[Spatial Distribution Characteristics of Chlorophyll-a and Nutrient Salts in Tributaries of Different River Sections in the Three Gorges Reservoir Area During the Flood Season].

The construction of the Three Gorges Reservoir has had certain effects on the ecological environment of the water and serious phytoplankton blooms have occurred in its tributary embayment. To explore the spatial distribution of nitrogen and phosphorus nutrients and chlorophyll-a in different tributaries of the Three Gorges Reservoir, a water quality study (June 2018) was conducted in the Xiangxi River, Shengnongxi River, and Daning River of the Three Gorges Reservoir. The results showed that the average TN in the three tributaries was 1.86 mg·L-1, 1.90 mg·L-1, and 1.43 mg·L-1, respectively, and average TP was 0.09 mg·L-1, 0.07 mg·L-1, and 0.05 mg·L-1, respectively. Single-factor ANOVA analysis showed that the spatial difference in TN was significant and occurred in the following order:Shennongxi River > Xiangxi River > Daning River. There were significant differences in the spatial distribution of TP, which were in the order off Xiangxi River > Shennongxi River > Daning River. The mean concentrations of chlorophyll-a in the three tributaries was 6.41 µg·L-1, 21.39 µg·L-1, and 9.85µg·L-1, respectively. The results from the Pearson correlation analysis, showed that chlorophyll-a concentrations were closely related to TP distribution in all tributaries, but Zeu/Zmix was also correlated with the distribution of chlorophyll-a in the Shennongxi River and Daning River. The ratio of TN and TP concentrations was 22.36, 26.76, and 28.6, respectively, which revealed that TP is a critical and limiting factor affecting phytoplankton growth in its tributary embayment.

[Spatial Distribution Characteristics of Nutrients and Chlorophyll A in the Lancang River Basin Under Cascade Reservoirs].

Construction of cascade reservoirs in Lancang River had a certain influence on the ecological water environment of the basin, dividing the water into natural reaches and reservoir reaches. To explore the impact of the cascade reservoirs on the ecological environment, the nutrient and the chlorophyll a distribution data were measured in the natural reaches, reservoir reaches, and tributaries in June 2017. The results showed that the TN ranged from 0.37 to 1.22 mg·L-1, with an average of 0.70 mg·L-1, and the TP ranged from 0.01 to 0.19 mg·L-1, with an average of 0.04 mg·L-1. One-way ANOVA analysis showed significant spatial differences in the TN, with the TN concentration following the order tributaries > reservior reaches > natural reaches. However, the TP concentration did not show a significant trend. The chlorophyll a concentration varied from 2.6 to 10.2 µg·L-1, with a mean of 5.8 µg·L-1. Pearson correlation analysis showed significant relationships between the chlorophyll a concentration and the TP, water temperature, and Zeu/Zmix. The relationship between chlorophyll a and Zeu/Zmix was particularly significant, which indicated the Zeu/Zmix caused by thermal stratification may be the key factor influencing the growth of phytoplankton.

[Dynamic Replenishment Process of Nutrients in Tributary of Channel Reservoir].

The process of phytoplankton succession and change in primary productivity are directly determined by the seasonal variations in nutrients in tributary bays of channel reservoirs. This study aimed at analyzing the effects of the main nutrient sources on seasonal distribution of nutrients in Xiangxi Bay based on the field data collected in 2010 and 2011. The tracing inorganic ions were Cl- and Na+ that showed significant differences (P<0.01) between the mainstream and the tributary. The nutrient contribution rates of different sources were calculated by the binary linear model. The results showed that the nutrient contribution rate of the mainstream was more than 75% during the dry season and the impoundment period. The intrusion of the mainstream was the main source of nutrients in Xiangxi Bay. The difference in the contribution rates between the mainstream and the upstream decreased during the pre-flood drawdown period and the flood season. The concentration of total phosphorus was higher in the upstream, while the concentration of total nitrogen was higher in the mainstream. The patterns of density currents were different and the nutrient contribution rates of different sources changed accordingly. Therefore, the nutrients of Xiangxi Bay changed regularly in different operation periods of the Three Gorges Reservoir.

[Estimation of releasing fluxes of sediment phosphorous in the Three Gorges Reservoir during late autumn and early winter].

In order to investigate the internal contamination load sources in the Three Gorges Reservoir (TGR), a field sampling campaign was carried out in November and December 2010. Phosphate contents (PO4(3-) -P) were determined in 6 mainstream and 9 estuary sediment cores of sediment-water interface in the TGR. The results showed that the PO4(3-) -P concentrations of pore water in sediments from tributaries and the corresponding overlying water were higher than those from the mainstream. The PO4(3-) -P contents in tributaries and mainstream ranged from 9.59-29.79 microg x L(-1) and 9.01-25.36 microg x L(-1), respectively. Based on calculations using the Fick's First Law, sediments located at GuoJiaba and Xiaojiang estuaries were the 'sink' of P, and the fluxes of sediment PO4(3-) -P were estimated to be -0.63 mg x (m2 x a)(-1) and -0.60 mg x (m2 x a)(-1), respectively. In other areas, PO4(3-) -P diffused from the pore water to the overlying water, and the diffusive fluxes were in the range of 0.15-2.47 mg x (m2 x a)(-1). With the assumption that molecular diffusion was the main process by which nutrients were transported from the pore water to the overlying water and the water body in the TGR was evenly mixed, the contribution of sediment phosphorus to the water body was only -0.011-0.098%. So far, with the Three Gorges Reservoir sediments as the internal contamination load sources, the phosphorous release didn't significantly influence the water quality. The sediments in the TGR may be a large P source in a period of future time after the external P source is controlled efficiently.

[Effects of intrusions from Three Gorges Reservoir on nutrient supply to Xiangxi Bay].

Frequent spring blooms have been observed in tributary bays of Three Gorges Reservoir (TGR) since its initial filling. In order to study Three Gorges Reservoir of nutrients by the River tributaries reverse effect, a well-designed field monitoring plan was conducted. The results show: there are significant intrusions from Three Gorges Reservoir to Xiangxi Bay to the surface, middle and bottom with three forms of intrusion respectively. The unique flow characteristics provide a hydrodynamic background of nutrient distributions of Xiangxi Bay. The average instantaneous fluxes of the input TN and TP of the intrusions from the confluence were 501.92 g x s(-1) and 48.17 g x s(-1), respectively; TN and TP loads originated from intrusions accounted for 43.4% and 21.5%, respectively to total amount in the whole year. The study shows that intrusion of the total nitrogen input, a large proportion of total phosphorus, and reducing the pollution loads of tributaries and upper reach basin of Three Gorges Reservoir is the fundamental way to eradicate algal blooms.