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Urban reservoirs serve many purposes including recreation and drinking water, and larger bodies of water can alter the surrounding air temperatures, making urban areas cooler in summer and warmer in winter. However, reservoirs may also be sinks for contaminants. One such group of contaminants, the polybrominated diphenyl ethers (PBDEs), are persistent organic pollutants known to accumulate in sediments and suspended particulate matter (SPM). Few studies have been conducted on PBDEs in water, SPM, and sediment from reservoirs of Shenzhen which is a mega city in South China. To this end, 12 PBDEs were measured in water, SPM, and sediment samples during the dry season (DS) and wet season (WS), to explain the spatiotemporal distribution, congener profiles, sources, and risks of pollutants in four reservoirs (A–D) and their tributaries in the study region. The concentration of ∑12PBDEs during the DS was found to be significantly higher than that during the WS. Source apportionment suggested that commercial penta-, octa-, and deca-BDEs are the major components of PBDEs, resulting mainly from atmospheric deposition, wastewater discharge, and external water-diversion projects. Further, attention should be paid to electronic equipment manufacturing factories in the study area. Risk assessment indicated risk of PBDEs (especially BDE-209) in sediment and SPM to be of concern. This study provides important data support for the control of PBDEs in natural drinking water sources. [ABSTRACT FROM AUTHOR]

In this study, nine congeners of polybrominated diphenyl ethers (PBDEs) and sixteen congeners of polycyclic aromatic hydrocarbons (PAHs) were measured in water samples to elucidate their spatial distribution, congener profiles, sources and ecological risks in the Guanlan River during both the dry season (DS) and the wet season (WS). The concentration of Σ 9 PBDE ranged from 58.40 to 186.35 ng/L with an average of 115.72 ng/L in the DS, and from 8.20 to 37.80 ng/L with an average of 22.15 ng/L in the WS. Meanwhile, the concentration of Σ 16 PAHs was ranged from 121.80 to 8371.70 ng/L with an average of 3271.18 ng/L in the DS and from 1.85 to 7124.25 ng/L with an average of 908.11 ng/L in the WS. The concentrations of PBDEs and PAHs in the DS were significantly higher than those in the WS, probably due to the dilution of the river during the rainy season. Moreover, the spatial distribution of pollutants revealed decreasing trend in the concentration from upstream to downstream and almost identical pattern was observed during both seasons. The source apportionment suggested that penta-BDE and to some extent octa-BDE commercial products were major sources of PBDEs in the study area. However, the sources of PAHs were mainly comprised of fossil fuels and biomass burning, followed by the petroleum products and their mixtures. The results of the ecological risk assessment indicated PBDEs contamination posed high ecological risks, while PAHs exhibited low or no ecological risks in the study area. Consistent with the environmental levels, the ecological risks of pollutants were relatively lower in the WS, compared to that in the DS. The results from this study would provide valuable baseline data and technical support for policy makers to protect the ecological environment of the Guanlan River. Image 1 • The concentrations of PBDEs and PAHs in the DS were higher than those in the WS. • The sources of PAHs were mainly comprised of fossil fuels and biomass burning. • Octa-BDE commercial products were major sources of PBDEs in the study area. • PBDEs posed high ecological risks, while PAHs posed low risks in the Guanlan River. • PBDEs and PAHs levels were affected by the content of TN, NH 4 -N, COD, BOD 5 and DO. Capsule: Rapidly urbanizing costal city Shenzhen is influencing the ecological resources of the Guanlan River through increasing the concentrations of PBDEs and PAHs. [ABSTRACT FROM AUTHOR]

To solve the shortage of land resources, many coastal cities have implemented coastal reclamation projects over the past few decades. Coastal reclamation can promote the economic development of coastal cities and improve human well-being in coastal zones. However, it can inevitably cause a series of ecological and environmental issues, such as coastal water pollution, ecosystem destruction, habitat loss, and land subsidence. Shenzhen and Hong Kong are two large neighboring Chinese coastal cities in southern China with different systems. As densely populated and economically developed cities, they face similar land shortage issues. However, recent coastal reclamation changes in Shenzhen and Hong Kong are unclear under different social and political systems. To fill this gap, this study aimed to monitor and compare recent annual coastal reclamation in Shenzhen and Hong Kong with totally different systems using free and open satellite products. Then, to compare the results of coastal reclamation between Shenzhen and Hong Kong. Large-scale coastal reclamation in Shenzhen and Hong Kong from 2000 to 2018 can be observed. The total area of coastal reclamation was 4140.7 hm2, of which the total coastal reclamation area in Shenzhen was 3409.8 hm2 and the total coastal reclamation area in Hong Kong was 730.9 hm2. Coastal reclamation in Shenzhen showed a temporal characteristic of "increasing slightly and then decreasing sharply". Before and after 2010, the area of accumulated coastal reclamation were 3202.9 hm2 and 206.9 hm2. Comparatively, coastal reclamation in Hong Kong exhibited a temporal characteristic of "first decreasing and then increasing and then decreasing". In 2002 and 2014, the scale of coastal reclamation was relatively large, with a total area of 501.8 hm2, accounting for 69.19% of its total area of coastal reclamation. The comparison between our produced coastal reclamation and the official area on coastal reclamation exhibited a good agreement based on correlation analysis (r = 0.99) and RMSE (Root Mean Square Error) (0.72). Since the 21st century, Shenzhen and Hong Kong have shown different, even opposite, policies on coastal reclamation. It will be necessary to continuously monitor future coastal reclamation driven by policies for better conducting sustainable coastal development in the Guangdong-Hong Kong-Macao Greater Bay Area. [ABSTRACT FROM AUTHOR]

• Multi clusters identify spatio-temporal-parametric heterogeneity in PRB. • PRB water quality is efficiently evaluated by NH 3 N-DO based WQImins. • Socioeconomic factors (>70%) drive water quality variations in PRB. • Urban river WQImins in periods align with identified diverse clusters in PRB. The Pearl River (PR) is China's second-largest river, playing a crucial role in regulating and supplying water in the southeast. However, for the last decade, the PR has been experiencing water quality deterioration due to population growth, rapid economic development, and diverse human activities, particularly in its delta areas. This study analyzed the characteristics and evolution of eight water quality variables, including pH values (pH), water temperature (WT), dissolved oxygen (DO), five-day biochemical oxygen demand (BOD 5), permanganate index (PI), total phosphorus (TP), ammonia nitrogen (NH 3 N), and fluoride (F−), which were monitored monthly at 16 water quality monitoring stations from January 2009 to August 2019. Overall, annual average BOD 5 and F− concentrations met Class I water quality standards, while TP and NH 3 N conformed to lower standards. The cluster results showed noticeable differences for parameter grouping (DO-organic parameters-nutrient and solutes), seasonal variation (wet and dry), and water quality status (contaminated-remediating-fine). The Water Quality Index (WQI) ranged from 8.3 ("very poor") to 91.7 ("excellent") in the entire basin from 2009 to 2019, and NH 3 N-DO based WQImins were identified using the All-Subsets Linear Regression method. The fitting results of the Generalized Additive Models displayed that the deviance explained by natural factors ranged from 37.2% to 61.3%, while the socioeconomic explanation exceeded 70%. The WQImin component evolution (2003–2019) of Shenzhen River estuary, the most important part of the PR estuary, agreed with key parameter variations in heterogeneous clusters in the entire basin. Moreover, Shenzhen's water quality remediation applications indicated that reasonable-efficient-powerful efforts and support from governments could accelerate recovery. For the management departments, consistent measures should be strictly enforced, and elaborate regionalized management based on clusters could be attempted to maintain excellent water quality. [Display omitted] [ABSTRACT FROM AUTHOR]

Limited studies have demonstrated the environmental concerns of perfluorinated compounds (PFCs) in the rivers flowing through the rapidly urbanizing areas. Therefore, this study aims to investigate the spatial and temporal distribution, major sources and ecological risks of PFCs in the surface water samples, collecting from the Guanlan River, Shenzhen, China. The concentrations of ∑PFCs ranged from 11.3 to 384 ng/L, with a mean value of 81.8 ng/L in the dry season, and ranged from 6.90 to 619 ng/L, with a mean value of 339 ng/L in the wet season. Short-chain PFCs such as perfluorohexane sulfonate (PFHxS) and perfluorobutane sulfonate (PFBS) were detected as the predominant compounds. Further, the spatiotemporal distribution revealed significantly higher levels of PFCs in the wet season than those in the dry season, and relatively higher levels in the tributaries than those in the mainstream. Source apportionment highlighted the industrial discharges, domestic wastewater, precipitation, and wastewater treatment plants as the major sources of PFCs. Moreover, the population density and associated urban sewage emissions observed as important indicators for PFCs uneven distribution in the area. The ecological risk assessment revealed perfluorotetradecanoic acid (PFTA, C14) posed high ecological risks to the aquatic organisms (especially for mysid) in the Guanlan River. Taken all together, this study not only unveiled the characteristics of PFCs contamination in the rapidly urbanizing catchment, but also provided the baseline data for policy makers to protect the ecological environment of the urban rivers in the rapidly growing area. Image 1 • Population density was key indicator for PFCs pollution in rapidly urbanizing area. • Uneven temporal distribution was due to the abundant precipitation in wet season. • Spatial variation in the mainstream was owing to efficient river management. • Source apportionment revealed mixed potential PFCs sources in the Guanlan River. • Long chain PFCs posed higher ecological risks to mysid in the Guanlan catchment. [ABSTRACT FROM AUTHOR]