[Source and spatio-temporal variation characteristics of dissolved inorganic carbon in Wanfenghu Reservoir, China].

The flux and form of dissolved inorganic carbon (DIC), an important part of carbon budget, play a key role in the biogeochemistry of aquatic ecosystem. By analyzing physicochemical parameters and water DIC and δ13CDIC characteristics in Wanfenghu Reservoir, we examined the behavior and source of DIC. In the epilimnion, water pH in the entire reservoir was conservative, being weakly alkaline. Nitrate (NO3--N) had the maximum coefficient of variation and a high spatio-temporal variation. Due to the dilution effect, the lowest values of electrical conductivity (EC), partial pressure of carbon dioxide (pCO2) and DIC appeared during the summer high flow phase. On the water column in summer, redox potential (Eh) and NO3--N did not change with water depth, while other indicators changed significantly, with greatest variation in the thermocline. Water temperature (T), pH and Eh all decreased with increasing water depth in both seasons, while pCO2 showed an opposite trend. Water EC, total alkalinity (TA), and DIC decreased with increa-sing water depth in summer, but with a smaller gradient of change in winter. The DIC in water was negatively correlated with water pH and Eh, while positively correlated with EC and pCO2 in both seasons. 2) The concentration of DIC was 2.66-4.9 mmol·L-1 in summer and 3.38-4.52 mmol·L-1 in winter. During the period of thermal stratification, the variation gradients of DIC and δ13CDIC in the thermocline were most significant. DIC was positively correlated with δ13CDIC of epilimnion in summer. DIC was negatively correlated with δ13CDIC in epilimnion in winter and on water column in both summer and winter. However, the variation of DIC and δ13CDIC with water depth was not obvious in winter. 3) In summer, δ13CDIC was -7.71‰- -1.38‰, indicating that the dissolution of carbonate minerals was dominant. In winter, δ13CDIC was -16.93‰- -9.44‰, signifi-cantly lower than that in summer but with a wider range, indicating biological input of CO2 and mineralization of organic matter were the main sources. The δ13CDIC varied significantly in different seasons and water depths because of differences in carbon sources and changes in the relative contribution proportion of carbon sources.

[Spatial and Temporal Distribution of Chlorophyll a and Its Relationship to Algae and Environmental Factors in Aha Reservoir].

As one of the drinking water sources for Guiyang City in southwest China, the Aha Reservoir has an area of 190 km2 and a volume of 5.42×108 m3. The water depth is less than 30 m, with an average depth of 13 m. Regulated by subtropical humid monsoon climate, it has cool summers and warm winters, with an annual mean air temperature of about 15.3℃ and an annual normal rainfall of approximately 1,129 mm. Impacted heavily by human activity (e.g., untreated industrial and domestic sewage and agricultural non-point pollution sources), the eutrophication problem in the Aha Reservoir has become more serious each year. In order to explore the spatial and temporal distribution characteristics of chlorophyll a (Chl-a) and its relationship to algae and the driving factors in the Aha Reservoir, phytoplankton and water samples were collected in the dry period, normal period, and flood period. The results showed a significant seasonal variation in Chl-a, same as biomass, but not the same as the algal abundance. Highest Chl-a concentration (91 µg·L-1) occurred in the mean season with the dinoflagellate bloom but during dry and wet seasons, they were only 8 µg·L-1 and 16 µg·L-1, respectively. During the dry and flood periods, the Chl-a concentrations in surface waters were slightly higher than the other layers caused by sufficient light and dissolved oxygen. But in the normal period, the Chl-a concentrations in surface waters were far higher than the other layers because of the dinoflagellate bloom assembling in surface waters. Located at the reservoir entrance of Jinzhong River, Dam sampling point owned higher Chl-a concentration than Kuzhong as a result of higher nutrients. Correlation analysis indicated that Dinoflagellate was positively correlated with Chl-a (R=0.798, P<0.01). Chl-a was positively associated with total phosphorus, dissolved oxygen, pH value, and total nitrogen (R=0.762, P<0.01; R=0.792, P<0.01; R=0.658, P<0.01; R=0.388, P<0.05) and it had a negative correlation with the N/P ratio and nitrate nitrogen (R=-0.37, P<0.05; R=-0.435, P<0.05). Stepwise regression analysis showed that TP, N/P ratio, and DO were the most important factors influencing the temporal and spatial distribution of Chl-a. Thermal stratification and water temperature were also the significant factors that could not be ignored.

[Response of Phytoplankton Functional Groups to Eutrophication in Summer at Xiaoguan Reservoir].

Hydrology and Water Resources Bureau of Guizhou Province, Guiyang 550002, China) Abstract: In order to explore the distribution characteristics of phytoplankton functional groups, eutrophication characteristics and response of phytoplankton functional groups to eutrophication in Xiaoguan Reservoir, phytoplankton and water samples were taken once a week from 25th July 2014 to 27th September 2014. The results showed that there were 22 phytoplankton functional groups, groups S1, D, J, B, G, MP, L0, SN, X1, Y, Xph, F, T and W1 were comparatively common functional groups, Wherein, S1, D and J were the dominant functional groups. Weekly dynamics of phytoplankton functional groups were: S1-->S1-->S1-->S1-->S1--S1-->S1-->J/D/S1-->Sl1- >/1D. group Sl1dominated over other groups, the cell abundance of S1 appeared two peaks at week 5 and week 7 respectively, but there was a slump at week 8, and rose again at last, compared to two peaks before, the cell abundance had dropped from 108cells · L⁻¹ to 107cells · L⁻¹ Water flush caused by discharge gate opening artificially was the main reason. Based on the three methods of eutrophication evaluation, the water was in moderately eutrophic and eutrophic states in Xiaoguan Reservoir in the summer of 2014. Multivariate analysis (RDA) indicated transparency was the main factor affecting the distribution of phytoplankton functional groups, and nutrients were no longer the limiting factor. The study suggested that phytoplankton functional groups could make a good response to eutrophication: groups S1 and J adapted to the turbid eutrophic water bodies, D adapted to shallow turbid waters and was sensitive to nutrient depletion. Also, common functional groups like G, X1, WW1 F etc. mostly adapted to eutrophic water bodies.

[Biogeochemical processes of the major ions and dissolved inorganic carbon in the Guijiang River].

Within the drainage basin, information about natural processes and human activities can be recorded in the chemical composition of riverine water. The analysis of the Guijiang River, the first level tributary of the Xijiang River, demonstrated that the chemical composition of water in the Guijiang River was mainly influenced by the chemical weathering of carbonate rocks within the drainage basin, in which CO2 was the main erosion medium, and that the weathering of carbonate rock by H2SO4 had a remarkable impact on the water chemical composition in the Guijiang River. Precipitation, human activities, the weathering of carbonate rocks and silicate rocks accounted for 2.7%, 6.3%, 72.8% and 18.2% of the total dissolved load, respectively. The stable isotopic compositions of dissolved inorganic carbon (delta13C(DIC)) indicated that DIC in the Guijiang River had been assimilated by the phytoplankton in photosynthesis. The primary production of phytoplankton contributed to 22.3%-30.9% of particulate organic carbon (POC) in the Guijiang River, which implies that phytoplankton can transform DIC into POC by photosynthesis, and parts of POC will sink into the bottom of the river in transit, which leads into the formation of burial organic carbon.