[Hydrochemical Evolution in the Yarlung Zangbo River Basin].

In order to explore the hydro-chemical evolution law of the Yarlung Zangbo River Basin from 1973 to 2020, the hydro-chemical characteristics and major ion sources were studied using a Piper diagram, Gibbs diagram, ion ratio, and correlation analysis, and the irrigation applicability of the Yarlung Zangbo River was evaluated using the sodium adsorption ratio (SAR), sodium percentage (Na+%), and permeability index (PI). The results showed that the mean value of TDS was (208.30±58.26) mg·L-1, which increased with time. Ca2+ was the dominant cation, accounting for (65.49±7.67)% of the total cations. HCO-3 and SO2-4 were the dominant anions, accounting for (68.56±9.84)% and (26.85±9.82)% of the main anions, respectively. The annual growth rates of Ca2+, HCO-3, and SO2-4 were respectively 2.07, 3.19, and 4.70 mg·(L·10 a)-1. The hydro-chemical type of the Yarlung Zangbo River was HCO3-Ca type, and the main ionic chemistry was controlled by the chemical weathering of carbonate rocks. The weathering of carbonate rocks during the period of 1973 to 1990 was mainly controlled by carbonation, whereas from 2001 to 2020 it was mainly controlled by both carbonation and sulfuric acid. The main ion concentrations in the mainstream of Yarlung Zangbo River were within the range of drinking water standards, with SAR between 0.11-0.93, Na+% between 8.00-36.73, and PI values between 0.39-0.87, demonstrating that the waters were suitable for drinking and irrigation. The results were of great significance to the protection and sustainable development of water resources in the Yarlung Zangbo River Basin.

[Species-habitat association of a deciduous broadleaved forest in the subtropical and tempe-rate transition zone]. / 亚热带-温带气候过渡区落叶阔叶林物种-ç”Ÿå¢ƒå ³è”åˆ†æž.

The species-habitat association analysis facilitates a better understanding of species coexis-tence and community assembly. Here, all trees in a 25-hm2 broadleaved deciduous forest plot in the Qinling Mountains of North-central China were classified into three life stages (i.e., seedling, sapling, and adult). The Torus-translation test was used to examine the species-habitat association. The results showed that the association of species with habitats varied across different species. Most species were significantly associated with high slopes, 95.7% of which showed negative association. 89.5% and 90.9% of tree species were negatively associated with low slopes and ridges, respectively. Most species had positive association with high valley, with only one negative association (0.03%). There were 80, 44 and 23 significant associations with habitats at seedling, sapling and adult stages, respectively, indicating that a greater dependence of seedlings on habitat. 38 species at seedling stage and 25 species at the sapling stage were associated with at least one habitat type, while only 17 species at the adult stage were significantly associated. The effects of habitat on species varied across life stages, showing a weaker species-habitat association at the later stage. Due to the specific environmental demands, most species showed different habitat preferences across life stages.

[Structure Characteristics and Driving Variables of Epilithic Algae Community in Lhasa River Basin of Qinghai-Tibet Plateau].

In order to explore the characteristics and driving factors of the epilithic algae community in the middle and lower reaches of the Lhasa River, epilithic algae was collected and identified in September 2019, the species composition and spatial distribution were analyzed, and the key environmental factors affecting the epilithic algae community were identified through redundancy analysis. The results indicated that 31 genera of epilithic algae belonging to six phyla were identified, and the average cell density of the epilithic algae was 1.92×106 cells·m-2. The number of species and cell density of the diatom phylum were the largest at each sampling point. The species number and cell density of the epilithic algae were significantly different between the main stream and tributaries. The main stream and tributaries contained relatively small differences in the dominant algae genera, which were Gomphonema, Fragilaria, Cymbella, and Planktolyngbya in the main stream and Gomphonema, Fragilaria, Cymbella, and Oscillatoria in the tributaries. The redundancy analysis revealed that temperature, pH, and dissolved oxygen were the main driving factors affecting the community structure of the dominant genus in the main stream, while HCO3- and flow velocity controlled the community structure of the dominant genus in the tributaries. This study provides basic data and the theoretical basis for the conservation of aquatic ecosystems and water quality management in the middle and lower reaches of the Lhasa River.

[Influence Factors of Potential Nitrification Rates and Functional Genes Abundance in the Jinshui River and the Qihe River of the Hanjiang River Basin].

In the context of increasing nitrogen loading in river systems worldwide, it is critically important to understand nitrification to maintain river ecosystem health. This comparative study was conducted to explore the relationships among the intensity of human disturbance, environmental factors, potential nitrification rate, and functional gene abundance in the Jinshui River (slightly disturbed basin) and the Qihe River (intensely disturbed basin). The results showed that AOA-amoA gene abundance was higher than that of AOB-amoA. The potential nitrification rate in the Qihe River was higher than that in the Jinshui River. There was no significant difference in AOA-amoA gene abundance between the two rivers; however, the AOB-amoA gene abundance in the Qihe River was significantly higher than that in the Jinshui River in the low flow season. The abundance of nitrification functional genes was significantly correlated with water temperature, pH, NO3-, NH4+, and organic carbon. The potential nitrification rate was positively correlated with water temperature, pH, and NO3-, and negatively correlated with AOB-amoA gene abundance. These results showed that the intensely disturbed sites had higher potential nitrification rates and nitrification functional genes abundances, and potential nitrification rates and abundances of nitrification function genes were significantly related to physical and chemical water and sediment factors. This study will be important for nitrogen pollution control in the river systems.

[Transportation and risk assessment of heavy metal pollution in water-soil from the Riparian Zone of Daye Lake, China].

Each 20 water samples and soil samples (0-10 cm, 10-20 cm) were collected from the riparian zone of Daye Lake in dry season during March 2013. Heavy metals (Cu, Ph, Cd, Zn) have been detected by flame atomic absorption spectrometric (FAAS). The results showed that the average concentrations of Cu, Pb, Cd, Zn in the water were 7.14, 25.94, 15.72 and 37.58 microg x L(-1), respectively. The concentration of Cu was higher than the five degree of the surface water environment quality standard. The average concentrations of Cu, Pb, Cd, Zn in soil(0-10 cm) were 108.38, 53.92, 3.55, 139.26 mg x kg(-1) in soil (10-20 cm) were 93.00, 51.72, 2.08, 171.00 mg x kg(-1), respectively. The Cd concentrations were higher than the three grade value of the national soil environment quality standard. The transportation of Pb from soil to water was relatively stable, and Zn was greatly influenced by soil property and the surrounding environment from soil to water. The transformation of heavy metal in west riparian zone was higher than that of east riparian zone. The potential environmental risk was relatively high. Cu, Pb, Cd, Zn were dominated by residue fraction of the modified BCR sequential extraction method. The overall migration order of heavy metal element was: Pb > Cu > Cd > Zn. There were stronger transformation and higher environmental pollution risk of Cu, Pb. The index of assessment and potential ecological risk coefficient indicated that heavy metal pollution in soil (0-10 cm) was higher than the soil (10-20 cm), Cd was particularly serious.

[Wet deposition of atmospheric nitrogen of the Jinshui watershed in the upper Hanjiang River].

The Jinshui River, a tributary of the Hanjiang River, is an important region of water conservation for the Middle Route of South to North Water Transfer Project. However, water quality has been deteriorated in recent years, in particular nitrogen increasing pollution. In this study, the wet deposition of atmospheric nitrogen in the Jinshui watershed was investigated between Feb. 2012-Feb. 2013, and the corresponding contribution to the river N loading was calculated using N retention model. The results indicated that the volume-weighted concentration of dissolved total nitrogen (DTN) was 0.24-2.89 mg x L(-1), consisting of ammonium (NH(4+)-N) (42.8%), nitrate (NO3- N) (13.3%) and dissolved organic nitrogen (DON) (43.9%), which decreased with rainfall volume as a result of dilution. The wet deposition of atmospheric N was mainly from anthropogenic pollution and the flux was between 4.97-7.00 kg x (hm2 x a)(-1), dominated by seasonal rainfall, of which about 81% occurred in spring and summer and the flux in a decreasing order of upstream, downstream, and middlestream. The wet deposition contributed approximately 34,000-46,000 kg N to the river, accounting for only 5.05%-6.78% of the contribution by fertilizers, which was too small to be the main source of the river N loading.

[Temporal and spatial pattern of phytoplankton community and its biodiversity indices in the Danjiangkou Reservoir].

Temporal and spatial patterns of phytoplankton community and their associated influencing factors using canonical correspondence analysis (CCA) were analyzed in the Danjiangkou Reservoir, China. Water quality of the reservoir was also assessed using phytoplankton cell density and biodiversity indices. Results showed that Bacillariophyta and Cyanophyta accounted for 51.08% and 18.39% of all the species, respectively. There was great seasonal variation in phytoplankton assemblage composition, cell density and biodiversity index. In summer, Cyanophyta was dominant and composed of 42.24% of the phytoplankton composition, whereas Bacillariophyta was dominant in spring, summer and winter, and accounted for 77.13%, 61.29% and 50.91% of all species, respectively. The phytoplankton density reached the maximum of 1.76 x 10(6) cells/L in summer, while the lowest value was 2.32 x 10(5) cells/L in autumn. Seasonal variability was the same for the indices of Shannon-Wiener, Simpson and Pielou, and they were 2.08, 0.77, 0.65 in autumn, and decreased to 0.85, 0.32, 0.28 in winter, respectively. Though the spatial variability was not significant in indices H', D, D(m) and J, the difference was significant between the Dan and the Han Reservoirs in terms of phytoplankton composition. The dominant phytoplankton was Bacillariophyta in Dan Reservoir and Cyanophyta in Han Reservoir. The results also indicated that conductivity was the main environmental factor influencing variation in phytoplankton composition except in autumn. The reservoir could be classified as oligotrophication by cell density and the middle level between beta-mesosaprobic zone and oligosaprobic zone using biodiversity indices. The research demonstrated the potential to use phytoplankton community and its biodiversity indices to monitor water quality in the Danjingkou Reservoir.

[Hydro-chemical characteristics in the Danjiangkou Reservoir (water source area of the middle route of the south to north water transfer project), China].

TDS, pH and major ions in the Danjiangkou Reservoir, the water source area of the Middle Route of the South to North Water Transfer Project of China were monitored during the period of 2004-2006 to systemically analyze hydro-chemical characteristics and water chemistry type. Analysis of variance (ANOVA) and correlation analysis were performed to explore their spatio-temporal pattern. The results show that the water is of low mineralized degree with a total dissolved solid ranging from 149.9-291.2 mg x L(-1), and soft water with a total hardness ranging from 40-50 mg x L(-1) x HCO3- accounts for 77.54%-77.87% of the total major anions with a content of 122.5-170.0 mg x L(-1), while Ca2+ accounts for 70.66%-77.93% of the total major cations with a content of 37.1-43.2 mg x L(-1), and the water is of a HCO3- -Ca type. Major ions show similar spatial variations, decreasing downstream in the Danjiang Reservoir, and reaching the lowest values in the Hanjiang Reservoir. The temporal and seasonal variations of the hydro-chemical characteristics show that the concentrations of major ions in the dry season are larger than those in the wet season. Hydro-chemical characteristics in the reservoir are mainly determined by the rock weatherization, while and anthropogenic activities in the upper-stream and the reservoir region have been influencing the NO3- concentration. Finally, conservation strategies of water resource in the reservoir and its upper stream are discussed.

[Seasonal variation in the major ion chemistry and their sources in the Hubei Danjiangkou Reservoir, China].

Water temperature, pH, EC, TDS, ORP, Si and major anions (Cl- , NO3- and SO4(2-)) and major cations (Na+, K+, Ca2+ and Mg2+) in the Danjiangkou Reservoir, the water source area of the Middle Route of the South to North Water Transfer Project of China were monitored during the period of 2004-2006. Analysis of variance (ANOVA) and principal component analysis (PCA) were performed to explore their seasonal variations and origins. The results show that the water is slightly alkaline with an average pH ranging from 7.9 to 8.4. The water is HCO3- -Ca type with low mineralized degree, and its total dissolved solid ranges from 174.6-209.1 mg x L(-1). The major ions range are as follows: Cl-, from (4.0 +/- 0.5) mg x L(-1) to (6.9 +/- 1.8) mg x L(-1); NO3-, from (4.6 +/- 0.9) mg x L(-1) to (6.8 +/- 1.7) mg x L(-1); SO4(2-), from (24.3 +/- 2.7) mg x L(-1) to (35.4 +/- 6.9) mg x L(-1); HCO3-, from (133.0 +/- 11.7) mg x L(-1) to (153.5 +/- 29.6) mg x L(-1); Na+, from (2.0 +/- 0.3) mg x L(-1) to (5.3 +/- 1.0) mg x L(-1); K+, from (0.7 +/- 0.09) mg x L(-1) to (1.6 +/- 0.7) mg x L(-1); Ca2+, from (33.0 +/- 2.1) mg x L(-1) to (46.6 +/- 0.8) mg x L(-1); Mg2+, from (8.0 +/- 2.5) mg x L(-1) to (10.5 +/- 3.2) mg x L(-1). Statistical analyses indicate that the water quality variables display significant seasonal differences except HCO3 and Si. In general, major ion concentrations in flood season are relatively lower due to the dilution of precipitation. HCO3- accounts for 75%-88% of the total major anions, while Ca2+ and alkali-earth metals (Ca2+ + Mg2+) account for 60%-80% and 87%-96% of the total major cations respectively, reflecting that carbonic acid weathering is the main proton producer in the water. The major ions have no adverse effects on human according to water drinking quality guidelines of China and WHO.