As sediments carried by rivers enter coastal waters, fine particles can reduce the amount of light that reaches the reef through light attenuation. The Fitzroy Estuary - Keppel Bay (FE-KB), being the ...second-largest source of sediments to the Great Barrier Reef (GBR) poses a significant threat to the GBR ecosystem such as coral reefs and seagrass meadows, and biogeochemical cycles that influence water clarity. While monitoring and modelling capabilities for catchment and marine settings are now well-developed and operational, a remaining key gap is to better understand and model the transport, dynamics and fate of catchment derived material through tidally influenced sections of rivers that discharge into the GBR. This study aims to reveal sediment transport in the FE-KB estuary by continuously monitoring the seasonal variability over a year-long period and build a high-resolution model to predict sediment budgets under different scenarios of physical forcing and river conditions. Multiple data sources, including field surveys, historical data, and numerical modelling were used to obtain a detailed understanding of the sediment transport processes during wet (high river flow) and dry (low-to-no river flow) seasons. The use of high-resolution bathymetry and survey data for sediment model parameterization allowed for accurate mapping of the morphological changes, while numerical modeling provided insights into the hydrodynamic and sediment transport processes in the estuary. Observation and model data confirm the existence of a Turbidity Maximum Zone (TMZ) in the FE-KB (approximately 35 – 40 km from estuary head), where the topography plays a critical role in trapping sediments. By utilizing the model, a closed sediment budget was calculated under varying flow conditions and the results were used to determine the estuarine trapping coefficient that ranges from 28% (during extreme wet condition) to 100% (during dry condition) of the total catchment loads. Morphodynamic modelling demonstrated a persistent erosion pattern in the upper reach of the FE. The lower FE and southern tidal creeks serve as a large sediment storage basin during both wet and dry seasons, and sediment is exported and deposited offshore during high river flow conditions.
Rapid urban expansion and increased human activities have led to the progressive deterioration of many marine ecosystems. The diverse microbial communities that inhabit these ecosystems are believed ...to influence large-scale geochemical processes and, as such, analyzing their composition and functional metabolism can be a means to assessing an ecosystem’s resilience to physical and chemical perturbations, or at the very least provide baseline information and insight into future research needs. Here we show the utilization of organic and inorganic contaminant screening coupled with metabolomics and bacterial 16S rRNA gene sequencing to assess the microbial community structure of marine sediments and their functional metabolic output. The sediments collected from Moreton Bay (Queensland, Australia) contained low levels of organic and inorganic contaminants, typically below guideline levels. The sequencing dataset suggest that sulfur and nitrite reduction, dehalogenation, ammonia oxidation, and xylan degradation were the major metabolic functions. The community metabolites suggest a level of functional homogeneity down the 40-cm core depth sampled, with sediment habitat identified as a significant driver for metabolic differences. The communities present in river and sandy channel samples were found to be the most active, with the river habitats likely to be dominated by photoheterotrophs that utilized carbohydrates, fatty acids and alcohols as well as reduce nitrates to release atmospheric nitrogen and oxidize sulfur. Bioturbated mud habitats showed overlapping faunal activity between riverine and sandy ecosystems. Nitrogen-fixing bacteria and lignin-degrading bacteria were most abundant in the sandy channel and bioturbated mud, respectively. The use of omics-based approaches provide greater insight into the functional metabolism of these impacted habitats, extending beyond discrete monitoring to encompassing whole community profiling that represents true phenotypical outputs. Ongoing omics-based monitoring that focuses on more targeted pathway analyses is recommended in order to quantify the flux changes within these systems and establish variations from these baseline measurements.
•Fjord function resolved via high-res sampling, open-water methods and models.•Metabolic balance in tide- and wind-driven fjords depends on regional connectivity.•Synoptic winds drive upwelling and ...corollary processes due to mid-fjord river input.•Salt fingering in Comau Fjord drives nutrient transport and may regulate metabolism.•Climate change will impact carbon storage and aquaculture resilience in fjords.
Biogeochemical cycling in fjords underpins crucial environmental and economic functions including carbon sequestration and food security, and a fundamental understanding of the controls on these cycles is essential for sustainable management of fjords that are facing increasing climate and anthropogenic stressors. However, the interaction of external forcing and local geomorphology in fjords leads to complex coupling that is challenging to measure using traditional methods, particularly in a connected coastal system like the Chiloe Inland Sea (CIS) in northern Patagonia. This study resolves key functional differences between the three major fjords (Reloncaví, Comau and Reñihue) in the CIS using high-resolution sampling of surface waters integrated with regional oceanographic and meteorological observations, models and historic data. The dominant geophysical control varied among the three fjords: river input in Reloncaví Fjord, synoptic winds in Comau Fjord and tidal forcing in Reñihue Fjord. Variable geomorphic characteristics, e.g., orientation and the location of the riverine input, resulted in contrasting physical-metabolic responses between fjords to otherwise similar meteorological and oceanic forcing conditions. Each fjord’s relative location and degree of connectivity to the CIS influenced its internal metabolic balance over synoptic to seasonal scales. In Comau Fjord, the salt fingering form of double diffusive mixing was linked to vertical density structure and wind forcing in the northern CIS; consistent trends in historical data suggest that salt fingering may be an important mechanism for delivery of nutrients to the euphotic zone. The highest metabolic rates in the study region occurred in Reñihue Fjord and were linked to vertical mixing of nutrient-rich waters to the surface in the central CIS. Climate change is predicted to result in decreasing river discharge and weakening zonal winds in northern Patagonia. Therefore, the functional relationships observed in this study imply-two key impacts of these altered forcing conditions in coming decades: 1) a lateral shift in the transfer of planktonic carbon to coastal sediments, i.e., moving landward from the CIS into fjords, and 2) greater biogeochemical variability in fjord surface waters, which will present greater management challenges for aquaculture.
Semiarid estuaries are characterized by pronounced seasonal variability, and a functional understanding of these systems requires constraint of coupled biogeochemical processes and relevant temporal ...and spatial scales. Here, we integrate 2 years of spatial surveys and time‐series measurements to quantify physical, chemical, and biological drivers in the largest estuarine system in the Great Barrier Reef region. During wet season, freshwater inputs of nutrients and sediment to estuaries were dominated by flood pulses, whereas carbonate input was also influenced by groundwater discharge. This carbonate input counteracted the minimum buffering zone that would otherwise occur at low salinities, thereby decreasing system‐wide air‐water CO2 fluxes. Sediment resuspension was a major control on the transformation and transport of material over tidal and seasonal scales. During wet season, tidal resuspension of benthic algae in nearshore mixing zones acted as an autotrophic filter, removing most bioavailable nutrients from the brackish plume. During dry season, upstream transport combined with hypersaline conditions trapped material in upper estuaries where denitrification and net heterotrophy were high. However, the role of sediment transport varied depending on tidal asymmetry and density‐driven circulation. Estuarine regions with large intertidal areas were dominated by salt flat erosion, which showed a diagenetic signature associated with mid‐Holocene swamp sediments. Tidal resuspension of these organic‐rich sediments appeared to be the dominant control on biogeochemical cycling in coastal waters. This study demonstrates that a holistic understanding of coastal ecosystem connectivity and function requires resolution of both along‐axis and water‐column gradients as well as a range of timescales from tidal to geological cycles.
Key Points
Tidal forcing and estuary morphology were the dominant controls on connectivity and the function of filtering and nutrient cycling pathways
Tidal asymmetry combined with baroclinic circulation controlled seasonal sediment fluxes in estuaries influencing metabolic and redox cycling
Erosion of salt flats exports relic organic matter from a long‐term reservoir to waters where frequent resuspension facilitates degradation
Agricultural run-off in Australia's Mackay-Whitsunday region is a major source of nutrient and pesticide pollution to coastal and inshore ecosystems of the Great Barrier Reef. While the effects of ...run-off are well documented for the region's coral and seagrass habitats, the ecological impacts on estuaries, the direct recipients of run-off, are less known. This is particularly true for fish communities, which are shaped by the physico-chemical properties of coastal waterways that vary greatly in tropical regions. To address this knowledge gap, we used environmental DNA (eDNA) metabarcoding to examine fish assemblages at four locations (three estuaries and a harbour) subjected to varying levels of agricultural run-off during a wet and dry season. Pesticide and nutrient concentrations were markedly elevated during the sampled wet season with the influx of freshwater and agricultural run-off. Fish taxa richness significantly decreased in all three estuaries (F = 164.73, P = <0.001), along with pronounced changes in community composition (F = 46.68, P = 0.001) associated with environmental variables (largely salinity: 27.48% contribution to total variance). In contrast, the nearby Mackay Harbour exhibited a far more stable community structure, with no marked changes in fish assemblages observed between the sampled seasons. Among the four sampled locations, variation in fish community composition was more pronounced within the wet season (F = 2.5, P = 0.001). Notably, variation in the wet season was significantly correlated with agricultural contaminants (phosphorus: 6.25%, pesticides: 5.22%) alongside environmental variables (salinity: 5.61%, DOC: 5.57%). Historically contaminated and relatively unimpacted estuaries each demonstrated distinct fish communities, reflecting their associated catchment use. Our findings emphasise that while seasonal effects play a key role in shaping the community structure of fish in this region, agricultural contaminants are also important contributors in estuarine systems.
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•Three estuaries and a harbour were sampled in a wet and dry season.•Seasonal changes in taxa richness and composition of fish communities were observed.•Seasonal changes were correlated to environmental variables such as salinity.•Within the wet season, fish community composition differed among locations.•Variation in the wet season was notably correlated to agricultural runoff.
Satellite imagery, UAV imagery, and geo-referenced underwater photo transects (from the surface) are different methods used in marine monitoring and benthic habitat mapping applications to collect ...observations at different spatial scales. There are however challenges in linking them all together to provide fine-grained mapping and analysis for underwater, benthic habitats with complex geometric and ecological properties. We propose a novel framework called SkySea that offers users access to aligned observational data at multiple spatial scales. SkySea can integrate satellite images (e.g., from SENTINEL-2 at 10m resolution), UAV images (<5cm ground sampling distance), detailed underwater images, 3D reconstruction of the seafloor/benthos from underwater images, and make the data available through a commonly used user interface, such as QGIS. Initial evaluation indicates that the spatial overlay achieves sub-meter-level accuracy, while the underwater 3D reconstruction reaches an average relative error of less than 10% for size estimation with reference objects. We believe that this is a novel and innovative framework to achieve a seamless connection across an enormous gap of scales from satellite images, regional UAV images, local underwater images and local 3D reconstruction of the underwater environment, for benthic habitat mapping. It enables marine biologists to perform survey planning, species mapping, and model validation tasks in an integrated pipeline.
Crown-of-Thorn Starfish (COTS) outbreaks are a major cause of coral loss on the Great Barrier Reef (GBR) and substantial surveillance and control programs are underway in an attempt to manage COTS ...populations to ecologically sustainable levels. We release a large-scale, annotated underwater image dataset from a COTS outbreak area on the GBR, to encourage research on Machine Learning and AI-driven technologies to improve the detection, monitoring, and management of COTS populations at reef scale. The dataset is released and hosted in a Kaggle competition that challenges the international Machine Learning community with the task of COTS detection from these underwater images.
Intercellular transfer of proteins across the immunological synapse is emerging as a common outcome of immune surveillance. We previously reported that target-cell MHC class I protein transfers onto ...natural killer (NK) cells expressing cognate killer Ig-like receptors (KIRs). We now show that, for both murine and human cells, target cells expressing inhibitory MHC class I ligands acquire cognate inhibitory NK receptors. Other cell-surface proteins, but not a cytoplasmic dye, also transferred from human NK cells to target cells across an inhibitory immunological synapse. The number of KIRs acquired from NK cells correlated with the level of expression of cognate MHC class I protein on target cells. Treatment with cytoskeletal inhibitors demonstrated that the target-cell cytoskeleton influences intercellular transfer of proteins in both directions. In contrast to constitutively expressed KIRs, a fraction of acquired KIRs could be removed by mild acid wash, demonstrating a difference between some of the acquired KIRs and constitutively expressed KIRs. An accumulation of phosphotyrosine at the location of the transferred KIRs implies a signaling capacity for NK cell proteins transferred to target cells. Thus, intercellular protein transfer between immune cells is bidirectional and could facilitate new aspects of immune cell communication.
Following efforts from leading centres for climate forecasting, sustained routine operational near-term climate predictions (NTCP) are now produced that bridge the gap between seasonal forecasts and ...climate change projections offering the prospect of seamless climate services. Though NTCP is a new area of climate science and active research is taking place to increase understanding of the processes and mechanisms required to produce skillful predictions, this significant technical achievement combines advances in initialisation with ensemble prediction of future climate up to a decade ahead. With a growing NTCP database, the predictability of the evolving externally-forced and internally-generated components of the climate system can now be quantified. Decision-makers in key sectors of the economy can now begin to assess the utility of these products for informing climate risk and for planning adaptation and resilience strategies up to a decade into the future. Here, case studies are presented from finance and economics, water management, agriculture and fisheries management demonstrating the emerging utility and potential of operational NTCP to inform strategic planning across a broad range of applications in key sectors of the global economy.
Multiple quantum wells (MQW) lattice matched to GaAs consisting of In 0.14 Ga 0.76 As wells balanced with GaAs 0.24 P 0.76 barriers have been used to extend the absorption of GaAs subcells to longer ...wavelengths for use in an InGaP/GaAs/Ge triple-junction photovoltaic cell. Thin barriers with high-phosphorus composition are capable of balancing the strain from the InGaAs wells; thus, creating conditions to allow for thicker wells and for carrier tunneling to dominate transport across the structure. As a result, a larger percentage of the depletion region is occupied by InGaAs quantum wells that absorb wavelengths beyond 875 nm and the indium composition is not limited by thermionic emission requirements. Measurements at elevated temperatures and reverse bias suggest that a thermally assisted tunneling mechanism is responsible for transport through the barriers.
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