Physicochemical conditions in coastal waters off Syndney, central NSW, Australia

The continental shelf off Sydney is narrow and characterized by extensive areas of rocky reef and sandy sediment. The overlying coastal waters are dynamic with a complex current structure. Important oceanographic processes include East Australian Current (EAC) activity, northward propagating coastal trapped waves, local wind driven currents and relatively high frequency internal tides and waves. These produce influences on a wide range of temporal and spatial scales. The activity of the EAC and its eddies has been associated with episodic incursions of waters which can quickly replace large parts of the shelf waters off Sydney. Thermal stratification and the episodic presence of cold, nutrient rich waters intruded from the continental slope are important features of the water column. Thermal stratification of up to 6°C generally exists for all but a few months of the year. Nutrient concentrations are generally low in surface waters but are higher and more variable at depth because of irregular intrusions of slope waters from depths greater than 150–200 m. The trace element levels in surface seawater entering the Sydney area are expected to be extremely low.     

Assessment of the Comparative Toxicity of Sewage Effluent from 10 Sewage Treatment Plants in the Area of Sydney, Australia using an Amphipod and Two Sea Urchin Bioassays

In 1995, Sydney Water Corporation undertook an ecological and human health risk assessment for 10 sewage treatment plants (STPs) that discharge primary (6 STPs) and secondary (4 STPs) treated effluents into coastal waters in the Sydney and Illawarra regions, NSW, Australia. A program of toxicity testing of effluent from the 10 STPs was undertaken to determine the toxic effects of the effluents and as a weight-of-evidence study for the risk assessment.

Three types of bioassays were used to test multiple samples of effluent from each STP. Tests used were the sea urchin (Heliocidaris tuberculata) fertilization and larval development bioassays and the amphipod (Allorchestes compressa) survival bioassay.

Comparing between STPs, primary treated effluent was slightly more toxic than secondary treated effluent for all three tests. The highest toxicity was recorded for those STPs that use primary treatment and discharge to the shoreline. Comparing between tests, the sea urchin fertilization bioassay was slightly more sensitive than the sea urchin larval development bioassay, with the amphipod survival bioassay being the least sensitive.

This paper will describe the results of this toxicity testing program and discuss the application of the study results as weight-of-evidence for the risk assessment study.     

Acoustic scattering in the coastal ocean at Monterey Bay,CA, USA: Fine-scale vertical structures

Fine-structure (centimeters to meters) in vertical profiles of acoustic volume scattering strength is a common and ecologically significant characteristic of the coastal marine water column. The processes that create these structures modify the availability of food and exposure to predation for secondary producers at and below spatial and temporal scales that characterize their daily ambits. Thin acoustic scattering layers may persist for weeks at a particular coastal location, but they may also appear and disappear in only a few hours. These layers are usually evidence of mesozooplankton and micronekton having aggregated at peaks, gradients, or boundaries in the vertical distribution of various water column properties that characterize a marine ecosystem. The behaviors of both predators and prey are implicated in the generation of complex, time-dependent patterns of fine-structure. Specifically, diel vertical migration to layers of prey, isolumes, isotherms, isopycnals, or chemoclines can be responsible for the nighttime formation of thin acoustic layers. Physical processes such as horizontal shear, internal waves, water mass intrusions, tidal forcing, wind mixing of the upper water column, and horizontal advection modify acoustic scattering patterns by changing the vertical distributions of organisms that scatter sound.     

Wave direction shift triggered severe erosion of beaches in estuaries and bays with limited post-storm recovery

Many estuaries contain sandy beaches that provide habitats and offer protective buffers for wetlands and infrastructure, alongside cultural and recreational resources. Research underpinning coastal management tends to focus on tide- and swell-dominated sandy beaches, but little attention is given to beaches in estuaries and bays (BEBs) that exist along a continuum of wind/swell wave, tide and riverine influence. BEBs are subject to less wave energy than open coast locations because of the generally narrow window of directions for which ocean waves can propagate through the entrance. However, when storm wave direction coincides with the orientation of the estuary or bay entrance, waves can penetrate several kilometres inside. Here we focus on eight BEBs in two major bays/estuaries in Sydney, Australia and present observations from before and after a major extratropical storm with waves from an atypical direction in June 2016. We quantify magnitudes of beach erosion and recovery rates for 3 years post-storm. We show that when high-energy storm waves penetrate bays and estuaries, BEBs can undergo up to 100% of subaerial beach erosion. Three years after the storm, only 5 of the 29 (17%) eroded subaerial beach profiles had recovered to their pre-storm volume. This is likely due to the lack of low-frequency, beach-building waves at BEBs under modal weather conditions in between storms, in contrast to open coast beaches. We also show that the recovery of BEBs may be limited by the absence of adjacent sediment reservoirs due to the dominance of tidal processes mid-channel. Our study highlights the unique behaviour of BEBs relative to beaches on the open coast, and that shifting wave direction needs to be considered in long-term beach resilience under climate change. © 2020 John Wiley & Sons, Ltd.     

Biological response to coastal upwelling and dust deposition in the area off Northwest Africa

Nutrient supply in the area off Northwest Africa is mainly regulated by two processes, coastal upwelling and deposition of Saharan dust. In the present study, both processes were analyzed and evaluated by different methods, including cross-correlation, multiple correlation, and event statistics, using remotely sensed proxies of the period from 2000 to 2008 to investigate their influence on the marine environment. The remotely sensed chlorophyll-a concentration was used as a proxy for the phytoplankton biomass stimulated by nutrient supply into the euphotic zone from deeper water layers and from the atmosphere. Satellite-derived alongshore wind stress and sea-surface temperature were applied as proxies for the strength and reflection of coastal upwelling processes. The westward wind and the dust component of the aerosol optical depth describe the transport direction of atmospheric dust and the atmospheric dust column load.     

Environmental variables and their association with faecal coliform and faecal streptococci densities at thirteen Sydney beaches

Environmental variables and their association with faecal coliform and streptococci densities were investigated at a number of Sydney's metropolitan beaches. High variability in faecal coliform and faecal streptococci densities was observed at most beaches. The ability of the various models to explain the observed variation in faecal coliform or streptococci levels was relatively low, although they did provide an insight into the more influential environmental factors involved. Rainfall has the single most important effect on faecal coliform and streptococci densities at Sydney beaches. Whether this is due to increased stormwater runoff at the beaches, increased discharge through the outfalls (both the deepwater ocean outfalls and the few remaining shoreline outfalls), or a combination of both is unclear and is likely to depend on the individual beach being considered. Elevated levels of faecal coliforms and streptococci are still occasionally observed at some beaches, but these levels are usually not as high nor as frequent as they were prior to commissioning of the deepwater outfalls. The significant associations of current and plume entrapment with faecal coliform and streptococci densities at some Sydney beaches suggest that under certain conditions, effluent from the deepwater ocean outfalls can still influence faecal coliform and streptococci densities at these beaches.     

High energy coastal sedimentary deposits; an evaluation of depositional processes in Southwest England

Sediments left by coastal flooding have been observed worldwide and have been variously ascribed to the action of storm surges and tsunami waves. To date, no study has attempted to unequivocally establish on stratigraphical, sedimentological, and palaeoecological grounds the means by which these two different processes might be distinguished in coastal sedimentary sequences. This paper examines the evidence for historical storm surges and tsunamis and shows that both high magnitude events have been documented over the past 250 years in southwest England. Sand layers of varying thickness are present within Holocene lagoonal and peat sequences of several shallow lakes of the Scilly Isles. Detailed analysis of Big Pool, St Agnes, indicates that the basal peats date from around 1000 BP. Within the basal peats are numerous thin sand layers. Above the basal peat is an extensive sand layer 15 to 40 cm thick. The base of this latter layer probably dates from the early to mid 18th century. Particle size, grain surface morphology, diatom, and mineral magnetic studies are used to try and determine the most likely mode of deposition. The results of all analyses are inconclusive, but the weight of evidence suggests that the increasing frequency of thin sand layers in the upper part of the basal peat may be related to the increasing frequency and intensity of Atlantic storms during the Little Ice Age superimposed upon a rising sea level. The thick sand layer may have been deposited by the tsunami wave generated by the Lisbon earthquake of November 1,1755. Due to the difficulties in distinguishing depositional processes in coastal environments known to have been affected by storm surges and tsunami waves, it is suggested that generally accepted sedimentological techniques are inadequate for discriminating depositional processes in coastal environments.     

Detection of anthropogenic Cu, Pb and Zn in continental shelf sediments off Sydney, Australia--a new approach using normalization with cobalt.

Concentrations of Co, Cu, Pb and Zn were determined in 107 surficial sediment samples from the continental margin adjacent to Sydney, Australia. The spatial distributions of trace metals in the sediments and the mud content are similar and increase with greater distance from the coast. In contrast, normalization of the concentrations of Cu, Pb and Zn in the total sediment with Co enables a coastal anthropogenic source to be identified. The spatial distribution of Co-normalized concentrations of Cu, Pb and Zn in total sediment is similar to the distribution of these trace metals in the fine fraction of sediment (<62.5 microm), indicating that Co may be used as a normalizing element for determining contaminant sources in the marine environment near Sydney.     

ST radar observations of atmospheric waves over mountainous areas: a review

Lee and mountain waves are dominant dynamic processes in the atmosphere above mountain areas. ST VHF radars had been intensively used to investigate these wave processes. These studies are summarized in this work. After discussing features of long-period quasi-stationary lee waves, attention is drawn to the frequent occurrence of freely propagating waves of shorter periods, which seem to be more common and characteristic for wave processes generated over mountainous areas. Characteristics of these waves such as their relation to the topography and background winds, the possibility of trapping by and breaking in the tropopause region and their propagation into the stratosphere is investigated. These orographically produced waves transport energy and momentum into the troposphere and stratosphere, which is considered an important contribution to the kinetic energy of the lower atmosphere. The occurrence of inertia-gravity waves in the stratosphere had been confused with lee waves, which is discussed in conclusion. Finally further questions on mountain and lee waves are drawn up, which remain to be solved and where investigations with ST radars could play a fundamental role.     

Review of the potential use of brown algal ecotoxicological assays in monitoring effluent discharge and pollution in southern Australia

The temperate near-shore reefs of southern Australasia possess diverse assemblages of brown algal macrophytes which underpin major grazing and detrital food chains in medium to high energy coastal habitats. These ‘kelp' communities are at risk from effluent discharge with documented decline of macrophyte stands in areas subject to outfall. Recent studies utilising reproductive endpoints of several Australian species in ecotoxicological assays have highlighted their sensitivity to pollution. Results indicate an acceptable degree of reproducibility for assays with variation in response between taxa presumably related to differing habitat requirements and potential for stress resulting from toxicant/pollution exposure. Species studied are drawn from the orders Laminariales and Fucales, with the latter in particular offering substantial scope for further investigation. The greatest diversity of fucoid algae is found in south-eastern Australia and closely related taxa occur in similar latitudes in both the southern and northern hemispheres. The broad distribution of taxa from both taxonomic groups enables ready comparison of assays from disparate locations and offers the potential for simple, routine toxicological testing and habitat monitoring across broad geographic ranges.     

Process study of coastal circulation over the inner Scotian Shelf using a nested-grid ocean circulation model, with a special emphasis on the storm-induced circulation during tropical storm Alberto in 2006

This study examines main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the inner Scotian Shelf (ISS) in June and July 2006 using a nested-grid coastal ocean circulation modeling system known as the NCOPS-LB. The nested-grid system has five relocatable downscaling submodels, with the outermost submodel of a coarse horizontal resolution of (1/12)° for simulating storm surges and barotropic shelf waves over the Eastern Canadian shelf and the innermost submodel of a fine resolution of ～180 m for simulating the 3D coastal circulation and hydrography over Lunenburg Bay of Nova Scotia in the default setup. The NCOPS-LB is driven by meteorological and astronomical forcing and used to study the storm-induced circulation over the ISS during tropical storm Alberto. Model results demonstrate that the coastal circulation and hydrographic distributions over the ISS are affected significantly by tides, local wind forcing, and remotely generated coastal waves during the study period.     

Coastal pollution hazards in southern California observed by SAR imagery: stormwater plumes, wastewater plumes, and natural hydrocarbon seeps

Stormwater runoff plumes, municipal wastewater plumes, and natural hydrocarbon seeps are important pollution hazards for the heavily populated Southern California Bight (SCB). Due to their small size, dynamic and episodic nature, these hazards are difficult to sample adequately using traditional in situ oceanographic methods. Complex coastal circulation and persistent cloud cover can further complicate detection and monitoring of these hazards. We use imagery from space-borne synthetic aperture radar (SAR), complemented by field measurements, to examine these hazards in the SCB. The hazards are detectable in SAR imagery because they deposit surfactants on the sea surface, smoothing capillary and small gravity waves to produce areas of reduced backscatter compared with the surrounding ocean. We suggest that high-resolution SAR, which obtains useful data regardless of darkness or cloud cover, could be an important observational tool for assessment and monitoring of coastal marine pollution hazards in the SCB and other urbanized coastal regions.     

The interaction with suspended and settled sedimentary materials of long-lived radionuclides discharged into United Kingdom coastal waters

Low-level liquid radioactive wastes are routinely discharged under authorization into United Kingdom coastal waters from nuclear reactor sites, from nuclear fuel reprocessing and fabrication plants, and from other facilities connected with the nuclear industries. The effluents contain a wide range of radionuclides, with greatly varying half-lives and in different chemical forms. The receiving environments are also markedly different. All of these factors need to be taken into account in order that the authorizations for discharge are based on a sound knowledge of the underlying environmental science as well as meeting the objectives of radiological protection.The largest research effort has been expended on the longer-lived nuclides discharged from the BNFL plant at Sellafield into the Irish Sea. These studies have focused on such aspects as the nature of the effluent, the dispersion of the soluble nuclides out of the Irish Sea, the retention of other nuclides within it, and the incorporation of radionuclides into settled sediments. Some comparisons have also been made between other sites by observing the concentrations of radionuclides in similar materials, at similar distances, per unit rate of discharge.Although these studies are useful in developing an understanding of the dynamics of radionuclides in coastal environments, it is essential to have a wider and more general knowledge if the long-term consequences of discharging radionuclides—or any other chemical waste—into coastal waters are to be fully evaluated. These consequences are assessed by the use of models which have, necessarily, to simplify many of the processes involved. It is therefore all the more important that the underlying science relating to the nature and behaviour of the wastes, and of the receiving environment, is fully explored, and that the assumptions used in the models can be satisfactorily validated.     

Reflection of equatorial Kelvin waves at eastern ocean boundaries Part I: hypothetical boundaries

A baroclinic shallow-water model is developed to investigate the effect of the orientation of the eastern ocean boundary on the behavior of equatorial Kelvin waves. The model is formulated in a spherical polar coordinate system and includes dissipation and non-linear terms, effects which have not been previously included in analytical approaches to the problem. Both equatorial and middle latitude response are considered given the large latitudinal extent used in the model. Baroclinic equatorial Kelvin waves of intraseasonal, seasonal and annual periods are introduced into the domain as pulses of finite width. Their subsequent reflection, transmission and dissipation are investigated. It is found that dissipation is very important for the transmission of wave energy along the boundary and for reflections from the boundary. The dissipation was found to be dependent not only on the presence of the coastal Kelvin waves in the domain, but also on the period of these coastal waves. In particular the dissipation increases with wave period. It is also shown that the equatorial β-plane approximation can allow an anomalous generation of Rossby waves at higher latitudes. Nonlinearities generally have a small effect on the solutions, within the confines of this model.     

Revising the paradigm of tidal analysis – the uses of non-stationary data

Surface elevation and current records contain non-tidal variance, often dismissed as noise. The processes responsible for the non-tidal component may also modulate the tidal signal, altering its strength and frequency structure. Because of their manner of generation and propagation, internal tides are inherently irregular. The non-stationary character of these and other tidal processes provides an integral and useful property of tidal records, because it provides an opportunity to obtain insights into tidal dynamics and the interaction of tidal and non-tidal processes. It is, moreover, productive to use multiple approaches in analyzing coastal and estuarine tidal processes so that both the time-varying and average frequency content are determined. Only by confronting the causes of non-stationary behaviour in this way can some of the remaining challenges in tidal analysis and prediction be overcome, e.g. shelf and estuarine currents, river tides, internal tides, tide-surge interactions and tidally influenced ecological processes. Several examples illustrate the utility of non-stationary tidal analysis methods.Responsible Editor: Jens Kappenberg     

Modeling seasonal circulation, upwelling and tidal mixing in the Arafura and Timor Seas

The extensive shallow tropical seas off northern Australia, encompassing the Arafura and Timor Seas, have been identified as one of the most pristine marine environments on the planet. However, the remoteness and the absence of major industrial development that has contributed to this status have the additional consequence that relatively little is known about these systems. This study is the first to model oceanographic conditions across the tidally dominated Arafura and Timor Seas, and their seasonal variability. The results are based on a high-resolution (0.05°) ocean circulation model forced by realistic winds, waves and tides. The main focus of the study is on physical processes that influence the distributions of sediments and primary productivity across the system. Regions of high bottom stress and tidal mixing have been identified, including a large offshore area around Van Diemen Rise (Timor Sea). Lagrangian particle tracks have revealed a seasonal overturning cell that stretches across the Gulf of Carpentaria (Arafura Sea) with upwelling and downwelling on either side of the Gulf. The presence of coastal upwelling and downwelling is shown to provide a dynamically consistent explanation for the persistent turbid boundary layer observed around the shallow coastal waters of the Gulf.     

Erosion and accretion processes in a muddy dissipative coast,the Chao Phraya River delta,Thailand

Seasonal variation in seabed elevation in the muddy intertidal zone of the Chao Phraya River delta, an area of serious coastal erosion for 40 years, was assessed using information on waves and tides predicted by numerical simulations. The study area is under the influence of the Southeast Asian monsoon climate and lies in the innermost part of a sheltered gulf, across which a low‐gradient slope has developed. Observations, aimed at evaluating the effectiveness of a prototype breakwater on mitigating coastal erosion, indicated that the seasonal variation in the seabed elevation, typically about 30 cm, was caused primarily by seasonal changes in wave direction and height. The breakwater seems to have contributed to a net rise in the seabed level at sites behind the structure. Seabed erosion was most apparent during the northeast monsoon, when waves are weak. Erosion under this low wave energy state was attributed to the combined effect of wave breaking and the low tidal level. A difference in the observed seabed accretion rate between the transitional intermonsoon period and the succeeding southwest monsoon period was attributed to the direction of the wave energy flux; offshore sediments seem to have been supplied efficiently to the study area by waves during the transitional period. Another potential cause of seabed erosion and accretion during the wet southwest monsoon season was the discharge of water and sediments from local canals associated with intense tropical rainfall; this discharge seems to be linked to land use in the coastal area. The results of this study show the importance of monitoring across‐shore sediment transport for better understanding of coastal erosion processes. Copyright © 2010 John Wiley & Sons, Ltd.     

The December 26, 2004, tsunami on Sumatra Island as a source of internal gravity waves in the earth’s atmosphere

Records of the coastal mareographs during the December 26, 2004, tsunami are used to study the fine structure of the tsunami wave power spectra. It is shown that a series of maxima is observed in their spectra near the source in a range of internal gravity wave frequencies of 0.2–1.2 mHz, which coincides with the frequencies of the natural oscillations of the Earth. This experimental finding enables us to propose a possible physical mechanism for the formation of tsunami waves as a result of oscillations in the sea bottom at these frequencies. Internal gravity waves in the Earth’s atmosphere excited in this way are found in the variations of the total electron content that resulted from this powerful earthquake.     

Observations of physical effects from tsunamis of December 30, 2002 at Stromboli volcano, southern Italy

On December 30, 2002, following an intense period of activity of Stromboli volcano (south Tyrrhenian Sea, Italy), complex mass failures occurred on the northwest slope of the mountain which also involved the underwater portion of the volcanic edifice for a total volume of about 2–3×10⁷ m³. Two main landslides occurred within a time separation of 7 min, and both set tsunami waves in motion that hit the coasts of Stromboli causing injuries to three people and severe damage to buildings and structures. The tsunamis also caused damage on the island of Panarea, some 20 km to the SSE from the source. They were observed all over the Aeolian archipelago, at the island of Ustica to the west, along the northern Sicily coasts to the south as well as along the Tyrrhenian coasts of Calabria to the east and in Campania to the north. This paper presents field observations that were made in the days and weeks immediately following the events. The results of the quantitative investigations undertaken in the most affected places, namely along the coasts of Stromboli and on the island of Panarea, are reported in order to highlight the dynamics of the attacking waves and their impact on the physical environment, on the coastal structures and on the coastal residential zone. In Stromboli, the tsunami waves were most violent along the northern and northeastern coastal belt between Punta Frontone and the village of Scari, with maximum runup heights of about 11 m measured on the beach of Spiaggia Longa. Measured runups were observed to decay rapidly with distance from the source, typical of tsunami waves generated by limited-area sources such as landslides.     

Effect of offshore waves and vegetation on the sediment budget in the Virginia Coast Reserve (VA)

The potential for rapid coastline modification in the face of sea-level rise or other stressors is alarming, since coasts are often densely populated and support valuable infrastructure. In addition to coastal submergence, nutrient-related water pollution is a growing concern for coastal wetlands. Previous studies found that the Suspended Sediment Concentration (SSC) of coastal wetlands acts as a first-order control of their sustainability, but SSC dynamics are poorly understood. Our study focuses on the Virginia Coast Reserve (VCR) Long Term Ecological Research (LTER) site, a shallow multiple tidal inlet system in the USA. We apply numerical modelling (Delft3D-SWAN) and subsequent analyses to determine SSC dynamics within the VCR. In particular, we consider two important controls on SSC in the system: vegetation (seagrass and salt marsh) and offshore waves. Our results show that vegetation colonies and increased wave energy lengthen water residence time. The reduction in the tidal prism decreases SSC export from the bay via tidal inlets, leading to increased sediment retention in the bay. We found that alongshore currents can enhance lagoon SSC by importing fine sediments from an adjacent inlet along the coastline. Our numerical experiments on vegetation seasonality can improve the understanding of wave climate impact on coastal bay sediment budget. Offshore waves increase sediment export from coastal bays, particularly during winter seasons with low vegetation density. Therefore, our study can help managers and stakeholders to understand how to implement restoration strategies for the VCR. © 2020 John Wiley & Sons, Ltd.