Xiaojiang River Research Articles

Impact of manganese mining on potentially toxic elements pollution and bioaccumulation in Spirogyra varians and Hydrilla verticillata in the Xiaojiang River.

Potentially toxic elements (PTEs) pose a significant threat to aquatic ecosystems. This study investigated the content and potential sources of PTEs (Cr, Mn, Ni, Cu, Zn, Cd, Pb) in water, sediment, and dominant aquatic plants (Hydrilla verticillata and Spirogyra varians) in the Xiaojiang River, located near the Zhaiying manganese mine in Guizhou Province, China. Correlation analysis, principal component analysis (PCA), and cluster analysis were employed to assess PTE distribution and potential sources. Water PTE concentrations complied with the Class II standard (GB3838-2002), indicating no water pollution. However, sediment PTE levels exceeded background values, particularly Mn, which exhibited moderate to strong contamination. Cd also showed moderate contamination, posing a considerable ecological risk. Cd was the main potential pollutant with the highest contribution rate. Mn and Cd were therefore identified as priority pollutants requiring targeted abatement strategies. Mining activities likely represent the primary source, but combined pollution from vehicle traffic and agriculture might also contribute. Hydrilla verticillata demonstrated a higher capacity for PTE enrichment from sediment compared to Spirogyra varians, suggesting its potential for sediment remediation (except for Cu). A significant correlation existed between both plant species and sediment PTE content. PCA supported the association between S. varians and sediment PTEs. Linear regression analyses revealed better correlations between S. varians and sediment Mn, Ni, Cu, and Zn (0.77, 0.68, 0.82, and 0.79, respectively). Taken together, these findings suggest that S. varians serves as an effective bioindicator for monitoring sediment contamination with PTEs.

Xiaojiang River Basin Ecological Environmental Quality Spatiotemporal Pattern and Evolutionary Trend Analysis Using GEE from 1990 to 2022

Assessment and monitoring of the quality of the ecological environment in the area is a very important fundamental task in the development of ecological civilization in the Xiaojiang River Basin in Yunnan Province, which serves as a demonstration area for ecological restoration in the upper reaches of the Yangtze River. The Landsat remote sensing images from 1990, 1995, 2000, 2005, 2010, 2014, 2018, and 2022 were chosen, and the four indexes of greenness （NDMVI）, humidity （WET）, dryness （NDBSI）, and heat （LST） were extracted. The remote sensing ecological index （RSEI） was created using the principal component analysis method, then the spatial and temporal patterns and trends of ecological quality in the Xiaojiang River Basin between 1990 and 2022 were examined using the GEE platform, ArcGIS 10.7 platform, and Python platform, combining the analysis methods of geographic information mapping, coefficient of variation, Mann-Kendall trend test, Sen's slope estimation, and Hurst's index. The findings demonstrated that： ① the ecological quality of the study area had more obvious geographic differentiation spatially, and by 2022, the areas with excellent and good ecological quality grades were primarily distributed in the areas with better alpine vegetation cover, and those with poor ecological quality were primarily distributed in the areas of the mudslide ravines with relatively low terrain. On a time scale, the study area's RSEI index increased from 0.41 in 1990 to 0.55 in 2022, with a fluctuating overall trend of ecological quality improvement and an average increase of 0.048（10 a） -1； this progress was directly related to a number of ecological construction initiatives that have been energetically carried out, such as converting farms to forests, preventing mudslides, saving soil and water, managing heavy metal contamination, etc. ② The RSEI was more appropriate for the evaluation of ecological quality in alpine ravine areas because, in comparison to the NDVI index, the NDVMI adopted in this study was more sensitive to vegetation information in topographic undulation areas, especially in shaded areas, and could more accurately and quantitatively describe the vegetation information. ③ The RSEI in the Xiaojiang River Basin had a mean coefficient of variation of 0.202. Overall, its volatility was low, and its high volatility was mostly concentrated in the mudslide gully area along both sides of the Xiaojiang River fracture zone, where the surface was made up of bare rocks and sediment that was easily impacted by the changing of the seasons, the climate, and human activity. ④ The quality of the ecological environment in the region was significantly improving, with the rising area reaching 85.72% of the total area and the declining area accounting for approximately 10.15% of the total area. The future trend of change will be dominated by ongoing improvement and future degradation, accounting for 44.75% and 39.97%, respectively. It is important to pay close attention to areas that could potentially degrade. The findings of this study can serve as a theoretical foundation for additional ecological environmental conservation, management, and sustainable development in the Xiaojiang River Basin.

Community structure of phytoplankton in different water layers and its relationship with environmental factors during the period of algal bloom in Xiaojiang River backwater area of Three Gorges Reservoir

Community structure of phytoplankton in different water layers and its relationship with environmental factors during the period of algal bloom in Xiaojiang River backwater area of Three Gorges Reservoir

Responses of biodiversity to microhabitat heterogeneity in debris flow gullies: Assessing the impact of hydrological disturbance

Rivers play a vital role in the maintenance of the biosphere and human society, since they participate in the global water cycle and provide varied habitats to support biodiversity. Microhabitat heterogeneity is regarded as a key factor driving biodiversity and it plays an active ecological role in different types of mountain rivers. Whether river microhabitat heterogeneity exhibits the same ecological patterns across hydrological periods remains unclear. Here, we analyzed the changes in macroinvertebrate community composition, functional traits, and multi-faceted α-diversity in five debris flow gullies in the Xiaojiang River Basin (southwestern China) between two different hydrological periods. We explored the responses of biodiversity to river microhabitat heterogeneity and its driving factors before and after hydrological disturbance. The results indicated that river microhabitat heterogeneity and three facets of macroinvertebrate α-diversity decreased after hydrological disturbance, with macroinvertebrate state traits becoming more unbalanced. Macroinvertebrate taxonomic diversity increased with increasing river microhabitat heterogeneity across hydrological periods, and this pattern was more prominent before hydrological disturbance. A high correlation emerged between macroinvertebrate phylogenetic diversity and river microhabitat heterogeneity only before hydrological disturbance. Hydrogeomorphic parameters prominently affected macroinvertebrate communities before hydrological disturbance. Water environmental parameters worked together with hydrogeomorphic parameters to shape macroinvertebrate communities in hydrologically disturbed debris flow gullies, indicating a reduced ecological role of river microhabitat heterogeneity. The ecological health of debris flow gullies can be improved by increasing vegetation coverage on river bank slopes to increase slope stability and mitigate hydrological disturbances, as well as placing large rocks into river channels to enhance riverbed stability and create habitats for more biological groups.

Analysis of the Characteristics of Groundwater Resources in the Section from Tongdu to Gela along the Xiaojiang River

Analysis of the Characteristics of Groundwater Resources in the Section from Tongdu to Gela along the Xiaojiang River

Characteristics and Dfferences of Dissolved Oxygen Stratification in Different Tributaries of Three Gorges Reservoir During Impoundment Period

Taking the Xiaojiang and Xiangxi Rivers, two typical tributaries of the Three Gorges Reservoir, as examples, this study analyzed and compared the hydrodynamic, thermal stratification, and temporal and spatial differences in dissolved oxygen (DO) and their responses to the water storage process in the two tributaries through field monitoring at different stages of the 2020 impoundment period. The results showed that:① at the initial stage of water storage, the DO in the surface layer of the Xiaojiang River was higher (7.00-13.00 mg·L-1) due to atmospheric reoxygenation and phytoplankton photosynthesis, and the oxycline appeared in the water depth of 3-5 m. A large area of anoxia (DO<2.00 mg·L-1) or even an anaerobic sublayer occurred in the water below 5 m. The DO in the Xiangxi River could be divided into three layers vertically:oxygen-rich surface water (8.00-12.00 mg·L-1), middle water (6.00-8.00 mg·L-1), and low-oxygen bottom water (4.00-6.00 mg·L-1). ② Thermal stratification provided a stable physical environment, whereas the upstream inflow and vegetation decomposition in the water-level fluctuation zone increased the content of organic matter, which likely increased the oxygen consumption which was conducive to the formation of an anaerobic bottom layer. In the Xiangxi River, the risk of hypoxia in the bottom water body was low because of the oxygen replenishment from the long-term downslope-bottom density current.③ Continuous monitoring also showed that the storage of the reservoir played a significant role in the replenishment of DO in tributaries, which effectively and rapidly improved the anaerobic phenomenon in the Xiaojiang River. In the Three Gorges Reservoir, it is feasible to ameliorate the water ecological problems such as anoxia and anaerobic conditions in the tributaries via reservoir operation. This study aids understanding of the characteristics and differences of DO stratification in different tributaries of the Three Gorges Reservoir, which can provide theoretical and technical support for reservoir ecological operation.

InSAR Study of Landslides: Early Detection, Three-Dimensional, and Long-Term Surface Displacement Estimation—A Case of Xiaojiang River Basin, China

Landslides, a major natural geohazard, obstruct municipal constructions and may destroy villages and towns, at worst causing significant casualties and economic losses. Interferometric Synthetic Aperture Radar (InSAR) technique offers distinct advantages on landslide detection and monitoring. In this paper, a more systematic workflow is designed for InSAR study of landslides, in terms of three levels: (i) early detection on regional scale, (ii) three-dimensional (3D) surface displacement rates estimation on detailed scale, and (iii) time series analysis on long-term temporal scale. The proposed workflow is applied for landslide research on the Xiaojiang River Basin, China, using ascending and descending Sentinel-1 images acquired from March 2017 to May 2019. First, the landslide inventory has been mapped and updated using InSAR stacking method, supporting geohazard prevention on a regional scale. A total of 22 active landslides are identified, ranging from medium to super large scale. Compared with the existing inventory, three unrecorded landslides are newly detected by our approach, and five recorded landslides are detected significant expansion of their boundaries. Then, specific to a detected landslide, Baobao landslide, a Total Least Squares–Kalman Filter-based approach is presented. Two outcomes are provided for further spatial-temporal pattern analysis: 3D displacement rates, providing an intuitive insight on the spatial characteristics and sliding direction of landslide, which are analyzed to deep the understanding of its kinematic mechanism, and long-term time series, which contribute to deduce the dynamic evolution of landslide, presenting benefits in landslide forecasting.

Characteristics of Ions Composition and Chemical Weathering of Tributary in the Three Gorges Reservoir Region: The Perspective of Stratified Water Sample from Xiaojiang River

River water chemistry offers information on watershed weathering and responds to the global carbon cycle. Watershed weathering processes and water chemistry in stratified water are still unclear in Xiaojiang River, as a major tributary of the Three Gorges Reservoir (TGR) which is the largest reservoir in the world. Major ions of river water at different depths were measured to reveal the ionic composition and chemical weathering properties by principal component analysis and stoichiometry in Xiaojiang River. Ca2+−HCO3− dominated the hydrochemical facies of river. Surface river water had the lowest total dissolved solid (146 mg/L) compared to other layers of water. According to principal component analysis, the major ions were divided into two principal components. PC1 was the weathering end-member of rocks, including the main ions except K+ and NO3–N, and PC2 may be the mixed end-member of atmospheric input and anthropogenic input. From stoichiometry, carbonate weathering dominated the cationic composition, with a contribution ratio of 56.7%, whereas atmospheric input (15.2%) and silicates weathering (13.9%) had similar extent of contribution. Compared with other major tributaries of TGR, Xiaojiang had more intense chemical weathering processes. The weathering rates of carbonates and silicates were 19.33 ± 0.68 ton/km2/year and 3.56 ± 0.58 ton/km2/year, respectively. Sulfuric acid as a proton may have participated less in the weathering processes of Xiaojiang River. The CO2 consumption budgets for silicates and carbonates weathering were 0.8 ± 0.2 × 109 mol/year and 2.8 ± 0.2 × 109 mol/year, respectively. These results enrich the watershed weathering information of TGR tributaries and provide data support for understanding the global carbon cycle.

Response of Fish Trophic Niche to Water Level Regulation of the Three Gorges Reservoir in its Backwater Bay Using a Stable Isotope Approach

To date, our ability to speculate how species interactions will change temporally and spatially in response to WLR still inadequate, especially within large river-reservoir ecosystems. Fish communities in backwater bay of the Xiaojiang River of the TGR (Three Gorges Reservoir) were studied in 2010 and 2016 using a stable isotope approach to explore variations in fish trophic niches associated WLR. We found that fish assemblages tended to have broader trophic diversity spaces in LBAs (large backwater areas) at a water depth of 175 m, suggesting that the assimilation of food resources might come from a greater diversity of habitats or prey items with distinct isotopic signatures. Many among-fish species trophic niches tended to overlap and have broader ranges in LBAs compared to SBAs (small backwater areas) at a water depth of 145 m, which indicated that the processes of impounding at 175 m can provide more similar food resources for different fish species. Our findings highlight that WLR dynamics are typical characteristics of the backwater bay of the Xiaojiang River aquatic ecosystems caused by the operations of the TGR, which has significant ecological effects on the fish trophic structure within this community. Understanding the pattern of changes in fish trophic niche associated with WLR will be meaningful for fishery resources management of the other tributaries in the TGR.

Exostoma dulongensis, a new glyptosternine catfish from the Irrawaddy basin, Yunnan, China (Siluriformes: Sisoridae)

Exostoma dulongensis sp. nov., a new species of sisorid catfish from the genus Exostoma Blyth, 1860, is described from the Xiaojiang River and Dulongjiang River, tributaries of N'mai Hka River in the Irrawaddy basin, Yunnan Province, China. Exostoma dulongensis sp. nov. is the seventeenth species reported within this genus and is most similar to Exostoma ericinum Ng 2018 in morphology but can be distinguished by the following characters: tip of pelvic fin far from anus vs. reaching when depressed; nasal barbel reaching or surpassing posterior edge of orbit vs. just reaching middle of orbit; greater preanal length (70.9%-80.1% SL vs. 67.7%-70.5%); and longer dorsal to adipose length (13.5%-23.8% SL vs. 8.0%-12.0%). The new species can also be distinguished from all known congeners by the following characters: adipose fin confluent with caudal fin and without incision; caudal fin weakly forked; 40-43 vertebrae; and pectoral fin extending to vicinity of dorsal fin origin.

Vegetation of the water-level fluctuation zone in the Three Gorges Reservoir at the initial impoundment stage

The water-level of Three Gorges Reservoir first reached a normal storage level 175 m in October 2010, resulting in a large-area water-fluctuating zone with an elevation difference of 30 m (145–175 m). We used the Geographic Information System (GIS) technology, the field quadrat survey, the species importance value calculation, and literature data to assess the natural environment situation, the vegetation regeneration status, and the ecological benefits of the dominant plant species in terms of mitigating agricultural non-point source pollution of the WLFZ in the Three Gorges Reservoir at the initial impoundment stage. The results showed that: (1) the WLFZ area presented an obvious trend of increasing first and then decreasing from west to east, and the exposed area at the elevation intervals of 145–175 m, 155–175 m, and 165–175 m accounted for 20, 37.49, and 42.51% of the total area, respectively; (2) the WLFZ area gradually decreased with increasing gradient, and the exposed area at the gradient intervals of <15°, 15–25°, 25–35°, 35–60°, and >60° accounted for 60.90, 18.62, 12.03, 8.06, and 0.39%, respectively, of the total area. (3) The vegetated area increased with increasing water level elevation, and the vegetation coverage area at elevation intervals of 145–155 m, 155–165 m, and 165–175 m accounted for 4.96, 16.09, and 44.77%, respectively, of the total area of the corresponding elevation interval. The vegetated area gradually decreased with increasing gradient, and at the sections Jiangjin-Changshou, Fuling-Yunyang, and Fengjie-Yiling, the vegetated area accounted for 15.30, 71, and 12.70%, respectively, of the total vegetation coverage area. (4) The important value calculation results indicate that the dominant species significantly differed among the different elevations in the three belt transects of the Yangtze River main stream (Zhongxian section), the Xiaojiang River (Kaizhou section), and the Xiangxi River (Guizhou section). The dominant annual herb species were Digitaria sanguinalis (Linn.) Scop., Conyza canadensis (Linn.) Cronq., Bidens frondosa Linn., Echinochloa crusgali (Linn.) Beauv., and Setaria viridis (Linn.) Beauv., while the dominant perennial herb species were Cynodon dactylon(Linn.) Pers. and Cyperus rotundus Linn.. (5) The water level elevation was the most important factor affecting vegetation restoration. At the initial impoundment stage, the naturally regenerating plant species Cynodon dactylon(Linn.) Pers. and Cyperus rotundus Linn. could be used to prevent and control regional agricultural non-point source pollution, combined with the establishment of plant hedges using the native species Morus alba L. and Vitex negundo Linn.. We provide a scientific basis for the development of measures to mitigate agricultural non-point source pollution in the Three Gorges Reservoir area, using ecological restoration.

Effects of copper mining on heavy metal contamination in a rice agrosystem in the Xiaojiang River Basin, southwest China

Metallic ore mining causes heavy metal pollution worldwide. However, the fate of heavy metals in agrosystems with long-term contamination has been poorly studied. Dongchuan District (Yunnan, southwest China), located at the middle reaches of the Xiaojiang River, is a well-known 2000-year-old copper mining site. In this work, a survey on soil heavy metal contents was conducted using a handheld X-ray fluorescence instrument to understand the general contamination of heavy metals in the Xiaojiang River Basin. Furthermore, river water, soil, and rice samples at six sites along the fluvial/alluvial fans of the river were collected and analyzed to implement an environmental assessment and an evaluation of irrigated agrosystem. V, Zn, and Cu soil levels (1724, 1047, and 696 mg·kg−1, respectively) far exceeded background levels. The geo-accumulation indexes (Igeo) showed that cultivated soils near the mining sites were polluted by Cd and Cu, followed by Zn, V, Pb, Cr, Ni, and U. The pollution index (Pi) indicated that rice in the area was heavily polluted with Pb, Cr, Cd, Ni, Zn, and Cu. The difference in orders of metal concentrations between the soil and rice heavy metal contamination was related to the proportion of bioavailable heavy metals in the soil. The crop consumption risk assessment showed that the hazard quotient exceeded the safe threshold, indicating a potential carcinogenic risk to consumers. The Nemerow integrated pollution index and health index indicated that the middle of the river (near the mining area) was the heaviest polluted site.

Macroinvertebrate communities characteristics and their responses to fluvial geomorphological feature of typical debris flow gullies in the Xiaojiang River Basin, Yunnan Province

云南小江流域为典型干热河谷区，该区域干热少雨，流域内泥石流沟众多，生态环境十分脆弱.2017年4月和9月对小江流域的吊嘎河、蒋家沟、蓝泥坪沟、清水沟、陶家小河5条泥石流沟及小江干流开展了系统调查，旨在摸清5条泥石流沟及小江干流河流地貌、水环境及底栖动物群落现状，分析不同河床结构发育程度的泥石流沟间的底栖动物群落差异，揭示底栖动物对反映河床结构发育程度的河流地貌特征参数凹凸度的响应关系.调查期间于5条泥石流沟及小江干流中共采集到底栖动物70种，隶属于4门6纲38科69属，其中环节动物6种，软体动物2种，节肢动物61种，扁形动物1种.从种类类群来看，5条泥石流沟及小江干流的底栖动物物种数、密度、生物量上均以节肢动物占绝对优势，分别占总量的78.0%~92.5%、98.7%~100%、65.0%~100%.从功能摄食类群上来看，5条泥石流沟及小江干流底栖动物密度上均以直接收集者为主，占总量的74.3%~96.3%.回归分析表明，5条泥石流沟中底栖动物物种数、密度及生物量均与河流地貌特征参数凹凸度呈正相关关系，由此可见，发育良好的河床结构在维持河流地貌稳定和改善河流生态方面起着举足轻重的作用.本研究结果可为小江流域山区河流泥石流沟河床结构重建及生态修复提供科学依据.;The Xiaojiang River Basin is a typical dry-hot valley area, characterized by high temperatures, little rain and many debris flow gullies, where ecological environment is very fragile. In April and September of 2017, field surveys were conducted in the five debris flow gullies (i.e., the Diaoga Creek, the Jiangjia Creek, the Lanniping Creek, the Qingshui Creek, and the Taojiaxiaohe Creek) and the Xiaojiang River. The purpose of this study is to understand fluvial geomorphological feature, water environment, and macroinvertebrate communities in the five debris flow gullies and the Xiaojiang River, to analyze the differences in macroinvertebrate communities among debris flow gullies with different riverbed structures, and to reveal the responses of macroinvertebrates to the fluvial geomorphological parameter (degree of concavity-convexity) reflecting the development degree of riverbed structure. A total of 70 taxa of macroinvertebrates were identified, belonging to 4 phyla, 6 classes, 38 families and 69 genera. With regard to the taxonomic groups, arthropods were dominant in the species richness, density, and biomass of macroinvertebrates in the five debris flow gullies and the Xiaojiang River, accounting for 78.0%-92.5%, 98.7%-100.0% and 65.0%-100.0% of the total richness, densities, and biomass, respectively. With regard to the functional feeding groups, collector-gatherers were all dominated in the five debris flow gullies and the Xiaojiang River, accounting for 74.3%-96.3% of the total densities. Regression analyses showed that the species number, density, and biomass of macroinvertebrates were all positively correlated with the fluvial geomorphological parameter (degree of concavity-convexity) of the five debris flow gullies. The present study indicated that the well-developed riverbed structure plays an important role in maintaining the stability of the fluvial geomorphology and ecological quality. The results of this study can provide scientific basis for riverbed structure reconstruction and ecological restoration of debris flow gullies in mountain regions of the Xiaojiang River Basin.

Comparative study on alkaline phosphatase activity of main tributaries of Three Gorges Reservoir

为进一步认识和理解三峡水库中磷的迁移、转化规律及其与富营养化之间的关系，于2014年7月至2015年7月对三峡水库12条典型支流的水体碱性磷酸酶活性进行跟踪观测与比较分析，同步监测各样点水体的理化指标.结果发现，各支流水体碱性磷酸酶活性的分布呈现显著的时空异质性，该异质性与各支流水体富营养化程度密切相关.从季节上看，春季碱性磷酸酶活性呈逐渐上升的趋势，到夏季达到高峰，秋季碱性磷酸酶活性逐渐下降，冬季降到全年最低点.从空间分布上看，水体碱性磷酸酶活性在各支流的总体分布趋势为：小江 > 香溪河 > 苎溪河 > 童庄河 > 青干河 > 袁水河 > 磨刀溪 > 梅溪河 > 汤溪河 > 草堂河 > 大宁河 > 神农溪.综合营养指数较高的小江、香溪河和苎溪河，其碱性磷酸酶活性较高；综合营养指数较低的大宁河和神农溪，碱性磷酸酶活性较低.相关分析显示，各支流碱性磷酸酶活性与水温、溶解氧、电导率、pH和浊度均存在显著正相关；与透明度呈显著负相关.在营养盐方面，碱性磷酸酶活性与可溶性活性磷呈显著负相关；与高锰酸盐指数、叶绿素a浓度和综合营养状态指数均呈显著正相关.不同时期不同生物的贡献和不同环境因素的影响是导致碱性磷酸酶时空异质性的主要原因.;To further understand the migration and transformation characteristics of phosphorus and its relationship with eutrophication in the Three Gorges Reservoir, the physical and chemical parameters, alkaline phosphatase activity of 12 typical tributaries of the reservoir were analyzed from July 2014 to July 2015. The research found significant seasonal and regional variations of alkaline phosphatase activity in the tributaries, and the heterogeneity was closely related to the degree of eutrophication. In temporal view, alkaline phosphatase activity was gradually increased from spring to summit in summer. The activity of alkaline phosphatase then dropped from autumn to bottom in winter. On the spatial side, the activity of alkaline phosphatase had high values in Xiaojiang River, Xiangxi River and Zhuxi River, which were at high level of eutrophication. The activity of alkaline phosphatase had low values in Daning River and Shennong River, which were at low level of eutrophication. The correlation analysis results showed that there was a significant positive correlation between alkaline phosphatase activity and water temperature, dissolved oxygen, conductivity, pH and turbidity; there was a significant negative correlation between alkaline phosphatase activity and transparency in each tributary. In terms of nutrient, alkaline phosphatase activity was significantly negatively correlated with soluble active phosphorus and positive correlated with chemical oxygen demand, chlorophyll-a and trophic state index. The contributions of different organisms and the influences of different environmental factors are the main causes of the spatial and temporal heterogeneity of alkaline phosphatase.

Organotins in the aquatic media of secondary anabranches in the Three Gorges Reservoir Region, China

The Three Gorges Reservoir Region (TGRR) is one of the most sensitive areas of ecological environment in China. As vital backwater areas, the secondary anabranches of the TGRR were prone to eutrophication in Spring which would affect the distribution and transfer of organotins (OTs) among aquatic media. This study quantified the concentrations of butyltins (BTs) and phenyltins (PhTs) in water columns and aquatic media of two anabranches of the TGRR, the Daning River (DR) and the Xiaojiang River (XR) during the state of eutrophication. Our results showed that the average concentrations of BTs and PhTs in surface water are 43.91, 81.25 ng Sn L−1 in the DR, and 63.49, 69.21 ng Sn L−1 in the XR, respectively, and there were no obvious differences in the concentrations of BTs and PhTs across the water columns in the DR and XR. PhTs, especially monophenyltin (MPhT), are predominated in the dissolved phase, whereas BTs, especially dibutyltin (DBT), are predominated in both suspended particulate matter (SPM) and the sediment. Shipping and agricultural activity were likely the sources of OTs in both the DR and XR. High concentrations of tributyltin (TBT) and triphenyltin (TPhT) are still present in the aquatic media of the TGRR, and pose a significant risk to aquatic organisms due to the potential for bioaccumulation. Therefore, it is necessary to further monitor and assess OTs especially PhTs in surface water, and to continue to restrict the use of OTs to protect the aquatic environment of the TGRR.

Experimental Study on the Shear Performance of Shallow Hinge Joints for Prefabricated Hollow Slab Bridges

To investigate whether shallow hinge joint fracture was caused by shear stress or flexural stress, during the demolition and reconstruction of Xiaojiang River bridge, two original girders were collected and shipped to the lab, and the shallow hinge joint between the two girders was rebuilt. Tests were performed to investigate the cracking load, failure mode, and force transmission performance of the hollow slab girder and shallow hinge joint under vehicle load. The test result shows that under eccentric load, when the load increases to 365 kN, the midspan bottom slab of the testing girder starts to fracture; as the load increases to 560 kN, the roof slab of the testing girder starts to fracture; the hinge joint has a maximum horizontal opening of 0.153 mm and vertical relative displacement of 0.201 mm; during the entire test loading process, the shallow hinge joint structure does not develop fracture and shear failure; and the shallow hinge structure demonstrates excellent shear stress transmission performance. In addition, based on hinge slab theory, the hinge joint internal force under vehicle load was calculated. Based on ACI 318‐05 specification, CAN/CSA‐S6‐00, and JTG D61‐2005, the hinge joint shear bearing capacity was calculated. Hinge joint stress resistances calculated from the three specifications all exceed the internal force. Among them, the calculation results from ACI 318‐05 and CAN/CSA‐S6‐00 are similar, while the result from JTG D61‐2005 specification significantly exceeds the internal force, which is mainly because the designed concrete direct shear strength fvd in the Chinese specification does not consider factors such as bonding surface coarseness, concrete pouring sequence, and material properties. Theoretical calculations and tests show that the actual failure mode of the shallow hinge joint in prefabricated hollow slab girder bridges is not caused by shear stress.

Evaluation of Temporal and Spatial Variation Characteristics of Nutrients in Surface Sediment in the Three Gorges Reservoir Area

With the construction of the Three Gorges Dam, the river flow pattern and sediment dynamics are expected to be affected. As a consequence, the sediment traits could be impacted by these changes. The temporal and spatial variation characteristics of the nutrient content from 2000 to 2015 in surface sediment were analyzed in the main stream from Jiangjin to the dam site section of the Yangtze River and in the estuaries of the representative input tributaries of the Three Gorges Reservoir, such as the Jialing River, Yulin River, Wujiang River, Xiaojiang River, Daning River, and Xiangxi River. Then, the state of the pollution was assessed. Results revealed that the average concentrations of total phosphorus (TP) in the surface sediments of the main stream ranged from 678.2 to 928.6 mg·kg-1, the average contents of total nitrogen (TN) ranged from 0.203% to 0.362%, the average contents of potassium ranged from 1.74% to 2.37%, and the average contents of organic matter ranged from 0.94% to 1.54%. The average concentrations of TP in the estuaries of the representative input tributaries ranged from 490.1 to 832.3 mg·kg-1, the average contents of TN ranged from 0.257% to 0.495%, the average contents of potassium ranged from 1.69% to 2.32%, and the average contents of organic matter ranged from 1.21% to 2.27%. The concentrations of TP and potassium in the study sections were generally within background concentration ranges, while the concentrations of TN were obviously above background levels, and the concentrations of organic matter were obviously below background levels. The nutrient contents in the surface sediment did not display significant differences among the study sites; however, the distributions of different nutrient contents along the river varied widely. Although the nutrient contents in the surface sediments fluctuated somewhat during different flow periods, they were seemingly unaffected by the impoundment, since no obvious enrichment was observed throughout the impoundment. The evaluation of organic index indicated a clean state for the surface sediments in the majority of the study area, while there was a moderately polluted state in some local sections. The evaluation of nitrogen pollution indicated a polluted state for most sections. Overall, the nutrients in the surface sediments of the Three Gorges Reservoir showed moderate ecological risks, possibly caused by TP and TN.

Analysis on Heavy Metal Distribution in Overlying Deposit and Pollution Characteristics in Drainage Basin of Xiaojiang River in Dongchuan District, China

The distribution characteristics of heavy metal (Cu, Zn, As, Pb and Cd) content in overlying deposit in Xiaojiang River is analyzed in this thesis, and potential ecological risk index is adopted to evaluate the potential ecological risk of heavy metal pollution in the overlying deposit. Results indicate that the heavy metal (Cu, Zn, As, Pb and Cd) content in overlying deposit in Xiaojiang River all has exceeded standard, especially the content near diggings which is much higher than the national first standard value. And this will affect the bottom mud and river system of Jinsha River to some extent. Cu and Cd are the key pollutants and should be taken as the key object of study. It can be seen from comparison between samples in wet season and that in dry season that pollutants in bottom mud will be released due to the effect of pH value, and secondary pollution of the river will be caused.

Phytoplankton communities determine the spatio-temporal heterogeneity of alkaline phosphatase activity: evidence from a tributary of the Three Gorges Reservoir

In order to reveal the role of phytoplankton in the spatio-temporal distribution of alkaline phosphatase activity (APA), monthly investigations were conducted in the Xiaojiang River, a tributary of the Three Gorges Reservoir in China. Different APA fractions, environmental parameters, and phytoplankton communities were followed. High spatio-temporal variations of APA were observed, with the highest value in summer and the lowest in winter. The annual average APAT (total alkaline phosphatase activity) ranged from 7.78–14.03 nmol∙L−1∙min−1 with the highest in the midstream and the lowest in the estuary. The dominant phytoplankton phyla in summer and winter were Cyanophyta and Bacillariophyta, respectively. The mean cell density in the midstream and in the estuary was 5.2 × 107 cell∙L−1 and 1.4 × 107 cell∙L−1, respectively. That APA>3.0 μm was significantly higher than APA0.45-3 μm indicating phytoplankton was the main contributor to alkaline phosphatase. Correlation analysis indicated the dominant species and cell density could determine the distribution pattern of APA. Turbidity, total phosphorus, chemical oxygen demand, water temperature (WT), pH and chlorophyll a were proved to be positively correlated with APA; soluble reactive phosphorus, conductivity, transparency and water level(WL) were negatively correlated with APA. It was concluded that spatio-temporal heterogeneity of APA determined by phytoplankton communities was related to WT and WL.

Use of fish species from different trophic levels to control algae and water quality: An enclosure experiment in eutrophic area of Xiaojiang River.

The effects of stocking both filter-feeding fish and piscivorous fish were compared to the effects of stocking only filter-feeding fish for suppressing algal blooms and improving water quality in the impoundment area of Xiaojiang River where catfish were dominant. Using only filter-feeding fish for algal suppression and water quality control was more effective in the short-term, but use of both filter-feeding fish and piscivorous fish was better in the long-term. Obvious suppression of phytoplankton biomass (PB) only occurred during the first 14 days regardless of the fish stocked. Adding fish to the enclosure clearly alters phytoplankton community structure and introducing piscivorous fish to an enclosure stocked with filter-feeding fish changed the relative densities of dominant algae species. While stocking filter-feeding fish decreased total nitrogen concentration by removing phytoplankton, it did not effectively decrease total phosphorus and Chlorophyll a concentrations. Introducing piscivorous fish to the enclosure weakened the relationship between nutrients and phytoplankton. Results indicate that stocking only filter-feeding fish to improve water quality and suppress phytoplankton in an impoundment area is insufficient and other technologies and means should be applied simultaneously.