Changes in mangrove community structures affecting sediment carbon content in Yingluo Bay of South China.

This study aimed to assess how sediment organic carbon (SOC) dynamics were affected by mangrove community structures. Sediment attributes and community structures of the Avicennia marina, Aegiceras corniculatum, Rhizophora stylosa, and Bruguiera gymnorrhiza communities were analyzed, based upon field investigation in Yingluo Bay of South China. Aboveground biomass (AGB), belowground biomass (BGB) and tree height obviously increased with the self-thinning process, while basal area significantly decreased. The self-thinning exponent was 1.382 for AGB and 1.254 for BGB, conforming to the 4/3 self-thinning rule. However, self-thinning exponent for basal area was only 0.4866. SOC content non-linearly increased with the increase of AGB, BGB, and tree height. Mangrove-derived carbon increased through in situ organic material inputs with mangrove growth. The negative correlation between tree density and SOC content was not in line with the previous studies for planted mangroves. SOC dynamics of natural mangroves may be partially different from planted mangroves.

Forest biomass-carbon variation affected by the climatic and topographic factors in Pearl River Delta, South China.

Subtropical forests function as important carbon sinks for atmospheric CO2. Nonetheless, there remain uncertainties about the effects of climate and topography on subtropical forest biomass-carbon stocks. A continuous biomass expansion factor (BEF) method was applied to forest inventory data to estimate biomass-carbon storage and carbon sink rate, and their changes along with abiotic and biotic factors in the Pearl River Delta (PRD) of South China. BEF equations were built using a set of field-based data. Biomass-carbon increased from 62.92 to 70.56 Mt along with forest growth and increasing forest area during the latest two periods of the national forest inventory (2004-8 and 2009-13). The PRD's forests continued to be net carbon sinks 0.51 t ha-1 yr-1. The PRD's forests have a high potential as biomass-carbon sinks in the future, because 46.75% of the forests are at the young or middle-aged stage. In addition, principal component analysis indicated that both biomass-carbon density and carbon sink rate were positively correlated with the area percentage of mature and over-mature forests, average annual precipitation and minimum temperature, but they were negatively correlated with average annual maximum temperature. Pearson correlation analysis demonstrated that biomass-carbon density and carbon sink rate affected by average altitude, while they were not related to the slope angle.

The influence of bioavailable heavy metals and microbial parameters of soil on the metal accumulation in rice grain.

A field-based study was undertaken to analyze the effects of soil bioavailable heavy metals determined by a sequential extraction procedure, and soil microbial parameters on the heavy metal accumulation in rice grain. The results showed that Cd, Cr, Cu, Ni, Pb and Zn concentrations in rice grain decreases by 65.9%, 78.9%, 32.6%, 80.5%, 61.0% and 15.7%, respectively in the sites 3 (far-away), compared with those in sites 1 (close-to). Redundancy analysis (RDA) indicated that soil catalase activity, the MBC/MBN ratio, along with bioavailable Cd, Cr and Ni could explain 68.9% of the total eigenvalue, indicating that these parameters have a great impact on the heavy metal accumulation in rice grain. The soil bioavailable heavy metals have a dominant impact on their accumulation in rice grain, with a variance contribution of 60.1%, while the MBC/MBN has a regulatory effect, with a variance contribution of 4.1%. Stepwise regression analysis showed that the MBC/MBN, urease and catalase activities are the key microbial parameters that affect the heavy metal accumulation in rice by influencing the soil bioavailable heavy metals or the translocation of heavy metals in rice. RDA showed an interactive effect between Cu, Pb and Zn in rice grain and the soil bioavailable Cd, Cr and Ni. The heavy metals in rice grain, with the exception of Pb, could be predicted by their respective soil bioavailable heavy metals. The results suggested that Pb accumulation in rice grain was mainly influenced by the multi-metal interactive effects, and less affected by soil bioavailable Pb.

The respective effects of soil heavy metal fractions by sequential extraction procedure and soil properties on the accumulation of heavy metals in rice grains and brassicas.

This study was carried out to examine heavy metal accumulation in rice grains and brassicas and to identify the different controls, such as soil properties and soil heavy metal fractions obtained by the Community Bureau of Reference (BCR) sequential extraction, in their accumulation. In Guangdong Province, South China, rice grain and brassica samples, along with their rhizospheric soil, were collected from fields on the basis of distance downstream from electroplating factories, whose wastewater was used for irrigation. The results showed that long-term irrigation using the electroplating effluent has not only enriched the rhizospheric soil with Cd, Cr, Cu, and Zn but has also increased their mobility and bioavailability. The average concentrations of Cd and Cr in rice grains and brassicas from closest to the electroplating factories were significantly higher than those from the control areas. Results from hybrid redundancy analysis (hRDA) and redundancy analysis (RDA) showed that the BCR fractions of soil heavy metals could explain 29.0 and 46.5 % of total eigenvalue for heavy metal concentrations in rice grains and brassicas, respectively, while soil properties could only explain 11.1 and 33.4 %, respectively. This indicated that heavy metal fractions exerted more control upon their concentrations in rice grains and brassicas than soil properties. In terms of metal interaction, an increase of residual Zn in paddy soil or a decrease of acid soluble Cd in the brassica soil could enhance the accumulation of Cd, Cu, Cr, and Pb in both rice grains and brassicas, respectively, while the reducible or oxidizable Cd in soil could enhance the plants' accumulation of Cr and Pb. The RDA showed an inhibition effect of sand content and CFO on the accumulation of heavy metals in rice grains and brassicas. Moreover, multiple stepwise linear regression could offer prediction for Cd, Cu, Cr, and Zn concentrations in the two crops by soil heavy metal fractions and soil properties.

The dust retention capacities of urban vegetation-a case study of Guangzhou, South China.

Urban vegetation increasingly plays an important role in the improvement of the urban atmospheric environment. This paper deals with the dust retention capacities of four urban tree species (Ficus virens var. sublanceolata, Ficus microcarpa, Bauhinia blakeana, and Mangifera indica Linn) in Guangzhou. The dust-retaining capacities of four tree species are studied under different pollution intensities and for different seasons. Remote sensing imagery was used to estimate the total aboveground urban vegetation biomass in different functional areas of urban Guangzhou, information that was then used to estimate the dust-retaining capacities of the different functional areas and the total removal of airborne particulates in urban Guangzhou by foliage. The results showed that urban vegetation can remove dust from the atmosphere thereby improving air quality. The major findings are that dust retention, or capture, vary between the four species of tree studied; it also varied between season and between types of urban functional area, namely industrial, commercial/road traffic, residential, and clean areas. Dust accumulation over time was also studied and reached a maximum, and saturation, after about 24 days. The overall aboveground biomass of urban vegetation in Guangzhou was estimated to be 52.0 × 10(5) t, its total leaf area 459.01 km(2), and the dust-retaining capacity was calculated at 8012.89 t per year. The present study demonstrated that the foliage of tree species used in urban greening make a substantial contribution to atmospheric dust removal and retention in urban Guangzhou.

The morphological structure of leaves and the dust-retaining capability of afforested plants in urban Guangzhou, South China.

PURPOSE: Air pollution is a serious health problem throughout the world, exacerbating a wide range of respiratory and vascular illnesses in urban areas. The mass artificial plantation is very helpful to absorb dust and reduce pollution for conservation of the urban environment. The foliar surface of plants is an important receptor of atmospheric pollutants. Therefore, selection of suitable plant species for urban environment is very important. METHODS: The dust-retaining capability of urban trees in Guangzhou was determined at four different types of urban area, and the morphological traits of their leaves such as wax, cuticle, stomata, and trichomes were observed under a scanning electron microscope. RESULTS: It was determined that the dust-retaining capability of any given tree species is significantly different in the same place. Of the four studied tree species in the industrial area (IA) and commercial/traffic areas (CTA) type urban areas, the highest amounts of dust removed by Mangifera indica Linn was 12.723 and 1.482 g/m(2), respectively. However, in contrast, the equivalent maxima for Bauhinia blakeana is only 2.682 g/m(2) and 0.720 g/m(2), respectively. Different plant species have different leaf morphology. The leaf of M. indica has deep grooves and high stomata density which are in favor of dust-retained, and thus, their dust-retained capability is stronger, while B. blakeana has the cells and epicuticular wax with its stomata arranging regularly, resulting in poor dust catching capability. Leaf size was also shown to be related to dust capture for the four studied tree species. CONCLUSIONS: The dust removal capacity of individual tree species should be taken into account in the management of greening plantation in and around an urban area. It was also shown that temporal variation in dust accumulation occurred over the 28-day observation period and this was discussed. Furthermore, spatial contrasts in dust accumulation were evidenced by the data. This reflected the differing pollution loadings of the four urban-type areas. The highest amount of dust accumulation was associated with the industrial area in which shipyard and steelworks occurred whilst the lowest dust accumulation was associated with the grounds of the University which was the control area.

Heavy metal concentrations in plants and soils at roadside locations and parks of urban Guangzhou.

Levels of Cu, Ni, Zn, Pb and Cr were measured in soils and trees in urban Guangzhou, China. Tree and soil samples were collected from the roadside, urban parks and a university campus. Mean concentrations of Cu, Ni, Zn, Pb and Cr in tree leaves were 28.3, 7.7, 142.1, 23.4, and 195.1 mg/kg respectively. In a comparison of heavy metal concentrations in tree leaves between roads and park locations, only Pb concentrations were significantly higher in the former. Heavy metal concentrations were lower in the roots compared to leaves. It indicated that heavy metal pollution of trees is mainly from air pollution. For all top soil samples the mean concentrations of Cu, Ni, Zn, Pb and Cr were 24.3, 17.3, 121.5, 63.9 and 88.7 mg/kg, respectively. Heavy metal concentrations in roadside soils were higher and their coefficient of variation was higher than those in urban parks. Comparing heavy metal concentrations in trees and soil between urban Guangzhou and Hainan Island, China, Cu, Ni, Zn, Pb and Cr levels in soils and plants in urban Guangzhou were evidently affected by the human impact. However the heavy metal content in the soil compared to some international standards do not give cause for concern. Some observations on the implications of the data for environmental monitoring are made.

Observations on carbon and nitrogen content of suspended matter in a headwater stream in Hong Kong.

The total carbon(C) and total nitrogen(N) content of suspended matter in a small undisturbed headwater drainage basin in the New Territories of Hong Kong has been monitored. Mean C and N contents were 12.85% and 0.99% respectively for 132 samples. Samples collected under stableflow conditions had mean C and N contents of 12.81% and 1.06% respectively. Stormflow samples had mean C and N values of 12.86% and 0.97% respectively, which were very similar to the levels observed under stableflow conditions. The mean C:N ratios of 12.47 and 13.39 for stableflow and stormflow also reveal little difference according to hydrologic conditions. When all the data is considered little difference is observed in C and N according to the season. However, in winter there is a significant difference in C and N content between stable and stormflow samples. When C and N are plotted against water level the scattergraphs suggested that as stage increases the percentage of C and N in the suspended matter declines. Scattergraphs of C and N against suspended sediment concentration reveal a negative association. Comparison has been made between fresh leaf C, N and C/N ratio for trees and shrubs and the suspended matter. Fresh leaves do not appear to contribute significantly to suspended matter. The C/N ratio of suspended matter would also seem to exclude woody material and algae as sources of suspended matter.

Rapid changes of precipitation pH in Qinghai Province, the northeastern Tibetan Plateau.

Rainfall monitoring programs were conducted in two industrial cities of China's Qinghai Province, Xining and Germu, in some periods of the 1980s and 1990s. The results show that the natural precipitation in this area is originally alkaline. Compared with the late 1980s records, pH values declined significantly from approximately 8 in the 1980s to below 7 in mid-1990s. Such rapid and drastic changes were attributed to fast industrial development that released a large amount of pollutants. Subsequent tough control on pollutant emission partly restored pH values back to above 7 in the late 1990s. The pH and rainfall chemical analyses indicate that alkaline rain in this continental arid region is caused by airborne dusts which originate from local alkaline soils. With decrease of pH value, the total ionic concentration of rainwater is increased because acids were added to the rainwater.

Acid rain, storm period chemistry and their potential impact on stream communities in Hong Kong.

Hong Kong experiences acid deposition, however, little is known about the potential impact upon aquatic ecosystems. In a small drainage basin observations reveal that despite acid rain runoff, both baseflow and stormflow, was close to neutral in terms of pH. During storm events chemical analysis reveals that calcium (Ca) concentrations tended to rise. It also appears that the input of acid rain may increase aluminium (Al) levels in the stream. Due to the increased levels of Ca and only slight changes in pH acid deposition may not be generating problems in this stream. The presence of mayflies reported elsewhere may further support the results of the chemical study.

Intrasite sampling of Hong Kong soils contaminated by Caesium-137.

Previous measurements of soil contamination by Caesium-137 (137Cs) in Hong Kong have been used both to estimate background levels prior to the construction of the Guangdong Nuclear Power Station (GNPS) at Daya Bay and to evaluate health hazards arising from the radionuclide. These measurements are reviewed and contrasted with recent advances in understanding of 137Cs distribution in soil. Preliminary research findings are used to illustrate the microscale variability of 137Cs in the Hong Kong environment and to suggest intrasite sampling methods for establishing suitable reference values.