A three-dimensional water quality model to evaluate the environmental capacity of nitrogen and phosphorus in Jiaozhou Bay, China

Prediction on daily spatial distribution of chlorophyll-a in coastal seas using a synthetic method of remote sensing, machine learning and numerical modeling

Harmful algal blooms (HABs) pose a severe environmental issue and have significant economic and ecological consequences on coastal oceans. Predicting the occurrence of these blooms has become increasingly vital for coastal communities. To facilitate this, chlorophyll-a (Chl-a) levels have been widely used to forecast algal blooms. Although Hydro-biogeochemical (HBGC) process-based models display reasonable accuracy in predicting hydrodynamic variables and nutrients, they are not as effective in predicting Chl-a. Purely data-driven machine learning techniques also have limitations in accurately predicting Chl-a of high spatio-temporal resolutions. In this study, a coupled HBGC-Convolutional Neural Network (CNN) model was developed to predict the daily surface Chl-a distribution. The HBGC-CNN model integrates the information gathered by the HBGC model on temperature, salinity, dissolved inorganic nitrogen, dissolved organic phosphorus, and zooplankton with the remote sensing Chl-a products for the CNN model training. The results revealed that the HBGC-CNN model can effectively reproduce both daily and seasonal Chl-a variations, and interpret spatiotemporal information related to an HAB event triggered by the heavy rainfall during typhoon Lekima in 2019. Furthermore, this method can be used for data reconstruction, producing gap-free Chl-a products for historical reanalysis, especially in nearshore regions. The successful implementation of the HBGC-CNN model in predicting Chl-a highlights its potential in being incorporated into an operational forecasting system from a regional scale to a global scale, reducing the adverse impact of HAB disasters and facilitating emergency treatment.

The impact of extreme precipitation on physical and biogeochemical processes regarding with nutrient dynamics in a semi-closed bay

An extreme precipitation event in August 2012 changed the ecosystem of Jiaozhou Bay (JZB), China. Biochemical variables in the sea, river mouths, and rainwater were monitored simultaneously during the event. The impact of the following excessive riverine input and wet atmospheric deposition on nutrient dynamics were studied before. However, regulatory processes of nutrient dynamics were not quantified and analyzed. Therefore, a coupled physical-biological model (FVCOM-ERSEM) was used to study the physical and biochemical mechanisms of the variation of the dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DISi), as well as chlorophyll-a (Chl-a). The results indicate that physical processes increase nutrients, while biological processes reduce them. The exchange with the Yellow Sea, as an important physical process, exports DIN to the Yellow Sea, but imports DIP and DISi to the JZB. Only 20 % of the excessive DIN due to extreme precipitation event was reduced by water exchange with the Yellow Sea. The rest (80 %) was reduced and changed into organic nitrogen through biological processes. This paper also examines the variation of the pelagic and benthic cycles of biochemical processes. In these cycles, phytoplankton take up and use nutrients in the bay, while zooplankton excretion in the pelagic cycle and benthic releases resupply them. Precipitation enriched the surface nutrients, which boosted primary production and organic matter transport to the bottom water.

Wastewater inputs reduce the CO2 uptake by coastal oceans

Every year a large quantity of wastewater is generated worldwide, but its influence on the carbon dioxide (CO2) uptake by coastal oceans is not well understood. Here, sea surface CO2 partial pressure (pCO2) and air-sea CO2 flux were examined in the Jiaozhou Bay (JZB), a temperate coastal bay strongly disturbed by wastewater inputs. Monthly surveys from April 2014 through March 2015 showed that surface pCO2 in the JZB substantially varied both temporally and spatially between 163 μatm and 1222 μatm, with an annual average of 573 μatm. During April-December, surface pCO2 was oversaturated with respect to the atmosphere, with high values exceeding 1000 μatm in the northeastern part of the bay, where seawater salinity was low mainly due to the inputs of wastewater with salinity close to zero. During January-March, surface pCO2 was undersaturated, with the lowest value of <200 μatm also mainly in the northeastern part because of low water temperature and strong biological production. Over an annual cycle, apparently sea surface temperature dominated the monthly variation of surface pCO2 in this shallow bay, while wastewater inputs and related biological production/respiration dominated its spatial variability. Overall, the JZB was a net CO2 source to the atmosphere, emitting 9.6 ± 10.8 mmol C m-2 d-1, unlike its adjacent western part of the Yellow Sea and most of the temperate coastal oceans which are a net CO2 sink. This was possibly associated with wastewater inputs that cause high sea surface pCO2 via direct inputs of CO2 and degradation of organic matter. Thus, from this viewpoint reducing wastewater discharge or lowering CO2 levels in discharged wastewater may be important paths to enhancing the CO2 uptake by coastal oceans in the future.

Evaluation of the Role of Self-cleaning Capacity on Marine Environmental Carrying Capacity: A Case of Ganh Rai Bay, Vietnam

Economic activities are constantly increasing in the southern key economic region (SKER), especially in Ho Chi Minh City (HCMC), which leads to the influx of large amounts of wastewater from this region into Ganh Rai Bay (GRB). The problem of assessing the marine environmental carrying capacity (MECC) of coastal areas is urgent, and the role of self-cleaning must be elucidated. Four typical pollution parameters were selected: ammonium (NH4+), biological oxygen demand (BOD), phosphate (PO43-), and coliforms. The study aims to propose a framework to assess the impact of the role of self-cleaning on MECC and to apply the proposed framework to GRB as a case study. A series of models were used to simulate hydrodynamics, and an advection-diffusion model with an ecological parameter set was used for water quality modelling. The land-ocean interactions in the coastal zone model were used to calculate the GRB and East Sea retention time. Finally, a multiple linear regression model was used to clarify the relationship between the MECC and self-cleaning factors. Calculation results show that the self-cleaning factor increased the MECCAmmonium by 60.30% in the dry season and 22.75% in the wet season; similar to MECCBOD, MECCPhosphate increased by 5.26%, 0.21% (dry season), and 11.04%, 0.72% (wet season), respectively. MECCCColiforms in the dry season increased by 14.83%; in the wet season, MECCColiforms doubled. The results provide medium-and long-term solutions to improve the water quality of the GRB, especially the selection of activities that conserve the ecological system and improve the self-cleaning capacity of the bay.

Experiments and simulation of adsorption characteristics of typical neonicotinoids in urban stream sediments

Sediment adsorption is one of the main environmental fates of neonicotinoids (NEOs) in aquatic environments. Little information is available on for the adsorption characteristics of NEOs on urban stream sediments. In this study, urban tidal stream sediments were collected to determine the adsorption properties of four selected NEOs. The influence of environmental factors on NEO adsorption was determined by the RSM-CCD method. The NEO adsorption rates on sediments were established by multiple regression equations. As a result, the adsorption of four NEOs onto sediments fitted a linear isotherm model. The adsorption amounts of thiacloprid (THA), clothianidin (CLO), acetamiprid (ACE), and imidacloprid (IMI) were 1.68 to 2.24, 1.71 to 2.89, 1.88 to 3.07, and 2.23 to 3.16 mg/kg, respectively. The adsorption processes of four NEOs on urban sediments were favorable. Moreover, adsorption behaviors of NEOs were typical physical adsorption and readily adsorbed onto urban sediments. The adsorption processes of NEOs were exothermic reactions, and their adsorption rates decreased with increasing pH. Flow rates and organic matter contents could promote the adsorption ratios of typical NEOs. Multiple linear regression was used to assess the relationships between the adsorption rates of NEOs and environmental factors. The p-values of the fitting equations of adsorption rates were all less than 0.05. Within the ranges of concentration of the investigated factors, the multiple regression equations were able to reasonably model and predict the sorption of typical NEOs onto urban stream sediments. Therefore, the adsorption rate equations effectively predicted the NEO adsorption performance of urban streams and were helpful for controlling risk assessment of NEOs.

Assessing marine environmental carrying capacity in semi-enclosed coastal areas - Models and related databases

Faced with the degradation of the marine environment, the Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESEMP) first presented the concept of marine environmental carrying capacity (MECC) in 1986, which confirmed that there is a need to pay attention to physical, chemical, biological, and biochemical processes, thereby indirectly suggesting the need for a modelling approach. Although studies on MECC have been published, further research is necessary and must be complemented by a new approach. In this study, an integrated system called SECAMECC (Marine Environmental Carrying Capacity Semi Enclosed for Coastal Areas) for semi-enclosed bays is proposed. SECAMECC comprises database of seven data groups and four models: 3D hydrodynamic, ecological, retention time estimation, and MECC calculation. The proposed system has been applied to a specific semi-enclosed bay as a case study to determine the MECC seasonally. The carrying capacities of ammonium (NH₄⁺), phosphate, total suspended solids (TSS), and biological oxygen demand were assessed in accordance with the baseline and forecast scenarios. The received results show that under the baseline, MECC no longer accepted PO₄^3-; meanwhile, NH₄⁺, TSS, and BOD₅ exhibited the following values in the dry and wet season, respectively: 1134 and 3514 (t/m); 110,578 and 144,458 (t/m); and 17,072 and 44,348 (t/m). Owing to the hydrodynamic factors, the carrying capacity in the dry season is always greater than that in the wet season. Furthermore, the relationship between MECC and environmental standards, current water quality, and hydrodynamic factors was clarified.

Advancing Three-Dimensional Coupled Water Quality Model of Marine Ranches: Model Development, Global Sensitivity Analysis, and Optimization Based on Observation System

Marine ranching is a stock enhancement project that has been an important part of aquaculture in China. Due to the lack of scientific management, disasters have occurred, resulting in millions of economic losses. Based on the observation system of marine ranches, a three-dimensional water quality model of marine ranches was developed to study the spatio-temporal variation of key ecological indicators, including the concentrations of chlorophyll-a, zooplankton, detritus, nutrients, and dissolved oxygen (DO). The model is coupled offline with the residual current, temperature, and salinity simulated by a regional oceanic modeling system (ROMS). The conservative characteristic finite difference (C-CFD) scheme is introduced to solve the equations, which guarantees model stability and mass conservation and allows for a larger time step compared to traditional difference schemes. In state-of-the-art water quality models, the biogeochemical processes are parameterized. Due to the complexity of the water quality model, a combination of global sensitivity analysis (GSA) and the adjoint method is introduced as the methodology to optimize the model parameters. Morris’ sampling method is implemented as the GSA method to find out the key factors of the water quality model. The optimization of sensitive parameters with the adjoint method significantly improves the model precision, while the other parameters can be set as empirical values. The results indicate that the combination of GSA and the adjoint method is efficient in the parameter optimization of the water quality model. The model is applicable in marine ranches.

Compound effect of land reclamation and land-based pollutant input on water quality in Qinzhou Bay, China

Based on a three-dimensional hydro-biogeochemical model, the compound and individual impacts of two types of human activities, i.e., land reclamation and land-based pollutant input, on coastal water quality were studied. In Qinzhou Bay (QZB), China, a total of 38.90 km² of tidal flat was reclaimed between 2004 and 2019, and the Chemical Oxygen Demand (COD) in the wastewater was reduced by over 40%. However, the Dissolved Inorganic Nitrogen (DIN) was increased by above 40%, and the Dissolved Inorganic Phosphorus (DIP) was increased by about 17%, leading to the continuous deterioration of water quality in QZB. Correspondingly, the model results show that the bay's average COD decreased by 6.86%, but the DIN and DIP increased by 57.53% and 17.39%, respectively. Considering the individual effects, land reclamation contributed 72.73%, 75.38%, and 25.01% to the changes in the COD, DIN, and DIP concentrations in QZB, respectively; and the remainder was caused by the variations in the land-based pollutant input. By considering the compound effect of these two types of human activities, it was found that land reclamation can hinder the water quality improvement induced by the decrease in land-based pollutant input; and it can intensify the water quality deterioration induced by the increase in land-based pollutant input. These results indicate that the impact of land-based pollutant input on coastal water quality was modulated by land reclamation. However, the modulation did not affect the DIP since the phosphorus was the restrictive element in QZB. The comparison of different experimental results revealed that restoring hydrodynamics to enhance the bay-shelf exchange would be a more effective method of ecological restoration than solely reducing the pollutant input.

Spatiotemporal variations in phosphorus concentrations in the water and sediment of Jiaozhou Bay and sediment phosphorus release potential

Phosphorus contamination in urbanized bays has been a major concern because the bay restoration is often hindered by complex P sources and behaviors. This study examined the spatiotemporal changes of P species and exchange potential in/between the water and sediment of the Jiaozhou Bay. The results indicated that dissolved P (TDP) and inorganic P (DIP) in the water ranged from 7.8-128.7 and 1.8-14.1 μg/L, respectively; while total P (TP) in the sediment ranged from 213.4-638.7 mg/kg. The TDP and DIP concentrations in the water were high in winter and low in summer, and generally decreased from northeastern or northern areas to southwestern or southern areas mainly due to phytoplankton bloom cycles and riverine and wastewater inputs. TP in the sediment was lower in the northwestern area due to solid dilution effect by the settlement of settled coarser suspended particles. Changes in aquatic geochemical conditions from rivers to bay caused P accumulation in estuarine sediment, with higher P partition in organic fraction (40%). Compared to the estuarine sediment, higher fractions of P were associated with carbonate (34%) and iron oxide (17%) minerals in the bay sediment. Equilibrium P concentrations at zero sorption (EPC₀) were 4.1-149.8 μg/L, which was substantially higher than the DIP concentration, demonstrating P release potential from the sediment. In addition, the P release potential was high in the northeastern area while P partition coefficient or buffer intensity (K_d) was high in the northwestern area. EPC₀ was significantly positively correlated with soluble and exchangeable P in the sediment while K_d was significantly negatively correlated. These results can provide improved insights into P behaviors in an urbanized bay, particularly the P release potential and spatiotemporal change.

Eutrophication model driven by light and nutrients condition change in sluice-controlled river reaches

River eutrophication has become a challenging environmental problem worldwide because of the strong interference of anthropogenic activities and hydraulic structures. The driving mechanism of algae growth in sluice-controlled river reaches (SCRRs) is more complicated than that of natural rivers, because the operation mode of the sluices is an important influencing factor which changes the light and nutrient conditions of the water body. The main purpose of this study was to assess algal growth in SCRRs under external conditions and sluice regulation. In this study, a eutrophication model for SCRRs was developed based on the mechanism of river hydrodynamics and algae growth kinetics, considering the variation in underwater light intensity and nutrient condition. By choosing the light intensity, phosphorus concentration and sluice gate opening size as the influencing factors, 16 different combination conditions were proposed by orthogonal experimental design, and eutrophication of water bodies in the SCRRs was simulated using a eutrophication model. In the scenario design, four gate opening sizes were set, and the light intensity and nutrients were enlarged or reduced based on the original monitoring data. The results showed that both light intensity and nutrient concentration can promote the algal growth within a suitable range, and increasing the gate opening size can inhibit algal growth.

Distribution characteristics of lipophilic marine phycotoxins in the sediment: A case study in Jiaozhou Bay, China

Marine sediments serve as a sink for environmental pollutants, such as lipophilic marine phycotoxins (LMPs). To reveal the fate of LMPs, we studied their distribution characteristics in sediments. From January 2016 to August 2017, we sampled surface sediments from Jiaozhou Bay (JZB) of the North Yellow Sea, and their solid-phase extracts were analyzed using liquid chromatography-tandem mass spectrometry. Three LMPs viz. okadaic acid (OA), dinophysistoxin-1 (DTX1), and pectentoxin-2 (PTX2) were predominant in the sediments. Also, PTX2 distribution was more extensive in the area, while OA and DTX1 were more concentrated. Having the same toxigenic algae origin, the spatial distribution of OA, DTX1, and PTX2 in the sediments was similar.

Methodology for forecast and control of coastal harmful algal blooms by embedding a compound eutrophication index into the ecological risk index

Harmful algae bloom (HAB) is a major global ecological hazard and is a serious problem in the Bohai Sea. There have been few successful controls of HABs associated with HAB accurate predictions due to a lack of link between ecological risks and control measures. A methodology is proposed that embeds the compound eutrophication index (CEI) into an ecological risk index (ERI) for HAB prediction, which can define critical factors associated with measures of HAB control. CEI can be calculated by means of a function with 15 control elements. These are multiplied with the occurrence probability and ecosystem vulnerability to HAB events to calculate the ERI of HAB. Based on the results of CEI and ERI, it has experienced eutrophication and has been at a high-risk state since 1989 in the Bohai Sea. There is good correlation between CEI and chlorophyll a concentration, and HAB risk evaluation in accordance with ERI embedded CEI is considerable reliability in both location and time in the Bohai Sea. The ERI value averages 24% ± 35% with peak values (73% ± 4.3%) in summer, and high values (at the level of grade III of ERI, 6%) are mostly in Bohai Bay, Laizhou Bay, Liaodong Bay and the coastal sea waters of Qinhuangdao city. The contribution of terrigenous pollutant emission and concentration effects to the ERI is 63%, with reclamation and hydrodynamic effects accounting for 22%, and runoff and sediment effects accounting for 15%. Thus, actions associated with terrigenous pollutant emission/concentration would be more effective than other measures in prevention and control of HAB.

Spatial-temporal characteristics of nitrogen degradation in typical Rivers of Taihu Lake Basin, China

In this study, we focus on the measurement of different nitrogen (N) forms and investigate the spatial-temporal variability of degradation coefficient in river channels. We aim to provide a new approach of deriving in-situ degradation coefficients of different N forms, and highlight factors that determine the spatial-temporal variability of degradation coefficients. Our results are based on a two-year field survey in 34 channels around the Taihu Lake Basin, eastern China. The derived degradation coefficients of different N forms based our newly-developed experimental device are: degradation coefficients of TN, NH₄⁺-N and NO₃-N range from 0.006-0.449 d^-1, 0.022-1.175 d^-1 and -0.096-2.402 d^-1, respectively. The degradation coefficients of N show strong dependence on N concentration and water temperature. The seasonal difference of water temperature and N concentration leads to spatial-temporal variability of degradation coefficients. The derived degradation coefficients of N are further verified through one-dimensional water quality model simulations. The degradation coefficient obtained in this study and the influencing factors of its spatial-temporal variability provide invaluable reference for studies in aquatic environment.

Hydro-biogeochemical modeling of the early-stage outbreak of green tide (Ulva prolifera) driven by land-based nutrient loads in the Jiangsu coast

The outbreak of a large-scale green tide (Ulva prolifera) will have a serious impact on marine environment, ecological functions, landscape, and coastal social economy. Eutrophication is generally considered to be the most important driving factor of this phenomenon. It is difficult to obtain the pressure-impact relationship between land-based loading and green tides by only surveying or monitoring, whereas modeling can perform this task easily. In this study, therefore, a hydro-biogeochemical model was established and verified by the measured hydrodynamic and water quality variables. In the initial outbreak area of Jiangsu coast, China, we studied the relationship between U. prolifera bloom and the driving factors of nutrient loads and structures by modeling different scenarios of land source inputs. It was found that the ratio of nitrogen to phosphorus could be affected significantly, which triggered the bloom of U. prolifera. When the land-based input doubled or halved, the dissolved inorganic nitrogen concentration increased 20.6% or decreased 9.5%, respectively, which might result in 14.5% increase or 46.3% decrease in the green tide, respectively. It was also found that the nutrient distribution and structure was affected by the land-based load, which caused the outbreak of U. prolifera. Moreover, the total nutrient load must be controlled to prevent the outbreak of green tide in the Jiangsu coast.

Size-based bioavailability of land-based DON and its impact on eutrophication of Jiaozhou bay

With the increase in human activities, dissolved organic nitrogen (DON) has been the major nitrogen pool, which might impact on eutrophication of coastal water. We studied the bioavailability of different molecular size DON from the major sources of agricultural, domestic, industrial, and urban non-point source, respectively, in Jiaozhou bay, China. By clarifying the relationship between the source and molecular size, the bioavailability of terrestrial DON can be further understood based on the aspects of bioavailability proportion (BDON%) and kinetics with the help of ultraviolet radiation. The bioavailability proportion of high molecular size DON (HDON; >1000 Da) was higher than that of low molecular size DON (LDON; <1000 Da), with values of 58.0% to 35.1% for the HDON and values of 47.2% to 29.5% for the LDON, respectively. There were significant differences in the degradation rate constants (p < 0.05), which varied from 0.30 to 0.67 d^-1 for HDON and from 0.13 to 0.75 d^-1 for LDON. The SUVA₂₅₄ values were significantly and negatively correlated with the bioavailabilities of DON, which can reflect to some extent the structure and molecular size. In order to study the influences of the different terrestrial DON inputs on the eutrophication of Jiaozhou bay, a modified 3D coupled biogeochemical model was used based on the survey data in August 2012. Two scenarios of DON loads from Haibo river and Dagu river were modeled. The impact on eutrophication of Jiaozhou bay is higher for the agricultural source of DON from Dagu river than for the domestic source from Haibo river.

Impact of tidally induced residual circulations on chemical oxygen demand (COD) distribution in Laizhou Bay, China

To understand the impact of hydrodynamics on pollutant transport in Laizhou Bay, China, we conducted numerical simulations using Mike 21. The model was calibrated with good agreements to field monitoring data at various monitoring stations. The simulation results show a clockwise and an anti-clockwise tidally-induced residual circulation in the western and eastern bay, respectively. Historical COD monitoring data also indicate two rings of high COD concentration in the same regions of the bay. This suggests that the hydrodynamics of tidal and residual currents is the main cause of the ring-shaped high COD concentration field in the bay. Pollutant inputs from inland rivers are also important for the COD distribution, making the near-shore side of the COD ring higher than the offshore side. Regions with higher retention time in the bay are usually associated with higher COD concentrations. This study is useful in understanding the mechanism of pollutant spatial distribution and subsequent pollution control in a sea bay.

Compound eutrophication index: An integrated approach for assessing ecological risk and identifying the critical element controlling harmful algal blooms in coastal seas

Current ecological risk assessment and controlling element identification methods of harmful algal blooms (HABs) are not connected. Here, we identified the controlling elements by correlation and principal component analyses, and the analytic hierarchy process. A compound eutrophication index (CEI) integrating risk assessment with controlling element identification was constructed and verified using data collected from Jiaozhou Bay, China. The CEI results agreed with the chlorophyll-a concentration and the main eutrophication assessment results. The HAB risk assessment of the CEI was more efficient than that of the nutrient quality index and Assessment of Estuarine Trophic Status. The contribution ratio of the loads and concentrations of nutrients (nitrogen, phosphorus, and chemical oxygen demand) to HABs in Jiaozhou Bay was 70%. In the high-risk areas, the contribution ratio of nutrients to HABs was 77%. Therefore, terrestrial nutrient inputs must be reduced to prevent and control HABs in the north-eastern areas of Jiaozhou Bay.

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.

A scalable dynamic characterisation approach for water quality management in semi-enclosed seas and archipelagos

In semi-enclosed seas, eutrophication may affect both the coastal waters and the whole sea. We develop and test a modelling approach that can account for nutrient loads from land as well as for influences and feedbacks on water quality across the scales of a whole semi-enclosed sea and its coastal zones. We test its applicability in the example cases of the Baltic Sea and one of its local archipelagos, the Archipelago Sea. For the Baltic Sea scale, model validation shows good representation of surface water quality dynamics and a generally moderate model performance for deeper waters. For the Archipelago Sea, management scenario simulations show that successful sea measures may have the most important effects on coastal water quality. This highlights the need to consistently account for whole-sea water-quality dynamics and management effects, in addition to effects of land drivers, in modelling for characterisation and management of local water quality.

Selective detection of chloramphenicol based on molecularly imprinted solid-phase extraction in seawater from Jiaozhou Bay, China

This study highlights an efficient sample pre-treatment method for preconcentration and detection of chloramphenicol in marine water using molecularly imprinted solid-phase extraction (MISPE). Chloramphenicol molecularly imprinted microspheres were prepared and evaluated on the base of morphology, capacity and selectivity. The imprinted microspheres exhibited specific recognition and high retention capability to chloramphenicol and were applied as special solid-phase extraction adsorbents. An off-line MISPE protocol has been optimized and a creative analytical method coupled to HPLC-DAD was successfully developed for the cleanup and determination of chloramphenicol in seawater samples. Method performance was satisfactory with recoveries ranging from 81 to 90% and relative standard deviation (RSD) was <4.93% (n = 3). Accuracy of the method was assessed at three spiking concentration levels and the limit of detection was 5 ng L^-1. Finally, five seawater samples from Jiaozhou Bay of China were determined and the results showed that there was no chloramphenicol detected.

Research on the Relationship between Water Diversion and Water Quality of Xuanwu Lake, China

Water diversion is often used to improve water quality to reach the standard of China in the short term. However, this large amount of water diversion can not only improve the water quality, but also lead to a decline in the water quality (total phosphorus, total nitrogen) of Xuanwu Lake. Through theoretical analysis, the relationship between water quality and water diversion is established. We also found that the multiplication of the pollutant degradation coefficient (K) and the water residence time (T) is a constant (N), K⋅T=N. The water quality changed better at first, with the increase of inflow discharge, and then became worse, and the optimal water quality inflow discharge is 180,000 m³/day. By constructing two-dimensional hydrodynamic and water quality models, the optimal diversion water plan is calculated. Through model calculations, it can be seen that reducing the inflow discharge makes the water residence time longer (15.3 days changed to 23.8 days). Thereby, increasing the degradation of pollutants, and thus improving water quality. Compared with other wind directions, the southwest wind makes the water quality of Xuanwu Lake the most uniform. The concentration of water quality first became smaller and then became larger, as the wind speed increased, and eventually became constant. Implementing these results for water quality improvement in small and medium lakes will significantly reduce the cost of water diversion.

A coastal three-dimensional water quality model of nitrogen in Jiaozhou Bay linking field experiments with modelling

With anthropogenic changes, the structure and quantity of nitrogen nutrients have changed in coastal ocean, which has dramatically influenced the water quality. Water quality modeling can contribute to the necessary scientific grounding of coastal management. In this paper, some of the dynamic functions and parameters of nitrogen were calibrated based on coastal field experiments covering the dynamic nitrogen processes in Jiaozhou Bay (JZB), including phytoplankton growth, respiration, and mortality; particulate nitrogen degradation; and dissolved organic nitrogen remineralization. The results of the field experiments and box model simulations showed good agreement (RSD=20%±2% and SI=0.77±0.04). A three-dimensional water quality model of nitrogen (3DWQMN) in JZB was improved and the dynamic parameters were updated according to field experiments. The 3DWQMN was validated based on observed data from 2012 to 2013, with good agreement (RSD=27±4%, SI=0.68±0.06, and K=0.48±0.04), which testifies to the model's credibility.

Improving optimization efficiency for the total pollutant load allocation in large two-dimensional water areas: Bohai Sea (China) case study

The total pollutant load allocation (TPLA) can be transformed into an optimization problem with regards to water quality constraints. The optimization calculation may become very time consuming when the number of water quality constraint equations is great. A Trial and Error Method (TEM) to remove the redundant points was first introduced through iterative calculations under structure and non-structure model grids. The TEM was applied for the TPLA in the Bohai Sea in China. The calculation time was reduced to about 2min under the condition that 103,433 model grids met the water quality standards. In the best case, the optimization efficiency was improved by 98.9%. The allocation results showed that approximately 90% of total nitrogen (TN) load should be reduced in the 56 pollution sources around the Bohai Sea; of these values, roughly 85% of the reduction could come from 10 pollution sources.

Determination of ciprofloxacin in Jiaozhou Bay using molecularly imprinted solid-phase extraction followed by high-performance liquid chromatography with fluorescence detection

A high selective pre-treatment method for the cleanup and preconcentration of ciprofloxacin in natural seawater samples was developed based on molecularly imprinted solid-phase extraction (MISPE). The ciprofloxacin imprinted polymers were synthesized and the characteristics of obtained polymers were evaluated by scanning electron microscopy, Fourier transform infrared spectroscopy and binding experiments. The imprinted materials showed high adsorption ability for ciprofloxacin and were applied as special solid-phase extraction sorbents for selective separation of ciprofloxacin. An off-line MISPE procedure was optimized and the developed MISPE method allowed direct purification and enrichment of the ciprofloxacin from the aqueous samples prior to high-performance liquid chromatography analysis. The recoveries of spiked seawater on the MISPE cartridges ranged from 75.2 to 112.4% and the relative standard deviations were less than 4.46%. Five seawater samples from Jiaozhou Bay were analyzed and ciprofloxacin was detected in two samples with the concentrations of 0.24 and 0.38μgL(-1), respectively.