Impact of human activities on subaqueous topographic change in Lingding Bay of the Pearl River estuary, China, during 1955-2013

Identification of suspended particulate matters as the hotspot of polycyclic aromatic hydrocarbon degradation-related bacteria and genes in the Pearl River Estuary using metagenomic approaches

Bacterial degradation is unequivocally considered as an important way for the cleanup of polycyclic aromatic hydrocarbon (PAHs) in the aquatic environment. However, the diversity and distribution of PAH-degrading bacterial communities and PAH degradation-related genes (PAHDGs) in ambient environment need to be investigated. In this study, bacteria in the water of the Pearl River Estuary (PRE) were initially separated as the particle-attached bacteria (PAB) and free-living bacteria (FLB), and were further characterized using metagenomic approaches. Proteobacteria (80.1 %) was identified as the most abundant PAH-degrading phylum in the PRE water, followed by Bacteroidetes, Actinobacteria, and Firmicutes. A substantial difference in the community structure was observed between PAH-degrading PAB and FLB. Both of PAH-degrading bacteria and PAHDGs were enriched on the suspended particulate matters (SPMs), with the range of enrichment factor (EF) from 7.84 × 10⁴ to 6.64 × 10⁶ (PAH-degrading bacteria) and from 1.14 × 10³ to 1.76 × 10⁵ (PAHDGs). The levels of PAH-degrading bacteria 16 S rRNA genes and PAHDGs on the SPMs were both significantly correlated with those in the aqueous phase (AP) in the PRE water (p < 0.05), indicating a dynamic distribution of PAH-degrading bacteria between these two phases. The total PAH concentrations on the SPMs of the PRE water were also significantly correlated with the total PAHDG levels in the PAB (p < 0.05). Our results suggested that the SPMs could be the important compartment for the elimination of PAHs from the aquatic environment.

The spatial distribution of benthic foraminifera in the Pearl River Estuary, South China and its environmental significance

Thirty surface sediment samples were collected from the Pearl River Estuary, South China, and benthic foraminifera were analyzed in order to understand the relationship between foraminiferal assemblages and environmental parameters. Multivariate analyses showed that the foraminferal assemblages (i.e., abundance and diversity) are correlated with the hydro-sedimentary gradients within the estuary. In addition, the dominant faunal composition seems to be largely influenced by food availability and trace metal contamination in surface sediments. A comparison with historical data from 1980s demonstrated that the foraminiferal abundance and diversity in the lower estuary have dramatically decreased over the last three decades, together with a significant shift in the dominant species. This is most likely due to the cumulative impacts of eutrophication and Cu contamination caused by human activities in the Pearl River basin. This work confirms the value of benthic foraminifera as bio-indicators in polluted estuarine environments.

Impact of anthropogenic activities on morphological and deposition flux changes in the Pearl River Estuary, China

The evolution of the Pearl River Estuary (PRE), China in recent decades has been dominated by human activities. Historical admiralty charts and remote sensing images indicated that from 1936 to 2017, the tidal flat area and water area decreased by 23.6 × 10⁷ m² and 60.7 × 10⁷ m², respectively. The average advancing rate of the coastline of the PRE to the sea from 1972 to 2017 reached approximately 64.8 m/year, which is several times or even dozens of times that since the mid-Holocene. Land reclamation was the main reason for the dramatic changes in the water area and coastline. Although the water volume of the PRE showed a decreasing trend from 1936 to 2017, the water volume reduction rates for 1996-2005 and 2005-2017 were only 29% (1.27 × 10⁷ m³/year) and 12% (0.53 × 10⁷ m³/year), respectively, of that for 1936-1972. The combined influences of channel dredging, sand mining, and sediment load reduction caused by dam construction have contributed to this change. From the perspective of the filling up of the estuary, channel dredging, sand mining, and dam construction in the river basin are beneficial for prolonging the life of the estuary.

Ecological restoration is not sufficient for reconciling the trade-off between soil retention and water yield: A contrasting study from catchment governance perspective

Ecological restoration program (ERP) is widely recognized as an effective measure to combat land degradation and improve environmental quality. However, inappropriate ERPs lead to trade-offs between soil retention and water yield as well as conflicts of soil and water resources between the midstream and the downstream of catchment. This study aims to assess the efficiency of ERPs in soil erosion control and identify the trade-offs between soil retention and water yield through the lens of runoff and sediment regimes in contrasting catchments of the Loess Plateau (LP) and the Karst Plateau (KP). Although favorable climate and rapid vegetation restoration substantially reduced water erosion in both these areas, the hydrological responses were not the same because of climate differences. In the arid LP, water and energy variables correlated closely with vegetation cover. Excessive afforestation programs in drylands increased vegetation transpiration and soil evaporation, further exhausting soil water resources, and eventually causing water yield reduction. However, soil and water conservation programs (SWCPs) in the humid KP reduced sediment yield substantially, and the runoff remained stable. Significant runoff reduction in the midstream of the Yellow River aggravated water scarcity and threatened the downstream water demand. Meanwhile, sediment load decline in the LP and the KP impacted sediment deposition in the downstream and estuary formation. From the perspective of integrated catchment governance, human interventions including ERP and SWCP should be more sustainable and consider not only the target process at the local scale (intracoupling effect), but also unprecedented non-target process at the regional scale (telecoupling effect). In addition, it should allow for the supply-demand balance of competing soil and water resources to achieve the coordinated development of resources, environment, and production.

Using Zn Isotopic Signatures for Source Identification in a Contaminated Estuary of Southern China

Zinc isotope ratios in water and suspended particles (SP) were measured in the Pearl River Estuary (PRE), China. Site-to-site δ⁶⁶Zn values in water varied by approximately 1.3‰ (i.e., -0.66‰ to 0.65‰ relative to IRMM-3702 in August 2017). There were larger variations in δ⁶⁶Zn values in water collected from the east shore (i.e., -0.66‰ to 0.37‰) of the PRE close to industrialized areas, in comparison to those from the western shore (i.e., -0.23‰ to 0.13‰), indicating that the PRE was influenced by different Zn sources. The variations in δ⁶⁶Zn values in water from estuarine locations were much larger than those collected from river mouths. Similarly, larger variations in δ⁶⁶Zn values were observed in suspended particles (i.e., -1.45‰ to 0.63‰) relative to the water. Zinc isotopic differences (i.e., Δ⁶⁶Zn‰) between particles and water were significantly (p < 0.05) and linearly correlated with Zn concentrations in particles between 0.8 and 10 μm in size at most of the estuary stations, suggesting that Zn partitioning between dissolved and particulate phases influences the observed differences in Zn isotope ratios. A significant (p < 0.0001) linear correlation between the predicted δ⁶⁶Zn values (using variations in water salinities) vs observed δ⁶⁶Zn values indicates that Zn isotope ratios in water in the PRE can be useful for predicting the mixing processes in the water.

Multi-hazards vulnerability assessment of southern coasts of Iran

Coastal vulnerability assessment has become one of the most important tools for decision making and providing effective managerial solutions to reduce adverse socio-economic impacts of multiple environmental hazards on coupled social-ecological systems of coastal areas. The aim of this study was to assess the vulnerability of the northern coasts of the Persian Gulf (PG) and the Gulf of Oman (GO) in the Hormozgan province of Iran. Nine variables of vulnerability that included the rate of coastline change, relative sea level rise, coastal slope, mean tidal range, coastal geomorphology, significant wave height (SWH), extreme storm surge, population density, and fishing intensity were weighted, mapped, and combined into the Coastal vulnerability index (CVI). Experts viewed sea level rise, shoreline change and extreme storm surge as most important for imparting vulnerabilities on the northern coasts of PG and GO. Socio-economic variables (i.e., population density and fishery intensity) were considered least important. Of the total length of the provincial shoreline, 27% were classified into the very low vulnerability class, 31% into the low, 17.4% into the moderate, 15.4% into the high, and 9.2% into the very high vulnerability class. About 1295 km (58%) of shorelines were classified into the low and very low vulnerability classes (CVI value ≤ 8.32) and mainly consisted of shorelines on the western coast along the PG. In contrast, 553 km (24.6%) of shorelines were classified into the high and very high vulnerability classes (CVI values > 13.39) and were located along the central coasts (especially in the Qeshm Island and Strait of Hormuz) and on the east coasts of the GO. At least a quarter of all shorelines in the province have high and very high vulnerability to environmental hazards that are the harbingers of climate change.

Multifractality and cross-correlation analysis of streamflow and sediment fluctuation at the apex of the Pearl River Delta

The fluctuation and distribution of hydrological signals are highly related to the fluvial and geophysical regime at estuarine regions. Based on the long daily streamflow and sediment data of Makou (MK) and Sanshui (SS) stations at the apex of the Pearl River Delta, the scaling behavior of the streamflow and sediment is explored by multifractal detrended fluctuation analysis (MF-DFA). The results indicated that there was significant multifractal structure present in the fluctuations of streamflow and sediment. Meanwhile, the multifractal degree and complexity of sediment were much stronger than streamflow. Although the scaling exponents of streamflow were larger than sediment at both MK and SS, no evident differences have been found on the scaling properties of streamflow and sediment for the ratios MK/SS. Moreover, the cross-correlation between streamflow and sediment is further detected by Multifractal Detrended Cross-Correlation Analysis (MF-DXA). The multifractal response between streamflow and sediment at small timescale is characterized by long-range correlations whereas it exhibits random behavior at large timescale. The interaction of the broadness of probability density function and the long-range correlations should be responsible for the multifractal properties of hydrological time series as the multifractal degree of surrogate and shuffled data was significantly undermined.