Study on load allocation of land-based total nitrogen in the Bohai Sea.

Total nitrogen (TN) is one of the terrigenous pollutants in the Bohai Sea. A reasonable releasing scheme can effectively improve the seawater quality. Based on the observed TN concentrations and the national pollution control requirements, the TN load ratios of four major rivers around the Bohai Sea are adjusted in multiple levels within the range of 50 %-200 % in the frame of total control. Then, a pollutant transport model is used to evaluate each load allocation scheme by calculating the area of different seawater qualities. The optimum scheme is loads of the Yellow River and Luan River are set to 50 % and 200 % of the levels in 2018, and thus the area of heavily polluted seawater can be decreased by 33.14 %. Additionally, the reasonable TN reduction amounts of four major rivers in 2018-2020 are calculated according to the optimum scheme, which can be provided as a decision-making basis of marine managements.

Correction: Critical role of hydrogen bonding between microcrystalline cellulose and g-C3N4 enables highly efficient photocatalysis.

Correction for 'Critical role of hydrogen bonding between microcrystalline cellulose and g-C3N4 enables highly efficient photocatalysis' by Zhaoqiang Wang et al., Chem. Commun., 2024, 60, 204-207, https://doi.org/10.1039/D3CC04800D.

Critical role of hydrogen bonding between microcrystalline cellulose and g-C3N4 enables highly efficient photocatalysis.

Developing a highly efficient photocatalyst for energy and environmental applications is urgently required. Herein, graphitic carbon nitride (CN) coupled with microcrystalline cellulose (MCC) (denoted as MCC-X/CN) shows excellent photocatalytic performance for tetracycline (TC) degradation and H2 evolution. And the optimized MCC-0.05/CN shows an improved TC degradation rate (Kapp = 0.019 min-1) and H2 evolution rate (642.71 µmol g-1 h-1), which are 1.9 and 22 times higher than those of pure CN, respectively. This improvement primarily results from hydrogen bonding (H-bonding) between CN and MCC, which enables excellent charge separation and migration, leading to the outstanding photoelectrochemical properties of MCC-0.05/CN.

Three-dimensional spatial interpolation for chlorophyll-a and its application in the Bohai Sea.

Assessing the health of coastal ecosystems is crucial for maintaining ecological balance. One significant indicator of water eutrophication is the distribution of chlorophyll-a (Chl-a), which makes obtaining a complete three-dimensional spatial distribution of Chl-a essential for assessment. This study utilized the linear radial basis function (RBF-Linear) method to obtain a comprehensive and reasonable spatial distribution of Chl-a. The method was applied to obtain the three-dimensional spatial field of Chl-a concentration in the Bohai Sea in March, May, August, and October from 2016 to 2018. The distribution pattern of Chl-a concentration in the Bohai Sea displayed characteristic spatial and temporal variations. Spatially, high Chl-a concentration was most concentrated in coastal waters, particularly in estuaries and mariculture areas. Temporally, there were two peaks in March and August. The total Chl-a and areas with high Chl-a concentration in four sub-regions of the Bohai Sea were also calculated to enable a comprehensive assessment of the marine ecological environment. By analyzing the temporal and spatial variation of Chl-a in the Bohai Sea and evaluating the marine ecological environment, we confirmed the feasibility and rationality of RBF-Linear. Our findings have the potential to contribute to improve the accuracy of ecological models and assessment of the satellite products.

Observation of near-inertial waves in the wake of four typhoons in the northern South China Sea.

Based on the velocity and temperature data recorded by two acoustic Doppler current profilers (ADCPs) at a mooring system deployed in the northern South China Sea (SCS), this study investigates the characteristics of near-inertial waves (NIWs) induced by typhoons Bebinca, Barijat, Mangkhut and Yutu in 2018. For the dynamical response, besides the motion of near inertial frequency induced by typhoons, the motion of 2 f ([1.80-2.20] f, f is the local inertial frequency) and f D1 (a harmonic wave with a frequency equal to the sum of frequencies of NIWs and diurnal tides) frequency will also increase. For near-inertial motions, the maximum near-inertial kinetic energy (NIKE) is confined to depths above 150 m. For stronger (weaker) wind forcing, the longer (shorter) the response time of the ocean to the atmospheric forcing is, and the shorter (longer) the response time is required in relaxation stage. There are upward and downward propagating energies after the passage of typhoons, and the upward propagating energy mainly occur in the stage of the geostrophic balance adjustment. The current structure suggests that the NIWs in the vertical direction are two antisymmetric rotary vortices in a near-inertial period, which is similar to the structure of the Langmuir circulation. Besides, the horizontal near-inertial currents (NICs) are much stronger than the vertical NICs, and the stronger the NIWs are, the stronger the horizontal NICs relative to the vertical NICs are. For the temperature response, the temperature variation reflects a clear stratified vertical structure. In the forcing stage, the upper layer becomes colder, the lower layer becomes warmer, and the thickness and intensity of the thermocline decrease. In the relaxation stage, the upper layer warms and the lower layer cools, and the thickness and intensity of thermocline increase.

On the identification of internal solitary waves from moored observations in the northern South China Sea.

Based on the temperature data recorded by a mooring system deployed in the northern South China Sea (SCS), this study compares the traditional methods of identifying and extracting internal solitary waves (ISWs): the whole water column isotherm (WCI) method and the single isotherm (SI) method, and proposes a novel method: the temperature superposition (TS) method. Results indicate that the TS method identifies the most ISWs, followed by the WCI method, and the SI method identifies the fewest. When the ISW amplitudes are smaller than 60 m, the TS method can identify the most ISWs. When the ISW amplitudes are greater than 60 m, the number of ISWs identified by the three methods is the same. The TS method removes the internal tides, takes into account the temperature of all depth layers, and amplifies the signal of ISWs to a certain extent, so as to effectively identify ISWs.

Production of Hydroxymethylfurfural Derivatives From Furfural Derivatives via Hydroxymethylation.

Hydroxymethylfurfural (HMF) derivatives such as 2,5-bis(hydroxymethyl)furan (BHMF) and furandicarboxylic acid (FDCA) are promising alternative of fossil-based diols and dicarboxylic acids for synthesis of polyesters such as polyethylene terephthalate (PET). However, high cost for preparing HMF from biomass discourages the commercialization of HMF-derived polyesters. Since producing furfural (FUR) from five-carbon sugars (e.g., xylose) via dehydration is an inexpensive and commercialized process, we herein reported a method to synthesize BHMF derivatives (5-(ethoxymethyl)furan-2-methanol (EMFM), 2,5-bis(hydroxymethyl)furan monoacetate (BHMFM) and 2,5-bis(hydroxymethyl)furan diacetate (BHMFD) from furfural derivatives, i.e., (2-(ethoxymethyl)furan (EMF) and furfuryl acetate (FA)). To avoid strong acid-induced side reactions (e.g., furan ring opening, condensation and carbonization), two reaction systems, i.e., a low-concentration HCl aqueous solution combined with formaldehyde and anhydrous acetic acid combined with paraformaldehyde, were found to be suitable for such a hydroxymethylation reaction and could lead to decent product yields. In order to improve the carbon utilization, condensed furanic byproducts were further converted into hydrocarbon fuels via a reported two-step hydrodeoxygenation (HDO) process. This study not only validates the possibility of synthesizing functional HMF derivatives (EMFM, BHMFM, and BHMFD) from commercially-available FUR derivatives (EMF and FA), but also provide a new way to transform condensed furanics to value-added hydrocarbon fuels.

Using poly(N-Vinylcaprolactam) to Improve the Enzymatic Hydrolysis Efficiency of Phenylsulfonic Acid-Pretreated Bamboo.

Chemical pretreatment followed by enzymatic hydrolysis has been regarded as a viable way to produce fermentable sugars. Phenylsulfonic acid (PSA) pretreatment could efficiently fractionate the non-cellulosic components (hemicelluloses and lignin) from bamboo and result in increased cellulose accessibility that was 10 times that of untreated bamboo. However, deposited lignin could trigger non-productive adsorption to enzymes, which therefore significantly decreased the enzymatic hydrolysis efficiency of PSA-pretreated bamboo substrates. Herein, poly(N-vinylcaprolactam) (PNVCL), a non-ionic surfactant, was developed as a novel additive for overcoming the non-productive adsorption of lignin during enzymatic hydrolysis. PNVCL was found to be not only more effective than those of commonly used lignosulfonate and polyvinyl alcohol for overcoming the negative effect of lignin, but also comparable to the robust Tween 20 and bovine serum albumin additives. A PNVCL loading at 1.2 g/L during enzymatic hydrolysis of PSA pretreated bamboo substrate could achieve an 80% cellulosic enzymatic conversion and meanwhile reduce the cellulase loading by three times as compared to that without additive. Mechanistic investigations indicated that PNVCL could block lignin residues through hydrophobic interactions and the resultant PNVCL coating resisted the adsorption of cellulase via electrostatic repulsion and/or hydration. This practical method can improve the lignocellulosic enzymatic hydrolysis efficiency and thereby increase the productivity and profitability of biorefinery.

Impact of ocean waves on transport of underwater spilled oil in the Bohai Sea.

To investigate the impact of ocean waves on transport of underwater spilled oil, a wave action module is developed and embedded into an underwater oil spill model. Combined with a validated hydrodynamic background data, the model is applied to a short-term numerical simulation of the 2011 Penglai 19-3 oil spill event in the Bohai Sea. Numerical result shows that the model result is rationally consistent with the field observation. In addition, waves can influence surface oil slick in both horizontal and vertical directions: in horizontal direction, Stokes drift tends to make oil slick spread more widely under the action of wind-waves; in vertical direction, breaking waves tend to entrain the surface oil into water column, and then affects the vertical distribution of spilled oil. Furthermore, sensitivity study shows that using different parameterizations of wave entrainment can make some difference to the model output, but the effect is limited. Besides, the impact of input wave errors varies on different model outputs. This study is expected to provide offshore oil spill emergency responders and researchers with useful information on oil spill monitoring, emergency plans and environmental damage assessment.

Variability of coherent and incoherent features of internal tides in the north South China Sea.

The coherent and incoherent features of internal tides (ITs) in the north South China Sea (SCS) are investigated based on observations and numerical simulations. The 11-month (from May 2011 to March 2012) moored current observations indicate that coherent semidiurnal ITs are obviously amplified, which can be attributed to the interference of ITs. Interference enhances coherent motions of semidiurnal ITs, but weakens those of diurnal ITs. Moreover, observations also show that semidiurnal ITs are more incoherent than diurnal ITs. Variations of vertical stratification and surface tide forcing can hardly affect the incoherence of ITs. The increase of incoherent signal is largely due to the influence of mesoscale eddies. Mesoscale eddies affect both amplitude and phase of ITs, making them more incoherent. Mesoscale eddies not only increase the intensity of background currents, but also induce horizontal variations of density. Variations of horizontal density and the influence of background currents lead to the increase of incoherent signals. And semidiural ITs are more sensitive to the influence of mesoscale eddies, making them more incoherent than diurnal counterparts. Incoherent ITs, which induce strong current shear, play essential roles in cascading tidal energy to small-scale motions, and contribute to turbulent mixing eventually. The findings help to better understand ITs and may offer reference for the improvement of parameterization of ocean turbulent mixing in the northern SCS.

Inversion of Wind-Stress Drag Coefficient in Simulating Storm Surges by Means of Regularization Technique.

In this study, water levels observed at tide stations in the Bohai Sea, Yellow Sea, and East China Sea during Typhoons 7203 and 8509 were assimilated into a numerical assimilation storm surge model combined with regularization technique to study the wind-stress drag coefficient. The Tikhonov regularization technique with different regularization parameters was tested during the assimilation. Using the regularization technique, the storm surge elevations were successfully simulated in the whole sea areas during Typhoons 7203 and 8509. The storm surge elevations calculated with the regularization technique and the elevations calculated with independent point method were separately compared with the observed data. Comparison results demonstrated that the former was closer to the observed data. The regularization technique had the best performance when the regularization parameter was 100. The spatial distribution of the inverted drag coefficient, storm surge elevations, and the wind fields during both typhoons were presented. Simulated results indicated that the change of drag coefficient is more significant in the coastal regions of the Bohai Sea and north of the Yellow Sea. Further analysis showed that the rising water elevation in the Bohai Sea is mostly attributed to the influence of onshore winds, and the negative storm surge in the South Yellow Sea is mainly caused by offshore winds.

Application of Dynamically Constrained Interpolation Methodology to the Surface Nitrogen Concentration in the Bohai Sea.

Observations of ocean pollutants are usually spatiotemporally dispersive, while it is of great importance to obtain continuous distribution of ocean pollutants in a certain area. In this paper, a dynamically constrained interpolated methodology (DCIM) is proposed to interpolate surface nitrogen concentration (SNC) in the Bohai Sea. The DCIM takes the pollutant transport advection diffusion equation as a dynamic constraint to interpolate SNCs and optimizes the interpolation results with adjoint method. Feasibility and validity of the DCIM are testified by ideal twin experiments. In ideal experiments, mean absolute gross errors between interpolated observations and final interpolated SNCs are all no more than 0.03 mg/L, demonstrating that the DCIM can provide convincing results. In practical experiment, SNCs are interpolated and the final interpolated surface nitrogen distribution is acquired. Correlation coefficient between interpolated and observed SNCs is 0.77. In addition, distribution of the final interpolated SNCs shows a good agreement with the observed ones.

Application of the Spline Interpolation in Simulating the Distribution of Phytoplankton in a Marine NPZD Type Ecosystem Model.

The available observations for the model are usually sparse and uneven. The application of interpolation methods help researchers obtain an approximate form of the original data. A marine nutrient, phytoplankton, zooplankton and detritus (NPZD) type ecosystem model is applied to simulate the distribution of phytoplankton combined with the spline interpolation (SI) and the Cressman interpolation (CI). In the idealized twin experiments, the performance of these two interpolation methods is validated through the analysis of several quantitative metrics, which show the minor error and high efficiency when using the SI. Namely, the given distributions can be better inverted with the SI. The actual distribution of phytoplankton in the Bohai Sea is interpolated in the practical experiment, where a satisfactory simulation result is obtained by the model with the SI. The model experiments and results verify the feasibility and effectiveness of SI.

Application of the Orthogonal Polynomial Fitting Method in Estimating PM2.5 Concentrations in Central and Southern Regions of China.

Sufficient and accurate air pollutant data are essential to analyze and control air contamination problems. An orthogonal polynomial fitting (OPF) method using Chebyshev basis functions is introduced to produce spatial distributions of fine particle (PM2.5) concentrations in central and southern regions of China. Idealized twin experiments (IE1 and IE2) are designed to validate the feasibility of the OPF method. IE1 is designed in accordance with the most common distribution of PM2.5 concentrations in China, whereas IE2 represents a common distribution in spring and autumn. In both idealized experiments, prescribed distributions are successfully estimated by the OPF method with smaller errors than kriging or Cressman interpolations. In practical experiments, cross-validation is employed to assess the interpolation results. Distributions of PM2.5 concentrations are well improved when OPF is applied. This suggests that errors decrease when the fitting order increases and arrives at the minimum when both orders reach 6. Results calculated by the OPF method are more accurate than kriging and Cressman interpolations if appropriate fitting orders are selected in practical experiments.