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Many tributaries of the Pearl River carry large amounts of terrestrial pollutants into estuarine areas. Heavy metals accumulate in estuarine sedimentary environments, and coupled and changing biogeochemical processes occur in estuarine areas. The results of this study showed that the heavy metal contents in the sediment were the highest near the confluence of the Humen and Jiaomen outlets in 2005 and 2019; they were the second-highest near the remaining outlets, and gradually decreased toward the lower reaches, with high contents on the western shore and low contents on the eastern shore. The heavy metal pollution mainly originated from the Pearl River runoff. The historical evolution of heavy metals in the Pearl River Estuary (PRE) effectively reflected the impacts of pollutant inputs from the river basin as well as industrial and agricultural production and anthropogenic activities in the Guangdong–Hong Kong–Macao Greater Bay Area (GBA). In 2019, the surface sediments were not contaminated with Hg, and the Pb and Zn contents decreased significantly, indicating significant advances in environmental management; however, the Cu and Cd levels still indicated heavy pollution level in the upper reaches. [ABSTRACT FROM AUTHOR]

The application of biosolids is common in the agricultural industry; it improves the soil condition as well as the nitrogen (N), phosphate (P), and potassium (K) concentrations in it. However, it may cause environmental risks, such as contamination of soil profiles, water sources, and even the food chain because of the accumulation of heavy metals. The effects of different concentration proportions of biosolid (0%, 5%, 10%, 15%, and 20%) in soils on the growth performance, nutrient contents, and toxicity performance of three ornamental species: Ixora chinensis, Schefflera heptaphylla, and Hibiscus rosa-sinensis were studied. Other common organic soil amendments like biochar, chicken manure (CM), and wood waste compost (WWC) were used to compare with the feasibility of biosolid applications. The results showed that the growth performance of the three ornamental species was similar. Soil treated with a 10% concentration of biosolids performed the best in terms of total nutrients in the soil for the three species. For the total nutrients in the plants, biosolids were the best followed by CM, WWC, and biochar. The levels of heavy metals were examined and nutrient balance efficiency was calculated. Undetectable amount of heavy metals was measured in the three ornamental species, meaning it is safe to use biosolids as fertilizers. The 10% concentration of biosolids also performed the best in nutrient balance efficiency, followed by soil treated with 20% CM. The results indicated that the function of biosolids and CM was significant, and these could be a substitute for biochar and WWC use in soils. Biosolid-amended soil can be one of the methods to relieve the landfill loading problem in Hong Kong. [ABSTRACT FROM AUTHOR]

Context: Quantitative information regarding tree species-specific size is an essential tool for landscape planning. It reflects tree-environment and human–environment interactions in the urban landscape. The effects of habitat types on tree allometry have seldom been evaluated. Objectives: Firstly, to derive size-related information of common urban tree species in Hong Kong. Secondly, to evaluate the effects of habitat types on tree allometry. Methods: A database of 28,622 trees was established by a field assessment. The allometric relationships (DBH-height and DBH-crown width relationships), by both OLS regression and quantile regression, and maximum size of 30 common urban tree species, and the effects of five main habitat types on tree allometry were determined. Species were assigned to groups according to dimensional traits by cluster analysis. Results: In general, the allometric relationships of height and crown width to DBH were significant and varied among species. The wide prediction intervals of the OLS regression indicated the high uncertainty of allometric relationships in our region. The 99th percentile crown width of most species reached 10 m, hinting the general failure of most habitats to meet the planting space requirement. Only two large-stature species have narrow crowns. Habitat types posed significant but small species-specific effects on tree allometry. Roadside tree pit was a particularly stressful environment. Conclusions: Our findings can act as a reference for landscape planning and management in Hong Kong and nearby cities, including species growth space requirement and habitat limitations. However, prediction of height or crown width from DBH must be carefully interpreted in our city. [ABSTRACT FROM AUTHOR]

• Build an evaluation model of trees considering transpiration and shading effects. • Study impact of trees to maximize environmental benefits in a subtropical climate. • Higher trees with a lower near-ground LAD reduce PET and improve air quality. • Windward larger or leeward smaller-crown trees minimize PET and enhance air quality. • Increasing plant density and LAI can reduce PET while increasing concentration. Planting trees is considered to relieve the thermal load. However, trees may "pollute" the air quality. Tree net effects should receive more attention, but only a few studies have simultaneously addressed thermal comfort and air quality. By computational fluid dynamics (CFD) simulations, we created an evaluation model of trees and investigated the overall effects of tree planting inside street canyons. We considered the following four parameters by comparing seven common tree species in Hong Kong (subtropical climate): three tree morphological indicators (leaf area index (LAI), tree height (H tree), and crown spread (S crown)) and tree planting density (P tree). The results demonstrated that under a high ambient wind speed, higher trees with a lower near-ground leaf area density are better options, which more greatly reduces the physiological equivalent temperature (PET) by up to 1.1 K but causes the least pollutant accumulation. Bigger-crown trees on the windward side are advocated, while smaller ones are suitable for the leeward side. In such a way, there was at least a 0.7 K decrease in PET on the tree-planted side while maintaining better air quality. Thermal comfort can be improved by increasing LAI or P tree , but a higher LAI or P tree causes a greater accumulation of pollutants. Increasing P tree can cause a 1.1 K reduction in PET, while the effect of changing LAI is relatively limited. When the length of a street is reduced, varying tree factors have a comparable effect. As canyon depth increases, the effect of trees is limited. [ABSTRACT FROM AUTHOR]

In arboricultural research, data analysis is important to the understanding of the characteristics of urban forest. This study attempted to apply machine learning techniques on a relatively small data set. This research aimed at exploring the biodiversity and structure of tree stands on verges and slopes along a highway, and analysing the influences of habitat characteristics on the tree stands with the aid of machine learning techniques. 53 slopes and 52 verges along San Tin Highway, Hong Kong were surveyed. 7209 trees belonging to 23 species were found. Dimension reduction proved successful in the concise characterisation of urban forest by a biodiversity component and an abundance component. The biodiversity component score of the slopes (0.625) was higher than that of the verges (−0.637). However, the abundance component scores of slopes (−0.059) and verges (0.060) showed slight difference, reflecting comparable tree abundance. A 75–25 train/test split was applied on a data subset consisting of slopes registered under a scheme called Systematic Identification of Maintenance Responsibility of Slopes in the Territory for regression analysis. The scores of the two components were regressed on several slope geophysical variables. Slope height and slope area served as significant predictors explaining biodiversity. Boosting improved the explanatory power and predictive accuracy of the regression model on the biodiversity component, as evidenced by an increase in adjusted R2 by 0.23 and a decrease in RMSE by 0.40. This research proved that component scores can serve as inputs for regression models for the explanation of urban forest characteristics by habitat-related variables. In future, small data sets from tree surveys can be analysed using the workflow demonstrated in this study for the generation of more management insights. • Corymbia citriodora (Lemon-scented gum) was the most abundant in San Tin Highway. • Two principal components, namely biodiversity and abundance, were identified. • Principal components showed different species composition between verges and slopes. • Outputs from dimension reduction can serve as inputs for regression model training. • Unsupervised and supervised machine learning are both useful in urban forest context. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied species diversity and tree performance in domestic gardens in Hong Kong. [•] Tree species composition was dominated by a small number of popular exotic species. [•] Tree species distribution was strongly associated with some habitat-tree variables. [•] Indicators of poor tree performance correlated with tree position and confinement. [•] Findings could enhance contribution of domestic gardens to urban biodiversity. [ABSTRACT FROM AUTHOR]

Abstract: Public housing estates (PHEs) in Hong Kong, accommodating 3.3 million of the 7-million population, have generous landscape planting in their grounds. The independent tree management regime generates a tree stock that deviates from the general urban-tree population. This study evaluated species composition, floristic diversity, importance value, and spatial distribution of trees in 102 PHEs (half of the total) occupying 8.31km2 (territory land area of 1104km2), assessed their contribution to urban biodiversity, and developed a species selection strategy to enrich urban biodiversity. 48,823 trees belonged to 232 species, 151 genera and 59 families. Natives contributed 69 species and 10,837 trees. Species profile was skewed toward exotic species and trees. The species were divided into six frequency groups. The signature group had 45 species each with >200 trees. The dominant, common and occasional groups had 20, 26 and 48 species, respectively. 59 species in the rare group and 34 in the solitary group denoted changing and diverse species selections, respectively. Nonmetric Multidimensional Scaling (NMDS) found that species distribution in PHEs was strongly associated with species diversity, estate area and estate age. However, district and region were not correlated with NMDS. Some 98 species were significantly correlated (Spearman) with one or both NMDS axes. Species groups were analyzed to inform a species selection strategy to improve future planting program and enrich urban biodiversity. The methods and findings could be applied to south-China and other cities to rationalize urban-forest programs with the help of objective research data. [Copyright &y& Elsevier]

Abstract: Heritage trees in a city, echoing factors conducive to outstanding performance, deserve special care and conservation. To understand their structural and health conditions in urban Hong Kong, 30 defect-disorder (DD) symptoms (physical and physiological) subsumed under four tree-position groups (soil-root, trunk, branching, and crown-foliage) and tree hazard rating were evaluated. The surveyed 352 trees included 70 species; 14 species with 233 trees were native. More trees had medium height (10–15m), medium DBH (1–1.5m) and large crown (>15m). In ten habitats, public park and garden (PPG) accommodated the most trees, and roadside traffic island (RTI) and public housing estate (PH) had the least. Tree dimensions and tree habitats were significantly associated. The associations between the 2831 DD and tree-position groups, tree habitats and tree hazard rating were analyzed. Fourteen trees from Ficus microcarpa, Ficus virens and Gleditsia fera had high hazard rating, 179 trees from 22 species moderate rating, and 159 trees from 55 species low rating. RTI, roadside tree strip (RTS), roadside tree pit (RTP), roadside planter (RP) and stone wall (SW) had more moderate hazard rating, and PPG, roadside slope (RS) and government, institutional and community land (GIC) more low rating. Redundancy analysis showed that DD were positively correlated with RTS, RTP, RP and SW, but negatively correlated with PPG, RS and GIC (p <0.05). The DD significantly increased tree hazard rating and failure potential. Future management implications for heritage-tree conservation and enhancement focusing squarely on critical tree defect-disorder in urban Hong Kong were explored, with application to other compact cities. [Copyright &y& Elsevier]

Abstract: Heritage trees play special ecological, historical and landscape roles in cities. The officially designated old-valuable trees (OVTs) in Hong Kong, threatened by urban intensification and improper care, demand deep understanding to inform management and conservation. This study evaluated their floristic diversity, biomass structure and importance value, and spatial pattern and differentiation by districts and tree-habitats. Data analysis was assisted by detrended correspondence analysis (DCA), similarity percentage analysis (SIMPER) and other statistical tests. New indices, namely district dissimilarity index (DDI), district heterogeneity index (DHI), habitat dissimilarity index (HDI) and habitat heterogeneity index (HHI) helped to assess spatial differentiation. The 352 OVTs belonged to 70 species, 56 genera and 36 families. Ficus microcarpa dominated with maximum importance value, accompanied by only three common species. Some 22 rare and 44 solitary species denote diverse origins due to inheritance and cultivation. Moraceae and Ficus were the dominant family and genus. The oldest districts accommodated more species, trees, and unique species, whereas newer districts had notably less. DCA showed higher floristic fidelity in old districts, and three common Ficus species were ubiquitous in districts. SIMPER results showed the highest DDI and lowest DHI in the newer district. Public park and garden (PPG) habitat harbours most species, trees, and botanical uniqueness. Three Ficus species were also ubiquitous in habitats. Public housing and PPG had the highest HDI. District and habitat dissimilarities were mainly contributed by dominant and common species. Management implications with reference to preservation and enhancement of OVTs were explored, with applications for other cities. [Copyright &y& Elsevier]

To understand vegetation development during the ecological succession of rehabilitated quarries, floristic composition and structure were evaluated at different restoration phases on three quarries in Hong Kong that were planted with exotic woody species over the course of 2-14 years. A total of 113 species, of which 82 were woody species, were recorded. Exotic species dominated the overstory, and species number, richness, and diversity increased with age. Some light-demanding early successional species were becoming dominant in the overstory vegetation at the older phases of revegetation. These species could be potential candidates for early enrichment planting with Acacia spp. Common secondary forest species occurred naturally in the understory vegetation, and were more abundant and dominant after 10 years of ecological development. The most successful restorations were on scree slopes using leguminous Acacia spp. as nurse species. [ABSTRACT FROM AUTHOR]

In densely populated cities that are dominated by concrete buildings, urban parks serve as major green infrastructures for ecological and environmental functions. Trees are one of the important components that support these green infrastructures. Despite plenty of urban parks established in Hong Kong in the last 20 years, knowledge of tree composition and diversity is outdated. There were also no studies that investigated the differences in tree diversity in relation to park history. Therefore, this study aims to identify the temporary changes in tree composition and diversity in Hong Kong, by conducting a plot-based tree survey in 32 urban parks of different ages. Overall, 2801 trees belonging to 181 species were recorded in 319 plots across all the parks. A ridit analysis was conducted and it indicated the mature size of trees were not significantly larger in old parks. However, the linear mixed-effects models and the post-hoc tests suggested that DBH, tree height and the proportion of crown dieback for each class of tree size were greater in the old parks. Moreover, the composition of top-ranking dominant tree species varied substantially, where more ornamental and exotic trees were adopted in new parks. For species richness, the sample-based species accumulation curves of different park age overlapped when the horizontal axis of the curve was scaled by the average number of combined individual trees. When the horizontal axis was scaled by the number of plots, the curve for the old parks was above the curve for the new parks. The differences derived from these two accumulation methods indicated a higher tree density in old parks. For species evenness, both the rank-abundance curves and Rényi diversity curves depicted a similar low species evenness in old and new parks. These results suggested that species diversity remained largely unchanged from old parks to new parks though the dominant tree species varied. Greater attention should be paid to increase the species evenness in all urban parks, increase tree density in new parks and improve tree maintenance in old parks. [ABSTRACT FROM AUTHOR]

• Serviceable tree volume evaluated the ecosystem services of ornamental trees. • Individual trees were assessed based on flowering traits and structural defects. • Defects on ornamental trees restrained the vast potential of ecosystem services. • Exotic species made up a considerable proportion of the ornamental tree stock. • Ornamental tree inventory was dominated by several keystone species. Ornamental trees bearing outstanding flowers bring notable ecosystem services to cities. Existing research often treated ornamental trees as a sub-category of urban trees. To investigate the contributions of ornamental trees, this study aimed to: (1) assess their provision of ecosystem services; and (2) examine their ecological composition and diversity. Comprehensive tree survey in 93 public housing estates in Hong Kong identified 12,516 ornamental trees. To characterise the ability to provide ecosystem services, an index termed serviceable tree volume was devised. This innovative quantity aided the evaluation of ornamental trees by visual amenities, olfactory trait and ecological benefits while considering the compromise due to structural defects. The comprehensive tree survey showed a significant tendency of planting exotics for ornamental purposes. Most ornamentals could potentially deliver high-quality ecosystem services which were unfortunately restrained by prevailing very poor health conditions particularly attributed to structural defects on major branches. By relative importance value, several species dominated the ornamental tree inventory, namely Bauhinia 'Blakeana', Delonix regia and Bombax ceiba. By incorporating serviceable tree volume in calculating relative importance value, the importance ranking of ornamental species was re-ordered. Using tree stem as the unit of analysis, Shannon-Wiener Diversity, Reciprocal Simpson and Pielou's Evenness of the ornamental tree stock stood at 3.08, 14.73 and 0.74 respectively, and they were reduced when the three indices incorporated serviceable tree volume. Diverse native ornamentals could be planted extensively in the urban forest in tandem with the preservation of important exotic species. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of height-asymmetric street canyon configurations on air temperature and air quality at the pedestrian level using the ANSYS Fluent® software. The study concerns the situation with a subtropical city where there is a predominant wind direction (as is the case in, e.g., Hong Kong) and where the direction of that wind is perpendicular to the street canyon, since this is the worst-case from air pollution and overheating point of view. In particular, this North-South oriented street has been studied with the realistic solar irradiance at two different sun directions, corresponding to morning (08:00) and afternoon (16:00) hours, respectively. Two step-up and two step-down North-South oriented street canyons are considered under two different incoming wind speeds (high and low). The corresponding ratios of upwind and downwind building heights are = 1/3, 2/3 and 3/1, 3/2, respectively. The results demonstrated that for the step-up canyon, a higher upwind building was found to produce a hotter air temperature only at a low wind speed and polluted more severely at both high and low wind speeds, compared with its lower upwind building counterpart. In contrast, for the step-down canyon, a higher downwind building was found to produce cooler air temperatures at both high and low wind speeds and accumulated more pollutants only at a low wind speed, compared with its lower downwind building counterpart. On the other hand, at the high wind speed, both air quality and thermal environment were better in the step-up canyon than in the step-down canyon. However, at the low wind speed, the air quality was higher in the step-down canyon than the step-up canyon, while the step-up canyon still provided better thermal environment than the step-down canyon. Moreover, a Richardson number (Ri) for the asymmetric street canyons is defined for the evaluation of the buoyancy force versus the inertial force. When | Ri| > 20, the flow field was mainly dominated by natural convection, and an increase of | Ri| resulted in an increase in the air temperature and a decrease in the pollutant concentration. In contrast, when | Ri| < 20, the flow field was dominated by forced convection, and the variation of | Ri| had an insignificant influence on air quality and air temperature. The simulated pollutant concentration and thermal environment results were further processed to obtain optimization guidelines for a north-south asymmetric canyon in the city centers of Hong Kong via the application of multivariate regression analysis with a group of dimensionless parameters. These guidelines will facilitate the renewal of north-south asymmetric street canyons while enhancing air quality and lowering air temperature by serving as a reference for architects. • Effects of asymmetric street canyons on thermal comfort and air quality are investigated. • Step-up canyon always has lower air temperature under both high and low wind speeds. • Step-down canyon can have lower pollutant concentration under low wind speed. • When.|Ri| > 20 in an asymmetric canyon, natural convection dominates the flow field [ABSTRACT FROM AUTHOR]

This paper systematically investigates the effects of the frontal area density of various three-dimensional (3D) array building models on the thermal comfort and air quality at the pedestrian level above four sidewalks (north, south, east and west). The buoyancy force for natural-convection flows and the realistic solar irradiance at local solar times (LSTs) from 0700 to 1700 are considered with five different frontal area densities (λ F = 0.0825–1.25). By a combination of the Rayman model and the ANSYS Fluent® software, the CO concentration and physiologically equivalent temperature (PET) are solved numerically. The simulated CO concentration and PET results are considered as outdoor parameters of the air quality and thermal comfort. A critical λ F is obtained for urban development by applying multivariable regression analysis to a group of dimensionless parameters. This analysis will facilitate the choice of building density and simultaneously enhance the air quality and thermal comfort. The results reveal that with an increase in λ F , the PET decreases above most of sidewalks during the daytime, while only is a steady reduction of air quality observed above west and east sidewalks of spanwise streets. According to the multivariable regression analysis for Hong Kong, the building density should have a λ F value between 0.82 and 0.84 to basically realize a PET <38 °C and CO concentration <30000 μg/m3 simultaneously in the daytime in June. • Effects of frontal area density on thermal comfort and air quality are investigated. • Outdoor thermal comfort is evaluated by PET considering realistic solar radiation. • Outdoor air quality is evaluated by CO concentration under realistic solar radiation. • A critical λ F is obtained for urban development by a regression analysis. [ABSTRACT FROM AUTHOR]

This experiment was conducted to investigate the impacts of dietary selenium yeast (SeY) on the growth performance, fish body composition, metabolic ability, antioxidant capability, immunity and inflammatory responses in juvenile black carp (Mylopharyngodn piceus). The base diet was supplemented with 0.00, 0.30 and 0.60 g/kg SeY (0.04, 0.59 and 1.15 mg/kg of selenium) to form three isonitrogenous and isoenergetic diets for juvenile black carp with a 60-day. Adequate dietary SeY (0.30 and 0.60 g/kg) could significantly increase the weight gain (WG), special growth rate (SGR) compared to the SeY deficient groups (0.00 g/kg) (P < 0.05). Meanwhile, 0.30 and 0.60 g/kg SeY elevated the mRNA levels of selenoprotein T2 (SEPT2), selenoprotein H (SEPH), selenoprotein S (SEPS) and selenoprotein M (SEPM) in the liver and intestine compared with the SeY deficient groups (P < 0.05). Adequate dietary SeY could promote glucose catabolism and utilization through activating glucose transport (GLUT2), glycolysis (GCK, HK, PFK, PK, PDH), tricarboxylic acid cycle (ICDH and MDH), glycogen synthesis (LG, GCS and GBE) and IRS/PI3K/AKT signal pathway molecules (IRS2b, PI3Kc and AKT1) compared with the SeY deficient groups (P < 0.05). Similarly, adequate dietary SeY could improve lipid transport and triglycerides (TG) synthesis through increasing transcription amounts of CD36, GK, DGAT, ACC and FAS in the fish liver compared with the SeY deficient groups (P < 0.05). In addition, adequate SeY could markedly elevate activities of antioxidant enzymes (T-SOD, CAT, GR, GPX) and contents of T-AOC and GSH, while increased transcription amounts of Nrf2, Cu/Zn-SOD, CAT, and GPX in fish liver and intestine (P < 0.05). However, adequate SeY notably decreased contents of MDA, and the mRNA transcription levels of Keap1 in the intestine compared with the SeY deficient groups (P < 0.05). Adequate SeY markedly increased amounts or levels of the immune factors (ALP, ACP, LZM, C3, C4 and IgM) and the transcription levels of innate immune-related functional genes in the liver and intestine (LZM, C3 and C9) compared to the SeY deficient groups (P < 0.05). Moreover, adequate SeY could notably reduce levels of IL-8, IL-1β, and IFN-γ and elevate TGF-1β levels in fish intestine (P < 0.05). The transcription levels of MAPK13, MAPK14 and NF-κB p65 were notably reduced in fish intestine treated with 0.30 and 0.60 g/kg SeY (P < 0.05). In conclusion, these results suggested that 0.30 and 0.60 g/kg SeY could not only improve growth performance, increase Se, glucose and lipid metabolic abilities, enhance antioxidant capabilities and immune responses, but also alleviate inflammation, thereby supplying useful reference for producing artificial feeds in black carp. • Adequate SeY could improve growth, serum biochemical indices and Se metabolism, facilitate glycolysis and lipid metabolism in black carp. • Adequate SeY could enhance immunity by elevating amount of immune effectors, promote antioxidant capabilities through Nrf2/Keap1 pathway. • Adequate SeY could alleviate the expression levels of inflammatory factors via inhibiting p38 MAPK/NF-κB pathway in black carp. [ABSTRACT FROM AUTHOR]

Trees offer a range of ecosystem services and remain important in providing human benefits. However, emerging literature questions the long-accepted view of trees being able to improve air quality in urban parks. The aerodynamic effect of trees was identified as a major reason for the change of pollutant distribution in near-road parks, where trees can act as porous barriers and cause localised concentration increase. Although not yet fully developed, planting strategies aiming to mitigate the negative effect of vegetation on air quality should be encouraged in future park design. In this study, we explored the effect of tree planting design on pollutant diffusion by integrating field surveys in urban parks in Hong Kong with computational fluid dynamic (CFD) modelling. A series of indicators associated with tree morphology and landscape were derived from the surveys and their influence on air pollutant distribution in parks was examined using ENVI-MET. Dense trees with low crown base were found effective in improving air quality within parks when planted as barriers with a width of ~15 m at borders. However, more extensive planting led to a decrease in wind velocity and an increase in pollutant concentrations, which should be avoided. Tall trees tended to have little influence on airflow at the pedestrian level, which means they seem appropriate for small urban parks where wide barriers are not applicable and rapid ventilation should be encouraged. The tree distribution also altered the airflow and pollutant dispersion in parks. Our study provides clues for thoughtful planting strategies which can optimise air quality in urban parks. • Indicators associated with tree morphology were quantified through field surveys. • Tree morphology and distribution alter pollutant dispersion in urban parks. • Vegetation barrier is only effective with dense foliage in a limited width. • Tall trees seem suitable for small urban parks where ventilation is to be encouraged. • Appropriate planting strategies can improve air quality in near-road urban parks. [ABSTRACT FROM AUTHOR]