Molybdenum selenide (MoSe2) is promising for the high-affinity capture of toxic metals, but its adsorption performance is limited by inefficient utilization of active sites. Herein, a simple and effective method was proposed to enhance the adsorption performance of MoSe2 nanosheets by phase engineering that modulated both in- plane and edge sites. NaBH4, acting as an electron donor, reduced the formation energy of 1T phase, induced the creation of Se vacancies and edge sites, and expanded the interlayer spacing. The improvement in Pb(II) adsorption was discussed in detail from characterizations, adsorption modelling, and theoretical calculations to identify the structure-performance relations of MoSe2. Notably, the 1T-rich MoSe2 exhibited a Pb(II) adsorption kinetic constant of 1.91 mg g-1 min-1, a high adsorption capacity of 945.2 mg g-1, and a distribution coefficient of 7.1 x 107mL g-1 for Pb(II), representing one of the best results among current materials. The phase transition of 1T-rich MoSe2 facilitated interfacial charge transfer and enhanced Pb capture via Pb-Se complexation and PbMoO4 crystallization. Additionally, macrostructural MoSe2 sponges were fabricated and their potential for real-world water treatment was validated through tests in various water matrices and continuous-flow conditions. This phase engineering strategy provides prospects for the application of two-dimensional materials in sustainable water treatment by tailoring active sites.

This study elucidates critical desorption thresholds of activated carbon in hydrocyclone which is used to treat printing and dyeing wastewater under high-turbulence flow fields. The effects of inlet adsorbent-wastewater ratio, inlet flow velocity and particle size on desorption critical adsorbent-wastewater ratio were studied through experiments. The results show that exists a critical adsorbent-wastewater ratio beyond which desorption occurs. When the inlet flow velocity is 1 m/s, the activated carbon with D= 0.2 mm has the maximum desorption critical adsorbent-wastewater ratio of 1.0 g/L. Meanwhile, for this particle, as the adsorbent-wastewater ratio increases, the variation of the desorption rate exhibits a two-stage phenomenon, namely a rapid growth stage and a plateau stage. For activated carbon particles with D= 0.3 mm, after the critical adsorbent-wastewater ratio, further increasing the ratio results in an increase in the desorption rate followed by a decrease. For activated carbon particles with D= 0.125 mm, the critical adsorbent-wastewater ratio reaches its minimum at V= 1 m/s, while beyond the critical gamma, the rate of desorption variation becomes smaller and attains the lowest numerical value. Additionally, an increase in the inlet flow velocity of the hydrocyclone leads to a decrease in both the critical adsorbent-wastewater ratio and the desorption rate.

Tides have significant effects on material and energy transports over the continental shelf. A mooring system located in the shelf region of the northeastern South China Sea observed strong and weak mean currents during the spring and neap tides in summer, respectively. The mechanism leading to this difference is investigated by using a three-dimensional circulation model. We find that the impact of tides (TI) on currents exhibited as current components opposing wind-driven circulation play an important role. The TI current components are stronger than the tidal residual currents in summer when vertical stratification enhances the tidal rectification. Tides can affect pressure gradient by modifying sea surface height on the shelf, while in shallow and shelf break regions, the non-linear advection and vertical diffusion become significant in momentum equations attributable to the interactions of tidal currents, bottom topography and water column stratification. Consequently, the along-shelf volume transport is reduced by about 21.6% due to the TI current components and only by about 6.1% due to the tidal residual currents. This study highlights the importance of both tidal mixing and tidal rectification in regulating shelf circulation in the northeastern South China Sea.

Water hypoxia and metal pollution are commonly co-existed in urbanized estuaries. This study focuses on the effect of an extended dissolved oxygen (DO) full-life dynamics (86 days) on metal behavior across the sediment-water interface through laboratory microcosms from two typical zones in Pearl River Estuary. Combining our time-series results of concentrations and fluxes, it showed that Co, Ni, and Zn consistently presented a release-precipitation-release trajectory with an oxic-hypoxic-anoxic-reoxic transition, characterized with highly variable behavior in the hypoxic-anoxic hotmoments. In parallel, changing DO dynamics significantly activated a repartitioning process of Co, Ni, and Zn among several species and elevated their risk in sediments, promoting the formation of more labile species in the 0–10 mm hotspots, where metals sensitively responded. Over DO transition, metal cycling was tightly co-related with Fe, Mn, and S elements. It was found that Mn was dominated in low oxygen-hypoxic period, but switched to S and Fe in anoxic stage, limiting sustained metal liberation to overlying water. Enlarging this experiment to practice, released Zn fluxes from sediments in hypoxic summer could contribute about ~2.0 % to their stocks in water column, while increase to 20 % (1 m bottom water) in highly-stratified zones. This study has certain significance in understanding the long-term metal behavior and fate in estuarine regions, even lakes and reservoirs.

The impact of thermal pollution caused by cooling water discharge of power plant on the surrounding marine ecology has been a hot issue in oceanographic research. To reveal the distribution pattern of cooling water discharge of Daya Bay Nuclear Power Plant in summer and the impact on the surrounding marine environment, this research established a high-resolution three-dimensional (3D) numerical model based on ECOMSED in the Daya Bay. The model results are consistent with the observations on the distribution of tide level and temperature. The simulated horizontal distribution of temperature rise is consistent with the distribution trend of remote sensing images. The study showed that the stratification of the Daya Bay water is stronger in summer. The cooling water mainly spreads in the surface layer, and the temperature rise in the bottom layer is not apparent. Quantitative analysis showed that around 18.8-21.6 km 2 of the area has 1°C surface temperature rises. The area of temperature rises that exceeds 2 °C is between 6.2 and 8.1 km 2 . The area of temperature rises that exceeds 4 °C is between no more than 1.2 km 2 . The area with a bottom temperature rises of 1 °C does not exceed 2.2 km 2 , and there is no area that has a bottom temperature rise over 1 °C. The tidal dynamics process influences on the dispersion of cooling water discharge from Daya Bay Nuclear Power Plant, where the influence is more significant in the spring tide period than in the neap tide period. Our findings are consistent with previous researches.

The influence of overlying hydrodynamics on the exchange behaviour and fluxes of heavy metals at the sediment-water interface (SWI) is poorly understood. In the study, metals exchange behaviour and exchange rate at the SWI under resuspended and undisturbed scenario were investigated The results showed that dissolved Cr, Cu, Zn, and Pb concentrations increased rapidly to attain maximum values between 0.3 and 0.5 N center dot m(-2) after the sediment resuspended. Following the quick release, metals concentrations gradually decreased and remained at relatively low levels, especially for Cu and Zn. Meanwhile, Cu, Zn, and Pb had higher potential remobilization potential in the undisturbed case. Calculating with the hydrodynamics in the Modaomen, the metals efflux under the resuspension scenario could reach 0.55 to 4130.83 mg center dot m(-2)center dot yr(-1), which were 1-3 orders of magnitudes higher than the undisturbed case. Whether or not resuspension events occurred, estuarine sediments were source of heavy metals, especially in the weakly mixed zone.

Shiziyang Bay, located in the upstream of the Pearl River Estuary, has frequently suffered from hypoxia since 2000, which has persisted in recent years despite effective controls on anthropogenic pollutant loads. To explore the underlying causes, changes in dissolved oxygen (DO), nutrients, chemical oxygen demand (COD), and chlorophyll a (Chl a) along the bay in response to altered pollutant inputs were investigated using observations collected in summers of 2015-2019 and historical data during 2000-2008. In addition, DO sources and sinks were calculated based on data from August 2020 and laboratory incubations for water column respiration (WCR) and sediment oxygen uptake, and were compared with their equivalents in August 2008 to elucidate changes in primary processes controlling hypoxia. The results showed that ammonia has decreased significantly with pollutant control, while other parameters responded in different trends, especially for Chl a (with a substantial increase over time). The intensified eutrophication contributed to high COD levels, leading to a strong WCR (as dominant oxygen depletion) close to that in the 2000s and thereby maintaining low-oxygen conditions despite reduced effluent discharges. The shifted primary oxygen-consuming substances from allochthonous inputs to in-situ phytoplankton production were also evidenced by significant correlation between oxygen consumption rate and Chl a in recent data. Simultaneously, the enhanced algal blooms could also modulate oxygen supply, resulting in higher photosynthetic oxygen production and lower air-sea reaeration compared with the past. Furthermore, the impact of major environmental changes on exacerbated eutrophication was explored and it was speculated that notable declined sediment loads would be important by improving light conditions to promote phytoplankton proliferation in the bay. Collectively, substantial control on eutrophication as well as tracking DO source-to-sink processes is of great importance to mitigate hypoxia in Shiziyang bay.

The summertime low-oxygen conditions in the Pearl River Estuary (PRE) have experienced a significant spatial expansion associated with notable deoxygenation in recent decades. Nevertheless, there is still a lack of quantitative data on the long-term trends and interannual variabilities in oxygen conditions in the PRE as well as on the driving factors. Therefore, the long-term deoxygenation in a subregion of the PRE (the coastal waters off Hong Kong) was comprehensively investigated in this study using monthly observations during 1994–2018. To evaluate the changes in scope and intensity of oxygen conditions, an indicator (defined as the low-oxygen index, LOI) that integrates several metrics related to low-oxygen conditions was introduced as the result of a principal component analysis (PCA). Moreover, primary physical and biogeochemical factors controlling the interannual variabilities and long-term trends in oxygen conditions were discerned, and their relative contributions were quantified by multiple regression analysis. Results showed that the regression models explained over 60 % of the interannual variations in LOI. Both the wind speeds and concentrations of dissolved inorganic nitrogen (DIN) played a significant role in determining the interannual variations (by 39 % and 49 %, respectively) and long-term trends (by 39 % and 56 %, respectively) in LOI. Due to the increasing nutrient loads and alterations in physical conditions (e.g., the long-term decreasing trend in wind speeds), coastal eutrophication was exaggerated and massive marine-sourced organic matter was subsequently produced, thereby resulting in an expansion of intensified low-oxygen conditions. The deteriorating eutrophication has also driven a shift in the dominant source of organic matter from terrestrial inputs to in situ primary production, which has probably led to an earlier onset of hypoxia in summer. In summary, the Hong Kong waters have undergone considerable deterioration of low-oxygen conditions driven by substantial changes in anthropogenic eutrophication and external physical factors.

Abstract. The summertime low-oxygen conditions in the Pearl River Estuary (PRE) have experienced a significant expansion in spatial extent associated with notable deoxygenation in recent decades. Nevertheless, there is still a lack of quantitative understanding of the long-term trends and interannual variabilities in oxygen conditions in the PRE as well as the driving factors, which was comprehensively investigated in this study using monthly observations in the eastern PRE during 1994–2018. To evaluate the changes in scope and intensity of oxygen conditions, an indicator (defined as the Low-oxygen Index, LOI) that integrates several metrics related to low-oxygen conditions was introduced through the principal component analysis (PCA). Moreover, primary physical and biogeochemical factors controlling the interannual variabilities and long-term trends in oxygen conditions were discerned, and their relative contributions were quantified by the multiple regression analysis. Results showed that the regression models explained over 60 % of the interannual variations in LOI. Both the wind speeds and concentrations of dissolved inorganic nitrogen (DIN) played a significant role in determining the interannual variations (by 39 % and 49 %, respectively) and long-term trends (by 39 % and 56 %, respectively) in LOI. Due to the increasing nutrient loads and alterations in physical conditions (e.g. the long-term decreasing trend in wind speeds), coastal eutrophication was exaggerated and massive marine-sourced organic matter was subsequently produced, thereby resulting in an expansion of intensified low-oxygen conditions. It has also driven a shift in the dominant source of organic matter from terrestrial inputs to in situ primary production, which has probably led to an earlier onset of hypoxia in summer. In summary, the eastern PRE has undergone considerable deterioration of low-oxygen conditions in the context of substantial changes in anthropogenic eutrophication and external physical factors.

本文利用2018年1月盐水上溯期间在磨刀门区域所获得的现场调查资料,分析该区域的重金属污染现状及空间分布特征,探究重金属的迁移转化特点以及盐度等环境因素对重金属分配结果的影响.基于水体盐度及层化水平将研究区域分为淡水区、混合区及咸水区.结果表明,颗粒态与溶解态重金属含量在淡水区与咸水区之间存在显著差异,颗粒态重金属含量均呈现出由陆向海方向随盐度增加而降低的趋势,各元素的空间变异程度依次为Cd＞Cr＞Zn＞Pb＞Cu＞As＞Ni＞Co;溶解态Pb、Cr、As、Co浓度沿向海方向呈逐渐升高趋势,而Cd、Cu、Ni、Zn浓度则呈现"低—高—低"的变化特征,各元素的空间变异程度依次为Zn＞Cr＞Cd＞Pb＞Cu＞Co＞As＞Ni.重金属的固液分配系数沿向海方向呈逐渐下降趋势,主成分分析结果表明,盐度和悬浮物浓度是影响磨刀门河口重金属分配的主要环境因素.

Our understanding of eutrophication-induced acidification in estuaries and coastal oceans is complicated by the seasonally and spatially changing interactions between physical and biochemical drivers. By combining the conservative mixing method and a physical-biogeochemical model, we present the seasonal and spatial dynamical analysis of eutrophication-induced acidification in the Pearl River Estuary in the northern South China Sea. In summer, the widespread eutrophication-induced acidification is regulated by two distinct physical drivers, which are the strengthened stratification in the hypoxia zone and the high turbidity in the Lingdingyang Bay. In the hypoxia zone, eutrophication-induced acidification is controlled by the combined effect of benthic remineralization and stratification, while it is dominantly regulated by local biochemical processes (nitrification and respiration) of the whole water column in other regions of the estuary. In winter with the enhanced vertical mixing, the eutrophication-induced acidification is still active in the Lingdingyang Bay, and its strength has largely decreased compared with summer condition. While for the hypoxia zone, the eutrophication-induced acidification peaks in summer and disappears in winter. Plain Language Summary Eutrophication in estuaries has accelerated the ocean acidification, which induced a negative impact on marine ecosystem. In the estuary, physical and biochemical processes lead to difficulties in understanding and evaluating the impact of eutrophication-induced acidification. High-resolution and coupled oceanographic models can reproduce the biogeochemical cycles in the marine system and present an integrated framework to understand ocean acidification. We revealed two distinct types of eutrophication-induced acidification in the estuary by using an oceanographic model. The model results show that these two types of eutrophication-induced acidification are regulated by different physical processes that are water stratification and turbidity, which result in their unique seasonal evolution patterns.

Located in the northern South China Sea, the Pearl River Estuary (PRE) is one of the most important estuaries in China and is surrounded by several megacities. Hypoxia mainly occurs in the bottom waters of the PRE during summer and is more prominent near the Humen outlet and the subestuary outside Modaomen and Jitimen. A well-validated three-dimensional (3-D) coupled physical-biogeochemical model was used to explore the changes in dissolved oxygen (DO) dynamics and hypoxic conditions in the PRE over an intra-annual cycle and elucidate the processes controlling the generation, development, and dissipation of hypoxia. In summer, oxygen consumption due to the high-intensity sediment oxygen demand (SOD) intensified by large inputs of riverine particulate organic carbon (POC) exceeded the DO supplemented by vertical diffusion (largely inhibited by strong fresh water–induced stratification), thus leading to a significant decrease in DO in the bottom waters; in other seasons, these DO source and sink terms were nearly balanced so that the bottom DO concentrations were maintained at higher levels. Moreover, the lag analysis shows that there is an approximately 2-month lag between riverine POC and SOD. By comparison, the low-oxygen area near Humen has a controlling mechanism distinct from that of the subestuary outside Modaomen and Jitimen. Specifically, the timely and sufficient oxygen supplement brought by vertical diffusion can replenish the bottom DO consumed by SOD in this region, and the formation and development of low-oxygen conditions (DO ≤ 4 mg L−1) is mainly affected by riverine low-oxygen inflows. In summary, our study clarified that the terrestrial organic pollutant input and low-oxygen water from the upper reaches have an important impact on the DO in different areas of the PRE, especially the low-oxygen area near Humen, which is controlled by the water quality of the upper reaches. This conclusion is of great significance for regional environmental management.

Many estuaries have undergone severe saltwater intrusion in addition to simultaneously experiencing serious heavy metal pollution. To explore the effect of water density stratification associated with saltwater intrusion on the behaviour of heavy metals (Cr, Co, Ni, Cu, Zn, As, Pb, and Cd) in water and sediments, a field survey was conducted in a typical estuary (Modaomen). The content, distribution, and mobility of heavy metals were investigated, as well as the influence of environmental factors on their future. The results showed that Modaomen estuary was characterised by a notable variation in salinity along the estuary, presenting total freshwater upstream, high salinity stratification water in the mouth, and saltwater offshore. Dissolved metals presented a prominent gradient vertically, with 1.2-2.1 times higher in bottom water than in surface water and the highest contents in the highly-stratified bottom water. Elevated salinity and restricted mixing induced by water stratification were likely the causes of this outcome. The distribution of heavy metals in sediments was greatly governed by grain size, Fe/Mn (hydr)oxides, total organic carbon, salinity, and dissolved oxygen. Comprehensive evaluation, combined with total contents and chemical fractions of heavy metals, indicated that internal release from sediments contributed a considerable part to the higher levels of heavy metals in bottom water, particularly for Zn and Pb, which was fully consistent with their status in water body, and elevated salinity and lack of oxygen were likely the primary driving factors. During the phase-partition processes between bottom water and sediments, partitioning coefficients were markedly lower in the highly stratified zone, implying that saltwater intrusion facilitated the mobility and repartitioning processes of metals. Because of increased levels and toxicity of heavy metals in water and extended residence time during saltwater intrusion, the potential damage to the estuarine ecosystem should receive more attention.

基于经过验证的三维水动力-水质模型,对珠江口夏季有机碳进行海陆源区分,并对海陆源有机碳的分布特征、贡献比重及其通量过程进行研究.结果表明,水平方向上,珠江口夏季陆源(海源)有机碳浓度从口门到外海逐渐降低(升高),在表、底层海水中平均浓度分别为1.45和0.87mg/L(0.97和1.05mg/L);垂直方向上,在层化水域陆源(海源)有机碳浓度从上到下逐渐递减(升高),在非层化水域海陆源有机碳浓度垂向分布较为均匀.珠江口夏季海源有机碳贡献率表层海水低于底层海水,平均贡献率为48.26％,沿向海方向海源有机碳贡献率逐渐增加——从内伶仃洋水域的4.43％逐渐提升到外伶仃洋东侧水域的8l.20％.珠江口水动力条件复杂,在径流、潮汐、季风等因素的作用下陆源有机碳向海输送且向海输送量逐渐递减;海源有机碳存不同水域动力输送特征不同,西南水域向海输送,向海输送量逐渐递增;东北水域向岸输送,向岸输送量逐渐递减.陆源有机碳生化反应活性较弱,只有小部分被生化过程消耗,其迁移转化主要由沉降过程控制,而海源有机碳的迁移转化,则由口门的动力输送过程主控向外海的生化耗碳过程主控过渡.此外,海源有机碳沉降作用明显低于陆源有机碳,生化作用明显高于陆源有机碳.

Human activities associated with estuaries have already affected estuarine carbon cycles and flows. Especially with rapid development and urbanization, widespread wastewater treatment plants in watersheds have altered the amounts and proportions of riverine nutrients and organic carbon, which has strongly impacted carbon dynamics and budgets in coastal oceans. In this study, a well-validated carbon cycle model was used to reveal the response of carbon dynamics to reasonable estimated disturbance to riverine inputs (i.e., nutrients, dissolved organic carbon (DOC) and particulate organic carbon (POC)) in the Pearl River Estuary (PRE). Scenario results demonstrate the distinct response patterns and spatial variability of carbon dynamics. Specifically, with phytoplankton blooms and biological production closely linked to riverine nutrients, riverine nutrient alterations mainly impact photosynthesis in the PRE, especially in the lower part of the PRE. As DOC fuels bacterial respiration in the water column, heterotrophic respiration is particularly sensitive to riverine DOC disturbances. POC not only relates to light penetration in turbid estuarine waters, which impacts photosynthesis, but also undergoes deposition, which affects the biochemical reactions in the sediment. Thus, perturbations to riverine POC input led to significant changes in both biological production and sediment dissolved inorganic carbon (DIC) release. Multiple linear regression results reveal that both net community production and sediment DIC release flux modulate the variations of air-sea CO2 flux in the PRE, which highlights the roles of terrestrial POC input and deposition in a shallow estuary. When delivered into the PRE, a high proportion of POC tends to be deposited and contribute to sediment DIC release or carbon sequestration, while a significant fraction of riverine DOC is transported offshore to shelf regions. This study underscores the impacts of intensive human activities on carbon cycle system in coastal oceans and the importance of terrestrial organic carbon reduction and nutrient control in upstream basins.

The identification and quantification of pharmaceutical and personal care products (PPCPs) in aquatic ecosystems is critical to further studies and elucidation of their fate as well as the potential threats to aquatic ecology and human health. This study used mass balances to analyse the sources, transformation, and transport of PPCPs in rivers based on the population and consumption habits of residents, the removal level of sewage treatment, the persistence and partitioning mechanisms of PPCPs, hydrological conditions, and other natural factors. Our results suggested that in an urbanized river of Guangzhou City, China, the daily consumption of PPCPs was the main reason for the variety of species and concentrations of PPCPs. Through the determination of PPCPs in the river water samples and a central composite design (CCD) methodology, the dominant elimination mechanisms of caffeine and carbamazepine from river water were photolysis and biodegradation, but that of triclosan was sorption rather than biodegradation. The mass data of 3 PPCPs were estimated and corroborated using the measured data to evaluate the accuracy of the mass balance. Finally, caffeine, carbamazepine and triclosan discharged from the Shijing River into the Pearl River accounted for 97.81%, 99.52%, and 28.00%, respectively, of the total mass of these three compounds in the surface water of Shijing River. The results suggest that photolysis are the main process of natural attenuation for selected PPCPs in surface waters of river systems, and the transfer processes of PPCPs is mainly attributed to riverine advection. In addition, the low concentration of dissolved oxygen inhibited the degradation of PPCPs in the surface water of Shijing River.

A carbon cycle model is built to describe the behavior of carbon materials in the Pearl River Estuary (PRE), China. The distributions and transformations of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC) are simulated in the water column and sediment for the year 2006. The terrestrial carbon input is the dominant factor that determines the seasonal variation of carbon, while physical and biochemical processes contribute to the spatial-temporal circulation of carbon. The simulation results reveal that the PRE acts as a net source for atmospheric CO2 throughout the year, and it buffers the export of DIC from the river and sediment to the adjacent system via the DIC consumption by primary production. As a consequence of biochemical processes, the PRE exports more organic carbon to the sediment and adjacent marine ecosystems than the amount that it receives from upstream river reaches. POC burial in sediment and refractory DOC export to the adjacent marine ecosystems are the main carbon fixation pathways in the PRE. The total amount of carbon fixation in PRE is estimated 6.92 x 10(10) mol C year(-1). Carbon fixation analysis shows that (1) 20.4% of the POC deposited into sediment is fixed through burial, while the remaining continues to participate in the circulation of carbon materials, and (2) the combined effects of river discharge and monsoon dominate the amount and direction of refractory DOC exports. Plain Language Summary Carbon cycle in estuaries is an important part of the global carbon cycle. Due to the intensive human impact and complicated biogeochemical processes, there exist great uncertainties in estimating carbon fixation and difficulties in illustrating the entire carbon cycle in estuaries. In this study, we chose the Pearl River Estuary as the study area and used a carbon cycle model to simulate the distribution and transformation of carbon materials. Our study found that the carbon cycle in the PRE is very active. Even though CO2 undergoes continuous evasion from the sea surface to the atmosphere, the PRE fixes 6.92 x 10(10) mol C year(-1) via particulate organic carbon burial into deep sediment and refractory dissolved organic carbon export to adjacent marine systems. In different seasons, with river discharge and monsoon changes, carbon fixation ability and the direction of carbon export flux vary as well. Key Points The entire carbon system of Pearl River Estuary is simulated in this study Carbon fixation pathways are estimated, and carbon fixation ability is simulated in this study

利用已经过验证的高分辨率三维海洋动力模型FVCOM,根据1984-2014年内伶仃洋的围填海变化情况,结合情景模拟案例,研究分析围填海对伶仃洋水流动力的影响,探究截流式和顺流式围填海对伶仃洋不同季节的水平余流场、垂向环流结构以及潮汐变化过程的影响.研究结果表明,围填海对伶仃洋的余流流向没有明显影响,但对余流速有较大的影响.在水平方向上,截流式围填海使得周边海域的余流速明显增大,增幅在0.02～0.25 m/s不等,其中口门区域受到的影响最大;相较于底层流场,表层流场受围填海的影响相对更大,围填海以南的较远海域在表层出现一条强度逐渐减弱的流速减小带,减幅在0.02～0.15 m/s不等,且影响范围与流场的分布密切相关,在夏季向南延伸,在冬季向西南延伸.顺流式围填海的影响则主要分布在伶仃洋两侧沿岸,并且不同季节的影响特点有一定区别,在夏季使得内伶仃洋东岸海域流速增大,但在冬季使其流速减小,变化幅度均在0.02 m/s以上.在垂直方向上,围填海使口门区域余流的纵向流速梯度增加,并且改变了伶仃洋余流的垂向分布情况,总体表现为远离围填海的海域表、底层余流的流速减小,中上层余流的流速增大;与此同时,围填海大幅度改变了周边海域的横向流速,并且在伶仃水道、矾石水道等区域产生了新的横向环流.围填海使得河口至围填海的余水位明显上升,使得伶仃洋海域的余水位下降,余水位梯度的增大是围填海周边余流速增大的主要原因.另外,围填海影响了伶仃洋的潮汐变化过程.在大潮期间,围填海改变了伶仃洋海域涨落潮时的潮流流速,使得周边海域落急流速增加,较远海域落急流速减小,而涨急流速都减小;同时,围填海使得海域涨落潮时的潮位受到一定影响.围填海最终使得伶仃洋的潮汐相位提前了20～35 min.

A validated hydrodynamic-biogeochemical model was applied to investigate the effects of physical forcing (i.e., river discharge, winds, and tides) on the summertime dissolved oxygen (DO) dynamics and hypoxia (DO < 3 mg L−1) in the Pearl River estuary (PRE), based on a suite of model sensitivity experiments. Compared with the base model run in 2006 (a wet year), the simulated hypoxic area in the moderate year (with 75% of river discharge of the base run) and the dry year scenario (with 50% of river discharge of the base run) was reduced by ~30% and ~60%, respectively. This is because under the lower river discharge levels, less particulate organic matter was delivered to the estuary that subsequently alleviated the oxygen demand at the water–sediment interface, and in the meantime, the water stratification strength was decreased, which facilitated the vertical diffusion of DO. Regarding the effect of winds, the highly varying and intermittent strong winds had a significant impact on the replenishment of bottom DO by disrupting water stratification and thus inhibiting the development of hypoxia. Sensitivity experiments showed that the hypoxic area and volume were both remarkably increased in the low wind scenario (with a bottom hypoxic zone extending from the Modaomen sub-estuary to the western shoal in Lingdingyang Bay), whereas hypoxia was almost absent in the strong wind scenario. The DO budget indicated that winds altered the bottom DO mostly by affecting the DO flux due to vertical diffusion and horizontal advection, and had a limited influence on the DO consumption processes. Moreover, the DO concentration exhibited remarkable fluctuations over the spring-neap tidal cycles due to the significant differences in vertical diffusion. The results of a tide-sensitivity experiment indicated that without tide forcing, most of the shallow areas (average water depth < 5 m) in the PRE experienced severe and persistent hypoxia. The tides mainly enhanced mixing in the shallow areas, which led to higher vertical diffusion and enhanced replenishment of bottom DO.

A three-dimensional unstructured-grid Finite Volume Community Ocean Model was applied to investigate the principal dispersal patterns and intraseasonal variability of the Pearl River plume in summer (June–August) during 1999–2010. The favorable forcing conditions and underlying dynamics for the formation of plume patterns were also explored. The model was validated against a suite of water level, salinity and temperature observations collected during the simulation periods. The simulated results agree well with the observed data, indicating that the model reasonably reproduces the main hydrodynamic processes occurring in the Pearl River estuary. Using Self-Organizing Maps, we extracted eight typical dispersal patterns of the Pearl River plume from the multiyear simulated daily surface salinity fields and estimated the occurrence frequency of each pattern. The eight plume patterns were further categorized into five types based on the morphologies and extension distances of each pattern, namely, west alongshore spreading, fettered spreading, offshore bulge spreading, bidirectional spreading and east offshore spreading; these five types account for 26.3%, 9.8%, 11.5%, 29.1% and 23.3% of the total occurrence frequency, respectively. The pattern that is characterized by bidirectional spreading with a strong eastward extension has the largest occurrence frequency among the eight patterns. Through an analysis of the best matching units derived from Self-Organizing Maps and the corresponding river discharge and wind conditions, we find that both wind and river discharge can significantly affect the Pearl River plume patterns. The plume orientation is mainly modulated by the wind, while the plume area and eastward extension distance are mainly affected by the river discharge. Generally, the favorable forcing conditions and underlying dynamics are different for each plume pattern, and various combinations of river discharge and wind can generate different dynamics to form different plume patterns. The climatological surface salinity field in summer shows a bidirectional structure with the plume extending westward attaching to the coast and eastward detaching from the coast. The areas and eastward extension distances of the Pearl River plume gradually decrease from June to August, affected by the intraseasonal changes in river discharge and wind. The statistical results of the daily plume patterns for June–August show that east offshore spreading, bidirectional spreading and west alongshore spreading are the primary types occurring in June, July and August, respectively. Furthermore, the occurrence frequencies of the west alongshore spreading and offshore bulge spreading increase, while the occurrence frequency of the east offshore spreading decreases from June to August.