Sydney Harbour Estuary Research Articles

Dehalobium species implicated in 2,3,7,8-tetrachlorodibenzo-p-dioxin dechlorination in the contaminated sediments of Sydney Harbour Estuary

Polychlorinated dibenzo-p-dioxins and furans (PCDD/F) are some of the most environmentally recalcitrant and toxic compounds. They occur naturally and as by-products of anthropogenic activity. Sydney Harbour Estuary (Sydney, Australia), is heavily contaminated with PCDD/F. Analysis of sediment cores revealed that the contamination source area in Homebush Bay continues to have one of the highest levels of PCDD/F contamination in the world (5207 pg WHO-TEQ g−1) with >50% of the toxicity attributed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), the most toxic PCDD/F congener. Comparison of congener profiles at the contamination source area with surrounding bays and historical data provided evidence for the attenuation of 2,3,7,8-TCDD and other congeners at the source area. This finding was supported by the detection of di-, mono- and unchlorinated dibenzo-p-dioxin. Microbial community analysis of sediments by 16S rRNA amplicon sequencing revealed an abundance of lineages from the class Dehalococcoidia (up to 15% of the community), including the genus Dehalobium (up to 0.5%). Anaerobic seawater enrichment cultures using perchloroethene as more biologically available growth substrate enriched the Dehalobium population by more than six-fold. The enrichment culture then proved capable of reductively dechlorinating 2,3,7,8-TCDD to 2,3,7-TriCDD and octachlorodibenzo-p-dibenzodioxin (OCDD) to hepta and hexa congeners. This work is the first to show microbial reductive dehalogenation of 2,3,7,8-TCDD with a bacterium from outside the Dehalococcoides genus, and one of only a few that demonstrates PCDD/F dechlorination in a marine environment.

HYDRODYNAMIC AND WATER QUALITY MODELLING IN SYDNEY HARBOUR

The Sydney Harbour waterway modelling suite examines the changes in water quality in the harbour estuary and its tributaries associated with stormwater runoff and wet weather sewage overflows from the upstream catchments, in Sydney Australia. This paper discusses the development and performance of the numerical models. The models have been used to investigate the spatial variability of catchment pollutant loads and the impacts of sewer overflows on the water quality in the Sydney Harbour estuary. The scenario modelling results demonstrate that sewer overflows have a minimal impact on the Sydney Harbour estuary water quality, with stormwater dominating most changes in water quality.

Numerical modelling of suspended-sediment transport in a geographically complex microtidal estuary: Sydney Harbour Estuary, NSW

A numerical study was conducted to investigate the sediment dynamics in a geographically complex estuary, the Sydney Harbour Estuary (SHE). The SHE is a good example of a microtidal estuary, with irregular shorelines and a complex bathymetry, characterized by many headlands and islands forming a meandering main channel. Horizontal sediment transport showed a local estuarine turbidity maximum (ETM) as a result of complex topography, independent of salinity fields and river flows during dry weather. The along-estuary advection of sediment was mainly driven by the mean advection, with a minor contribution by tidal pumping. Mean advection associated with barotropic forcing drives sediment flux seaward in the upper estuary and landward in the middle estuary, leading to a longitudinal convergence of sediment transport, without upstream or downstream migration of ETM during high river flows. The interactions between tidal currents, complex topography and asymmetric vertical mixing led to spring-neap and flood-ebb variations in sediment distribution. The Singular Spectrum Analysis (SSA) method was used to calculate the relative contributions of the identified environmental forcing frequencies (tidal range, tidal frequency, river discharges, wind stress) to the variability in suspended-sediment concentration. Tidal frequency and river discharges were the major contributors to this variability. Tidal range made the highest contribution in the middle estuary, where the ETM was located, driving the spring-neap cycle of the ETM.

Carbon Budget for a Large Drowned River Valley Estuary Adjacent to an Emerging Megacity (Sydney Harbour)

AbstractAnnual organic and inorganic carbon budgets were constructed for the Sydney Harbour Estuary. Net ecosystem metabolism was the main control on carbon fluxes in the system. Sydney Harbour Estuary was slightly net heterotrophic, which is consistent with a small CO2 emission of 0.8 × 108 mol C yr−1. Terrestrial carbon loads were 70% dissolved inorganic carbon, 21% dissolved organic carbon, and 9% particulate organic carbon. Dissolved inorganic carbon was exported to the ocean (4.19 × 108 mol C yr−1), and an import of organic carbon (1.92 × 108 mol C yr−1) from the ocean was required to balance the budget. Sydney Harbour had high sediment organic carbon burial rates similar to other river valley estuaries including the Hudson River and Chesapeake Bay. Productivity was the main sink of inorganic carbon followed by sediment burial, emissions of CO2 to the atmosphere, and oyster sequestration. This study highlights the importance of determining the sources, sinks, and transformations of all carbon forms in constructing estuarine budgets.

Submarine groundwater discharge and associated nutrient and carbon inputs into Sydney Harbour (Australia)

The effects of urbanization and scales on submarine groundwater discharge (SGD) remain poorly understood. Here, we used radium isotopes to quantify SGD-derived fluxes of nitrogen, phosphorus and dissolved organic carbon (DOC) into Sydney Harbour estuary, Australia. Sydney is the most populated city of Oceania, with several localised cases of historical groundwater pollution. We sampled top and bottom waters at the harbour scale (~20 km) and also at four small scale embayments (~2 km). A decreasing gradient in radium isotope concentrations from upstream to downstream was observed. Mass balances constructed with 224Ra, 223Ra, and 226Ra revealed that total SGD ranged from 42 to 121 × 104 m3 d−1 depending on assumptions and isotope. These fluxes were related mostly to saline SGD (recirculated seawater), and are equivalent to >60 times the mean annual freshwater river discharge into Sydney Harbour (0.68 × 104 m3 d−1). The estimated SGD rates (2.2 ± 1.5 cm d−1) were comparable to the global average radium-derived-SGD in other urban estuaries (~3.1 cm d−1). No obvious relationships were observed between SGD and scale in Sydney Harbour. However, higher SGD rates estimated for embayments closer to the ocean indicate that a combination of waves, tides and urbanization control SGD. SGD derived fluxes exceeded maximum riverine nutrient fluxes by a factor of 2 for DOC, 6 for PO43−, 40 for NH4+ and 1.3 for NOX. Previous work has suggested that nutrients enter Sydney Harbour primarily through rivers or stormwater following episodic rain events. Our results imply that diffuse saline SGD can also be an important but overlooked source of nutrients, potentially sustaining primary productivity in times of no river flow.

Stormwater influences phytoplankton assemblages within the diverse, but impacted Sydney Harbour estuary.

Sydney Harbour is subjected to persistent stress associated with anthropogenic activity and global climate change, but is particularly subjected to pulse stress events associated with stormwater input during episodic periods of high rainfall. Photosynthetic microbes underpin metazoan diversity within estuarine systems and are therefore important bioindicators of ecosystem health; yet how stormwater input affects their occurrence and distribution in Sydney Harbour remains poorly understood. We utilised molecular tools (16S/18S rRNA and petB genes) to examine how the phytoplankton community structure (both prokaryotes and eukaryotes) within Sydney Harbour varies between high and low rainfall periods. The relative proportion of phytoplankton sequences was more abundant during the high rainfall period, comprising mainly of diatoms, an important functional group supporting increased productivity within estuarine systems, together with cyanobacteria. Increased spatial variability in the phytoplankton community composition was observed, potentially driven by the steepened physico-chemical gradients associated with stormwater inflow. Conversely, during a low rainfall period, the proportion of planktonic photosynthetic microbes was significantly lower and the persistent phytoplankton were predominantly represented by chlorophyte and dinoflagellate sequences, with lower overall diversity. Differences in phytoplankton composition between the high and low rainfall periods were correlated with temperature, salinity, total nitrogen and silicate. These results suggest that increased frequency of high-rainfall events may change the composition, productivity and health of the estuary. Our study begins to populate the knowledge gap in the phytoplankton community structure and substantial changes associated with transient environmental perturbations, an essential step towards unravelling the dynamics of primary production in a highly urbanised estuarine ecosystem in response to climate change and other anthropogenic stressors.

Numerical modelling of the Sydney Harbour Estuary, New South Wales: Lateral circulation and asymmetric vertical mixing

A fully calibrated three-dimensional hydrodynamic model of the Sydney Harbour Estuary was used to determine the dominant forcing of regulating estuarine circulation in a sinuous channel under conditions of low river discharge during dry weather. The system, characterized by stratified flood and mixed ebb during spring tides, and stratified flood and ebb during neap tides, was analysed using model results of current profiles, density field, eddy viscosity and gradient Richardson number at a mooring station and cross-channel transect. The magnitude and direction of lateral circulation was modulated in the flood-ebb and spring-neap cycles due to changes in the interactions between the tides and the complex geometry. During spring tides, a differential-advection-induced lateral baroclinic pressure gradient tends to drive the lateral circulation and stratifies the water column. When the along-estuary circulation is strong enough to break the stratification induced by the lateral baroclinic pressure gradient, centrifugal force works in concert with nonlinear advection establishing a classical two-layer helical flow across the channel. Channel bends also induce vertical mixing as a result of the overturning of the density fields. The lateral circulation redistributes the differential-advection-induced lateral shear of the along-estuary momentum and is transferred to either reinforce or cancel the along-estuary circulation. The lateral bathymetry variability in a channel is therefore the key factor causing the intratidal asymmetries in the along-estuary circulations. Stratification suppresses lateral circulation during neap tides, and generates a three-layer lateral circulation structure in the water column during stratified ebb.

Applying acoustic telemetry to understand contaminant exposure and bioaccumulation patterns in mobile fishes

Contamination in urbanised estuaries presents a risk to human health, and to the viability of populations of exploited species. Assessing animal movements in relation to contaminated areas may help to explain patterns in bioaccumulation, and assist in the effective management of health risks associated with consumption of exploited species. Using polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/Fs) contamination in Sydney Harbour estuary as a case study, we present a study that links movement patterns resolved using acoustic telemetry to the accumulation of contaminants in mobile fish on a multi-species basis. Fifty-four individuals across six exploited species (Sea Mullet Mugil cephalus; Luderick Girella tricuspidata; Yellowfin Bream Acanthopagrus australis; Silver Trevally Pseudocaranx georgianus; Mulloway Argyrosomus japonicus; Yellowtail Kingfish Seriola lalandi) were tagged with acoustic transmitters, and their movements tracked for up to 3years. There was substantial inter-specific variation in fish distribution along the estuary. The proportion of distribution that overlapped with contaminated areas explained 84–98% of the inter-specific variation in lipid-standardised biota PCDD/F concentration. There was some seasonal variation in distribution along the estuary, but movement patterns indicated that Sea Mullet, Yellowfin Bream, Silver Trevally, and Mulloway were likely to be exposed to contaminated areas during the period of gonadal maturation. Acoustic telemetry allows examination of spatial and temporal patterns in exposure to contamination. When used alongside biota sampling and testing, this offers a powerful approach to assess exposure, bioaccumulation, and potential risks faced by different species, as well as human health risks associated with their consumption.

CO2 emissions from a temperate drowned river valley estuary adjacent to an emerging megacity (Sydney Harbour)

The Sydney Harbour Estuary is a large drowned river valley adjacent to Sydney, a large urban metropolis on track to become a megacity; estimated to reach a population of 10 million by 2100. Monthly underway surveys of surface water pCO2 were undertaken along the main channel and tributaries, from January to December 2013. pCO2 showed substantial spatio-temporal variability in the narrow high residence time upper and mid sections of the estuary, with values reaching a maximum of 5650 μatm in the upper reaches and as low as 173 μatm in the mid estuary section, dominated by respiration and photosynthesis respectively. The large lower estuary displayed less variability in pCO2 with values ranging from 343 to 544 μatm controlled mainly by tidal pumping and temperature. Air-water CO2 emissions reached a maximum of 181 mmol C m−2 d−1 during spring in the eutrophic upper estuary. After a summer high rainfall event nutrient-stimulated biological pumping promoted a large uptake of CO2 transitioning the Sydney Harbour Estuary into a CO2 sink with a maximum uptake of rate of −10.6 mmol C m−2 d−1 in the mid-section of the estuary. Annually the Sydney Harbour Estuary was heterotrophic and a weak source of CO2 with an air-water emission rate of 1.2–5 mmol C m−2 d−1 (0.4–1.8 mol C m−2 y−1) resulting in a total carbon emission of around 930 tonnes per annum. CO2 emissions (weighted m3 s−1 of discharge per km2 of estuary surface area) from Sydney Harbour were an order of magnitude lower than other temperate large tectonic deltas, lagoons and engineered systems of China, India, Taiwan and Europe but were similar to other natural drowned river valley systems in the USA. Discharge per unit area appears to be a good predictor of CO2 emissions from estuaries of a similar climate and geomorphic class.

Spatiotemporal Dynamics of Vibrio spp. within the Sydney Harbour Estuary.

Vibrio are a genus of marine bacteria that have substantial environmental and human health importance, and there is evidence that their impact may be increasing as a consequence of changing environmental conditions. We investigated the abundance and composition of the Vibrio community within the Sydney Harbour estuary, one of the most densely populated coastal areas in Australia, and a region currently experiencing rapidly changing environmental conditions. Using quantitative PCR (qPCR) and Vibrio-specific 16S rRNA amplicon sequencing approaches we observed significant spatial and seasonal variation in the abundance and composition of the Vibrio community. Total Vibrio spp. abundance, derived from qPCR analysis, was higher during the late summer than winter and within locations with mid-range salinity (5–26 ppt). In addition we targeted three clinically important pathogens: Vibrio cholerae, V. Vulnificus, and V. parahaemolyticus. While toxigenic strains of V. cholerae were not detected in any samples, non-toxigenic strains were detected in 71% of samples, spanning a salinity range of 0–37 ppt and were observed during both late summer and winter. In contrast, pathogenic V. vulnificus was only detected in 14% of samples, with its occurrence restricted to the late summer and a salinity range of 5–26 ppt. V. parahaemolyticus was not observed at any site or time point. A Vibrio-specific 16S rRNA amplicon sequencing approach revealed clear shifts in Vibrio community composition across sites and between seasons, with several Vibrio operational taxonomic units (OTUs) displaying marked spatial patterns and seasonal trends. Shifts in the composition of the Vibrio community between seasons were primarily driven by changes in temperature, salinity and NO2, while a range of factors including pH, salinity, dissolved oxygen (DO) and NOx (Nitrogen Oxides) explained the observed spatial variation. Our evidence for the presence of a spatiotemporally dynamic Vibrio community within Sydney Harbour is notable given the high levels of human use of this waterway, and the significant increases in seawater temperature predicted for this region.

Metal-contaminated resuspended sediment particles are a minor metal-uptake route for the Sydney rock oyster (Saccostrea glomerata) — A mesocosm study, Sydney Harbour estuary, Australia

Resuspension of surficial sediments is considered a key process influencing bioaccumulation of metals in filter-feeders in the contaminated Sydney Harbour estuary (Australia). However, previous investigations were unable to establish a significant relationship between metals in sediments or suspended particulate matter (SPM) and oyster tissue concentrations. This study used a 60-d laboratory mesocosm experiment to expose Sydney rock oysters, Saccostrea glomerata, to a natural range of SPM concentrations with different SPM-metal concentrations. Dissolved metal concentrations were low and the availability of algae provided as food was constant for all treatments. Tissue metal concentrations of Cu, Pb and Zn increased significantly, however, no relationship was determined between tissue metal concentrations in the oyster and either SPM or SPM-metal concentrations. The results indicated that exposure to resuspended contaminated sediment particles contributed little to the observed metal uptake. Dissolved or algae food sources appear to be more important for metal accumulation in these oysters.

Differential proteomic response of Sydney rock oysters (Saccostrea glomerata) to prolonged environmental stress

Exposure to prolonged environmental stress can have impacts on the cellular homeostasis of aquatic organisms. The current study employed two-dimensional electrophoresis (2-DE) to test whether exposure to impaired water quality conditions in the Sydney Harbour estuary has significantly altered the proteomes of the resident Sydney rock oyster (Saccostrea glomerata). Adult S. glomerata were sampled from four bays in the estuary. Each bay consisted of a “high-impact” site adjacent to point sources of chemical contamination (e.g., storm drains/canals or legacy hotspots) and a “low-impact” site located ∼5km away from point sources. A mixture of environmental stressors differed significantly between high- and low-impact sites. Specifically, PAHs, PCBs, tributyltin, Pb, and Zn were significantly elevated in oyster tissues from high-impact sites, together with depleted dissolved oxygen and low pH in the water column. A 2-DE proteomics analysis subsequently identified 238 protein spots across 24 2-DE gels, of which 27–50 spots differed significantly in relative intensity between high- and low-impact sites per bay. Twenty-five percent of the differential spots were identified in more than one bay. The identities of 80 protein spots were determined by mass spectrometry. HSP 70, PPIB, and radixin were the three most highly expressed differential proteins. Despite the largely unique proteomes evident in each bay, functional annotations revealed that half of the differentially expressed proteins fell into just two subcellular functional categories—energy metabolism and the cytoskeleton. These findings provide a framework to further investigate adaptation of cellular mechanisms to prolonged stress in S. glomerata.

Spatial and rainfall related patterns of bacterial contamination in Sydney Harbour estuary

Water quality in recreational areas in Sydney Harbour, Australia, was analysed first to identify spatial patterns in faecal coliform and enterococci densities, and then to determine the relationship between bacterial densities and catchment rainfall. Non-metric multidimensional scaling separated sites closest to the mouth of the harbour from those further up the harbour's west and north-west arms. Sites closest to the harbour mouth generally had lower frequencies of high bacterial densities that exceeded median water quality guideline values. We attribute this to greater tidal flushing at sites closer to the harbour mouth. Eight site groups were identified within the harbour. Within each group, multiple regression analyses indicated rainfall accounted for between 15 and 66% of the variability in the bacterial densities. Variation in bacterial densities explained by rainfall was lower for sites closer to the harbour mouth where tidal flushing is greatest. Thus, our findings indicate that simple rainfall-based regression models are appropriate for predicting bacterial concentrations when flushing at a site is limited. More complex models incorporating a suite of environmental variables may improve the ability to predict bacterial concentrations at well-flushed sites, but even then, their predictive ability may be low.