River Inlet Research Articles

Hydrological connectivity controls on the dynamics of particulate organic matter in a semi-enclosed mariculture bay

Semi-enclosed bay provides favorable conditions for mariculture, however, mariculture activities can disrupt hydrological connectivity of river-coastal continuum and create a bioreactor for particulate organic matter (POM). The impacts of increasing mariculture activities on POM dynamics, including sources, transportation, and transformation, associated dissolved oxygen and nutrients in semi-enclosed bays remain unclear. This study investigated carbon and nitrogen contents, as well as the stable isotopic compositions of POM (δ13CPOC and δ15NPN) in a semi-enclosed bay, Sansha Bay, which is the largest mariculture bay for large yellow croaker in China and is influenced by riverine input and nearshore coastal waters. Our findings revealed that, spatially, riverine POM dominated along main channel that connects river inlet and bay outlet under the influence of water mixing (C:N ratios ∼ 5.7–15.8, δ13CPOC ∼ −21‰--24‰, and δ15NPN ∼ 13‰-17‰). On top of water mixing, autochthonous POM dominates in off-main channel (C:N ratio 5–9, δ13CPOC -21‰--17‰, and δ15NPN 7.0‰-8.5‰). Using a three end-member isotopic mixing model, our data shows that the POM in main channel comprises ∼ 90% of riverine POM and ∼ 10% of phytoplankton production, while in off-main channel, ∼ 59% of POM was contributed by autochthonous phytoplankton production and the rest ∼ 41% was sourced from main channel. Furthermore, riverine POM degradation consumes oxygen along main channel, forming consistent with the classic Redfield stoichiometry of aerobic respiration (N:O2, ∼ 0.13 ± 0.02). In contrast, in off-main channel where water exchange is slower, the degradation of fish feed regenerates dissolved inorganic nitrogen, which subsequently stimulates phytoplankton production, leading to oxygen production following the canonical Redfield stoichiometry of phytoplankton photosynthesis (N:O2, ∼ 0.10 ± 0.01). Our results highlight the influence of hydrological connectivity, superimposed by mariculture activity, in shaping POM biogeochemistry and dissolved oxygen dynamics in semi-enclosed bays. These findings provide important insights for the remediation of risks of hypoxia and harmful algal blooms in coastal mariculture ecosystems.

Spatial and temporal distribution of heavy metals pollution and risk indices in surface sediments of Gomal Zam Dam Basin, Pakistan.

Sediments were considered a sink and potential source of heavy metals in the aquatic system. For this purpose, the present study examined surface sediments for spatial and temporal variation of heavy metals pollution and risk indices in the Gomal Zam Dam Basin (GZDB), Pakistan. Sediment samples (n = 20) were collected from the GZDB, i.e., Gomal Zam Dam, its inlets, and outlets in the winter and summer seasons of 2020, and examined for heavy metals such as zinc (Zn), nickel (Ni), manganese (Mn), lead (Pb), chromium (Cr), copper (Cu), iron (Fe), and cobalt (Co) concentrations. Among GZDB, results showed that the Zhob River Inlet had a higher levels of heavy metals in both seasons. The results revealed that pollution load index values were < 1, observing no pollution in the aquatic system. The risk indices values revealed that sampling sites showed no or very low risk during the summer, 84% of samples showed no or very low risk during the winter, and the rest noted withreasonable risks. Winter seasonshowed higher average values of contamination and risk indices than summer. Statistical analyses revealed that the heavy metals contaminations were mainly due to geogenic sources of rock weathering and ore deposits, with minor contributions from anthropic activities. This study recommends regular monitoring of temporalstudies on heavy metals contamination in the water of the GZDB.

Relating Lake Circulation Patterns to Sediment, Nutrient, and Water Hyacinth Distribution in a Shallow Tropical Highland Lake

Excess sediment and nutrient losses from intensifying agriculture degrade water quality and boost plant growth. The relationship between circulation patterns, spatial water quality degradation, and water hyacinth infestation is not adequately studied. The objective of this study is, therefore, to investigate the effect of lake circulation patterns on sediment and nutrient distribution and its implication on the spread of water hyacinth in a tropical lake. This study was carried out in Lake Tana, the largest freshwater lake in Ethiopia, where sediment and nutrient concentrations are increasing, and water hyacinths have become a challenge since 2011. The lake circulation pattern was simulated by the Delft3D model based on a bathymetry survey, discharge, and meteorological forcings. To predict the transport path of sediments and dissolved nutrients, an inert tracer was released in the four main river inlets of the lake. Observed lake water level measurements were used to validate the model. Our results show that the lake circulation pattern could explain the transport path of sediment and nutrients and the location of the water hyacinths found in the northeast of the lake. Sediments and nutrients from the largest river, Gilgel Abay, in the southeast of Lake Tana, flow through the two outlets nearby with little sediment deposition due to the relatively short retention time. The phosphorus-rich sediments of the 24 h at 105 °C remaining three main rivers joining the lake at the north and east are transported to the northeast. Thus, the management and control of water hyacinths should focus on the northern and eastern catchment areas of Lake Tana.

Microplastic Contamination in Waters and Sediments in the Selorejo Reservoir, Malang Regency, East Java

Microplastics are small plastic particles under 5 mm in size that have contaminated a lot of ecosystems, both aquatic and on land. The existence of heaps of garbage and the existence of fishing activities around residential areas are some examples of anthropogenic activities that are on the edge and water bodies of the Selorejo Reservoir. This study aims to observe the contamination of various types of microplastics and their abundance in water and sediment samples taken from the Selorejo Reservoir. Sampling was carried out using the selected method (purposive sampling) at five different stations, including the Konto River inlet, Kwayangan River inlet, settlements (blendrang), tourism areas, and reservoir outlets. Each station has 3 transects (as replicates) and about 100 liters of water and 1000 grams of sediment are taken. Destruction of water and sediments uses 30% H2O2 and 30% H2SO4 acid to remove organic components that are still attached and to facilitate observation under a stereo microscope with 400X magnification. Based on the results of an analysis of the abundance of microplastics in the waters of each station, the highest abundance of microplastics was successively found in the Konto river inlet with a total abundance value of 39.27x101 particles/liter, then in the residential part (blendrang) a number of 35.34x101 particles/liter, tourist areas 33.67x101 particles/liter, outlet 30.36x101 particles/liter and Kwayangan river inlet 29.67x101 particles/liter. Meanwhile, the highest total abundance of microplastics found in sediments in the Selorejo Reservoir was found successively in the Konto river inlet with a total abundance value of 3.68 particles/gram, then in the tourist area 2.08 particles/gram, in the Kwayangan river inlet 1.56 particles/gram, in the residential part (blendrang) a number of 1.2 particles/gram and outlets 1.12 particles/gram. Each type of microplastic is then counted based on the amount found. The results of the identification of microplastic contamination in waters and sediments in the Selorejo Reservoir found several types of microplastics, namely fibers, fragments, filaments, and films. The dominating type and color of microplastic is black fiber.

IDENTIFIKASI TIPE DAN KELIMPAHAN MIKROPLASTIK PADA IKAN NILA (Oreochromis niloticus) DI WADUK LAHOR KABUPATEN MALANG JAWA TIMUR

Plastics can be degraded into microplastics and easily to dispersed in waters, including reservoirs as water damming locations. Lahor Reservoir is known to be used as a location for aquaculture, one of which is nile tilapia (Oreochromis niloticus) and is fed by the Lekso river, Lahor river, and Dewi river. This certainly increases the potential for microplastic contamination and has a negative impact on aquatic biota and humans. The purpose of this study was to determine the potential for microplastic contamination in the digestive tract of nile tilapia in Lahor Reservoir, Malang Regency, East Java. The study was conducted at 4 sampling stations including Lekso river inlet, Lahor river inlet and Dewi river, Residential area of Karangkates village, and Lahor Tourism Park. 5 Fishes samples were taken at each station and the repetition process was carried out 3 times. Sample preparation with 20 ml of 30% HzO2 solution and 20 ml of 10% KOH. Identification types and abundance of microplastics was carried out with a 40× magnification stereo microscope. The results showed the discovery of several types of microplastics which is fiber, filament, fragment, and film and the highest total abundance value of microplastics was found in the Lahor river inlet and Dewi river at 6.47 particles / individual.

Distribution, sources and influencing factors of organic carbon in the surface sediments of the coastal tidal flats in Jiangsu Province

Coastal tidal flats are situated in the interaction zone between the ocean and land and are vulnerable to natural changes, human activities, and global changes; these areas serve as an important mixing zone and burial area for carbon and nitrogen storage. Coastal tidal flats contribute significantly to the global carbon cycle due to their high biological productivity, high sedimentation rate, and low decomposition rate. However, there is a lack of research on the sources and influencing factors of organic carbon in surface sediments in the coastal tidal flat area of Jiangsu Province. In this study, fourteen surface sediment samples were collected from the Jiangsu coastal tidal flats, and the distribution of organic carbon was analyzed. The sources and influencing factors of sediment organic carbon were also investigated by analyzing the contents, ratios and stable isotopes of carbon and nitrogen in the sediments. The results indicated that the total organic carbon (TOC) and total nitrogen (TN) contents in the surface sediments of Jiangsu coastal tidal flats ranged from 0.09% to 0.82% and from 0.01% to 0.1%, with mean values of 0.36% and 0.04%, respectively, and that there was a significant positive correlation between TOC and TN. Moreover, the high-value areas were located mostly along the borders or in sections covered in vegetation, whereas the mudflat areas without vegetation had lower values. Considering the status of the Jiangsu coastal zone, the abandoned Yellow River estuary, Yangtze River inlet, marine benthic microalgae, C3 plants and C4 plants were selected as end members of organic carbon concentrations. The contributions of different sources were quantified using a Bayesian mixture model (MixSIAR). Among them, the abandoned Yellow River estuary and Yangtze River inlet contributed 28.1% and 19.3%, respectively, followed by marine benthic microalgae with a contribution of 26%, whereas C3 and C4 plants made limited contributions of 9% and 8.8%, respectively. Additionally, the sediment particle size, hydrodynamics, and tidal flat vegetation such as Spartina alterniflora were the key factors influencing the organic carbon distribution. In general, this study contributes to a better understanding of the biogeochemical processes and sources of organic carbon in coastal tidal flats. It also provides a solid foundation for the creation of carbon sink measures in nearshore tidal flats.

Variational RANS modeling of hydraulic jumps

The hydraulic jump is a phenomenon which frequently appears in nearshore, estuarine and riverine regions; it plays a major role for example in the development and migration of sand waves in mobile beds, and in controlling the propagation of infra-gravity water waves from the nearshore into the river through bar-built, shallow estuaries. Although the prediction of these natural flows becomes crucial in many circumstances, it is difficult because hydraulic jumps are complex flows, and their modeling is far from simple. The steady-state hydraulic jump may be undular or broken, and their physical properties differ significantly. Undular jump profiles are dominated by the deviation of the fluid pressure from hydrostatic conditions, with turbulence playing a secondary role. In contrast, broken hydraulic jumps are determined by the differential advection of momentum due to breaking, and turbulence stresses. Between both types, there is a complex transition involving the interaction of non-hydrostaticity and turbulence, which is difficult to mimic with depth-averaged models. Simulations of these flows are typically conducted by resorting to vertically-averaged models either using the Saint-Venant or the Serre-Green-Naghdi equations, but none of them are fully satisfactory. In this work, an alternative approach for hydraulic jumps is proposed by developing a variational Reynolds-Averaged Navier-Stokes (RANS) model which uses Kantorovich-Krylov expansions of the flow variables, and a novel depth-averaged, eddy viscosity approach suitable for non-hydrostatic flows. The model is validated through results of simulations of both undular and broken jumps compared against detailed experiments. New experiments were conducted in a simplified bar-built shallow river inlet; the variational RANS model was found to reproduce well the flow profile over the bar, the hydraulic jump position and dynamic pressures over the bar surface.

Analysis of retaining walls along the Beas River’s meandering curve

In the field of river engineering, complex flow behavior emerges at acute bends in waterways such as rivers or streams. Thus, understanding the flow structure, especially along the banks, is critical. Due to the river's turbulence, obtaining all necessary details through field observation and lab experiments is challenging, time-consuming, and expensive. Computational fluid dynamics (CFD) is a common approach used to predict flow behavior and analyze water retention structures. The site of the meandering bend of the Beas River is located in Mandi town, in the Mandi district of H.P. The geometry of the site is curvilinear, and a retaining wall is to be constructed there. The retaining wall along the left side of the river is 490 m long, while the right-side wall is 495 m. The river's inlet width is 90 m, and the outlet width is 95 m. The channel depth is 5 m, and the channel geometry bed slope is constant throughout the river's length [1]. The Reynolds-averaged Navier-Stokes (RANS) equations are solved using the standard k-ω turbulent model, and numerical simulations are performed using ANSYS FLUID FLUENT. The results indicate that as the length of the retaining wall increases, the wall shear stress increases up to a certain length, then decreases towards the outlet. Additionally, the inner bank, or convex side, of the meandering curve always has a higher longitudinal velocity, while the inner side, or concave side, has a lower longitudinal velocity [2].

Spatial Distribution of Microplastics in Water and Sediments of Main Rivers in Taihu Lake Basin

Contemporary research on microplastic pollution has mainly focused on the ocean as a large sink, with a few studies involving relatively small sinks such as inland rivers and lakes. Taihu Lake is a typical inland lake and is the third largest freshwater lake in China. In this study, the spatial and temporal distribution, abundance, particle size, polymer composition, and ecological risk indices of microplastics in the water and sediments of 15 major inlet rivers in the Taihu Lake basin were investigated. The abundance of fibrous microplastics was the highest among the four characterized microplastic types. The particle size of microplastics in the water column and sediment was mainly in the range of 20–200 μm. The main component of microplastics in the water column was polyurethane, while in the sediment the main component of microplastics was polyurethane. Fibrous microplastics with a principal size of 20–100 μm are the main component of microplastics in landscape river sediments. The navigable rivers had the highest abundance of microplastics. All three river types have an environmental risk rating of III, which is at a medium to high level. The results of this study provide a reliable basis for the study of this sink in inland lakes.

Modelling compound flooding: a case study from Jakarta, Indonesia

The paper investigates compound flooding from waves, sea surge and river flow in northern Jakarta, Indonesia, which is a global hotspot of flooding, by combining process-based coastal and river models. The coastal hydrodynamic modelling of Jakarta Bay in Indonesia shows that coastal storms can lead to a substantial increase in sea water level due to wind and wave setup in the nearshore areas, including Muara Angke river inlet. The compound flood hazard from a range of flood scenarios was simulated and analysed. The results reveal that low-lying areas around the river inlet are prone to flooding even during regular, low-intensity storm events, while rarer storms caused extensive floods. Floods were not caused by direct overwashing of sea defences but by overspill of the banks of the river inlet due to high sea water level caused by wind set up, wave setup, and sea surge obstructing the drainage of the river and elevating its water level during storms. We also found that the sea level rise combined with rapid land subsidence will inundate the existing coastal flood defences during storms in future. The majority of the city will be below mean sea level by 2100. The overflow of existing coastal defences will lead to extensive flooding in northern, western, and eastern Jakarta unless the defences are upgraded to keep up with future sea level rise.

Occurrence Distribution and Risk Assessment of Organophosphate Esters in A Typical Area of the Estuary in the Yellow River Basin

As a type of emerging pollutant, organophosphate esters (OPEs) have the characteristics of toxicity, persistence, and bioaccumulation. Due to their wide use in production and life, OPEs pose potential risks to ecosystems when they enter the environment. In this study, the concentrations of 14 species of OPEs in surface water were determined using UPLC-MS/MS, and the spatial distribution of the OPEs in the surface water of the estuary of the Yellow River basin was further analyzed. The pollution sources were analyzed using correlation analysis and principal component analysis, and the ecological risk was evaluated. The results indicated that the concentration of Σ14OPEs in surface water ranged from 183.81 to 1674.52 ng·L-1, with an average concentration of 638.25 ng·L-1. Tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propanyl) phosphate (TCPP) were the main OPEs. The Xiaoqing River flowing through the urban area differed from the main stream of the Yellow River and other branches in terms of OPEs composition characteristics, which showed a greater impact from human activities. The distribution of Σ14OPEs showed an obvious regional pattern, with a trend of increasing and then decreasing along the direction of the Yellow River inlet. The results of source analysis revealed that human activities such as industrial wastewater discharge from different industries, transportation, and atmospheric deposition were the sources of OPEs in surface water. The ecological risk assessment results indicated that TCEP posed a high risk to aquatic organisms in the main stream of the Yellow River, Xiaoqing River, and Zhimai River, and tri-n-butyl phosphate (TnBP) and triphenyl phosphate (TPhP) posed a low risk at some sites.

Scenario-based modelling of waves generated by sublacustrine explosive eruptions at Lake Taupō, New Zealand

Abstract. Volcanogenic tsunami and wave hazard remains less understood than that of other tsunami sources. Volcanoes can generate waves in a multitude of ways, including subaqueous explosions. Recent events, including a highly explosive eruption at Hunga Tonga-Hunga Ha'apai and subsequent tsunami in January 2022, have reinforced the necessity to explore and quantify volcanic tsunami sources. We utilise a non-hydrostatic multilayer numerical method to simulate 20 scenarios of sublacustrine explosive eruptions under Lake Taupō, New Zealand, across five locations and four eruption sizes. Waves propagate around the entire lake within 15 min, and there is a minimum explosive size required to generate significant waves (positive amplitudes incident on foreshore of &gt; 1 m) from the impulsive displacement of water from the eruption itself. This minimum size corresponds to a mass eruption rate of 5.8×107 kg s−1, or VEI 5 equivalent. Inundation is mapped across five built areas and becomes significant near shore when considering only the two largest sizes, above VEI 5, which preferentially impact areas of low-gradient slope. In addition, novel hydrographic output is produced showing the impact of incident waves on the Waikato River inlet draining the lake and is potentially useful for future structural impact analysis. Waves generated from these explosive source types are highly dispersive, resulting in hazard rapidly diminishing with distance from the source. With improved computational efficiency, a probabilistic study could be formulated and other, potentially more significant, volcanic source mechanisms should be investigated.

Influence of dyke-type causeway on Urmia Lake (NW Iran); insights from water physico-chemical parameters seasonal (2019) changes

The Urmia Lake in NW Iran, the world’s second-largest hypersaline lake, has been exposed to rapid water level fall in the last two decades due to water resources mismanagement, building up of dams on inlet rivers, and the causeway construction in the lake. This human intervention has divided the lake into northern and southern parts and caused an extreme disturbance in the hydro-chemical and hydrodynamic systems, namely current direction reversal.To fully understand the current situation, water depth and lake surface and deepwater physico-chemical parameters (i.e. density, temperature, acidity, electrical conductivity, and total dissolved solids) are analysed in the wet and dry seasons of 2019. In the wet season, deepwaters have a higher density than surface waters, and the northern part of the lake contains denser water compared to its southern counterpart. The formation of density gradients creates an anticlockwise direction lake current. Deepwaters show higher electrical conductivity and total dissolved solids than surface waters in the wet season. Unlike the wet season, the lake water becomes more homogenised due to wave action and evaporation in the dry season. Our study clearly demonstrates that the water passageway of the causeway does not allow for a complete yearly balance between water and sediment exchange. Results suggest that the northern and southern parts of the lake have almost independent hydro-chemical and hydrodynamic systems. In the undeniable reality of global warming trends, anthropogenic interventions into sensible ecologic systems need to be better planned if we were to prevent the ecological disasters we now have to face.

Large Methane Emission from the River Inlet Region of Eutrophic Lake: A Case Study of Lake Taihu

Lakes are important natural sources of atmospheric methane (CH4), which should be considered in global CH4 budget estimations. However, the CH4 emissions from lakes can be highly variable, and the emissions from the river inlet region were less studied, which seriously hamper our understanding of CH4 budget estimates of lakes. Here, field measurements from over six years (2012 to 2017) at Lake Taihu, a large eutrophic shallow lake with a complicated river network, were conducted to address the issue. Results show that the river inlet region of the lake was a hot spot of CH4 emission. The CH4 emission at the river inlet region with an annual mean value of 0.183 mmol m−2 d−1 was seven times higher than that at pelagic region (0.028 mmol m−2 d−1). Peak CH4 emission occurred in warm seasons, and the lowest in cold seasons at the pelagic region, but peak emission occurred in cold seasons at the river inlet region. The seasonal CH4 emission at the pelagic region can be explained by water temperature; however, less temperature dependency of CH4 emission at the river inlet region was found. The variability of CH4 emission was linked to pollution loadings, and CH4-rich water in the inflowing river likely sustained the large CH4 emission of river inlet region.

Water pollution at Lake Natron Ramsar site in Tanzania: A threat to aquatic life

Lake Natron Ramsar site is a recognized Ramsar site and Important Bird and Biodiversity Area (IBA) in Tanzania. It is a breeding site for 75% of the global population of lesser flamingo (Phoeniconaias minor). Water quality changes can affect the plankton composition and diversity, causing alteration of LNRS ecosystem abundance. Water quality assessment at LNRS was conducted after reported alkaline tilapines (Alcolapia species) and pelican (Pelecanus onocrotalus) mortalities. Water samples were collected from five sampling sites in Engaresero and Pinyinyi rivers during wet and dry seasons. Physico-chemical parameters including pH, turbidity, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), nitrates, chloride, sodium, ammonium, electrical conductivity and total alkalinity were assessed. Additionally, plankton composition and abundance were analyzed to investigate the cause of reported mortalities. Observation method was used to assess the anthropogenic activities taking place along inlet rivers. BOD, COD, ammonium and pH values were higher compared to the Tanzania Environmental Management Act of 2004 and World Health Organization recommended values for freshwater, resulting into low DO levels. There were no zooplankton or phytoplankton colonies observed from sampled water. The study observed anthropogenic activities (unsustainable crop cultivation, deforestation and overgrazing) at the LNRS catchment. The reported physico-chemical changes could be due to such anthropogenic activities at the LNRS catchment which could have resulted into the reported fish mortalities. Watershed management using nature-based solutions such as restoration of riparian vegetation and environment management awareness are recommended for LNRS ecosystem sustainability.

Determining Strain Threshold Values for Bridge Condition Assessment Using Normal Mixture Models

Structural health monitoring (SHM) enables bridge owners to evaluate bridge conditions efficiently and accurately. When implementing SHM, a popular method to detect the abnormal response of a structure is statistical pattern recognition. This often involves unsupervised statistical analysis due to a lack of measured SHM data from abnormal conditions. In this study, a novel methodology to calculate strain threshold indices (STIs) and establish decision boundaries (DBs) was used to detect the abnormal responses of the Indian River Inlet Bridge (IRIB), Sussex County, Delaware. First, a series of statistical models were applied and compared. Gaussian three mixture distributions were the optimal statistical models for the heavy vehicle-induced strain peaks. Threshold values for the strain gauges were selected using 99% uppers limits (USLs), and these limits were used to detect the abnormal response of the IRIB. The outlier ratios (R) for the sensors were calculated based on the threshold values. Corresponding STIs were defined by analyzing R, and DBs were determined using a t-distribution. The abnormal responses of the IRIB were detected by comparing the STI and DBs. The validity and sensitivity of the proposed methodology were demonstrated through simulated data that was created by perturbing the actual collected SHM data. Varying degrees of simulated damage were successfully detected using the proposed DBs. The proposed methodology showed promise when short and long-term abnormal responses and could provide practical guidance for bridge owners when using SHM data in their decision-making process.

Numerical Modeling of COD Transportation in Liaodong Bay: Impact of COD Loads from Rivers Flowing into the Sea

Pollution loads pose a major threat to the health of the marine environment and the long-term viability of the coastal economy. The present study developed a coupling model to simulate the chemical oxygen demand (COD) transport in upper rivers (1D) and subsequent diffusion in the coastal zone (2D) in Liaodong Bay, based on the HydroInfo system. Three main seagoing rivers, including Daliao, Liao, and Daling Rivers, were selected and investigated for hydrodynamic and hydrochemical analyses. The mathematical model was evaluated by monitoring data from state-controlled cross-sections scattered along the three rivers, and the observation data showed good agreement with simulated values, confirming the model’s accuracy in terms of spatial and temporal distribution. The transport and propagation process of COD in inlet rivers, such as Daliao, Liao, and Daling, including the sea area of Liaodong Bay, were simulated and analyzed. Simulated results revealed that the pollution range of COD in Liaodong Bay was 258–391 km2 in different seasons. The pollutant leakage scenarios for the three rivers entering the sea were simulated utilizing the developed mathematical model. The study simulated and predicted that, in the event of a sudden water pollution accident (e.g., sneak discharge and leakage at various sections of sea-entering rivers, such as Daliao, Liao, and Daling), pollutants might take 2–11 days to reach the sea-entering mouth, and the sea area would take 8–32 days to reach the maximum pollution range. Our numerical modeling may be used to analyze and make decisions on pollution control in Liaodong Bay and major sea-entry rivers, and be useful to water environment management in sea-entry rivers and Liaodong Bay, and water pollution emergency responses.

Water quality shifts the dominant phytoplankton group from diatoms to dinoflagellates in the coastal ecosystem of the Bohai Bay.

In this study, we conducted two cruises in the Bohai Bay (China) focusing on phytoplankton community and relation to water quality. The evaluation revealed that most of the open area was non-eutrophic, whereas the river inlet had severe eutrophication. Phytoplankton populations respond differently to different aquatic environments and are controlled by more than two factors, as revealed by aggregated boosted tree analysis. Notably, a shift in the phytoplankton community structure was observed during the seasonal transition, from the dominance of diatoms to the co-dominance of diatoms-dinoflagellates. However, the relative abundance of dinoflagellates increased by 14% in autumn, when the harmful algae species Akashiwo sanguinea exclusively predominated; this was primarily linked to the nutrient ratios, temperature, and dissolved oxygen. The eutrophication and organic pollution had direct effects on phytoplankton abundance. Overall, our findings may provide further insights into the impacts of eutrophic environments on phytoplankton community structure in coastal systems.

Model calibration of a long-span concrete cable-stayed bridge based on structural health monitoring data: Influence of concrete variability

Structural Health Monitoring (SHM) systems, in combination with controlled load tests, can provide valuable data for calibrating high fidelity bridge models, which can then be used for evaluating the long-term performance of the bridge, improved load ratings, and permit vehicle evaluation. The objective of this research was to calibrate a 3D model of the Indian River Inlet (IRIB) cable-stayed bridge, using strains recorded by the bridge SHM system during a controlled load test. The bridge was modeled in STAAD-Pro and calibrated using a pre-commercialized software platform that uses a Generic Algorithm to minimize the error between the measured and predicted strains. The calibration parameters were the elastic modulus of groups of the main longitudinal edge girder/deck elements, which once calibrated, could be related to the measured concrete strength of the members. Four different models were investigated, using 6, 10, 14, and 18 parameter element groups of the edge girder members. Of the different models, the 14 and 18 parameter models yielded the best results. The “design” model yielded errors as high as 42% when compared to the measured strains; the error was less than 10% for the majority of measurements for the 14-parameter model. Including the effect of the traffic barriers in the model, the weighted average concrete strength of the calibrated model was within 4% of the measured weighted strength. The calibration was shown to be insensitive to measurement noise and was validated using several unique single and multi-vehicle load cases that were heavier and more offset from the centerline of the bridge. The calibration procedure was able to capture the variability in flexural stiffness of the edge girders due to the variability of the concrete, resulting in significantly better agreement between the live load measured strains and the model predicted strains.

Lead isotopic fingerprinting as a tracer to identify the sources of heavy metals in sediments from the Four Rivers’ inlets to Dongting Lake, China

In this study, Pb isotopic composition of bulk sediments and 1 M HCl leachates/residues of samples from the Four Rivers’ inlets to Dongting Lake (China) was determined to identify and differentiate the source of Pb inputs. Results highlighted that Xiangjiang river (XY-QS) sediments were highly enriched in Pb with less radiogenic Pb isotopes (e.g., 206Pb/207Pb ratios of 1.1830 ± 0.003), indicating the predominance of anthropogenic Pb inputs. In contrast, sediments of the Zijiang, Yuanjiang and Lishui rivers (ZD-LH) were moderately enriched in Pb and exhibited more radiogenic Pb (e.g., 206Pb/207Pb ratios of 1.1880 ± 0.008). Results from 1 M HCl extraction of XY-QS sediments illustrated that anthropogenic Pb was removed, which resulted in differentiation of 206Pb/207Pb isotope ratios between leachates (1.1740 ± 0.005) and residues (1.1846 ± 0.008), however, this difference was not observed in ZD-LH sediments (leachates: 1.1887 ± 0.009; residues: 1.1887 ± 0.008). Residual Pb isotope ratios suggested that Pb isotopic composition of lithologically inherited Pb in inlet sediments was similar, which was attributed to mixing, hydrological sorting, and averaging of different Pb sources from diverse geological settings. Pb isotopic tracing showed that Pb in XY-QS sediments resulted from the mixing of two end member sources, an anthropogenic source (less radiogenic Pb) from downstream ore smelting and upstream ore mining activities (53%) and a lithological source (37%) from granite through weathering. In contrast, Pb in ZD-LH sediments resulted from the mixing of multiple sources including Pb from upstream mining activities (20%), coal combustion (20%), and lithologically inherited Pb (60%) while surface sediments from the Yuanjiang river contained Pb from diesel oil usage (50%). Results from this study highlight the utility of a Pb isotope approach for identifying and differentiating Pb source inputs in diverse sediments from the Four River inlets to Dongting Lake (China).