Influence of suspended sediment front on nutrients and phytoplankton dynamics off the Changjiang Estuary: A FVCOM-ERSEM coupled model experiment

Under embargo until: 2021-12-27High-turbidity water is a common feature in the estuary and inner shelf. Sediment suspension functions as a modulator that directly influences the interactions among nutrients, phytoplankton and other related ecosystem variables. A physical-biological coupling model system was applied to examine the impact of sediment front on interactions among on suspended sediment, vertical mixing, nutrients and phytoplankton over the inner shelf off the high-turbidity, phosphate-limited Changjiang Estuary. The physical model was the Finite-Volume Community Ocean Model (FVCOM) and the biological model was the European Regional Seas Ecosystem Model (ERSEM). Results revealed that in the nearshore region the growth of phytoplankton over the spring-summer seasons was limited by suspended sediments and intensified vertical mixing during the autumn-winter seasons extended the sediment-induced suppression extended offshore to restrict the phytoplankton growth over the shelf. Nutrients were diluted by spreading of freshwater discharge and significantly decreased off the suspended sediment front due to the depletion by the offshore phytoplankton growth. The simulation results showed that although the diatom phytoplankton dominated the Chlorophyll a (Chl-a) concentration, the non-diatom group had a more contribution to the biomass. The relatively high phytoplankton biomass was found over the offshore deep underwater valley area as results of remote advection by the Taiwan Warm Current and weak turbulent mixing.acceptedVersio

Developments in Earth observation for the assessment and monitoring of inland, transitional, coastal and shelf-sea waters

The Earth's surface waters are a fundamental resource and encompass a broad range of ecosystems that are core to global biogeochemical cycling and food and energy production. Despite this, the Earth's surface waters are impacted by multiple natural and anthropogenic pressures and drivers of environmental change. The complex interaction between physical, chemical and biological processes in surface waters poses significant challenges for in situ monitoring and assessment and often limits our ability to adequately capture the dynamics of aquatic systems and our understanding of their status, functioning and response to pressures. Here we explore the opportunities that Earth observation (EO) has to offer to basin-scale monitoring of water quality over the surface water continuum comprising inland, transition and coastal water bodies, with a particular focus on the Danube and Black Sea region. This review summarises the technological advances in EO and the opportunities that the next generation satellites offer for water quality monitoring. We provide an overview of algorithms for the retrieval of water quality parameters and demonstrate how such models have been used for the assessment and monitoring of inland, transitional, coastal and shelf-sea systems. Further, we argue that very few studies have investigated the connectivity between these systems especially in large river-sea systems such as the Danube-Black Sea. Subsequently, we describe current capability in operational processing of archive and near real-time satellite data. We conclude that while the operational use of satellites for the assessment and monitoring of surface waters is still developing for inland and coastal waters and more work is required on the development and validation of remote sensing algorithms for these optically complex waters, the potential that these data streams offer for developing an improved, potentially paradigm-shifting understanding of physical and biogeochemical processes across large scale river-sea continuum including the Danube-Black Sea is considerable

The spatio-temporal distribution and transport of suspended sediment in Laizhou Bay: Insights from hydrological and sedimentological investigations

Suspended sediment transport and deposition are crucial physical processes controlling the geomorphological evolution of estuaries and bays. Specially, under the context of worldwide coastal erosion, knowledge of the spatio-temporal distribution of suspended sediment concentration (SSC) and its associated sediment load have become increasingly important for bay management. However, our understanding of the mechanisms of suspended sediment dynamics continues to be hampered by the lack of high-resolution observations. Here, we present a study of the transport mechanisms and controlling factors of suspended sediment over Laizhou Bay. For this, we conducted continuous measurements of SSC, salinity, temperature, and flow velocity at nine stations throughout Laizhou Bay for one 25-h period during each of the spring and moderate tides. Based on these data, residual current, gradient Richardson numbers, and suspended sediment flux were calculated. Our results indicate that a strong current field occurs near the Yellow River mouth, corresponding to the zone with high SSC. The overall diffusion characteristics of suspended sediment are controlled by the tidal current field. Furthermore, our findings suggest that different degrees of stratification occur in the water column, which inhibit the effective vertical diffusion of suspended sediment; Higher water temperature was the main cause of stronger water column stratification of spring tide than moderate tide. Finally, our results reveal that the type of seabed sediment is an important factor controlling SSC by influencing resuspension flux. We conclude that the primary mechanisms controlling suspended sediment transport in Laizhou Bay are advection and tidal pumping, especially advection. Our research provides both a foundational reference for the sediment source-to-sink process from the Yellow River to the sea, as well as guideline implications for coastal engineering construction and channel dredging

Exploring Himawari-8 geostationary observations for the advanced coastal monitoring of the Great Barrier Reef

Larissa developed an algorithm to enable water-quality assessment within the Great Barrier Reef (GBR) using weather satellite observations collected every 10 minutes. This unprecedented temporal resolution records the dynamic nature of water quality fluctuations for the entire GBR, with applications for improved monitoring and management

Modelling study on hydrodynamics and sediment dynamics in estuarine environment: three case studies in Yalu River Estuary, Darwin Harbour and Batemans Bay in China and Australia

The coastal area is an important geographical unit connecting the ocean and terrestrial environments, with frequent interactions and transformation of energy and materials. An understanding of sediment dynamics is fundamental for studies of estuarine geomorphology, local light attenuation, primary production and ecosystems in coastal areas. Many factors can influence the sediment dynamics in estuaries: the estuarine circulation can influence the sediment transport and contribute to the formation of turbidity maximum zone (TMZ); the strong wave events and tidal currents can increase the bottom shear stress and lead to the seabed and beach erosion, causing damage to the coastal infrastructure. Sediment dynamics in estuaries can be also strongly affected by human activities (such as land reclamation, dredging and channel deepening). Therefore, the hydrodynamics, sediment dynamics and coastal zone management issues are of increasing relevance for local governments and researchers in recent years. In this thesis, three related case studies were conducted on estuarine hydrodynamics after a review of previous studies and an analysis of the characteristics of the estuary. These case studies quantitatively explored the effects of wave, estuarine circulation and human activities on sediment dynamics of two macro-tidal estuaries (the Yalu River estuary and Darwin Harbour in China and Australia) and one micro-tidal estuary (the Batemans Bay in Australia), by using the field measurements and the three-dimensional (3D) Finite-volume Coastal Ocean Model (FVCOM). The model predictions of hydrodynamic and sediment dynamic variables were calibrated against the field measurements, such as the water elevation, current velocity, significant wave height and suspended sediment concentration (SSC). The calibrated model combined with the field data provided a new approach to better understand the mechanisms of the hydrodynamics, sediment dynamics and human activities effect in the coastal areas. In the first study, the baroclinic model in the Yalu River Estuary (YRE) was firstly set up to simulate the along-channel/cross-channel estuarine circulation due to the baroclinic influence, and their effect on the sediment dynamics. The along-channel estuarine circulation was found to exhibit a two-layer structure with landward flow at the bottom layer and seaward flow at the surface layer. The asymmetric tidal mixing (ATM) and density driven flow were found to play the dominant role in generating the along-channel circulation. During periods of low river discharge, the estuarine circulation is mainly driven by ATM, which can transport sediment upstream and trap the sediments near the residual flow null point, combined with strong sediment resuspension there, contributing to the formation of turbidity maximum zone at upper estuary. During wet seasons with high river discharges, the landward residual flow occurred in the lower estuary, mainly caused by strong density and ATM driven flow, which can transport and trap large amount sediment, forming TMZ at lower estuary. The effects of reclamation on estuarine circulation and TMZ was also discussed in this study: a two-layer structure of lateral circulation was found spanning the cross-section, which is mainly induced by the combined effects of Coriolis, non-linear advection and pressure gradients (CAP). After reclamation, due to the westward baroclinic and barotropic pressure gradient forcing, eastward CAP became weaker, inhibiting and weakening the eastward residual flow in the main channel, causing the westward movement of TMZ. The sediment dynamics under wave effects in Darwin Harbour during the monsoon season were simulated and explored in the second study. The modeled SSC in the outer harbour rose dramatically during the monsoon. When the wave forcing was not included, a significantly different SSC distribution was obtained in the outer harbour, showing the importance of waves for the sediment dynamics in the outer harbour. However, there was almost no difference in the inner harbour when waves were not included with wave effects, and the influence of waves on sediment dynamics in the inner harbour was negligible. Our findings show that both Eulerian velocity and tidal pumping dominated the SSC flux in Darwin Harbour. Although sediment flux was landward at the entrance to the harbour during the monsoon due to the result of tidal pumping, the sediment flux formed an eddy at the entrance to the harbour and East Arm, which prevented sediment from being transported into the upper arms. As a result, there was negligible landward sediment flux in the inner harbour during the monsoon. The SSC in the outer harbour was significantly influenced by waves during spring tide even though the tidal range was about 7 m; the combination of tidal currents and waves dramatically increased the bottom shear stress and resuspended large amounts of sediment near the seabed. Therefore, the criterion of Mehta (1988) for neglecting wave forcing in macro-tidal environments is inaccurate, and the effect of waves on the sediment dynamics can still be strong in waters with a large tidal range such as Darwin Harbour. In the third study, the first 3D current-wave-sediment coupled numerical model was set up and applied to simulate the sediment dynamics in the Batemans Bay (BB) during summer and winter in 2018. The formation of the flood-tide delta (FTD) near the Cullendulla Beach and effects of human activities were also explored as a case study. Our model results show that the monthly-averaged residual flow at bottom layer was from outside the tidal inlet into the inner bay in January 2018; when we removed the tidal effect, the model results are similar with model results with wave and tidal effects, indicating the tidal effects is weak in the BB; however, when wave forcing was not included, significantly different hydrodynamic and sediment dynamics patterns were obtained in BB: the residual flow became weaker, especially on the FTD; and due to the absence of wave effects, the bottom stress on the FTD decreased, the magnitude of sediment flux and SSC also dropped dramatically compared with the model results with wave effects, indicating that the strong wave events can cause the increase of wave forcing and the generation of nearshore current. The model results in July 2018 are similar with that in January, but with lower magnitude sediment flux and SSC. This is because the significant wave height in July was slightly lower, and smaller amount of sediment was suspended compared with that in January. Therefore, wave effects played the dominant role in controlling the hydrodynamics in BB, and then influence the sediment dynamics. This conclusion can be applied to other similar partly sheltered micro-tidal estuaries. In addition, we took the FTD near the Cullendulla Beach as an example to understand the dynamic process of the FTD in BB. Based on the model results, we found that the strong wave events can accelerate the erosion of the FTD due to the shallow water depth and large bottom stress. The erosion pattern is similar with the bathymetry change pattern retrieved by Landsat 8. When the water depth of the FTD was eroded to ~2.0 meters, a siltation would be expected to occur (this equilibrium depth of 2.0 m was calculated based on the hydrodynamic and sediment configuration in our study in January 2018). An important result of the study is: the FTD actually developed at the ‘wave shadow areas’ behind the headland in Batemans Bay, which were dominantly controlled by sheltering effects. Despite being termed a ‘Flood-Tide Delta’, ‘Tide’ here is misleading, and a new name of ‘Wave Shadow Shoal’ should be given to describe such wave-dominated coastal features. Furthermore, we also discussed the effect of human activities on Corrigans Beach. We concluded that the construction of the training wall can accelerate the accretion at the northern Corrigans Beach demonstrating the important role human activities play on the hydrodynamics and sediment dynamics in BB

Satellite Ocean Colour: Current Status and Future Perspective

Spectrally resolved water-leaving radiances (ocean colour) and inferred chlorophyll concentration are key to studying phytoplankton dynamics at seasonal and interannual scales, for a better understanding of the role of phytoplankton in marine biogeochemistry; the global carbon cycle; and the response of marine ecosystems to climate variability, change and feedback processes. Ocean colour data also have a critical role in operational observation systems monitoring coastal eutrophication, harmful algal blooms, and sediment plumes. The contiguous ocean-colour record reached 21 years in 2018; however, it is comprised of a number of one-off missions such that creating a consistent time-series of ocean-colour data requires merging of the individual sensors (including MERIS, Aqua-MODIS, SeaWiFS, VIIRS, and OLCI) with differing sensor characteristics, without introducing artefacts. By contrast, the next decade will see consistent observations from operational ocean colour series with sensors of similar design and with a replacement strategy. Also, by 2029 the record will start to be of sufficient duration to discriminate climate change impacts from natural variability, at least in some regions. This paper describes the current status and future prospects in the field of ocean colour focusing on large to medium resolution observations of oceans and coastal seas. It reviews the user requirements in terms of products and uncertainty characteristics and then describes features of current and future satellite ocean-colour sensors, both operational and innovative. The key role of in situ validation and calibration is highlighted as are ground segments that process the data received from the ocean-colour sensors and deliver analysis-ready products to end-users. Example applications of the ocean-colour data are presented, focusing on the climate data record and operational applications including water quality and assimilation into numerical models. Current capacity building and training activities pertinent to ocean colour are described and finally a summary of future perspectives is provided

A gravel-sand bifurcation:a simple model and the stability of the equilibrium states

A river bifurcation, can be found in, for instance, a river delta, in braided or anabranching reaches, and in manmade side channels in restored river reaches. Depending on the partitioning of water and sediment over the bifurcating branches, the bifurcation develops toward (a) a stable state with two downstream branches or (b) a state in which the water discharge in one of the branches continues to increase at the expense of the other branch (Wang et al., 1995). This may lead to excessive deposition in the latter branch that eventually silts up. For navigation, flood safety, and river restoration purposes, it is important to assess and develop tools to predict such long-term behavior of the bifurcation. A first and highly schematized one-dimensional model describing (the development towards) the equilibrium states of two bifurcating branches was developed by Wang et al (1995). The use of a one-dimensional model implies the need for a nodal point relation that describes the partitioning of sediment over the bifurcating branches. Wang et al (1995) introduce a nodal point relation as a function of the partitioning of the water discharge. They simplify their nodal point relation to the following form: s*=q*k , where s* denotes the ratio of the sediment discharges per unit width in the bifurcating branches, q* denotes the ratio of the water discharges per unit width in the bifurcating branches, and k is a constant. The Wang et al. (1995) model is limited to conditions with unisize sediment and application of the Engelund & Hansen (1967) sediment transport relation. They assume the same constant base level for the two bifurcating branches, and constant water and sediment discharges in the upstream channel. A mathematical stability analysis is conducted to predict the stability of the equilibrium states. Depending on the exponent k they find a stable equilibrium state with two downstream branches or a stable state with one branch only (i.e. the other branch has silted up). Here we extend the Wang et al. (1995) model to conditions with gravel and sand and study the stability of the equilibrium states

CIRA annual report FY 2014/2015

Reporting period July 1, 2014-March 31, 2015

Hyperspectral Imaging for Fine to Medium Scale Applications in Environmental Sciences

The aim of the Special Issue “Hyperspectral Imaging for Fine to Medium Scale Applications in Environmental Sciences” was to present a selection of innovative studies using hyperspectral imaging (HSI) in different thematic fields. This intention reflects the technical developments in the last three decades, which have brought the capacity of HSI to provide spectrally, spatially and temporally detailed data, favoured by e.g., hyperspectral snapshot technologies, miniaturized hyperspectral sensors and hyperspectral microscopy imaging. The present book comprises a suite of papers in various fields of environmental sciences—geology/mineral exploration, digital soil mapping, mapping and characterization of vegetation, and sensing of water bodies (including under-ice and underwater applications). In addition, there are two rather methodically/technically-oriented contributions dealing with the optimized processing of UAV data and on the design and test of a multi-channel optical receiver for ground-based applications. All in all, this compilation documents that HSI is a multi-faceted research topic and will remain so in the future