A review and critical assessment of sedimentary metal indices used in determining the magnitude of anthropogenic change in coastal environments.

The current critical review examines the application of 11 frequently used sedimentary metal indices in their ability to accurately assess the magnitude of human-induced change (enrichment) in the highly vulnerable and intensely developed coastal environment. The plethora and rapidly increasing number of sedimentary metal indices should, if not derived for special purposes, produce a consistent assessment on the basis that they use the same suite of metals and concentrations. Inconsistent numerical results produced by different index formulations should, when combined with their associated classification scheme, produce a common assessment of environmental condition. However, such a consistent outcome is seldom observed. Significant differences in assessment results are partly due to the historical evolution of indices and to the extraordinary diversity of background and reference values and materials being applied to account for pre-anthropogenic metal levels and confounding due to variable sediment characteristics. Size-normalised sample and background metal data used in the mCd and MEQ indices do not require reference values to account for textural variability and provide a quasi-direct measurement of enrichment with minimal computation (simple division). These priority indices should be combined into a single index (Enrichment Quotient, EQ). Results produced by the EF index were strongly correlated to mCd and MEQ and provide a similar classification and is recommended if normalised data are unavailable. Other indices assessed (MPI, PI, mPI, SEF, Igeo, PLI and Cf, original and current) provided a range of results, which either over- or under-estimated enrichment. The confusion concerning the choice and application of background and reference values in the assessment process is reviewed and their use in local and global assessment is clarified. Single- and combined-metal evaluations are recommended to provide detailed, local and more comprehensive assessments, respectively.

Unusually high sedimentary metal concentrations in intermittently closed and open lakes and lagoons (ICOLLs) in the northern lagoons of Sydney (Australia).

The environmental status of three Intermittently Closed and Open Lakes and Lagoons (ICOLLs) (Manly, Curl Curl and Dee Why Lagoons) in northern Sydney (Australia) were assessed using sedimentary metals. Results identified the highest sedimentary metal enrichment in the Australian central east coast estuaries, with only a moderate ecological risk. A comparison with surficial sediment concentrations from 1996 to 2008 indicated declining metal concentrations, which is largely supported by subsurface metals data. Extensive low-lying areas of the catchments were historically reclaimed by infilling wetlands, which may have resulted in contaminated groundwater influx to the lagoons. An analysis of the sedimentary metals mix in lagoons surrounded by extensive infilling and estuaries with minor reclamation were statistically distinct. ICOLLs are environmentally sensitive due to large catchment/estuary ratios and restricted access to the ocean. A full set of baseline data is provided to support future monitoring of anthropogenic impacts on the system.

Comparison of mangrove (Avicennia marina) metal tissue concentrations to ambient sediment with an extensive range of contaminant levels in a highly-modified estuary (Sydney estuary, Australia).

Statistically distinct 'high', 'moderate' and 'low' metal contamination positions were distinguished across five Sydney estuary embayments for total sedimentary metal concentrations of Ni, Pb and Zn. While statistically distinct total sedimentary As, Cd, Co and Cu concentrations were indicated for the 'low' position samples. Mangrove (Avicennia marina) pneumatophore tissue metal concentrations from 'high' position trees were statistically distinct for Cd, Ni, Pb and Zn, while root tissue samples from 'low' position trees were statistically distinct for As, Cd and Zn. Outcomes from CAP, simple linear regression and DISTLM modelling indicated sedimentary metals were predominantly assimilated into mangrove root tissue, with smaller uptake into pneumatophore tissue. A comparison of floristic tissue metal concentrations indicated mangrove (A. marina) root tissue assimilated higher sedimentary metal concentrations than leaf and root tissue of seagrasses (Zostera capricorni and Halophila ovalis), which had relatively higher metal concentrations than those from pneumatophore and leaf mangrove tissue.

Baseline assessment of anthropogenic change and ecological risk of an estuary bordered by an urbanized catchment and a pristine national park (Port Hacking estuary, Australia).

Port Hacking is a tide-dominated, drowned river valley at the southern edge of the Sydney conurbation (Australia) and is bordered by intense urbanization to the north and native bushland in the south. The current work provides a first-time, baseline evaluation of the magnitude of human-induced change and risk posed by sedimentary metals in Port Hacking and catchment. The estuary separates fluvial and estuarine sediment enriched in metals exhibiting moderate ecological risk from sediments with minimal anthropogenic change and no biological risk. A full set of baseline data is provided in support of new monitoring of recent and future anthropogenic impacts on the system.

An assessment of aluminum and iron in normalisation and enrichment procedures for environmental assessment of marine sediment.

An increasing use of Al and Fe as normalising elements in assessment of anthropogenic change (metal enrichment) in marine environments has prompted the current study. This investigation was facilitated by a unique, large data set comprising total- and size-normalised sedimentary metals data from 41 estuaries (n = 3494) in central New South Wales, Australia. Total sediment Al and Fe concentrations varied substantially in these estuaries, even for samples comprising 100% fine fraction (ff), due to changes in the clay mineral mix and variable clay mineral chemistry. Normalising sedimentary metals to 100% ff produced variable results, however this approach improved markedly when samples with <10% ff was removed. The technique of normalising sedimentary metals by adjusting total Al to 50,000 µg/g considered to represent 100% ff was critically assessed. Results showed that total Al for 100% ff varied between estuaries and the most appropriate Al concentration for normalisation was the intercept value of the trend line in total Al vs ff bivariate plots and the 100% ff axis. It is recommended that, in the absence of size-normalised metals data, this intercept value be used as the normalising Al concentration, which should be determined locally for 100% ff. Iron was also assessed as a normalising element using the same approach and provided similar results, but was less attractive due to diagenetic alteration. The post-extraction normalisation (PEN) method provided valid, normalised metals data capable of estimating enrichment (magnitude of anthropogenic change) in marine environments.

Sediment metal enrichment and ecological risk assessment of ten ports and estuaries in the World Harbours Project.

Ten global harbours were assessed for sediment quality by quantifying the magnitude of anthropogenic change and ecological risk. Anthropogenic change (enrichment) was high for Derwent River and Sydney estuary, moderate for Santander Harbour, Rio de Janeiro and Dublin Port, slight for Hong Kong, minimal for Darwin. All 10 enrichment indices used showed similar results. Derwent River sediment was rated at high ecological risk, followed by Sydney and Santander estuaries with moderate risk. Auckland and Darwin sediments exhibited minimal ecological risk and sediment in the remaining harbours (Dublin, Hong Kong, Ravenna, Ria de Vigo and Rio de Janeiro) were assessed at slight ecological risk. The extraordinary variety of environments and types/quantities/qualities of data investigated resulted in as much a critique and development of methodology, as an assessment of human impact, including unique techniques for elemental normalisation and contaminant classification. Recommendations for an improved technical framework for sediment quality assessment are provided.

Using bivariate linear mixed models to monitor the change in spatial distribution of heavy metals at the site of a historic landfill.

To improve accuracy and efficiency of monitoring remediated sites, the current study proposed the use of bivariate linear mixed modelling and subsequent hypothesis testing to determine significant change in contaminant concentrations over time. The modelling method integrated soil heavy metal (arsenic-As, lead-Pb and zinc-Zn) concentrations obtained from Bicentennial Park, Sydney, Australia, in the years 1990 (n = 144) and 2015 (n = 60), alongside potential influencing factors as predictor variables. Following variable selection, significant predictors included As (1990)-plan curvature, land cover change; As (2015)-multi-resolution ridge top flatness (MRRTF); Pb (1990)-elevation, MRRTF, type of nearest road; Pb (2015)-land cover change; Zn (1990)-distance to the nearest road and road type; and for Zn (2015)-aspect and land cover change. Model quality statistics (standardised squared prediction error; SSPE) indicated relatively good estimates of the prediction variance (mean ~ 1.0 for all metals, median = 0.512 for As (1990), 0.420 for As (2015), 0.417 for Pb (1990), 0.388 for Pb (2015), 0.342 for Zn (1990) and 0.263 for Zn (2015)), however Lin's concordance correlation coefficient indicated poor prediction of point estimates (LCCC = 0.263 for As (1990), 0.414 for As (2015), 0.250 for Pb (1990), 0.166 for Pb (2015), 0.233 for Zn (1990) and 0.408 for Zn (2015)). Pb in 1990 exceeded the Australian guide value of 600 mg kg-1 in small, isolated areas of the park, and by 2015, these 'hotspots' had significantly diminished (P < 0.05). Concentrations of As were low in both 1990 and 2015, not exceeding the 300 mg kg-1 guide; yet, in 2015, As had significantly increased in the south of the study area (P < 0.2). Zn concentrations in 1990 were elevated but did not exceed the guide value of 30,000 mg kg-1. Overall, the models exhibited good estimation of prediction variance and therefore are suitable for hypothesis testing; however, they exhibited poor prediction quality at times. Despite this, bivariate linear mixed modelling is worth exploring as it provides an advantage over modelling single time points and can assist with tracking potential contaminant sources before they cause harm.

Deepwater ocean outfalls: A sustainable solution for sewage discharge for mega-coastal cities (Sydney, Australia): Influence of deepwater ocean outfalls on shelf benthic infauna.

In the early 1990s, a cliff-face disposal-system discharging approximately 940 ML/day, or 80% of sewage generated by the City of Sydney (Australia) (population 3.3 million) was replaced by three deepwater ocean outfalls. An 18-year benthic infauna monitoring study was undertaken to address earlier concerns of long-term accumulation from sewage discharges and potential adverse effects on the marine environment. Assessment of outfall community structure indicated organic input from discharges has not resulted in sediment anoxia. The current post-commissioning investigation detected a gradual change in community structure from north to south in the study area, which was also displayed in taxonomic turnover south of the Malabar outfall. Temporal fluctuation in community structure detected at the three outfall and three reference locations in the current study was also noted in the pre-commissioning study at these locations. Evidence provided by this study indicated the Sydney deepwater ocean outfalls do not cause significant ecological impact.

Deepwater ocean outfalls: A sustainable solution for sewage discharge for mega-coastal cities (Sydney, Australia): A synthesis.

In 1990-91 three deepwater ocean outfalls replaced three cliff-face outfalls discharging approximately 940 ML/day, or 80% of sewage generated by the City of Sydney (Australia) (population 3.3 million). Operation of these outfalls was assessed for the first two years and performed well, mitigating most of the environmental problems previously experienced from shoreline discharge. However, a concern remained for the unknown long-term effects on the marine environment. The current series of articles examine over 20 years of monitoring, for possible accumulative effects. Oceanographic modelling provided an understanding of particle settling, dispersion and distribution of discharged wastewater and monitoring assessed potential impact of offshore discharges on beach bathing water quality, sediment chemistry and benthic infauna. These four articles demonstrate that properly designed ocean outfalls are a viable, sustainable solution to sewage disposal for mega-coastal cities, however, continued monitoring is required to assess possible long-term environmental degradation.

Deepwater ocean outfalls: A sustainable solution for sewage discharge for mega-coastal cities (Sydney, Australia): Influences on beach water quality.

Shoreline discharge representing approximately 80% of sewage generated by Sydney (Australia) was replaced with three deepwater ocean outfalls between 1990 and 1991. Beachwatch bacterial monitoring data collected between 1989 and 2016 were analysed to assess the impact of commissioning on bathing water quality along 32 km of coastline. Bacterial contamination was reduced by 26-99% during the first 32 months post-commissioning and in the longer post-commissioning period, 1993 to 2016, bathing water quality improved for 31 beaches. Relatively stable bathing water quality was observed for five other beaches after the 2001 upgrade of another shoreline wastewater treatment plant. Bacterial contamination of bathing water in this 24-year post-commissioning period was most influenced by rainfall in the 24-h to 9 am on the day of sampling. Bacterial contamination from surfacing shore-blown wastewater plumes was not evident, whereas stormwater-delivered bacterial contamination was apparent and varied between beaches.

Metal concentrations in Sydney Cockle (Anadara trapezia) tissue and ambient sediment in a highly-modified estuary (Sydney estuary, Australia).

The influence of sedimentary metals on the cockle A. trapezia tissue was examined using a strong difference in sedimentary metal concentrations in an embayment (Hen and Chicken Bay) highly contaminated in Cu and an adjacent cove (Iron Cove), strongly enriched in Cd, Cu, Pb and Zn within the heavily-urbanised Sydney estuary catchment (Australia). Statistically significant differences were recorded for cockle tissue metal concentrations between the study locations reflecting differences in surficial sediment metal concentrations. Low metal uptake was apparent in A. trapezia tissue, which were considerably less than background sedimentary concentrations and was of low-risk for human consumption. Dissimilar bioconcentration of Cd, Cu, Pb and Zn was apparent in tissue of cockles (A. trapezia), prawns (Metapenaeus bennettae), mussels (Mytilus galloprovincialis) and oysters (Saccostrea glomerata), due possibly to different feeding patterns and biogeochemical conditions in bottom sediments.

Deepwater ocean outfalls: A sustainable solution for sewage discharge for mega-coastal cities (Sydney, Australia): Influence of deepwater ocean outfalls on shelf sediment chemistry.

A cliff-face disposal system discharging approximately 940 ML/day, or 80% of sewage generated by the City of Sydney (Australia) (population 3.3 million) was replaced by three deepwater ocean outfalls in the early 1990s. Enrichment of anthropogenic chemicals from cliff-face discharges raised concerns regarding long-term accumulation of sewage particulates and associated contaminants in offshore sediments and for reduced beach water quality. The current post-commissioning investigation detected a southward gradient of sediment fining and increased total organic carbon in the study region. Deepwater ocean discharges have not contributed to an accumulation of fines, or to increased metallic/nonmetallic chemicals of concern with no elevated risk of adverse biological effects beyond pre-commissioning conditions. Instead, the best modelled relationship was recorded between benthic infauna and sedimentary fines and not to contaminants. Historic sea dumping prior to 1932 in the north of the study area has resulted in enrichment of some non-bioavailable sedimentary metals.

Baseline physio-chemical characteristics of Sydney estuary water under quiescent conditions.

The current study establishes baseline water quality properties for Sydney estuary, Australia for long periods of quiescence, which characterize the region. The study was undertaken in response to numerous requests for such data by researchers, government agencies and contractors. During quiescent periods, the range in Secchi depth transparency, turbidity, salinity and total suspended solid (TSS) values was 0.3-5.3 m, 18.6-0.1 NTU, 26.4-35.3 PSU and 8.3-1.0 mg/L in the upper and lower estuary, respectively. Baseline particulate metal concentrations were high, however TSS metal mass was greater during high rainfall. Tables and GIS-based maps allow baseline physio-chemical values to be extracted from the database for any location in Sydney estuary for quiescent conditions. Strong inter-parameter baseline relationships enable interpolation between water quality data. Baseline physio-chemical values were used to assess the impact of a high-precipitation event to demonstrate the utility of the new database.

A review of chemical-based sediment quality assessment methodologies for the marine environment.

This review of 19 chemical approaches used in assessing sediment quality are classified into empirical, mechanistic and sediment quality indices (SQI) groups. Empirical sediment quality guidelines (SQGs), based on matching chemical and biological-effects data and the mechanistic techniques, founded on equilibrium partitioning principals (EqP), are well established and most used. Empirical SQGs provide a useful screening tool to initially identify locations and chemicals of most concern, but are not regulatory criteria. The EqP approach is causally linked however, the scheme assumes porewater chemistry largely controls sediment toxicity. SQIs are not based on matching chemical-biological data and combine schemes with multiple narrative intents. The 41 SQGs reviewed show a considerable range in upper and lower guideline values. Grain size and organic content should be included into SQGs, however inclusion of suspended sediment into SQGs raises concerns. SQGs are built into decision-tree schemes with other lines-of-evidence and evaluated in a weight-of-evidence framework.

Metal concentrations in seagrass (Halophila ovalis) tissue and ambient sediment in a highly modified estuarine environment (Sydney estuary, Australia).

Research into sediment-seagrass tissue metal relationships has been undertaken in Sydney estuary due to the recognized role contamination plays in threats to seagrass health. Seagrass (Halophila ovalis) leaf tissue concentrations are elevated in Cu, Pb and Zn and contain the highest reported root Cr concentrations. Seagrass metal concentrations were significantly different between species H. ovalis and Zostera capricorni; between root and leaf tissue; and between sampling locations. Greatest tissue enrichment was for Pb, however metals were not enriched in seagrass relative to surficial sediment. Fine and total sediment metal concentrations were temporally consistent between collection years 2013/15, whereas root tissue metals changed between years and sites and leaf metal contents were temporally inconsistent. Extractable metal concentrations in fine sediment (<62.5 µm) showed moderate significant correlation with root tissue and a weak significant relationship with leaf tissue, whereas total sediment metal showed no such relationships. Management implications are provided.

The relationship between metal concentrations in seagrass (Zostera capricorni) tissue and ambient fine sediment in modified and near-pristine estuaries (Sydney estuaries, Australia).

Seagrass (Zostera capricorni) tissue metal concentrations in Sydney estuary are some of the highest reported for urban environments. A strong declining metal (As, Co, Cr, Cu, Mn, Pb and Zn) concentration gradient in fine sediment from highly modified to the near-pristine estuarine environments was matched by a concurrent and statistically significant, moderately strong, relationship with declining metal concentrations for leaf, rhizomes and root tissue types. Leaf tissue more consistently expressed metal concentration uptake from sediment. Rhizome tissue contained the highest concentrations for all metals, except Mn, while leaf concentrations were higher for Cr and Zn and roots were more elevated in Cr and Pb. Tissue Cr, Pb and Zn were close to background for reference sites for leaves. Maximum tissue enrichment over background was 25, 19, 47 and 8 times for Cr, Cu, Pb and Zn. Bio-sediment accumulation factors were generally <1 for all metals.

Complex relationships between shallow muddy benthic assemblages, sediment chemistry and toxicity in estuaries in southern New South Wales, Australia.

Synoptic sediment quality triad (contaminants, benthic assemblages, toxicity testing) data were collected for sites in Sydney estuary, adjacent Cooks River and five less-modified southern estuaries. Matching data tested relationships between contaminants and benthic assemblages, correlations with specific contaminants, and the ability of sediment quality guidelines to predict the risk of adverse effects. Significant but weak relationships occurred in complex patterns between assemblages, contaminant concentrations and environmental variables. Maximum benthos abundance occurred where sediment contamination was high and was dominated by polychaetes. Spionidae (polychaete) and Galeommatidae (mollusc) abundances were strongly correlated with site environmental characteristics and with varying mixtures of metals and organic contaminants. The risk of adverse effects on benthic assemblage structure increased with increasing sediment toxicity except for areas of very high contamination and for non-bioavailable anthropogenic chemicals. The overall weight-of-evidence scores differentiated the highly modified sites from less-contaminated southern estuaries, where toxicity scores were higher than predicted.

Modelling drivers and distribution of lead and zinc concentrations in soils of an urban catchment (Sydney estuary, Australia).

The human population is increasing globally and land use is changing to accommodate for this growth. Soils within urban areas require closer attention as the higher population density increases the chance of human exposure to urban contaminants. One such example of an urban area undergoing an increase in population density is Sydney, Australia. The city also possesses a notable history of intense industrial activity. By integrating multiple soil surveys and covariates into a linear mixed model, it was possible to determine the main drivers and map the distribution of lead and zinc concentrations within the Sydney estuary catchment. The main drivers as derived from the model included elevation, distance to main roads, main road type, soil landscape, population density (lead only) and land use (zinc only). Lead concentrations predicted using the model exceeded the established guideline value of 300mgkg-1 over a large portion of the study area with concentrations exceeding 1000mgkg-1 in the south of the catchment. Predicted zinc did not exceed the established guideline value of 7400mgkg-1; however concentrations were higher to the south and west of the study area. Unlike many other studies we considered the prediction uncertainty when assessing the contamination risk. Although the predictions indicate contamination over a large area, the broadness of the prediction intervals suggests that in many of these areas we cannot be sure that the site is contaminated. More samples are required to determine the contaminant distribution with greater precision, especially in residential areas where contamination was highest. Managing sources and addressing areas of elevated lead and zinc concentrations in urban areas has the potential to reduce the impact of past human activities and improve the urban environment of the future.

Assessment of human-induced change and biological risk posed by contaminants in estuarine/harbour sediments: Sydney Harbour/estuary (Australia).

A rapid, simple yet scientifically sound scheme providing two important types of information used in assessment of estuarine sediments is presented. The mean enrichment quotient (MEQ) (fine contemporary sediment metal concentration/fine fraction background metal concentration) for Cu, Pb and Zn provides the magnitude of human-induced change, (deviation from the pristine condition), while sediment quality guidelines (SQGs) assess the risk posed by sedimentary contaminants to the benthic community. Maximum metal enrichment for sediment in Sydney estuary (Australia) is >100 times for Cu, Pb and Zn and the MEQ is >10 times for most of the estuary. Adverse effect on benthic populations due to Cu, Pb and Zn are expected in 2%, 50% and 36% of the waterway, respectively. SQGs for contaminant mixtures predict ~2% of the estuary has the highest risk of adverse effects, while 25% has intermediate risk. The scheme is well suited to initial assessments of estuarine sediments worldwide.

Determination of sediment metal background concentrations and enrichment in marine environments - A critical review.

'Background' is the concentration of metals in pristine sediment, unaltered by human activity and 'enrichment' is the extent present-day sediment metal concentrations exceed pre-anthropogenic levels (the magnitude of human-induced change). Background and enrichment are becoming more frequently used for management measures to bring sediment and the environment back to near-pristine levels. Of the six empirical methods reviewed for determining background (global values, pristine marine and fluvial sediments, catchment soils and rocks), the use of sedimentary cores has the greatest advantage. Most of the eight statistical methods reviewed are adversely affected by the polymodality and an absence of normality or log-normality, however robust regression procedures are most commonly used. Sorption hypothesis techniques require further development. Indices used to determine enrichment incorporate background levels (enrichment indices) or do not (contamination indices). Of the 20 indices reviewed, the New Nemerow Index and the Mean Enrichment Quotient rate highly in performance, based on 5 beneficial attributes assessed: use of background and normalised data, provision of thresholds, a classification scheme, and inclusion of multiple metals. Variance in background metal concentrations determined in the 43 global projects reviewed is surprisingly moderate, however regional variability may be considerable due to local catchment mineralisation. Chemical analysis of sediment should not include metals bound in the mineral matrix and weak acid extractions are advisable. The use of appropriate and effective indicators of environmental condition are critical to the protection and restoration of marine regions and ensuring that human activities are carried out in a sustainable manner to promote safe, healthy and productive ecosystems.