[Spatial distributions and environmental control of diatom functional groups in sediments of Haixi Lake, Southwest China.] / åŸºäºŽç¡ è—»åŠŸèƒ½ç¾¤ç‰¹å¾æ­ç¤ºæµ·è¥¿æµ·è¿‘çŽ°ä»£ç”Ÿæ€çŽ¯å¢ƒå˜åŒ–.

Functional group classification based on the morphological, physiological and ecological characteristics of diatoms is advanced in describing the tolerance and sensibility of diatoms to environmental stressors. In this study, we examined the spatial distribution of diatom functional groups in surface sediments of Haixi Lake and explored the relationships between diatom distributions and environmental variables using multivariate analyses. Principal components analysis (PCA) and redundancy analysis (RDA) results showed that water depth and total nitrogen (TN) were the key drivers for the heterogeneous distribution of diatom functional groups. Water depth of ca. 8 m was the threshold depth in influencing diatom functional group structures linking with thermal stratification. These results provided a basis for fossil record interpretation of the short core. Diatom functional groups fluctuated over the last century, in keeping with mean annual temperature, sediment TN, and median grain size. Climate warming, accelerated nutrient enrichment and intensified hydrological changes led to the dominance of functional group D, MP and P. Additionally, climate warming and nutrient enrichment led to increased diatom functional group diversity, while increased water depth (led by damming and reservoir reinforcement) contributed to diversity loss around 1957 and 1990 AD, respectively.

[Spatial Variations of CO2 Degassing Across Water-air Interface and Its Impact Factors in Summer in Guijiang River, China].

River is characterized by obvious spatial heterogeneity in catchment, which is exacerbated by special environment features of calcium-rich, alkaline and DIC-rich(dissolved inorganic carbon) in karst river. Thus, it also leads to significant spatial variation in the CO2 degassing across water-air interface. Main ions, physicochemical parameters, δ13CDIC value and two common approaches(floating chamber(FC) and thin boundary layer models(TBL) were used to analyze the CO2 degassing characteristics in Guijiang River, a karst river, China. The results were as follows:1 Hydrochemistry in Guijiang River basin showed a significant spatial change. All of HCO3-, Ca2+, specific conductivity, total dissolved solids(TDS), SIc and pCO2 showed similar distribution characteristics in the following order:tributaries in the middle reaches > middle reaches > Downstream > Upstream of Guijiang River. 2 During the monitoring period, CO2 degassing occurred in all the sampling sites and it was the CO2 source for the atmosphere. The mean CO2 evasion was 237 mg·(m2·h)-1 in Guijiang River, which located in the range of average CO2 evasion of global river. However, significant spatial variations also occurred along Guijiang River. The CO2 degassing flux in tributaries of the middle reaches and middle reaches of the mainstream were obviously larger than those in downstream and upstream of the mainstream. 3 CO2 degassing was mainly affected by carbonate equilibrium system in tributaries in the middle reaches and middle reaches in the mainstream of the Guijiang River basin, which resulted in obviously larger CO2 degassing than those in downstream and upstream of mainstream. However, the CO2 degassing flux in tributaries of the middle reaches was also simultaneously affected by biological photosynthesis, and the minimum CO2 degassing flux[6.38 mg·(m2·h)-1] appeared in tributaries of the middle reaches. In addition, the CO2 degassing flux in mainstream upstream was mainly affected by atmospheric environmental factors, while it was synergetically influenced by many factors in mainstream downstream.

[Impacts of Thermal Stratification on the Hydrochemistry and Dissolved Inorganic Carbon in a Typical Karst Reservoir in Summer].

Thermal stratification leads to significant stratification characteristics of hydrochemistry and aquatic organisms in reservoirs, and thus affects the biogeochemical cycle in the reservoir. This study aims to understand physico-chemical properties and dissolved inorganic carbon change processes and its factors in a karst groundwater-fed reservoir, Dalongdong Reservoir, located in Shanglin County, Guangxi Zhuang Autonomous Region, China. The eight sampling points were placed along the direction of the water flow on June 19-21, 2015. The results show that: ① The reservoir exhibited obvious thermal stratification in the summer. There were significant differences in physical and chemical parameters, such as pH and conductivity (Spc) between the epilimnion and thermocline; ② The dissolved oxygen (DO) and chlorophyll a (Chl-a) content from the surface to the bottom did not show a single decreasing trend, but the maximum value occurred 2.5 m or 5 m below the surface; ③ From the surface to the bottom, dissolved inorganic carbon (DIC) concentrations showed an increasing trend with the average DIC concentration of 2.03 mmol·L-1 in the epilimnion and the average DIC concentration of 4.18 mmol·L-1 at the bottom of the thermocline. The value of stable carbon isotope (δ13CDIC) was more positive in the epilimnion than in the thermocline, where δ13CDIC gradually became partially negative with water depth. Possible reasons of these results include: ① The significant differences in temperature, distribution of aquatic organisms, and strength and direction of metabolisms in different water layers due to thermal stratification; ② The DIC variations in the epilimnion were mainly affected by the carbonate precipitation process and phytoplankton photosynthesis, thereby affecting the DIC stable isotope fractionation. DIC was mainly controlled by biological respiration and the organic matter decomposition process in the thermocline.