative correlations between in-stream E. coli concentrations with the riparian buffer areal coverage (Pearson's r = -0.95, Spearman's ρ = -0.90) and the ratio of buffer length to stream length (Pearson's r = -0.87, Spearman's ρ = -0.90). We find that riparian buffers potentially disrupt transport pathways that govern E. coli movement, which in-turn can affect the concentration-discharge relationship. This reinforces the importance of protecting and restoring riparian buffers along drainage lines in agricultural and rural-residential catchments to improve downstream microbial water quality.

The emergence, trajectory, and impacts of emerging contaminants publications in the Journal of Environmental Quality.

As analytical capabilities in the early 2000s began to enable the detection of chemicals in environmental media at increasingly small concentrations, chemicals with the potential to cause adverse human and ecosystem health effects began to be found nearly ubiquitously worldwide. The types of chemicals that were targeted for analysis included natural and synthetic hormones, human and veterinary pharmaceuticals, chemicals in personal care products, novel pesticides, nanoparticles, microplastics, and other chemicals of natural and synthetic origin. The impacts of these chemicals on environmental and human health in many cases remain unknown. Collectively, these chemicals became known as "emerging contaminants" or "contaminants of emerging concern." Much progress has been made toward understanding the sources of these contaminants in the environment, the processes that control their fate and transport once they are released into the environment, and the ability of technology and/or best management practices to mitigate their occurrence. As the Journal of Environmental Quality (JEQ) celebrates its 50th anniversary, we sought to understand how publications in the journal have made impactful contributions in the research area of emerging contaminants. Here, we present the trajectory of publications in JEQ that have shaped knowledge in this field, highlight the importance of these contributions, and conclude with opportunities for JEQ to continue attracting high-quality emerging contaminants research.

Mercury atmospheric emission, deposition and isotopic fingerprinting from major coal-fired power plants in Australia: Insights from palaeo-environmental analysis from sediment cores.

Despite Australia's high reliance on coal for electricity generation, no study has addressed the extent to which mercury (Hg) deposition has increased since the commissioning of coal-fired power plants. We present stratigraphic data from lake sediments in the Hunter Valley (New South Wales) and Latrobe Valley (Victoria), where a significant proportion of Australia's electricity is generated via coal combustion. Mercury deposition in lake sediments increased in the 1970s with the commissioning of coal-fired power plants, by a factor of 2.9-times in sediments of Lake Glenbawn (Hunter Valley) and 14-times in Traralgon Reservoir (Latrobe Valley). Sediments deposited after the commissioning of power plants have distinct Hg isotope compositions, similar to those of combusted coals. Mercury emission, estimated using an atmospheric model (CALPUFF), was higher in the Latrobe Valley than in the Hunter Valley. This is a result of higher Hg concentrations in lignite coal, lax regulation and older pollution-control technologies adopted by coal-fired power plants in the Latrobe Valley. Near-source deposition of Hg in Australia is significantly higher than North America and Europe, where better emission controls (e.g. wet flue gas desulfurization) have been in effect for decades. The challenge for Australia in years to come will be to ratify the Minamata Convention and develop better regulation policies to reduce Hg emissions.

Solving the puzzle of mercury fate and emissions by coal-fired power plants: The potential of hydrodynamic-atmospheric modelling.

There is currently a significant gap in knowledge about the emission and deposition of mercury (Hg) from coal-fired power plants in Australia. To fill this gap, we propose a novel method that combines several sources of information (stratigraphic data, hydrodynamic modelling and atmospheric modelling), to identify the sources and fates of Hg emitted from coal-fired power plants. The stratigraphic record from Lake Macquarie (Australia) shows that mercury deposition increased up to 7-times since the 1950s, which is when coal-fired power plants were commissioned in the catchment. The stratigraphy also shows a decrease in Hg deposition with power plant retrofits. Using results from multiple models (statistical modelling, hydrodynamic modelling, particle density modelling and atmospheric emissions modelling), we found that ash dams contribute little Hg to Lake Macquarie. Instead, most of the Hg contamination in the lake is a result of atmospheric emissions from the power plants, and these power plants are also depositing Hg in the urban areas to the west of the lake. Our results demonstrate that the multi-proxy approach demonstrated in the paper can be used to provide clues as to the source of Hg, so that appropriate mitigation strategies and regulatory frameworks can be implemented.

A multi-model approach to assessing the impacts of catchment characteristics on spatial water quality in the Great Barrier Reef catchments.

Water quality monitoring programs often collect large amounts of data with limited attention given to the assessment of the dominant drivers of spatial and temporal water quality variations at the catchment scale. This study uses a multi-model approach: a) to identify the influential catchment characteristics affecting spatial variability in water quality; and b) to predict spatial variability in water quality more reliably and robustly. Tropical catchments in the Great Barrier Reef (GBR) area, Australia, were used as a case study. We developed statistical models using 58 catchment characteristics to predict the spatial variability in water quality in 32 GBR catchments. An exhaustive search method coupled with multi-model inference approaches were used to identify important catchment characteristics and predict the spatial variation in water quality across catchments. Bootstrapping and cross-validation approaches were used to assess the uncertainty in identified important factors and robustness of multi-model structure, respectively. The results indicate that water quality variables were generally most influenced by the natural characteristics of catchments (e.g., soil type and annual rainfall), while anthropogenic characteristics (i.e., land use) also showed significant influence on dissolved nutrient species (e.g., NOX, NH4 and FRP). The multi-model structures developed in this work were able to predict average event-mean concentration well, with Nash-Sutcliffe coefficient ranging from 0.68 to 0.96. This work provides data-driven evidence for catchment managers, which can help them develop effective water quality management strategies.

A Low-Cost Water Depth and Electrical Conductivity Sensor for Detecting Inputs into Urban Stormwater Networks.

High-resolution data collection of the urban stormwater network is crucial for future asset management and illicit discharge detection, but often too expensive as sensors and ongoing frequent maintenance works are not affordable. We developed an integrated water depth, electrical conductivity (EC), and temperature sensor that is inexpensive (USD 25), low power, and easily implemented in urban drainage networks. Our low-cost sensor reliably measures the rate-of-change of water level without any re-calibration by comparing with industry-standard instruments such as HACH and HORIBA's probes. To overcome the observed drift of level sensors, we developed an automated re-calibration approach, which significantly improved its accuracy. For applications like monitoring stormwater drains, such an approach will make higher-resolution sensing feasible from the budget control considerations, since the regular sensor re-calibration will no longer be required. For other applications like monitoring wetlands or wastewater networks, a manual re-calibration every two weeks is required to limit the sensor's inaccuracies to ±10 mm. Apart from only being used as a calibrator for the level sensor, the conductivity sensor in this study adequately monitored EC between 0 and 10 mS/cm with a 17% relative uncertainty, which is sufficient for stormwater monitoring, especially for real-time detection of poor stormwater quality inputs. Overall, our proposed sensor can be rapidly and densely deployed in the urban drainage network for revolutionised high-density monitoring that cannot be achieved before with high-end loggers and sensors.

The impact of stormwater biofilter design and operational variables on nutrient removal - a statistical modelling approach.

Biofiltration systems can help mitigate the impact of urban runoff as they can treat, retain and attenuate stormwater. It is important to select the optimal design characteristics of biofilters (e.g., vegetation, filter media depth) to ensure high treatment performance. Operational conditions (e.g., infiltration rate) can also lead to significant changes in biofilter treatment performance over time. The impact of specific operational conditions on water quality treatment performance of stormwater biofilters is still not well understood. Furthermore, despite the importance of design characteristics and operational conditions on biofilter treatment performance, there is a lack of models that can be used to determine the optimal design and operation. In this paper, we developed a series of statistical models to predict the Total Phosphorus (TP) and Total Nitrogen (TN) removal performance of stormwater biofilters using various numbers of design characteristics and operational conditions. These statistical models were tested using data collected from four extensive laboratory-scale biofilter column studies. It was found that all models performed relatively well with a Nash-Sutcliffe Efficiency (NSE) of 0.42 - 0.61 for TP and 0.37 - 0.63 for TN. The most important design characteristics were filter media type and depth for TP treatment, and vegetation type and submerged zone depth for TN treatment. In addition, infiltration rate and inflow concentrations were the operational conditions that greatly influence outflow TP and TN concentrations from stormwater biofilters. As such, these variables need to be carefully considered when designing and operating stormwater biofilters. Sensitivity analysis results indicate that the model was quite sensitive to all regression coefficients and intercepts. Additional modelling exercises show that the model could be further simplified by reducing the number of cross-correlated parameters. These models can be used by practitioners for not just optimising the design, but also operating biofilters using real-time monitoring and control to achieve optimum performance.

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.

Best Management Practices for Diffuse Nutrient Pollution: Wicked Problems Across Urban and Agricultural Watersheds.

Extensive time and financial resources have been dedicated to address nonpoint sources of nitrogen and phosphorus in watersheds. Despite these efforts, many watersheds have not seen substantial improvement in water quality. The objective of this study is to review the literature and investigate key factors affecting the lack of improvement in nutrient levels in waterways in urban and agricultural regions. From 94 studies identified in the academic literature, we found that, although 60% of studies found improvements in water quality after implementation of Best Management Practices (BMPs) within the watershed, these studies were mostly modeling studies rather than field monitoring studies. For studies that were unable to find improvements in water quality after the implementation of BMPs, the lack of improvement was attributed to lack of knowledge about BMP functioning, lag times, nonoptimal placement and distribution of BMPs in the watershed, postimplementation BMP failure, and socio-political and economic challenges. We refer to these limiting factors as known unknowns. We also acknowledge the existence of unknown unknowns that hinder further improvement in BMP effectiveness and suggest that machine learning, approaches from the field of business and operations management, and long-term convergent studies could be used to resolve these unknown unknowns.

Assessing environmental contamination from metal emission and relevant regulations in major areas of coal mining and electricity generation in Australia.

The Hunter and Latrobe Valleys have two of the richest coal deposits in Australia. They also host the largest coal-fired power stations in the country. We reconstructed metal deposition records in lake sediments in the Hunter and Latrobe Valleys to determine if metal deposition in freshwater lakes have increased in the region. The current regulatory arrangement applied to metal emissions from coal-fired power stations in Australia are presented, discussing their capacity to address future increases in metal deposition from these sources. Sediment records of spheroidal carbonaceous particles (SCPs), a component of fly-ash, were also used as an additional line of evidence to identify the contribution of industrial activities related to electricity generation to metal deposition in regions surrounding open-cut coal mines and coal-fired power stations. Sediment metal concentrations and SCP counts in the sedimentary records, from the Hunter and Latrobe Valleys, both indicated that open-cut coal mining and the subsequent combustion of coal in power stations has most likely resulted in an increase in atmospheric deposition of metals in the local region. In particular, the metalloids As and Se showed the greatest enrichment compared to before coal mining commenced. Although the introduction of bag filters at Liddell Power Station and the decommissioning of Hazelwood Power Station appear to have resulted in a decrease of metal deposition in nearby lakes, overall metal deposition in the environment is still increasing. The challenge for the years to come will be to develop better regulation policies and tools that will contribute to reduce metal emissions in these major electricity production centres in Australia.

Understanding spatiotemporal variability of in-stream water quality in urban environments - A case study of Melbourne, Australia.

To support sustainable urban planning and the design of water pollution mitigation strategies, the spatial and temporal trends of water quality in urban streams needs to be further understood. This study analyses over ten years of surface water quality data from 53 upstream catchments (20 of them predominated by a single type of land use) and two lowland sites across Greater Melbourne, Australia. We evaluated the impact of various catchment characteristics, especially urban land uses, on spatial and temporal urban water quality trends. Here, we focused on common urban pollutants: total suspended solids (TSS), total phosphorous (TP), total nitrogen (TN), zinc (Zn), copper (Cu) and nickel (Ni). Site median nutrient and heavy metal concentrations were negatively correlated with the catchment's elevation and its average annual rainfall. Further analysis shows that such trends were driven by the geographical pattern of Melbourne - i.e. low-laying sites tend to have less rainfall and be more urbanised. Only median concentrations of heavy metals (Zn and Cu) were correlated to catchment imperviousness. Further characterising of the urban environment was done into specific land uses (residential, industrial and commercial), yet median concentrations of all pollutants were not significantly correlated with land uses. This is because simple metrics, such as land use proportions, do not adequately reflect the significant variability in pollution sources that can exist even within the same land use type. Indeed, our temporal analysis found that the water quality difference between catchments with similar land uses is likely caused by their site-specific pollutant sources (construction and illegal discharge) and environmental management actions (wastewater management actions) regardless of similarities in land use. A 3-stage urbanisation cycle (development, operation and renewal) is suggested to further explain the urban water quality variance, but more data from small areas of an urban catchment is required to directly understand the unique impact of each urbanisation stage on water quality.

River Bank Erosion and the Influence of Environmental Flow Management.

Environmental flows aim to influence river hydrology to provide appropriate physical conditions for ecological functioning within the restrictions of flow regulation. The hydrologic characteristics of flow events, however, may also lead to unintended morphologic effects in rivers, such as increases in riverbank erosion beyond natural rates. This may negatively impact habitat for biota, riparian infrastructure, and land use. Strategic environmental flow delivery linked to monitoring and adaptive management can help mitigate risks. We monitor riverbank condition (erosion and deposition) relative to environmental flows on the Goulburn River, Victoria, Australia. We describe the process of adaptive management aimed at reducing potential impacts of flow management on bank condition. Field measurements (erosion pins) quantify the hydrogeomorphic response of banks to the delivery of planned and natural flow events. Managed flows provide opportunities for monitoring riverbank response to flows, which in turn informs planning. The results demonstrate that environmental flows have little influence on bank erosion and visual perceptions in the absence of monitoring are an unreliable guide. This monitoring project represents a mutually beneficial, science-practice partnership demonstrating that a traditional 'know then do' approach can be foreshortened by close collaboration between researchers and managers. To do so requires transparent, often informal lines of communication. The benefits for researchers-a more strategic and targeted approach to monitoring activities; and benefits for the practitioners-reduced time between actions and understanding response; mean that a learn by doing approach is likely to have better outcomes for researchers, stakeholders, the public, and the environment.

Identifying heavy metal levels in historical flood water deposits using sediment cores.

When designing mitigation and restoration strategies for aquatic systems affected by heavy metal contamination, we must first understand the sources of these pollutants. In this study, we introduce a methodology that identifies the heavy metal levels in floodplain lake sediments deposited by one source; fluvial floods. This is done by comparing sediment core heavy metal profiles (i.e., historical pollution trends) to physical and chemical properties of sediments in these cores (i.e., historical flooding trends). This methodology is applied to Willsmere and Bolin Billabongs, two urban floodplain lakes (billabongs) of the Yarra River (South-East Australia). Both billabongs are periodically inundated by flooding of the Yarra River and one billabong (Willsmere Billabong) is connected to an urban stormwater drainage network. 1-2-m long sediment cores (containing sediment deposits up to 500 years old) were taken from the billabongs and analysed for heavy metal concentrations (arsenic, chromium, copper, lead, nickel, zinc). In cores from both billabongs, arsenic concentrations are high in the flood-borne sediments. In Bolin Billabong, absolute metal levels are similar in flood and non-flood deposits. In Willsmere Billabong, absolute copper, lead and zinc levels were generally lower in fluvial flood-borne sediments in the core compared to non-fluvial sediments. This suggests that heavy metal concentrations in Bolin Billabong sediments are relatively similar regardless of whether or not fluvial flooding is occurring. However for Willsmere Billabong, heavy metal concentrations are high when overland runoff, direct urban stormwater discharges or atmospheric deposition is occurring. As such, reducing the heavy metal concentrations in these transport pathways will be of great importance when trying to reduce heavy metal concentrations in Willsmere Billabong sediments. This study presents a proof-of-concept that can be applied to other polluted aquatic systems, to understand the importance of river floods in the contamination of the bed sediments of aquatic systems. As a cost effective and less time consuming alternative to extensive field monitoring, our proposed method can be used to identify the key sources of pollution and therefore support the development of effective management strategies.

Presence and survival of culturable Campylobacter spp. and Escherichia coli in a temperate urban estuary.

Urban estuaries throughout the world typically contain elevated levels of faecal contamination, the extent of which is generally assessed using faecal indicator organisms (FIO) such as Escherichia coli. This study assesses whether the bacterial FIO, E. coli is a suitable surrogate for Campylobacter spp., in estuaries. The presence and survival dynamics of culturable E. coli and Campylobacter spp. are compared in the water column, bank sediments and bed sediments of the Yarra River estuary (located in Melbourne, Australia). The presence of E. coli did not necessarily indicate detectable levels of Campylobacter spp. in the water column, bed and bank sediments, but the inactivation rates of the two bacteria were similar in the water column. A key finding of the study is that E. coli and Campylobacter spp. can survive for up to 14days in the water column and up to 21days in the bed and bank sediments of the estuary. Preliminary data presented in this study also suggests that the inactivation rates of the two bacteria may be similar in bed and bank sediments. This undermines previous hypotheses that Campylobacter spp. cannot survive outside of its host and indicates that public health risks can persist in aquatic systems for up to three weeks after the initial contamination event.

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 site-specific 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.

Sediment cores as archives of historical changes in floodplain lake hydrology.

Anthropogenic activities are contributing to the changing hydrology of rivers, often resulting in their degradation. Understanding the drivers and nature of these changes is critical for the design and implementation of effective mitigation strategies for these systems. However, this can be hindered by gaps in historical measured flow data. This study therefore aims to use sediment cores to identify historical hydrological changes within a river catchment. Sediment cores from two floodplain lakes (billabongs) in the urbanised Yarra River catchment (Melbourne, South-East Australia) were collected and high resolution images, trends in magnetic susceptibility and trends in elemental composition through the sedimentary records were obtained. These were used to infer historical changes in river hydrology to determine both average trends in hydrology (i.e., coarse temporal resolution) as well as discrete flood layers in the sediment cores (i.e., fine temporal resolution). Through the 20th century, both billabongs became increasingly disconnected from the river, as demonstrated by the decreasing trends in magnetic susceptibility, particle size and inorganic matter in the cores. Additionally the number of discrete flood layers decreased up the cores. These reconstructed trends correlate with measured flow records of the river through the 20th century, which validates the methodology that has been used in this study. Not only does this study provide evidence on how natural catchments can be affected by land-use intensification and urbanisation, but it also introduces a general analytical framework that could be applied to other river systems to assist in the design of hydrological management strategies.