Evaluating the spatial and temporal distribution of emerging contaminants in the Pearl River Basin for regulating purposes

Little information is available on how the types, concentrations, and distribution of chemicals have evolved over the years. The objective of the present study is therefore to review the spatial and temporal distribution profile of emerging contaminants with limited toxicology data in the pearl river basin over the years to build up the emerging contaminants database in this region for risk assessment and regulatory purposes. The result revealed that seven groups of emerging contaminants were abundant in this region, and many emerging contaminants had been detected at much higher concentrations before 2011. Specifically, antibiotics, phenolic compounds, and acidic pharmaceuticals were the most abundant emerging contaminants detected in the aquatic compartment, while phenolic compounds were of the most profound concern in soil. Flame retardants and plastics were the most frequently studied chemicals in organisms. The abundance of the field concentrations and frequencies varied considerably over the years, and currently available data can hardly be used for regulation purposes. It is suggested that watershed management should establish a regular monitoring scheme and comprehensive database to monitor the distribution of emerging contaminants considering the highly condensed population in this region. The priority monitoring list should be formed in consideration of historical abundance, potential toxic effects of emerging contaminants as well as the distribution of heavily polluting industries in the region.

A composite index coupling five key elements of water cycle for drought analysis in Pearl River basin, China

Drought, as a natural disaster, has widespread consequences and is notoriously difficult to manage. Critical to developing a drought management strategy is the identification and assessment of drought. To that end, this study developed a new composite index, called the standardized water cycle index (SWCI) based on the water cycle and water balance. The SWCI couplesd the key elements of the water cycle, including precipitation, evapotranspiration, leaf area index, surface runoff, and subsurface runoff, and requires the joint distribution of these elements which was determined using the D-vine copula. The Kendall transform was used to reduce the dimensionality of the five-element joint probability density function, which was then inversed to obtain the SWCI which was then evaluated with the data from the Pearl River basin obtained using the CMIP6. Results showed that the SWCI satisfactorily evaluated drought conditions, while reflecting the drought-mitigating effect of vegetation and subsurface runoff. The SWCI was also able to evaluate drought in areas with a high level of human activity.

Stepwise clustering future meteorological drought projection and multi-level factorial analysis under climate change: A case study of the Pearl River Basin, China

Climate change has significant impacts on the Pearl River Basin, and the regional ecological environment and human production may face severe challenges in the future due to changes in temperature and precipitation, as well as their derivative disasters (e.g., drought). Therefore, a full understanding of the possible impacts of climate change on Pearl River Basin is desired. In this study, the potential changes in temperature, precipitation, and drought conditions were projected through a stepwise clustering projection (SCP) model driven by multiple GCMs under two different RCPs. The developed model could facilitate specifying the inherently complex relationship between predictors and predictands, and its performance was proven to be great by comparing the observations and model simulations. A multi-level factorial analysis was employed to explore the major contributing factors to the variations in projecting drought conditions. The results suggested that the Pearl River Basin would suffer significant increasing trends in T_mean (i.e., 0.25-0.34 °C per decade under RCP4.5 and 0.42-0.60 °C per decade under RCP8.5), and the annual mean precipitation would increase under both RCPs. The drought events lasting for 1-2 months would be decreased by 7.7%, lasting for 3-4 months would be increased by 4.3%, and lasting for more than five months would be increased by 3.4% under RCP4.5, respectively. While they changed to 6.1%, 1.4%, and 4.7% under RCP8.5, respectively. More medium and long-term drought events with higher drought severity would occur. GCM has dominant influences on four different responses of drought duration, accounting for 50.20%, 52.61%, 56.71%, and 56.24% of total variabilities, respectively. Meanwhile, the effects explained by GCM*RCP interactions cannot be neglected, with an average contribution rate of 44.37%, 37.86%, 37.66%, and 35.83%, respectively.

Application of the RUSLE for Determining Riverine Heavy Metal Flux in the Upper Pearl River Basin, China

A novel model was developed to estimate heavy metal flux at regional scale by using the Revised Universal Soil Loss Equation (RUSLE) to estimate soil erosion. This model was then used to estimate the fluxes of heavy metals including Zn, Cu, Cr, Ni, Cd, and As in three mono-lithologic regions in upper Pearl River Basin including carbonate rock (CR) basin, black shale (BS) basin, and basalt (BT) basin. Results show that the total annual erosions of the watershed were 8.56 × 10⁵ t a ^-1, 3.26 × 10⁶ t a^-1, and 5.09 × 10⁵ t a^-1 in CR, BT, and BS basins, respectively. The heavy metal flux was lowest for Cd (0.87 kg km^-2 a^-1, 0.46 kg km^-2 a^-1, and 1.07 kg km^-2 a^-1 in CR, BS, and BT basins, respectively). The heavy metal flux was highest for Zn in CR basin (16.29 kg km^-2 a^-1), Cr in BS basin (27.25 kg km^-2 a^-1) and Cu in BT basin (259.59 kg km^-2 a^-1). These findings have important implication to understand transport and distribution of heavy metals in the Pearl River Basin, and make regulations for controlling of non-point source heavy metal pollution.