Water Renewal Research Articles

On the use of hydrodynamic modelling and random forest classifiers for the prediction of hypoxia in coastal lagoons

Hypoxia is one of the fundamental threats to water quality globally, particularly for partially enclosed basins with limited water renewal, such as coastal lagoons. This work proposes the combined use of a machine learning technique, field observations, and data derived from a hydrodynamic and heat exchange numerical model to predict, and forecast up to 10 days in advance, the occurrence of hypoxia in a eutrophic coastal lagoon. The random forest machine learning algorithm is used, training and validating a set of models to classify dissolved oxygen levels in the lagoon. The Orbetello lagoon, in the central Mediterranean Sea (Italy), has provided a test case for assessing the reliability of the proposed methodology. Results proved that the methodology is effective in providing a reliable short-term evaluation of DO levels, with a high resolution in both time and space throughout an entire lagoon. An overall classification accuracy of up to 91 % was found in the models, with a score for identifying the occurrence of severe hypoxia - i.e. hourly DO levels lower than 2 mg/l - of 86 %. The use of predictors extracted from a numerical hydrodynamic model allows us to overcome the intrinsic limitation of machine learning modelling approaches which rely on input data from relatively few, local field measurements, i.e. the inability to capture the spatial heterogeneity of DO distributions, unless several measuring points are available. The methodological approach is proposed for application to similar eutrophic environments.

Dynamics and correlations of maximum water age zones and nutrients in the Changjiang Estuary, China

The hydrological process dominates the spatial and temporal concentrations of nutrients and other biogeochemical compounds in the large estuary where river and ocean meet. Water age is a measure of water renewal timescale and a characteristic parameter of hydrodynamics and contaminant transport. A large-scale river-sea linked and multi-process coupled 2D EFDC model was constructed from Datong hydrometric station of Changjiang River to the East China Sea. The effects of changes in river discharge on hydrodynamics and nutrients in the Changjiang Estuary were simulated and analyzed. Pollutant loads to the Changjiang Estuary are mainly from upstream inflows and local inputs. The proportion of total phosphorus (TP) loads from upstream is greater than the total nitrogen (TN) loads, accounting for about 90% and 78%, respectively. As the river discharge decreases, TN concentrations decrease in most regions, except for near large sewage discharges where TN concentrations increase while TP concentrations show a decreasing trend. When the river flow drops from over 60000 m3/s to a relatively low value of 10000 m3/s, the average TN concentration in the southern channel of the Shanghai section of the Changjiang Estuary increases by nearly 13%, while TP concentration decreases by nearly 5%. The model results show that the water age inside the river mouth is inversely proportional to the flow rate. In contrast, the water age outside the mouth is negatively with the river discharge. The water age maximum zones (WAMZ) are found in the estuary, ranging from within the estuary to 90 km from the mouth, and are likely to coincide with the positions of the turbidity maximum zones (TMZ), which move seawards or landwards with the increase or decrease of river discharge in the Changjiang Estuary. In addition to location, the value of water age maxima varies negatively with river discharge, which is also relevant to turbidity intensity likely. Water age and WAMZ can be the indicators to predict the changes in the water environment and nutrient sinks in the Changjiang Estuary.

A robust and well-balanced finite volume solver for investigating the effects of tides on water renewal timescale in the Nador lagoon, Morocco

Coastal lagoons, particularly those not well-connected to the sea, are highly susceptible to continuous water retention, adversely affecting water quality and ecosystems. Understanding and quantifying the processes governing water renewal in such semi-enclosed regions is crucial. Using the principles of constituent-oriented age and residence time theory (www.climate.be/cart), we calculated timescales to explain the water renewal process in semi-enclosed areas. To improve our understanding and define the dynamics of the Nador lagoon, we use two distinct time scales: residence time and exposure time. Residence time indicates the length of time a parcel of water leaves the region of interest for the first time, while exposure time represents the overall length of time a parcel of water remains in that region, including any subsequent inflows. The modeling system adopts an Eulerian approach, including two interlinked model components: the shallow-water equations incorporating bottom friction, eddy viscosity, wind shear stresses, momentum diffusion, and Coriolis forces for modeling hydrodynamics, and a transport-diffusion equation utilized to simulate the advection and diffusion of the passive tracer concentration. The entire system is integrated into a high-order finite volume solver that employs unstructured meshes, upwind numerical fluxes, and slope limiters to achieve precise resolution of steep bathymetric gradients that may arise in the approximate solution. The scheme is non-oscillatory and preserves the conservation properties. In this research, we explore various situations related to the connection between the Mediterranean Sea and the Nador lagoon. Specifically, we suggest novel entry points that have the potential to significantly decrease the water residence within the lagoon.

Differential metal and metalloid contents in fresh and cooked Charu mussels (Mytella charruana) from a southeastern Brazilian estuary and associated human health risks

Sepetiba Bay, a key estuarine ecosystem in southeastern Brazil, faces significant metal inputs, with a differential pollution gradient from the bay's entrance to inner areas, raising environmental and public health concerns. This study assessed metal levels in fresh and cooked samples of highly consumed Charu mussels (Mytella charruana) from three bay areas, one near the bay entrance (P1), with higher water renewal rates, one in the northern bay area (P2) and one the eastern bay (P3), presenting lower water renewal rates. Variations in metal and metalloid concentrations across sites were observed, with P3 exhibiting higher levels in fresh mussels for most elements, except for As, which was higher at P2 (0.35 ± 0.45 mg kg−1). Cooked samples demonstrated similar trends for Cu (1.30 ± 0.39 mg kg−1), Ni (0.28 ± 0.20 mg kg−1), and V (0.75 ± 0.28 mg/kg−1), indicating that cooking in contaminanted estuary water does not significantly reduce contamination. Significant differences were detected for Ni, Cd (0.014 ± 0.008 mg kg−1), Zn (14.28 ± 2.50 mg kg−1), and V at P1, which were significantly higher than at P3. Significant Fe (246 ± 68 mg kg−1), Al (109 ± 33 mg kg−1), and Mn increases were observed from P1 to P3. Mussels sampled from P3, near an abandoned military area and urban center, exhibited high Fe and Al levels, attributed to both natural processes and industrial activities. Metal concentrations in Charu mussels often exceeded regulatory limits set by Brazilian, North American, and European agencies. Calculated Se molar ratios indicate that while Se can mitigate Hg toxicity, high Hg levels in Sepetiba Bay's Charu mussels still pose significant health risks. Similarly, high levels of Ag, Cd, and Pb suggest ineffective Se protection. However, Se appears effective against As toxicity. The Health Benefit Value of Selenium (HBVSe) indicate Se's overall protective benefits against Hg toxicity. Higher HBVSe values in cooked mussels at P1 and P2 suggest that cooking increases Se bioavailability. However, raw mussels at P3 had higher HBVSe values than cooked ones, highlighting the need for site-specific assessments. Calculated Hazard Indices indicate general high health risks from mussel consumption, and As levels in Charu mussels indicate high carcinogenic risks. These findings emphasize the need for comprehensive Charu mussel monitoring and environmental management efforts at Sepetiba Bay.

Empowering Aquarists a Comprehensive Study On IOT-Enabled Smart Aquarium Systems For Remote Monitoring And Control

owadays, a lot of people keep fish as pets at home and the aquarium keeper has been feeding the fish in the tanks, therefore appropriate setup and upkeep are required. Taking care of the aquarium appears to be somewhat tough for aquarists. The fish's quality of life depends on the aquarium being kept up properly. Changes in water quality, fish feeding, temperature management, light control, and the challenge of physically inspecting aquarium conditions are these problems are experienced.. As such, it is important to monitor the physical characteristics regularly and to improve the quality of the water. It has water quality management, which levels the aquarium to the perfect conditions by keeping an eye on the physical variations in the tank. Thus, the system that this model suggests is capable of real-time operation and is fitted with sensors. It carries out turbidity system, water renewal, temperature monitoring, and pH level detection in water and all these things are carried out in the ESP32 controller which contains an inbuit WiFi module. For large-scale aquaculture, an embedded system with a wireless network technology and a water quality testing unit was proposed. The aquarium's state is tracked and sent to the user's mobile application via Thingspeak IoT platfrom.

Deciphering the Ages of Saline Water in the Baltic Sea by Anthropogenic Radiotracers

AbstractThe slow water renewal endows the Baltic Sea a strong retention of pollutants/nutrients. Constraining water age is a practical way to depict the transport timescales for water masses and accompanying soluble substances. Although the water ages in the Baltic Sea have been resolved by 3D ocean models 20 year ago, the simulated results have not been verified. In this work, we exploited two anthropogenic radionuclides (129I and 236U) to constrain the ages of inflowing North Sea saline waters into the Baltic Sea by using the Tracer Age and Transit Time Distribution approaches. Our results indicate that the Baltic Sea has a highly stratified structure with a more diffusive bottom circulation and a more advective surface circulation. The circulation timescale for the saline water in the Baltic Sea was estimated to be >30 years from the bottom of Arkona Basin to the surface of central Baltic Sea. This work demonstrates the power of anthropogenic radiotracers in investigating circulation timescale and mixing processes in the Baltic Sea and provides the first observation‐based proof for the multi‐decadal retention of (radioactive) pollutants within the Baltic Sea.

Vertical water renewal and dissolved oxygen depletion in a semi-enclosed Sea

The limited water renewal in semi-enclosed seas may contribute to the oxygen deficiency and thereby may exacerbate the ecological degradation. Previous research has focused more on horizontal water renewal, while the role of vertical water renewal remains poorly documented despite its significance to the bottom oxygen supply. This study explores the vertical water renewal process in the Bohai Sea, a semi-enclosed sea prone to oxygen deficiency, by developing a water age model, incorporated into a developed Delft3D hydrodynamic model. Findings unveiled the key role of thermal stratification, tides, and winds on vertical water renewal. Results revealed significant spatial heterogeneity and seasonal variations in water age in the Bohai Sea. During summer, stratified from the upper water column, the deep basin water age can reach up to 30 days. Thermal stratification was crucial in regulating vertical water renewal, acting as a constraint and impediment. Spring tides and neap tides can positively and negatively influence vertical water renewal by strengthening and weakening thermal stratification, respectively. Wind forces intensified the vertical water exchange by changing the flow field structure. Additionally, higher bottom water age coincides with the oxygen-poor areas and deep-water regions. Based on this, we employed the product of the oxygen consumption rate and the bottom water age (oxygen consumption duration) to approximate oxygen depletion. This method was applied to successfully estimate vertical oxygen depletion in the Bohai Sea. The findings will serve environmental management and oxygen-poor attribution analysis.

Intense lateral intrusion of offshore sub-surface waters in Halifax Harbour

The main physical processes affecting the circulation variability in Halifax Harbour (HH), including the intense lateral intrusion of offshore sub-surface waters into Bedford Basin (BB), are studied using a nested-grid modelling system (NGMS). The annual and monthly mean circulation in HH are characterized by a typical two-layer estuarine circulation, with seaward currents in the upper layer and landward currents in the lower layer, both showing strong temporal and spatial variability. The intense lateral intrusion of offshore sub-surface waters into BB occurs at time scales of a few days. The intense intrusion, in combination with winter connection, is important for the renewal of deep waters in BB. The model sensitivity experiments suggest that the persistent northwesterly winds strengthen the near-surface seaward currents and the lateral intrusion of offshore sub-surface waters into BB. The persistent southwesterly winds can also trigger the lateral intrusion, but are less effective than the northwesterly winds. The southeasterly winds, on the contrary, reduce significantly the seaward currents in the surface layer and prevent the lateral intrusion. The accumulative effects of winds and tides on the 3D hydrodynamics in HH are also examined. Local winds have dominant effects on the 3D currents and temperature/salinity, through driving vertical mixing and coastal upwelling. By comparison, tides play a secondly role in affecting the currents and temperature/salinity in BB but are important in the Narrows.

A Review: Microbes and Their Effect on Growth Performance of Litopenaeus vannamei (White Leg Shrimps) during Culture in Biofloc Technology System.

In the modern era of Aquaculture, biofloc technology (BFT) systems have attained crucial attention. This technology is used to reduce water renewal with the removal of nitrogen and to provide additional feed. In BFT, microorganisms play a crucial role due to their complex metabolic properties. Pathogens can be controlled through multiple mechanisms using probiotics, which can promote host development and enhance the quality of the culture environment. During culturing in a biofloc technology system, the supplementation of microalgae and its accompanying bacteria plays a beneficial role in reducing nitrogenous compounds. This enhances water quality and creates favorable environmental conditions for specific bacterial groups, while simultaneously reducing the dependency on carbon sources with higher content. The fluctuations in the bacterial communities of the intestine are closely associated with the severity of diseases related to shrimp and are used to evaluate the health status of shrimp. Overall, we will review the microbes associated with shrimp culture in BFT and their effects on shrimp growth. We will also examine the microbial impacts on the growth performance of L. vannamei in BFT, as well as the close relationship between probiotics and the intestinal microbes of L. vannamei.

Assessment of the in situ biomethanation potential of a deep aquifer used for natural gas storage.

The dihydrogen (H2) sector is undergoing development and will require massive storage solutions. To minimize costs, the conversion of underground geological storage sites, such as deep aquifers, used for natural gas storage into future underground hydrogen storage sites is the favored scenario. However, these sites contain microorganisms capable of consuming H2, mainly sulfate reducers and methanogens. Methanogenesis is, therefore expected but its intensity must be evaluated. Here, in a deep aquifer used for underground geological storage, 17 sites were sampled, with low sulfate concentrations ranging from 21.9 to 197.8µM and a slow renewal of formation water. H2-selected communities mainly were composed of the families Methanobacteriaceae and Methanothermobacteriaceae and the genera Desulfovibrio, Thermodesulfovibrio, and Desulforamulus. Experiments were done under different conditions, and sulfate reduction, as well as methanogenesis, were demonstrated in the presence of a H2 or H2/CO2 (80/20) gas phase, with or without calcite/site rock. These metabolisms led to an increase in pH up to 10.2 under certain conditions (without CO2). The results suggest competition for CO2 between lithoautotrophs and carbonate mineral precipitation, which could limit microbial H2 consumption.

Training and tool supply to enhance food safety behaviors among ready-to-eat chicken vendors in informal markets in Ouagadougou, Burkina Faso: A randomized-controlled trial

In Burkina Faso, street food vendors are key in ensuring food safety in urban markets, particularly within the poultry value chain. The sale of high-risk ready-to-eat chicken by these vendors poses substantial health hazards, emphasizing the urgency for capacity-building to enhance food safety practices. This study evaluated the effect of a participatory interactive three-day training program coupled with tool supply on self-reported and observed behavior, and knowledge, attitudes, and cognitions of vendors of ready-to-eat chicken meat in Ouagadougou's informal markets. A two-armed RCT was conducted, including pre- and post-training vendor surveys, along with direct outlet observations. Total sample size comprised 162 vendors, with 72 in the treatment group and 90 in the control group. Self-reported behavior - measured on a five-point scale - significantly improved in the treatment group including higher frequency of mask wearing (1.8 ± 0.8 vs 2.5 ± 1.2, p < 0.001) and inspecting nail hygiene (4.3 ± 0.8 vs. 4.7 ± 0.6, p < 0.001). Treatment outlets improved on securing adequate evisceration platforms (1.3 ± 0.6 vs. 1.0 ± 0.5, p = 0.054), regular carcass water renewal (61.8% vs. 36.4%, p = 0.038), and handwashing during carcass management (1.1 ± 0.5 vs. 0.9 ± 0.3, p = 0.008). Better adherence to handwashing (1.1 ± 0.4 vs. 0.9 ± 0.3, p = 0.051), fork use (58.9% vs. 41.8%, p = 0.029), proper handwashing facilities (38.4% vs. 20.9%, p = 0.014), and waste management (64.4% vs. 37.8%, p < 0.001) were observed in treatment outlets. Trained vendors scored significantly higher than controls on knowledge (effect size 0.75, p < 0.001). Vendors rated the perceived usefulness and perceived ease of use, trust in materials/tools - measured on a five-point scale - as high, and perceived mean increased daily profits (21,242 FCFA) and number of customers (8.3) following training. In conclusion, training combined with a tool package proved effective in fostering significant food safety behavior changes, underscoring its substantial impact beyond just knowledge enhancement. For lasting behavior changes, ongoing training and support, an enabling environment, and strong incentives that prioritize vendor food safety behaviors in informal markets are crucial.

Water renewal and stratification modelling in small estuaries

Water renewal and flushing in small, intermittently open or closed estuaries is receiving increasing attention particularly in light of the climate change induced alterations in run-off, wave and sediment transport conditions along coasts. The challenges of predicting the stratification-circulation state and the balance between tidal or freshwater flushing in response to the mouth dynamics of small, wave-dominated estuaries is the focus of the paper. Such predictions are required for determining estuary freshwater requirements or establishing an estuary's capacity to maintain sound water quality under pollutant discharges. Advances in simulating changes in stratification-circulation over long time scales are limited. Instead attention has focused on generating indices of stratification or water quality state using heuristic methods. In this paper, systems dynamics modelling is applied to simulate the non-linear response of the estuary to changes in river and marine water fluxes. The estuary is modelled as a basin with a specified water volume to water level relationship, connected to the sea by a channel with variable sill height, but fixed width. The direction and magnitude of the flow through the mouth determines whether the sill height erodes or accretes and hence the mouth dynamics (see Slinger, 2017). The tidal flux through the mouth co-determines the volumetric exchange of salt, influencing both the stratification state of the estuary and the degree of tidal or freshwater flushing. This is also influenced by run-off. The resulting dynamic balance is captured in two bulk indices, the Estuarine Richardson number and the bulk densimetric Froude number. Using measured data from the Great Brak Estuary, South Africa, the model is calibrated. Model simulations demonstrate the importance of tidal flushing and concomitant mouth breaching for water renewal as freshwater flushing declines under scenarios of increased water abstraction. Although the estuary remains partially mixed, there is increased average salinity and a more uniform the water column. Water releases and mouth breaching bring about a more natural stratification-circulation state, but these effects are short-lived.

Linking northeastern North Pacific oxygen changes to upstream surface outcrop variations

Abstract. Understanding the response of the ocean to global warming, including the renewal of ocean waters from the surface (ventilation), is important for future climate predictions. Oxygen distributions in the ocean thermocline have proven an effective way to infer changes in ventilation because physical processes (ventilation and circulation) that supply oxygen are thought to be primarily responsible for changes in interior oxygen concentrations. Here, the focus is on the North Pacific thermocline, where some of the world's oceans' largest oxygen variations have been observed. These variations, described as bi-decadal cycles on top of a small declining trend, are strongest on subsurface isopycnals that outcrop into the mixed layer of the northwestern North Pacific in late winter. In this study, surface density time series are reconstructed in this area using observational data only and focusing on the time period from 1982, the first full year of the satellite sea surface temperature record, to 2020. It is found that changes in the annual maximum outcrop area of the densest isopycnals outcropping in the northwestern North Pacific are correlated with interannual oxygen variability observed at Ocean Station P (OSP) downstream at about a 10-year lag. The hypothesis is that ocean ventilation and uptake of oxygen is greatly reduced when the outcrop areas are small and that this signal travels within the North Pacific Current to OSP, with 10 years being at the higher end of transit times reported in other studies. It is also found that sea surface salinity (SSS) dominates over sea surface temperature (SST) in driving interannual fluctuations in annual maximum surface density in the northwestern North Pacific, highlighting the role that salinity may play in altering ocean ventilation. In contrast, SSS and SST contribute about equally to the long-term declining surface density trends that are superimposed on the interannual cycles.

Hydrodynamic Modeling of Water Renewal Time and Potential Dissolved Matter Using TELEMAC: Applications to Shediac Bay (New Brunswick, Canada)

This study examines the hydrodynamic regimes in Shediac Bay, located in New Brunswick, Canada, with a focus on the breach in the Grande-Digue sand spit. The breach, which was developed in the mid-1980s, has raised concerns about its potential impacts on water renewal time and water quality in the inner bay. The aims of this study, using mathematical modeling approaches, were to evaluate the flow regimes passing through the breach and influences on the distribution of dissolved matter, providing insights into whether the breach should be allowed to naturally evolve or be artificially infilled to prevent contaminant stagnancy in the bay. The study considered three simulation scenarios to comprehend the water renewal time and the role of the breach in the environmental management of Shediac Bay. Results indicated that completely closing the breach would significantly increase the water renewal time in the inner bay, although the spatial extent of this increase is limited. However, the study identified some limitations, including the need to better define the concentration limit for considering water as renewed and the lack of consideration of dynamic factors such as wind and wave effects.

Half-century trends of radioactivity in fish from Danish areas of the North Sea, Kattegat, and Baltic Sea

This work reports comprehensive time-series datasets over the past 50 years for natural (210Po) and anthropogenic (134Cs and 137Cs) radionuclides in three fish species (cod, herring and plaice) from Danish marine areas covering the North Sea, Kattegat, and Baltic Sea. Impact from the global fallout of atmospheric nuclear weapons testing, radioactive discharges from the European nuclear reprocessing plants and release from Chernobyl accident are clearly detected in the fish samples. While 210Po concentrations in each fish species demonstrated comparable levels across the three regions without notable temporal trends, significantly higher median 210Po concentration was observed in the lower trophic level fish, namely herring and plaice, compared to cod. In contrast, 137Cs concentrations in all three species steadily decrease over time after the Chernobyl-attributed peaks in late 1980s in the entire study area, whereas 137Cs always demonstrated higher concentrations in cod than herring and plaice. Our calculated concentration factors (CFs) for 137Cs in this work indicate that the mean CFs for 137Cs over the past 50 years are significantly different across the three species, following the order of cod < herring < plaice. Based on the time-series data, ecological half-lives (Teco) of 137Cs in fish from Danish marine areas were estimated to evaluate the long-term impact of anthropogenic radioactive contamination in different regions. Our results indicate no significant difference in Teco across different fish species, whereas the weighted mean Teco for fish in the Baltic Sea (29.3 ± 3.9 y) is significantly longer than those of the North Sea (9.8 ± 0.9 y) and Kattegat (11.7 ± 1.2 y), reflecting the strong ‘memory effect’ of the Baltic Sea due to its slow water renewal. However, the dose assessment demonstrates that the contribution of the natural radionuclide 210Po to ingestion dose from fish consumption is 1–2 order of magnitude higher compared to that of 137Cs.

Hatchery practices for Patella aspera and P. ordinaria: evaluating culture vessels requirements

Innovation in limpet production requires knowledge of the optimal qualities and limitations of the culture vessels. Two limpet species from Madeira fishery, Patella aspera and P. ordinaria, were used to evaluate the influence of culture vessel shape (microtubes, test tubes, centrifuge tubes, specimen cups, disposable cups, vials, flasks and beakers), composition (polypropylene and glass), volume (1.5 ml to 1.5 L) and stocking density on oocyte incubation and larval culture through nine assays. Moreover, three assays evaluated the use of microtubes and the isolation of trochophores, instead of pediveligers, for eventual settlement induction. The results showed effective hatching in most culture vessels regardless of composition or volume, except when the shape of the bottom caused oocyte clustering. Larval culture was not influenced by any variable under scrutiny (shape, composition, volume or rearing density). Microtubes were useful for settlement, while the placement of trochophores in the settling vessels, instead of pediveligers, proved inefficient and even led to failed cultures. The best settlement was obtained when the pediveligers were isolated from the water column of the beakers and transferred to clean vessels with renewed water and coralline algae as substrate. The current findings could be extrapolated to other marine invertebrates that share similar life stage requirements.

Water Renewal Time in Lakes with Transformed Water Distribution in the Catchment Areas

Water exchange in lake basins is a very important process in regulating the health of the aquatic environment, e.g., by shaping algal blooms. Thus, knowledge of the process is also required to develop management strategies. The paper presents a dynamic of water renewal time in the Uściwierz chain of lakes, in which the natural hydrological connectivity of the catchment areas has been altered due to human impact. Calculations of water renewal were limited to the part of the lake basin corresponding to the active (dynamic) retention layer. A comparative analysis of the rate of potential water renewal, based on the structure difference index, was used as an indicator of the degree of anthropogenic transformation of water distribution in the lake catchments. The smallest differences in the structure of the water renewal rate between the neighboring lakes in the chain system were observed in the cold period, and the largest differences were observed in the warm period. The results showed that the shorter the timescale (5-day period), the higher the similarity in the structure of the water renewal rate between the lakes. Very large differences between the structure of the potential water renewal rate in Lakes Uściwierz and Bikcze indicated a significant transformation of the water cycle down the lake chain. The water renewal rate proved to be a good indicator of the degree of anthropogenic transformation in the catchments located in close proximity.

Vertical water age and water renewal in a large riverine reservoir

Water quality and hypoxia in lakes and reservoirs are strongly associated with water renewal. Yet vertical water exchange is still not fully understood and challenging to evaluate in highly dynamic systems. Here, we applied a scaling approach using the vertical timescale, vertical water age (VWA), defined as time since a water parcel last touched the water surface. We established a 3D hydrodynamic-based age model to quantify the vertical water renewal in Xiangxi Bay, a tributary bay of the Three Gorges Dam. The integrated effects of hydrodynamic processes like stratification, intruding density currents from the mainstream, and upstream inflow on the vertical renewal were accounted for. Results indicated that the spatial–temporal distribution of VWA in Xiangxi Bay depended on stratification and forms of intruding density currents. Age was large in spring and summer, and small in autumn and winter, reaching a maximum of 25 days in April. The vertical water renewal was faster during bottom intrusions from the mainstream than during middle and surface intrusions. At times, the epilimnion contained old water due to circulations, and the hypolimnion contained young water due to upstream flushing. In contrast to natural lakes, the bottom water was often younger than overlying intermediate waters. This demonstrated that mixed layer depth was insufficient to fully capture the vertical exchange in riverine systems with significant surface/bottom intrusion. The findings suggested VWA as a quantitative measure of vertical water transport in highly dynamic systems and its usability for environmental water management.

Nacre-inspired starch-based bioplastic with excellent mechanical strength and electromagnetic interference shielding

Bioplastics have aroused significant interest in researchers to relieve the serious environmental pollution caused by the ubiquity of petroleum-based plastics. However, it remains a great challenge to construct functional bioplastics with excellent mechanical strength, water resistance, and heat resistance. Inspired by the interesting structure of nacre, a novel starch-based bioplastic was prepared via a self-assembly technique, using 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers modified starch, nano-montmorillonite, and reduced graphene oxide as raw materials. Due to the unique layered structure and rich interfacial interaction, the starch-based bioplastic exhibited excellent mechanical properties, while the tensile strength was up to 37.39 MPa. Furthermore, it represented outstanding water resistance, heat resistance, repairability, renewability and biodegradability. Especially, the starch-based bioplastic demonstrated a strong electromagnetic interference shielding effectiveness (EMI SE), which was higher than 35 dB with a thickness of 0.5 mm. These powerful properties provided the possibility for functional applications of starch-based bioplastics.

Current Circulation and Water Renewal Time in the Enclosed Marine Area of Pagasitikos Basin, Greece

Current Circulation and Water Renewal Time in the Enclosed Marine Area of Pagasitikos Basin, Greece