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In order to understand the pollution status of metals in the riparian soils along the Wujiang River, 26 sampling sites in the mainstream and tributary streams were selected for investigation. The geo-accumulation index (Igeo), Nemerow integrated pollution index, and potential ecological risk index were applied to evaluate the contamination status and ecological risks of metals. Results revealed that the average concentrations of As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn were 12.20, 0.51, 84.01, 57.42, 922.57, 38.37, 38.06, and 127.82 mg/kg, respectively. The metal contamination degree and ecological risks in the upper reaches were significantly higher than those in the middle and lower reaches of the Wujiang River. Cd was the dominant contamination metal. Significant non-carcinogenic and carcinogenic risks of metals were found in children based on the hazard index and carcinogenic risk. As was the main non-carcinogenic and carcinogenic pollutant metal in both adults and children. According to principal component analysis, hierarchical clustering analysis, and absolute principal component scores-multiple linear regression, anthropogenic sources (mining and agricultural activities) contributed most to Zn, Pb, Cr, Cd, Cu, and Ni, with contribution rates of 89.14, 82.32, 74.46, 72.12, 68.52, and 61.02%, respectively. Natural sources contributed most to Mn, with a contribution rate of 83.07%. Unidentified sources contributed most to As, with a contribution rate of 47.27%. [ABSTRACT FROM AUTHOR]

Purpose: Exploring the different characteristics and influencing factors of sediment phosphorus (P) migration and transformation in lakes and reservoirs in different basins helps to identify the function of sediments in maintaining the steady state and key mechanism. Materials and methods: Two lakes (Lake Chaohu and Lake Qingling) within the Yangtze River basin and three reservoirs (Dongfeng Reservoir, Puding Reservoir, and Wujiangdu Reservoir) on Wujiang River were studied, and different P and nitrogen species in surficial and pore water, organic material and related exocellular enzyme, and sediment P fractions and iron, as well as P sorption in sediments, were analyzed. Results and discussion: In eutrophic lakes within the Yangtze River basin, the decomposition of organic matter in sediment can stimulate enzymatic hydrolysis release of organic P and the anaerobic desorption of iron binding P (Fe-P). In oligotrophic reservoirs on the Wujiang River, anaerobic desorption of Fe-P caused by mineralization of organic matter did not happen, but Fe-P was still the main P species released from sediment. Calcium-bound P (Ca-P) exhibited markedly different characteristics in these two types of water. Ca-P can be converted into bioavailable P by phosphorolytic bacteria in eutrophic lakes within the Yangtze River basin, but on account of high content of calcium ions in the reservoirs of Wujiang River, coprecipitate with phosphate and formation of Ca-P occurred. Although there was a higher potentiality of sediment P release in the reservoirs of Wujiang River, in terms of higher equilibrium P concentration, P in sediments was mainly static release driven by interstitial water concentration gradient due to larger water depth. Frequent wind and waves, especially in the open water area, in lakes within the Yangtze River basin, caused sediment resuspension, resulting in excessive P release from sediments. Conclusions: The different lake or reservoir morphology, physical and chemical environment, and organic matter properties codetermined the different sediment P migration and transformation characteristics in the studied lakes and reservoirs, which in turn maintained their own steady state. [ABSTRACT FROM AUTHOR]

Quantitatively separating the influence of climate change and human activities on runoff is crucial to achieving sustainable water resource management in watersheds. This study presents a framework for quantitative assessment by integrating the indicators of hydrologic alteration, the whale optimization algorithm and random forest (WOA-RF), and the water erosion prediction (WEP-L) models. This framework quantifies the differences in hydrological conditions and their driving forces at multi-timescales (annual, seasonal, and monthly). The results indicate that the runoff of the Wu River has decreased since 2005. Climate factors were found to influence the interannual variation of runoff mainly. Meanwhile, human activities had a more significant impact in autumn, with a relative contribution rate of 59.0% (WOA-RF model) and 70.8% (WEP-L model). Monthly, the picture is more complex, with the results of the WOA-RF model indicating that climate change has a significant impact in July, August, and September (88.8%, 92.7%, and 79.3%, respectively). However, the WEP-L model results showed that the relative contribution of land use is significant in April, May, June, October, and November (51.24%, 64.23%, 63.63%, 53.16%, and 50.63%, respectively). The results of the study can be helpful for regional water allocation. HIGHLIGHTS Based on indicators of the hydrologic alteration range of variation approach, the changes of hydrological regime in the Wujiang River basin in the past 30 years were analyzed.; Natural runoff was reconstructed by the whale optimization algorithm and random forest and the water erosion prediction models.; The effects of climate change and human activities on runoff change on annual, monthly, and seasonal scales were quantified.;

Exploring the characteristics of uneven temporal and spatial distribution of precipitation in mountain watersheds can provide a reference for regional agricultural development and resource utilization, and contribute to the protection of the ecological environment. Based on the daily precipitation observation data of 40 meteorological stations in the Wujiang River Basin from 1963 to 2021, the temporal- and spatial-variation characteristics of the precipitation concentration degree (PCD) and precipitation concentration period (PCP) were analyzed using the Randall S analysis method, Mann–Kendall test method, Pettitt method, wavelet analysis and empirical orthogonal function (EOF). The results showed that the fluctuation range of PCD in Wujiang River Basin from 1963 to 2021 was 0.34–0.59, with a multi-year average of 0.47, which was obviously higher than the national average level and is showing a trend of slowly increasing. The fluctuation range of PCP was between 17.1 and 21.5 days, with a multi-year average of 19.0. The annual precipitation was mostly concentrated around the middle of July and showed a slowly decreasing trend. The abrupt change in PCD and PCP occurred around 1983 and 2001, respectively. There is an obvious Hearst phenomenon in PCP. In the future, the trend of precipitation concentration in the middle period will remain in advance, and the degree of precipitation concentration will continue to increase. The maximum precipitation in the flood season will continue to be delayed. The spatial pattern of the first mode of PCD and PCP in the Wujiang River basin was consistent and showed an opposite pattern between the upper reaches and the middle-lower reaches of the basin, which reflects the influence of the topography of the basin on the spatial distribution of precipitation. The distribution of precipitation is affected by topography. The elevation change in the basin was complex, and the leeward slope varied a lot. Therefore, it has a significant impact on precipitation. Areas with less precipitation are at higher elevations and on mountain leeward slopes, with a lack of moist air flow. The area with more precipitation was the summer monsoon mountain windward slope, and the topography blocks the increase in precipitation. The elevation of the central region is relatively uniform and the terrain is flat. Therefore, the distribution of precipitation is more uniform. [ABSTRACT FROM AUTHOR]

In order to assess the metal pollution in the Wujiang River, concentrations of Cu, Zn, Fe, Mn, Pb, Cd, As, and Hg in the water, sediments, and two fish species Cyprinus carpio and Pelteobagrus fulvidraco from the middle reaches (Tuomugang, TMG) and lower reaches (Wulong, WL) of the Wujiang River were examined. The results indicated that all metal concentrations were lower than the values for grade one water quality according to the Environment Quality Standard for Surface Water of China (GB 3838–2002). The bioavailable fraction concentrations of Zn, Fe, Mn, Pb, and Hg in WL were significantly higher than those in TMG (p < 0.05), indicating that these metals in sediments of WL have higher bioavailability and mobility. The Cu, Zn, Fe, Pb, As, and Hg were mainly related to the residual fraction, while the Mn and Cd were mainly associated with the non-residual fraction. The risk assessment code (RAC) and the secondary phase to the primary phase (RSP) values indicated that Mn and Cd have a high risk of secondary release. The mean metal concentrations in the liver of the two fish species were higher than those in muscle. The higher metal concentrations of fish in WL suggested that bioaccumulation of metals in fish could be influenced by metal bioavailability. No identical relationships between metal concentrations and fish length were manifested in the present study. The values of target hazard quotient (THQ) and hazard index (HI), and carcinogenic risk (CR) of metals for the consumption of C. carpio and P. fulvidraco indicated that the anglers would likely not experience significant non-carcinogenic risk, but the carcinogenic risk of As cannot be ignored. Thanks to prohibited commercial fishing in the Wujiang River, the metal pollution will probably not pose a health risk to the general public for wild fish consumption. [ABSTRACT FROM AUTHOR]

Exploring the characteristics of uneven temporal and spatial distribution of precipitation in mountain watersheds can provide a reference for regional agricultural development and resource utilization, and contribute to the protection of the ecological environment. Based on the daily precipitation observation data of 40 meteorological stations in the Wujiang River Basin from 1963 to 2021, the temporal- and spatial-variation characteristics of the precipitation concentration degree (PCD) and precipitation concentration period (PCP) were analyzed using the Randall S analysis method, Mann–Kendall test method, Pettitt method, wavelet analysis and empirical orthogonal function (EOF). The results showed that the fluctuation range of PCD in Wujiang River Basin from 1963 to 2021 was 0.34–0.59, with a multi-year average of 0.47, which was obviously higher than the national average level and is showing a trend of slowly increasing. The fluctuation range of PCP was between 17.1 and 21.5 days, with a multi-year average of 19.0. The annual precipitation was mostly concentrated around the middle of July and showed a slowly decreasing trend. The abrupt change in PCD and PCP occurred around 1983 and 2001, respectively. There is an obvious Hearst phenomenon in PCP. In the future, the trend of precipitation concentration in the middle period will remain in advance, and the degree of precipitation concentration will continue to increase. The maximum precipitation in the flood season will continue to be delayed. The spatial pattern of the first mode of PCD and PCP in the Wujiang River basin was consistent and showed an opposite pattern between the upper reaches and the middle-lower reaches of the basin, which reflects the influence of the topography of the basin on the spatial distribution of precipitation. The distribution of precipitation is affected by topography. The elevation change in the basin was complex, and the leeward slope varied a lot. Therefore, it has a significant impact on precipitation. Areas with less precipitation are at higher elevations and on mountain leeward slopes, with a lack of moist air flow. The area with more precipitation was the summer monsoon mountain windward slope, and the topography blocks the increase in precipitation. The elevation of the central region is relatively uniform and the terrain is flat. Therefore, the distribution of precipitation is more uniform.

The increase of affected river reaches by reservoirs has drastically disturbed the original hydrological conditions, and subsequently influenced the nutrient biogeochemistry in the aquatic system, particularly in the cascade reservoir system. To understand the seasonal variation of nitrogen (N) behaviors in cascade reservoirs, hydrochemistry and nitrate dual isotopes (δ15N-NO3− and δ18O-NO3−) were conducted in a karst watershed (Wujiang River) in southwest China. The results showed that NO3−–N accounted for almost 90% of the total dissolved nitrogen (TDN) concentration with high average concentration 3.8 ± 0.4 mg/L among four cascade reservoirs. Higher N concentration (4.0 ± 0.8 mg/L) and larger longitudinal variation were observed in summer than in other seasons. The relationship between the variation of NO3−–N and dual isotopes in the profiles demonstrated that nitrification was dominated transformation, while assimilation contributed significantly in the epilimnion during spring and summer. The high dissolved oxygen concentration in the present cascade reservoirs system prevented the occurrence of N depletion processes in most of the reservoirs. Denitrification occurred in the oldest reservoir during winter with a rate ranging from 18 to 28%. The long-term record of surface water TDN concentration in reservoirs demonstrated an increase from 2.0 to 3.6 mg/L during the past two decades (~ 0.1 mg/L per year). The seasonal nitrate isotopic signature and continuously increased fertilizer application demonstrated that chemical fertilizer contribution significantly influenced NO3−–N concentration in the karst cascade reservoirs. The research highlighted that the notable N increase in karst cascade reservoirs could influence the aquatic health in the region and further investigations were required. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai University / Shanghai Daxue Xuebao is the property of Journal of Shanghai University (Natural Sciences) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Shanghai University / Shanghai Daxue Xuebao is the property of Journal of Shanghai University (Natural Sciences) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Study region: The impounded Wujiang River, Southwest China. Study focus: Thermal stratification is an important factor shaping aquatic ecosystems in karst hydropower reservoirs. However, the underlying mechanism of thermal stratification formation is still unclear. Therefore, water temperature and related environmental factors were investigated to understand how reservoir hydraulic load (i.e., the ratio of the mean water depth to water retention time) affects thermal stratification in eight karst hydropower reservoirs on the Wujiang River. New hydrological insights for the region: The reservoir surface water had a higher temperature than the inflowing and released waters. The variation in the reservoir thermal stratification showed an obvious seasonal pattern, but the extents of the thermal stratification were different among the reservoirs. The rate of water temperature change is proposed to characterize reservoir thermal stratification and is significantly negatively correlated with reservoir hydraulic load, suggesting the control of both water depth and retention time on thermal stratification. This empirical relationship will be helpful in quantitatively evaluating the hydrological effect on thermal stratification, which further affects basic environmental parameters (including pH, dissolved oxygen, and chlorophyll a) in narrow and deep karst cascade hydropower reservoirs.

Copyright of Asian Journals of Ecotoxicology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Energy storage control is one of the important methods of hydropower operation scheduling. Keeping hydropower stations operating in a reasonable energy storage range can reduce the impact of uncertain factors such as natural runoff and load demand, it also can reduce the scheduling risk. A new method and application rules of energy storage control chart were proposed for the issue of determining the reasonable energy storage range of cascade hydropower stations by taking the Wujiang River as an example and according to the key factors of actual operation scheduling, such as runoff characteristics, power station characteristics, grid dispatching requirements and generation rules. The calculation of the example shows that energy storage control chart can be used to guide the medium and long-term power generation plans with convenient use and reasonable results. [ABSTRACT FROM AUTHOR]

Wang, J.; Peng, T., and Shen, T., 2019. Temporal and spatial variation characteristics analysis of precipitation days and intensity over the Wujiang River Basin in flood season. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 209–219. Coconut Creek (Florida), ISSN 0749-0208. Based on the observation data of 41 surface meteorological stations in Wujiang River Basin from 1960 to 2016, the temporal and spatial variation laws of precipitation days and intensity in flood season (May to September) in Wujiang River Basin are analyzed. It is found that the distribution of precipitation in Wujiang River Basin is characterized by inhomogeneity of spatial change and tendency of temporal change. In terms of spatial distribution, affected by geographical position and topography, Wujiangdu is regarded as the boundary in terms of latitude. From the topographic point of view, because of the terrain in the vicinity of high mountains, precipitation frequency and value are larger, and precipitation also has a good correlation with the spatial distribution of temperature, humidity and wind speed; in the time variation, the frequency of rain days has an upward trend while the corresponding average precipitation is declining. The proportion of heavy rain days is decreasing while the corresponding average precipitation is increasing, and the relative humidity is decreasing. The surface air temperature is on the rise while the wind speed is on a fast downward trend. [ABSTRACT FROM AUTHOR]

Based on the observation data of 41 surface meteorological stations in Wujiang River Basin from 1960 to 2016, the temporal and spatial variation laws of precipitation days and intensity in flood season (May to September) in Wujiang River Basin are analyzed. It is found that the distribution of precipitation in Wujiang River Basin is characterized by inhomogeneity of spatial change and tendency of temporal change. In terms of spatial distribution, affected by geographical position and topography, Wujiangdu is regarded as the boundary in terms of latitude. From the topographic point of view, because of the terrain in the vicinity of high mountains, precipitation frequency and value are larger, and precipitation also has a good correlation with the spatial distribution of temperature, humidity and wind speed; in the time variation, the frequency of rain days has an upward trend while the corresponding average precipitation is declining. The proportion of heavy rain days is decreasing while the corresponding average precipitation is increasing, and the relative humidity is decreasing. The surface air temperature is on the rise while the wind speed is on a fast downward trend. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • River δD and δ18O can response to cumulative effects of cascade dams. • Reservoir δD and δ18O are influenced by retention time and mean water depth. • Water δD and δ18O show a jagged increase from upstream to downstream of the impounded Wujiang River. Abstract Cascade dams are known to influence the river water cycle, but their cumulative effects (CEs) are still not well understood. Water hydrogen (H) and oxygen (O) isotopes are hypothesized to be used to characterize the CEs. To test this hypothesis, we investigated water δD, δ18O, and related environmental factors in cascade reservoirs on the Wujiang River, Southwest China. The δD and δ18O ranged from −64.2‰ to −45.4‰ and from −9.7‰ to −6.8‰, respectively, and showed obvious temporal and spatial variations. Water temperature is an important factor influencing these variations. After damming, an increase of water retention time caused the enrichment of heavy H-O isotopes in reservoir surface water, and thermal stratification induced a decrease of δD and δ18O with depth. Due to bottom discharge, released water showed more negative δD and δ18O than reservoir surface water, and these δD and δ18O differences were controlled by water retention time and mean water depth of the reservoir. Overall, the CEs of cascade dams caused δD and δ18O to display a jagged increase from upstream to downstream in the impounded Wujiang River. Therefore H-O isotopes can be used to estimate the CEs of cascade dams. As cascade dams can modify H-O isotope signatures, caution should be exercised when using H and O isotopes to trace the source of the impounded river water. [ABSTRACT FROM AUTHOR]

Currently, there is a lack of systematic knowledge concerning carbon (C) biogeochemical cycles in impounded rivers. In this study, we investigated different C species and related environmental factors from July 2007 to June 2008 and from May 2011 to May 2012 in the impounded Wujiang River, SW China to understand the influence of dam construction on the riverine C cycle. The results showed that average concentrations of dissolved CO 2 , dissolved inorganic C (DIC), dissolved organic C, and particulate organic C (POC) were 81.73 μmol/L, 2283.55 μmol/L, 158.11 μmol/L, and 37.54 μmol/L, respectively. Meanwhile, δ 13 C DIC ranged from − 10.07‰ to − 4.92‰ with an average of − 8.33‰, while δ 13 C POC ranged from − 35.30‰ to − 22.28‰ with an average of − 29.20‰. Thermal and chemical stratifications developed seasonally and exerted a significant influence on the C cycle of the released water. The C species and related δ 13 C showed remarkable heterogeneity in time and space. Evidence from δ 13 C demonstrated that the C system in this river was primarily influenced by carbonate weathering, whereas in the reservoir, it was primarily controlled by algal activity. The coefficients of variance for different C species in the reservoir and released water were higher than those in the river. Our study indicated that biological activity became a key controlling factor for the C biogeochemical cycle and accelerated it after damming, especially in the warm seasons. The results of this study have important implications for understanding the C cycle in elongated and deep reservoirs. [ABSTRACT FROM AUTHOR]

With the development of hydropower in the karst area of Southwest China, a series of cascade canyon reservoirs have been formed through the construction of dams. Given that hydrodynamic conditions in canyon reservoirs play a pivotal role in controlling the spatiotemporal distribution of physical and chemical properties of the stored water, hydrodynamic characteristics are of great importance in understanding biogeochemical cycles in those reservoirs. To further this understanding, a field campaign was conducted in the Wujiangdu Reservoir of Guizhou Province. It was found that from the reservoir inlet to the front of the dam, velocity ( v) was negatively correlated and had a logarithmic relationship with distance along the ship track ( s) under dry-season flow conditions [ v = −0.104ln ( s) + 0.4756]. Analysis showed that dry-season flow velocity had no significant correlation with water temperature, pH, or dissolved oxygen (DO). However, when velocity decreased to 0.061 m/s, water depth increased abruptly. In addition, DO displayed a sudden drop and the trend in pH changed from increasing to decreasing, while water temperature showed an opposite trend, indicating the existence of a transition zone from the river to the reservoir. [ABSTRACT FROM AUTHOR]

Carbonate weathering and the CO 2 consumption in karstic area are extensive affected by anthropogenic activities, especially sulfuric and nitric acids usage in the upper-middle reaches of Wujiang River, China. The carbonic acid would be substituted by protons from sulfuric and nitric acids which can be reduce CO 2 absorption. Therefore, The goal of this study was to highlight the impacts of sulfuric and nitric acids on carbonate dissolution and the associated deficit of CO 2 uptaking during carbonate weathering. The hydrochemistries and carbon isotopic signatures of dissolved inorganic carbon from groundwater were measured during the rainy season (July; 41 samples) and post-rainy season (October; 26 samples). Our results show that Ca 2 + and Mg 2 + were the dominant cations (55.87–98.52%), and HCO 3 – was the dominant anion (63.63–92.87%). The combined concentrations of Ca 2 + and Mg 2 + commonly exceeded the equivalent concentration of HCO 3 − , with calculated [Ca 2 + + Mg 2 + ]/[HCO 3 − ] equivalent ratios of 1.09–2.12. The mean measured groundwater δ 13 C DIC value (− 11.38‰) was higher than that expected for carbonate dissolution mediated solely by carbonic acid (− 11.5‰), and the strong positive correlation of these values with [SO 4 2 − + NO 3 − ]/HCO 3 – showed that additional SO 4 2 − and NO 3 − were required to compensate for this cation excess. Nitric and sulfuric acids are, therefore, suggested to have acted as the additional proton-promoted weathering agents of carbonate in the region, alongside carbonic acid. The mean contribution of atmospheric/pedospheric CO 2 to the total aquatic HCO 3 – decreased by 15.67% (rainy season) and 14.17% (post-rainy season) due to the contributions made by these acids. The annual mean deficit of soil CO 2 uptake by carbonate weathering across the study area was 14.92%, which suggests that previous workers may have overestimated the absorption of CO 2 by carbonate weathering in other karstic areas worldwide. [ABSTRACT FROM AUTHOR]

The effects of optimized operation principles implemented at reservoirs on the Wujiang River in southwest China between September 2009 and April 2010 under drought conditions were analyzed based on operational data collected from the Guizhou Wujiang Hydropower Development Co., Ltd. A set of linear regression equations was developed to identify the key factors impacting the electric power generation at reservoirs. A 59% reduction in the inflow discharge at the Hongjiadu Reservoir led to a decrease of only 38% in the total electric power generation at the Hongjiadu, Dongfeng, Suofengying, and Wujiangdu reservoirs on the Wujiang River, indicating that optimized operation can play an important role in drought management. The water level and the amount of other water inputs at the Hongjiadu Reservoir and the outflow discharge at all of the reservoirs except the Wujiangdu Reservoir were key factors affecting the total electric power generation at reservoirs on the Wujiang River under optimized operation.

In order to protect aquatic system health of Wujiang River and achieve the win-win goal of the water energy resources development and ecological environment, the ecological operation of cascade hydropower stations along Wujiang River in Guizhou provience is studied. The minimum, suitable and ideal ecologically flow demands of the Hongjiadu, Wujiangdu and Silin stations were analyzed. And the multi-objective combination optimization scheduling model of Cascade Hydropower Stations there was built and solved. Mean annual and typical year generating capacity of 9 reservoirs are calculated. Ecological water period guaranteed rate and the scheduling process of 3 main control sections are showed. The results show that this study can increase the ecological water period guaranteed rate of Wujiang River, as well as guarantee benefits of flood control and power generation. As for low flow year, it is hard to reach the ideal ecological flow demand. [ABSTRACT FROM AUTHOR]

To better understand the decreases observed in pH levels downstream from the associated hydroelectric dam, the impounded Wujiang River in Southwest China was investigated. Study results indicate that the average pH decrease from upstream to downstream of the hydroelectric dam could be up to 0.47 units, and pH differences were particularly apparent during water thermal stratification. Notably, pH was controlled by [CO]/[CO] ratios in this impounded river. The decrease in [CO]/[CO] ratios and associated increases in pH at the surface of the reservoirs were mainly due to the prevalence of photosynthesis, while the reverse phenomenon was observed at the bottom due to respiration. The evidence from δC clearly demonstrated these processes. The increase in phytoplankton biomass enhanced this pH decrease, while dissolved organic carbon had limited impacts on the pH variation. The decrease in pH downstream from the hydroelectric dam resulted from the development of pH stratification in the water profile and the dam operations that release bottom waters for hydropower generation. Consequently, the cascade in hydropower development could increase the risk of river acidification. [ABSTRACT FROM AUTHOR]

Wang, J.; Peng, T., and Shen, T., 2019. Temporal and spatial variation characteristics analysis of precipitation days and intensity over the Wujiang River Basin in flood season. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 209–219. Coconut Creek (Florida), ISSN 0749-0208. Based on the observation data of 41 surface meteorological stations in Wujiang River Basin from 1960 to 2016, the temporal and spatial variation laws of precipitation days and intensity in flood season (May to September) in Wujiang River Basin are analyzed. It is found that the distribution of precipitation in Wujiang River Basin is characterized by inhomogeneity of spatial change and tendency of temporal change. In terms of spatial distribution, affected by geographical position and topography, Wujiangdu is regarded as the boundary in terms of latitude. From the topographic point of view, because of the terrain in the vicinity of high mountains, precipitation frequency and value are larger, and precipitation also has a good correlation with the spatial distribution of temperature, humidity and wind speed; in the time variation, the frequency of rain days has an upward trend while the corresponding average precipitation is declining. The proportion of heavy rain days is decreasing while the corresponding average precipitation is increasing, and the relative humidity is decreasing. The surface air temperature is on the rise while the wind speed is on a fast downward trend. [ABSTRACT FROM AUTHOR]

The Wujiang River is an important tributary to the Changjiang River that has been intensively impounded for hydropower exploitation. To understand the potential impact of reservoir construction on the riverine inorganic carbon transport, seasonal longitudinal sampling was conducted in four reservoirs Hongjiadu (HJD), Dongfeng (DF), Suofengying (SFY) and Wujiangdu (WJD) along the Wujiang River from April 2006 to January 2007. Results indicated that damming the river induced an obvious discontinuity of water chemistry in the warmer seasons. δC of dissolved inorganic carbon (DIC) ranged from −3 to −11.4 ‰, likely as the results of photosynthesis, respiration and carbonate weathering. During periods of thermal stratification, the addition of CO from respiration to hypolimnion and the deep water release for hydropower generation led to higher pCO downstream, as well as C depletion in DIC and undersaturated to calcite. An estimate of DIC budget indicated that only DF reservoir was the sink for DIC while reservoirs HJD, SFY and WJD were the sources for DIC. However, when the retained water was taken into account, for the reason of water storage occurring mainly in HJD and DF, all reservoirs became the sources for DIC with exporting rates of 26.68, 7.97, 6.22 and 11.80 % for HJD, DF, SFY and WJD, respectively. [ABSTRACT FROM AUTHOR]

To determine the impact of damming on the geochemical behavior of dissolved inorganic carbon (DIC) in the Wujiang River basin, field measurements and samples were collected semimonthly for a year. The surface waters of the reservoirs contained concentrations of chlorophyll a up to 5.6 times higher than the upstream river. Compared with the entering waters, the contributions of HCO and dissolved CO to DIC decreased, and the contribution of CO to DIC and the carbon isotopic composition of DIC ( δC) increased in the surface waters of the reservoirs, while in the waters released, the DIC species showed reverse geochemical behaviors. The δC ranged from −10.2 ‰ to 2.5 ‰, indicating that significant contributions were from carbonate weathering, photosynthesis, and respiration. After the damming of a river, the bioactivity of phytoplankton was enhanced, and this affected the geochemistry of DIC compared to an unimpacted river and δC can be used to discern these changes. High-frequency monitoring of river-reservoir systems is necessary to evaluate the efflux of CO and provide a better understanding of the carbon sinks and sources in the impounded river. [ABSTRACT FROM AUTHOR]

Abstract: The grain-size distribution (based on cumulative probability curves) in the sediments produced by potential palaeofloods at the Shiniusi archaeological site is similar to that of modern flood sediments from the Wujiang River Drainage in the upper Yangtze River. There is an obvious pattern in the curves, with two segments, and the mean grain size (Mz), standard deviations (σ1), skewness, and kurtosis are all similar. Combined with the AMS14C dating data and the ages judged based on the presence of cultural remains, our data suggests frequent palaeoflood events within the Wujiang River Drainage. We hypothesize the existence of seven high flood possibility layers in the QST4 unit from Shiniusi archaeological site: during the periods of the Ming Dynasty (1368–1644 AD) to the Qing Dynasty (1616–1911 AD), and the end of the Eastern Zhou Dynasty (770 BC–256 BC) to the Shang Dynasty (1600–1100 BC). We also hypothesize ten high flood probability layers in the QST2 unit from Shiniusi archaeological site: during the periods of the Ming Dynasty to the Qing Dynasty, the periods of Song Dynasty (960–1279 AD) to the Yuan Dynasty (1206–1368 AD), as well as during the Han Dynasty (207 BC–220 AD) to the Eastern Zhou Dynasty (770 BC–256 BC). These results are consistent with palaeoflood events inferred from pollen and spore analysis and from historical records in other rivers. [Copyright &y& Elsevier]

Abstract: Presently, the fluvial fluxes of Dissolved silicate (DSi) by many famous rivers in the world have been reported significantly decreased in the past several decades. DSi retention by river damming hence becomes a great concern. In this study, the impact on DSi retention and transport by cascade reservoirs in the Karst area were investigated. Based on the monitoring data for four seasons, budget of DSi in these reservoirs were calculated. Results showed that, only the downstream eutrophic Wujiangdu reservoir (WJD) was the sink for DSi, with a value of ca. 3.5kT DSi trapped annually. The new Hongjiadu reservoir (HJD) in the headwater area revealed to be an important source for DSi. Both Dongfeng (DF) and Suofengyin (SFY) reservoirs also released more DSi to the downstream than entering them. The great discrepancy of DSi source and sink effects among these reservoirs indicates that, (i) DSi was obviously taken up in summer and spring, and the concentration of DSi could be dropped down to below 30μΜ; (ii) during the period of thermal stratification, the concentration stratification of DSi is also developed along the water column. Possibly DSi releasing from inundation soil and bottom sediment was the important compensation for the silicon depletion in the epilimnion. In the newly constructed reservoirs (e.g. HJD and SFY), the releasing flux of DSi can significantly exceed the assimilating flux by diatom; and (iii) due to the hypolimnion introducing for hydropower operation, water leaving the dam generally had high DSi content, and then masked the DSi taking up in the epilimnion. This process also decreased the ratio of DIN to DSi, mitigating the silicon limiting situation in the downstream. [Copyright &y& Elsevier]

Surface runoff in the Wujiang River watershed was simulated by a GIS-based method using precipitation, hydrology data, and land-use data. The volume of surface runoff is chiefly controlled by climates, topographical characteristics and types of land use at the watershed. Five subwatersheds that can represent the whole watershed were chosen and their average annual precipitation, average annual surface runoff and current land use were calculated respectively in the grid model of the Wujiang River watershed based on the climate and hydrology data from 1965 to 2000 and the land-use data acquired in the year of 2000. Surface runoff is assumed to be a function of precipitation and land use and the multiple regression tool is used to determine the relationship between surface runoff, precipitation and present land use. Thus, the rainfall-runoff model for each land-use type has been established. When calibrating these models, the results show that the percent errors are all below 7%, which indicates that the accuracy of this simulation is high. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

The distribution of nutrients (N, P, Si, C) in the Wujiang River surface water was studied during the high-flow and low-flow periods in 2002. The results showed that nitrate nitrogen (NO3-N) is the main form of dissolved inorganic nitrogen (DIN) in the Wujiang River Basin. It accounts for about 90% of DIN, The average NO3-N concentrations in the mainstream are 147.5 µM in the high-flow period and 158.0 µM in the low-flow period, respectively. The average concentrations of total phosphorus (TP) are 6.43 µM in the high-flow period and 4.18 µM in the low-flow period, respectively. Of the various forms of phosphorus, particulate phosphorus (PP) has the highest percentage (62.9%) of TP in the high-flow period. In the low-flow period, however, phosphate is the main form of phosphorus, which accounts for 49% of TP. With the Wujiangdu Reservoir as the boundary, the concentrations of DIN and phosphorus in the upper reaches are different from those in the lower reaches of the Wujiang River. As a whole, the concentrations of DIN and phosphorus are both higher in the low-flow period than in the high-flow period. The spatial and temporal variations of DIN and phosphorus concentrations suggested that DIN and phosphorus come from agricultural and domestic wastewaters and groundwaters and that the Wujiangdu Reservoir has an important impact on the concentrations and distribution of DIN and phosphorus in the Wujiang River. The distribution patterns of dissolved silica (DSi) and dissolved organic carbon (DOC) are similar. Both of them maintain no change in the whole course of the river and their concentrations (with the exception of the reservoir itself) are higher in the high-flow period than in the low-flow period. The average DSi and DOC concentrations in the mainstream are 85.4, 84.6 µM in the high-flow period and 60.8, 53.9 µM in the low-flow period, respectively. The concentrations of nutrients in most of the major tributaries are lower than in the mainstream. This suggested that the contributions of most tributaries are relatively small but importance should he attached to the influence of some individual tributaries such as the Qingshuijiang River and the Weng'an River on the mainstream. [ABSTRACT FROM AUTHOR]

Particulate inorganic carbon (PIC) is one of the most important components of carbon cycle in hydropower reservoirs. However, the processes of production, migration, and transformation of PIC in hydropower reservoirs are still unclear. As such, we investigated the concentration and carbon isotope composition of PIC and dissolved inorganic carbon and related environmental parameters of hydropower reservoirs on the Wujiang River, Southwest China, to understand these processes. The observed δ13C datasets demonstrated that the river PIC is derived from exogenous carbonate weathering and endogenous carbonate precipitation, whereas the reservoir PIC is dominated by authigenic PIC driven by phytoplankton. The reservoir PIC concentration and δ13C PIC showed seasonal stratification in the water profile, the extent of which depends on surface photosynthesis and bottom respiration. The influence of phytoplankton on the production and transformation of PIC was different among the reservoirs with different ages and trophic levels, and the δ13C technique can reveal these processes very well. This study improves the comprehensive understanding of carbon cycling in hydropower reservoirs and environmental effects of river damming. [Display omitted] [ABSTRACT FROM AUTHOR]

• Phytoplankton functional group concept was applied in hydroelectric reservoirs. • Phytoplankton community succession exhibits obvious spatial–temporal variation. • RWCS was the key factor for the succession of functional groups. Hydrological conditions are a critical factor for phytoplankton ecology in hydroelectric reservoirs, and how this factor contributes to the succession of phytoplankton functional groups is still unclear. Therefore, we investigated the phytoplankton functional groups, relative water column stability, and related environmental factors in the Wujiang cascade reservoirs to understand this process. Altogether five phyla and thirteen functional groups were identified, and they showed evident variations across space and time. The B , D , P , and J groups were dominant, and the Lo and X1 groups existed only in the reservoirs. Relative water column stability rather than nutrient availability affects the succession and distribution of phytoplankton functional groups in the study area, and high relative water column stability usually increases phytoplankton biomass. This indicates that hydrologic conditions are an important factor controlling phytoplankton composition in hydroelectric reservoirs, and this study enriches the understanding of reservoir phytoplankton ecology. [ABSTRACT FROM AUTHOR]

• RSTI was developed to investigate the coupled effect of rainfall and reservoir. • Linear or nonlinear regression models were set up to simulate the sediment load. • Sediment load had a striking decreasing trend and a significant change-point. • Nonlinear regression had the better performance than linear regression model. • Coupled effect of rainfall and reservoir can better explain sediment load change. Sediment load is a critical issue in hydrologic process analysis and river basin management. Many studies have analyzed the impacts of rainfall or reservoir separately on the downstream sediment load; however, few researches investigated the coupled effect of rainfall and reservoir on sediment load change. In this study, a rainfall-augmented sediment trapping index (RSTI) that combines the impacts of effective rainfall and reservoir sediment trapping capacity was developed to attribute the sediment load change in the Wujiang River Basin (WRB) during the period of 1952–2017. Eight linear or nonlinear regression models were set up to investigate how to best utilize the proposed RSTI to reveal the coupled effect of rainfall and reservoir on the downstream sediment load of WRB. It is found that observed sediment load has a large decrease after 1984 when the Wujiangdu Reservoir was put into full operation while rainfall had only a slight change in the same period. The nonlinear regression model with RSTI as an explanatory variable (NSE = 0.837) has the best performance in simulating the observed sediment load series. These results might be helpful for the downstream sediment management under a changing environment. [ABSTRACT FROM AUTHOR]

• Biogeochemical processes of sulfur were enhanced by damming, especially in summer. • Damming decreased seasonal differences but increased spatial differences of SO 4 2– and δ34S-SO 4 2−. • SO 4 2– decreased whilst δ34S-SO 4 2– increased from upstream to downstream. • Cumulative effects on δ34S-SO 4 2− could derive from HRT and mean depth of reservoir. • SO 4 2− and δ34S-SO 4 2− could be useful indicators in assessing the damming effects. Damming effects on sulfur (S) cycling remains unclear at basin scales due to the lack of basic data prior to dam construction. To explore the influence of damming on the riverine S cycle, we investigated the spatiotemporal variations of water chemistry, sulfate (SO 4 2–) concentration, and δ34S-SO 4 2– in January 2017 and July 2017 in the impounded Wujiang River, and the measured results in this study were compared with the data in 2002 when no dams were built in the middle and lower reaches. Results showed that SO 4 2– was the second dominant anion and accounted for up to 30% of the total anions, and sulfuric acid played a vital role in carbonate weathering. Sulfate reducing process and organic S oxidation were markedly enhanced by seasonal thermal stratification induced by damming, particularly in summer. The seasonal differences of SO 4 2– concentration and δ34S-SO 4 2– in this study were not readily discernable compared to those in 2002, when the average SO 4 2– concentration and δ34S-SO 4 2– in winter were 31.0% and 63.3% greater than that in summer respectively. The δ34S-SO 4 2– from upstream WJD reservoir to downstream YP reservoir in 2002 increased by 17.2% in summer; however, in this study, it drastically increased by 76.7%. The reduced seasonal variations and increased spatial differences of SO 4 2– concentration and δ34S-SO 4 2– reflected the damming effect of cascade dams on S cycling in river waters. Interestingly, SO 4 2– concentration gradually decreased while the δ34S-SO 4 2− value became positive from upstream to downstream reservoir, but both their variations inside reservoirs were homogenized to narrow ranges, which could be derived from the cumulative effects of cascade dams. After damming, the increased hydraulic retention time and water depth caused significant seasonal thermal stratification in reservoirs, which enhanced the S biogeochemical process, and this damming effect was accumulated through bottom released water. Therefore, SO 4 2− concentration together with δ34S-SO 4 2− could be useful indicators in assessing the damming effects of cascade dams in the river-reservoir systems. [ABSTRACT FROM AUTHOR]