Xijiang River Research Articles

Quantification of the relationship between multiple metal(loid) distribution and integrated effect of internal-external factors in riverbed sediments across Xijiang River basin, South China

Understanding the integrated effect of external factors (e.g., human activities) and internal factors (e.g., hydrodynamics, sediment properties) on metal(loid) distributions is necessary for relevant decision-makers to develop river basin management strategies. In attempts to understand the possible causes of the distribution of nine target metal(loid)s in riverbed sediments across Xijiang River basin in China, we grouped and portrayed the multiple metal(loid) distributions by calculating metal(loid)'s normalised-and-weighted average concentrations, and then canonical correlation analysis combined with a series of statistical operations, collectively called optimized CCA analysis, was applied to quantify the strength of relationship between multiple metal(loid) distribution and integrated effect of internal-external factors. Results showed that the target metal(loid)s can be divided into three groups according to their distribution patterns: Group A (including Zn, As, Cd, Sb and Pb), Group B (including Cr, Ni and Cu) and Group C (including Tl). Among them, metal(loid)s in Group A was significantly enriched in comparison with the reference values of Chinese sediments, and the wide-ranging accumulation of Cd and Sb in the whole study area needs paying great attention to. For those metals in natural states (e.g., metals in Group B), the affinity of sediment (e.g., Fe and Mn oxides) is responsible for their distributions. By contrast, when metal(loid)s (e.g., metal(loid)s in Group A and Group C) had obvious anthropogenic sources, the interferences of anthropogenic inputs (e.g., non-ferrous metal enterprises' waste-discharging activities) and the specific sedimentary characteristics (e.g. karst topography and low-energy hydrodynamic depositional conditions) in study area can weaken the correlation between the binding affinity of sediment and the contents of metal(loid)s. The optimized CCA analysis can be an alternative and advantageous statistical operation for determining the main types of causes of multiple metal(loid) distribution in the case of observations with relatively low case-per-variable ratios.

Applications of multiple change point detections to monthly streamflow and rainfall in Xijiang River in southern China, part II: trend and mean

This article, as part II, illustrates applications of other two algorithms, i.e., the scanning F test of change points in trend and the scanning t test of change points in mean, to both series of the normalized streamflow index (NSI) at Makou section in the Xijiang River and the normalized precipitation index (NPI) over the watershed of Xijiang River. The results from these two tests show mainly positive coherency of changes between the NSI and NPI. However, some minor negative coherency patches may expose somewhat impacts of human activities, but they were often associated with nearly normal climate periods. These suggest that the runoff still depends upon well the precipitation in the Xijiang catchment. The anthropogenic disturbances have not yet reached up to violating natural relationship on the whole in this river.

Spatial Distribution Study and Pollution Assessment of Pb in Soils in the Xijiang River Drainage of Guangxi

To obtain data for the accumulation of Pb and its risk in soils in the Xijiang River drainage of Guangxi, 2594 samples were collected from nonferrous metal mining soils, farmland soils (paddy soils and dryland soils), and the background soils in the drainage area. Geostatistical analysis combined with GIS was used to study the soil spatial distribution characteristics and pollution distribution of the soil Pb content. The results showed that the Pb background value of the soil was 51.84 mg ·kg-1 in the Xijiang River Basin, and the results of the single sample T test showed that the soil background value was significantly higher than that of a previous study (22.08 mg ·kg-1) and the soil background value (20.50 mg ·kg-1) in Guangxi province. The geometric mean concentration of Pb in the mining soils, dryland soils, and paddy soils were 655.9, 116.7, and 40.63mg ·kg-1, respectively, significantly higher than that in other soils. Using GB 15618-1995 and the baseline as the limiting value, the corresponding exceedance rate of the mining soils, dryland soils, and paddy soils were 57.69%, 16.40%, and 8.92% and 54.95%, 8.09%, and 2.03%. The mining soils and farmland soils had an obvious lead accumulation trend. There was an obvious spatial autocorrelation of Pb in the soil, and the structural variation was dominant. The content of Pb in the upper reaches of the Xijiang River reached the middle and lower reaches of the Xijiang River, and the soil Pb was characterized by an obvious decrease. The accumulation of high Pb content in the upper reaches of Diaojiang River is much larger than that in the lower reaches of Diaojiang River. The content of Pb in soil samples in the Xijiang River Basin was mainly rated between mild pollution and moderate pollution, and the pollution was concentrated in the municipal administrative area and the mining activity area. The pollution of the soil in Jinchengjiang and Nandan counties was closely related to the frequent local mining activities.

Applications of multiscale change point detections to monthly stream flow and rainfall in Xijiang River in southern China, part I: correlation and variance

This article, as part I, introduces three algorithms and applies them to both series of the monthly stream flow and rainfall in Xijiang River, southern China. The three algorithms include (1) normalization of probability distribution, (2) scanning U test for change points in correlation between two time series, and (3) scanning F-test for change points in variances. The normalization algorithm adopts the quantile method to normalize data from a non-normal into the normal probability distribution. The scanning U test and F-test have three common features: grafting the classical statistics onto the wavelet algorithm, adding corrections for independence into each statistic criteria at given confidence respectively, and being almost objective and automatic detection on multiscale time scales. In addition, the coherency analyses between two series are also carried out for changes in variance. The application results show that the changes of the monthly discharge are still controlled by natural precipitation variations in Xijiang’s fluvial system. Human activities disturbed the ecological balance perhaps in certain content and in shorter spells but did not violate the natural relationships of correlation and variance changes so far.

Accumulation of Cd and Its Risks in the Soils of the Xijiang River Drainage Basin in Guangxi

To understand the distribution and risk of soil cadmium (Cd) in the Xijiang River drainage basin in Guangxi, a total of 2512 soil samples were collected nonferrous metal mining area, farmland (paddy soils and dryland soils) and the background soils, in the Xijiang River drainage basin in Guangxi.The results showed that Cd concentration was 0.514 mg·kg-1 in background soils significantly higher than previously resulted(0.148 mg·kg-1)and that in Guangxi background soil(0.267 mg·kg-1). The geometric average concentration of Cd in dryland soils, paddysoils and mining soils was 0.559, 0.787, 5.71 mg·kg-1, respectively, which were significantly higher than background soils. The Cd concentration exceeded the background soils and baseline by 51.2% and 35.2% in dryland soil, 66.7% and 39.6% in paddy soil, 77.8% and 71.4% in mining soil, high Cd concentration occurred in the Nandan County, Dahua County, Duan County, Huanjiang County and Yizhou City, as well as Liujiang County, These regions have developed severe and even extremely serious pollution, medium-high pollution accumulation and higher-extremely high potential ecological risks. The Cd-pollution in soils in agricultural and mining soils in upstream of Xijiang River in Guangxi is serious, due to mining activities and high Cd geological background. People in the mining area and surrounding areas who live on local crops, vegetables, may expose to the Cd-pollution. It is recommended to further develop a Cd risk assessment through a soil-plant-human system, taking appropriate measures to control risk.

Triplophysa anshuiensis, a new species of blind loach from the Xijiang River, China (Teleostei, Nemacheilidae).

A new cave-dwelling fish, Triplophysa anshuiensis, is described here based on specimens collected from a karst cave in Guangxi Zhuang Autonomous Region, China, interconnected with the Hongshui River system, a tributary of the Xijiang River in the Pearl River (Zhu Jiang) Drainage. The species can be distinguished from its congeners by a combination of morphological characters. A key to the cave-dwelling species of Triplophysa in the Xijiang River is provided.

Spatial Variability and Contamination of Arsenic in Soils of Xijiang River Basin

In this study, 2585 soil samples were collected in the Xijiang River Basin in Guangxi Zhuang Autonomous Region and the spatial variability and contamination of Arsenic in soils were evaluated using geostatistical and GIS tools. The results showed that the concentrations of As in surface soils (23.82 mg·kg-1) were higher than the background values of the Guangxi and Xijiang Rivers in natural soils; the upstream values (Diaojiang River and Huanjiang River) (30.22 mg·kg-1) were significantly higher than those in other regions. Concentrations of As in soil samples were in the order of soil in mining areas > soil in dryland > natural soil > paddy soil. As in mining areas were significantly higher than in other areas; high As concentrations were measured in the upstream of the Diaojiang River basin and the downstream of the Huanjiang River Basin. Low concentration clusters were in the six villages of Nandan, which are far from the mine, and in the upper reaches of the Dahuanjiang River and Xiaohuanjiang River Basin. Spatial autocorrelations of arsenic in the watershed soil were evident and the structural variability was dominant. The concentration of As in the upper reaches decreased from the northwest to the southeast. High As concentrations were distributed naturally along the river basin; concentrations in the middle and lower reaches of the basin were between 0.44 mg·kg-1 and 40 mg·kg-1. The concentration levels of As in total soil samples ranged from no-pollution to slight pollution, and the pollution was mainly distributed in the administrative areas of the city and the intensive areas of mining activities, among which the soil pollution in Jinchengjiang River and Nandan counties was more prominent. Effective measures should be taken to strengthen the safety level of tailings reservoirs during the rainy season, so as to maintain the production levels while protecting living standards of local residents.

Ecological Operation Objectives for Four Major Chinese Carps Spawning in the Xijiang River

The river basin cascade development has prominent influence on water ecology for breeding of four major Chinese carps, and the determination of ecological operation objectives is an important basic work to carry out the ecological operation. This study determines the main control indexes of reservoir operation by analysing the relationships between larval population of Xijiang Dongta spawning ground and impact indexes like water temperature, flood process and flow velocity. Taking peak flow, initial discharge, flow rising range, daily increasing rate of flow and duration of water level rising of the spawning ground as the control indexes, the target flow process of reservoir ecological operation can be determined. Furthermore, the drifting velocity of fish eggs is used as the test index to control the section flow in the scheduling river reach. The proposed method is applied to the ecological operation of Dongta spawning ground, and the target flow processes of ecological operation under low, medium and high flow levels are obtained.

Application of Hybrid Particle Swarm Optimization Algorithm in the Optimal Water Operation of Cascade Reservoirs in Dry Season

In this paper, a hybrid particle swarm optimization (HPSO) algorithm is proposed to solve the problem of optimal water operation of cascade reservoirs in dry season. Based on the basic particle swarm optimization (PSO) algorithm, chaos algorithm is introduced to traverse the search space to generate the initial population and improve the global searching ability of the algorithm. A self-adaptive inertial weighting method based on optimized inertial weighting coefficient is adopted to improve the ability of particle individual search and avoid local optimum. The proposed algorithm is applied to the optimal water operation in dry season of cascade reservoirs on the mainstream of Xijiang River. The results show that the HPSO algorithm can effectively improve the guarantee degree of ecological flow and suppressing salinity flow in the control reach of Wuzhou station under different typical dry year scenarios.

Payment for Ecological Services and River Transboundary Pollution: Policy Inspirations from a Contingent Valuation (CV) Study on the Xijiang River Drainage Basin in South China

Payment for Ecological Services and River Transboundary Pollution: Policy Inspirations from a Contingent Valuation (CV) Study on the Xijiang River Drainage Basin in South China

Genetic diversity and population demographic history of Ochetobius elongatus in the middle and lower reaches of the Xijiang River

Genetic diversity and population demographic history of Ochetobius elongatus in the middle and lower reaches of the Xijiang River

Distribution and risk assessment of heavy metals in river surface sediments of middle reach of Xijiang River basin, China

ABSTRACTXijiang River is the main surface water source in Guangxi province, South China. This study was carried out to investigate the distribution and potential ecological risks of seven heavy metals (Cu, Pb, Zn, As, Cd, Ni, and Cr) in surface sediments in Xijiang River basin. The results illustrated that the average concentrations of Zn, Pb, Cd, Cu, As, Ni, and Cr were 483.9, 207.5, 13.35, 23.50, 312.1, 28.75, and 50.62 mg/kg, respectively. Among them, Zn, Pb, Cd, and As were the major heave metals with concentration exceeding Class 3 threshold value of Chinese national standard. The result also showed samples with high ecological risk were mainly located in the upstream of Xijiang River basin as Diaojiang River, Hongshui River, Jincheng River, and Dahuan River. Based on the pollution risk assessment, the area manifested composite pollution of heavy metals in the sediments, signifying As, Pb, and Cd as the dominant heavy metals, and there were high ecological risk in sediments for these metals. According to correlation matrix and factor analysis (FA), the seven heavy metals were divided into three types/classes, Cd, as and Zn attributed by anthropogenic sources, natural sources corresponds for Ni and Cr while both natural and anthropogenic sources were attributed to Cu.

Spatial and temporal variation of H and O isotopic compositions of the Xijiang River system, Southwest China

ABSTRACTRatios of stable isotopes of hydrogen and oxygen (2H/1H and 18O/16O) in river waters were measured to investigate the hydrological pathway of the Xijiang River, Southwest China. The δ2H and δ18O values of river waters exhibit significant spatial and temporal variations and the isotopic compositions vary with elevation, temperature and precipitation of the recharge area. Spatially, δ18O values of river waters from high mountain areas are lower than those from the lower reaches of the Xijiang River due to lower temperature and higher elevation for the recharge area. However, both 2H and 18O are enriched differently in river waters from the middle reaches during the high flow season, depending on the season and degree of anthropogenic disturbances (e.g. water impoundments). In contrast, deuterium excess (d-excess) values of waters from the middle reaches are substantially lower than those from the upper and lower reaches, suggesting that river waters may be resided in the reservoir and evaporation increases in the middle reaches of the Xijiang River.

Evaluation on uncertainty sources in projecting hydrological changes over the Xijiang River basin in South China

Projections of hydrological changes are associated with large uncertainties from different sources, which should be quantified for an effective implementation of water management policies adaptive to future climate change. In this study, a modeling chain framework to project future hydrological changes and the associated uncertainties in the Xijiang River basin, South China, was established. The framework consists of three emission scenarios (ESs), four climate models (CMs), four statistical downscaling (SD) methods, four hydrological modeling (HM) schemes, and four probability distributions (PDs) for extreme flow frequency analyses. Direct variance method was adopted to analyze the manner by which uncertainty sources such as ES, CM, SD, and HM affect the estimates of future evapotranspiration (ET) and streamflow, and to quantify the uncertainties of PDs in future flood and drought risk assessment. Results show that ES is one of the least important uncertainty sources in most situations. CM, in general, is the dominant uncertainty source for the projections of monthly ET and monthly streamflow during most of the annual cycle, daily streamflow below the 99.6% quantile level, and extreme low flow. SD is the most predominant uncertainty source in the projections of extreme high flow, and has a considerable percentage of uncertainty contribution in monthly streamflow projections in July–September. The effects of SD in other cases are negligible. HM is a non-ignorable uncertainty source that has the potential to produce much larger uncertainties for the projections of low flow and ET in warm and wet seasons than for the projections of high flow. PD contributes a larger percentage of uncertainty in extreme flood projections than it does in extreme low flow estimates. Despite the large uncertainties in hydrological projections, this work found that future extreme low flow would undergo a considerable reduction, and a noticeable increase in drought risk in the Xijiang River basin would be expected. Thus, the necessity of employing effective water-saving techniques and adaptive water resources management strategies for drought disaster mitigation should be addressed.

The complete mitochondrial genome of Pseudocrossocheilus bamaensis (Cypriniformes: Cyprinidae: Labeoninae)

Pseudocrossocheilus bamaensis is endemic to the upstream of Xijiang River, Guangxi, China and its natural population has been declining due to overfishing and habitat destruction. Here, we first report the complete mitogenome of this species, which is 16,594 bp in length, containing 13 protein-coding genes, 22 tRNA genes, two rRNA genes, as well as a putative light strand origin of replication (OL) and a putative control region (D-loop). The overall base composition is 31.8% of A, 15.7% of G, 26.8% of T and 25.7% of C, with a high A + T content (58.6%). Phylogenetic analysis suggests that P. bamaensis is closely related to Ptychidio jordani and Rectoris posehensis. These results will contribute to the molecular evolution and phylogenetic research of Labeoninae and further protection of its fish species.

Acoustic assessment of fish resources in subtropical run-off-river hydropower plant in the Pearl River

As the utmost downstream dam in the main stream of Xijiang River, Changzhou Hydro-Junction has changed the original hydrological characteristics and ecological environment of Xijiang River. In order to grasp the fish distribution and standing crops after reservoir impoundment, a split beam echo-sounder EY60 (120 kHz) was used in the river channel from Guiping to Wuzhou in April 2014, 2015, and 2016. The average fish density in the survey area was 0.1215±0.4198 ind.m-3 in 2014, 0.0190±0.1232 ind.m-3 in 2015 and 0.0107±0.0186 ind.m-3 in 2016. According to the horizontal distribution data, fish density showed significant difference in different area and the density in the upper area was significantly higher than that in other areas. Moreover, fish density was negatively correlation with water depth. As a whole, the Target Strength (TS) decreased in the past three year, TS was significantly different among the three areas and showed a decreasing tendency from the dam area to the upper area. Fish resources decreased gradually, as indicated by the decreased fish density and miniaturized fish sizes in the past three years.

Spatial Variation and Environmental Significance of δ18O and δD Isotope Composition in Xijiang River

The H and O isotope composition of the Xijiang water was investigated on 54 samples collected from the mainstreams and main tributaries in June 2014 and January 2015.It was found that in the Xijiang river, there was a remarkable linear relationship between δ18 O and δD. This relationship was more significant in the dry season. In both seasons, the 18 O and D values distributed along the meteoric water line, which indicated that precipitation was the source of the Xijiang River. Due to the direct water recharge through karst forms (i.e. sinkholes, vertical shaft and funnel) to the underground river, the d-excess value was higher in the rainy season. While during the dry season, water recharge came from the storage in fissures and pores. Affected by altitude and evaporation effect, along the mainstream Hongshui River-Xunjiang and tributary Youjiang-Yujiang reach, the δ18 O and δD values were gradually approaching positive value in general. However, along the short tributary Guijiang reach, the altitude difference was not dramatic, and the discharge was less, the same phenomenon was not observed. By establishing a linear regression model between δ18 O and altitude, it revealed that the change rate of Xijiang water with altitude was -0.44‰·(100 m)-1 in the rainy season, and -0.45‰·(100 m)-1 in the dry season. The result reflected the height effect of the precipitation, which has a considerable meaning for the study of hydrological cycle in a river basin.

Sulfate sources constrained by sulfur and oxygen isotopic compositions in the upper reaches of the Xijiang River, China

While it is critical to accurately understand the sources and transformation of sulfate based on time-series analysis, there are limited studies on temporal variation of sulfate in rivers and on rock weathering by sulfuric acids. We conducted a monthly sampling campaign in the Beipan, Nanpan, and Hongshui Rivers over the course of one hydrological year. This study examined seasonal variations in riverine sulfate impacted by the monsoon climate in the upper reaches of the Xijiang River basin. In general, the SO42− contents in these rivers dropped from relatively high levels to low values during the high-flow season, in response to increasing discharge. The sulfate was generally enriched in heavy isotopes during the low-flow season compared to the high-flow season. The calculated results indicate that the riverine sulfate was mainly derived from sulfide oxidation, but that evaporite dissolution could be an important source during the low-flow season, based on isotopic evidence. Mine drainage is likely an important source of sulfate to these rivers during the high-flow season due to contributions from fast surface flow, which responds to frequent heavy rain in monsoonal climate regions. A relatively high proportion of HCO3− was found to be derived from rock weathering by sulfuric acid during the high-flow season when compared to that observed during the low-flow season. The results suggest that approximately one quarter of the HCO3− in the Hongshui River originated from carbonate weathering by sulfuric acid derived from the oxidation of sulfide. Such information on the specific dual isotopic characteristics of riverine sulfate throughout a hydrological year can provide unique evidence for understanding the temporal variability of sulfate concentrations and weathering processes in rivers.

Correlation between hydrological drought, climatic factors, reservoir operation, and vegetation cover in the Xijiang Basin, South China

The Xijiang River is known as the Golden Watercourse because of its role in the development of the Pearl River Delta Regional Economic System in China, which was made possible by its abundant water resources. At present, the hydrological regime of the Xijiang River has now become complicated, the water shortages and successive droughts pose a threat to regional economic development. However, the complexity of hydroclimatological processes with emphasizes on drought has not been comprehended. In order to effectively predict and develop the adaptation strategies to cope with the water scarcity damage caused by hydrological droughts, it is essential to thoroughly analyze the relationship between hydrological droughts and pre/post-dependent hydroclimatological factors. To accomplish this, the extreme-point symmetric mode decomposition method (ESMD) was utilized to reveal the periodic variation in hydrological droughts that is characterized by the Standardized Drought Index (SDI). In addition, the cross-wavelet transform method was applied to investigate the correlation between large-scale climate indices and drought. The results showed that hydrological drought had the most significant response to spring ENSO (El Niño-Southern Oscillation), and the response lags in sub-basins were mostly 8–9months except that in Yujiang River were mainly 5 or 8months. Signal reservoir operation in the Yujiang River reduced drought severity by 52–95.8% from January to April over the 2003–2014 time period. Similarly, the cascade reservoir alleviated winter and spring droughts in the Hongshuihe River Basin. However, autumn drought was aggravated with severity increased by 41.9% in September and by 160.9% in October, so that the land surface models without considering human intervention must be used with caution in the hydrological simulation. The response lags of the VCI (Vegetation Condition Index) to hydrological drought were different in the sub-basins. The response lag for the Hongshuihe, Yujiang, and Liujiang River Basins were mostly 0–4months, 0–1months, and 2–3months, respectively, but there was no obvious regular change pattern in the Guijiang River Basin.

Spatiotemporal Distribution of Droughts in the Xijiang River Basin, China and Its Responses to Global Climatic Events

The Xijiang River is a main branch of the Pearl River, the largest river in South China. Droughts in this area have seriously influenced local water resource utilization, and socio-economic development. The spatiotemporal distribution of droughts and its responses to global climatic events are of critical significance for the assessment and early warning of drought disasters. In this paper, the spatiotemporal patterns of droughts characterized by Rotated Empirical Orthogonal Function/Rotated Principal Components (REOF/RPC) in the Xijiang River Basin, China were evaluated using the Self-calibrated Palmer Drought Severity Index (Sc-PDSI). The drought responses to El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), India Ocean Dipole (IOD), and North Atlantic Oscillation (NAO) were analysed by Pearson correlation and multiple stepwise regression. The results showed that one year earlier NAO was the dominant factor impacting the droughts in the Xijiang Basin. Its contribution for the RPC2s of the annual, the first and second half years, winter, summer, autumn, and February were −0.556, −0.419, 0.597, −0.447, 0.542, 0.600, and −0.327, respectively. Besides the two adjacent Pacific and India oceans, the droughts seem be influenced by distant Atlantic climatic events. These results offer new reference insights into the early warning of droughts as well as the planning and management of water resources in the study area.