| Since the impoundment of the Three Gorges Reservoir(TGR), there is great change of hydrology characteristics of the main stream in the TGR. The influence to biogenic elements transportation in the river is showing in the four aspects.(1) Erosion and transportation effects of the river change to lacustrine sedimentation effects under strong dynamic condition.(2) Increasing autochthonous source contribution is caused by increasing primary production.(3) Limnology effects like stratification of water body.(4) Spatial and temporal cycling changes are caused by reservoir operation. Though the TGR has finished the water level change process of the whole year, it is still under ecology system reconstruction process. There is still existing uncertainty of transportation and transformation of carbon and nitrogen. In order to reveal these characteristics in the TGR, the study about different forms of carbon and nitrogen(particulate and dissolved) and sedimentation fluxes was carried in summer(low water level operation) and winter(high water level operation). Carbon and nitrogen source contributions were analyzed combining with stable isotopes based on Stable Isotopes Analysis in R model. The main conclusions of the paper are showed as following,(1)Concentration and sedimentation fluxes of suspended particles in the TGR are high in summer and low in winter. And there is a decreasing trend along the river. In summer, mean concentration of particulate carbon(PC) and particulate nitrogen(PN) are 2.30±0.63 mg/L and 0.52±0.39 mg/L respectively; mean sedimentation fluxes are 102.2±75.6 g?m2?d-1 and 9.8±6.7 g?m2?d-1 respectively. In winter, mean concentration of particulate carbon(PC) and particulate nitrogen(PN) are 0.35±0.35 mg/L and 0.04±0.02 mg/L respectively; mean sedimentation fluxes are 2.91±4.50 g?m2?d-1 and 0.15±0.20 g?m2?d-1 respectively.(2)Dissolved total carbon(DTC) is 50.72±2.24 mg/L in summer which is lower than that in winter(61.84±3.09mg/L). There is no significant difference among stations for both seasons. Nitrate is the main form of the dissolved total nitrogen(DTN). Concentration of DTN and NO3- are 1.75±0.33 mg/Land 1.23±0.65 mg/L in summer respectively; 1.59±0.13 mg/L and 1.34±0.15 mg/L in winter.(3)According to the characteristics of the reservoir partition, fine particles of PC and PN(<10?m) are the main form in the lacustrine zone. And coarse particles of PC and PN(>50?m) are the main form in the midstream of the TGR(Fuling to Wanzhou). In winter, size range of PC in Zhutuo and Cuntan are <30?m, and <10?m in transitional zone and lacustrine zone(Zhongxian to Zigui). And PN in the whole river is <10?m. The main reason for the above changes is rain and runoff. Flow cytometry is used in algae and heterotrophic bacteria. Then it is found that there is plenty allochthonous nutrition in summer which is suitable for reproduction of heterotrophic bacteria. And there is less allochthonous nutrition in winter which restricts reproduction of heterotrophic bacteria. Then heterotrophic bacteria replied on algae for absorbing nutrition. Distribution of PC and PN are influenced by algae and heterotrophic bacteria significantly.(4)?13CPOM and ?15NPOM of particulate organic matter(POM) in water column in summer are-28.22~-25.12 and-0.38 ~ 9.04 respectively;-27.43~-20.14 and 0.21 ~ 10.91 in winter. After SIAR model analysis, C3 plants source of soil is the main source of POM for most stations. And there is no significant difference under different reservoir operation. As for four different sources contribuitons, there is same characteristics for most stations, C3 plants>algae>macrophytes>C4 plants. High runoff from upstream and dry steep river bank are convenient for soil erosion in the TGR in summer. Drawdown area is inundated for raising water level in winter. Then dissolved biogenic elements released from drawdown area are the main form.(5)Under different reservoir operation, there is little change of ?15N-NO3-(4.82 ~ 6.61). Comparing to other water body, ?18O-NO3- is much heavier in the TGR. But is still in a low lever(-4.88 ~ 4.74 ) especially in winter. From SIAR model analysis, there is no significant difference of nitrate source under different reservoir operation. Soil nitrogen is the main source of the nitrate, while NO3- in precipitation made the minor contribution. Correlation analysis between ?15N-NO3- in surface water and ?15NPOM in bottom sediments show that ?15N-NO3- in surface water could transfer to ?15NPOM in bottom sediments directly in summer which may due to low water level, short hydraulic resident time, complex flow state and so on. In winter, ?15N-NO3- in water column could only transfer to ?15NPOM in sediments of the same water level. Characteristics of nitrogen could make changes during sedimentation which may due to high water level, long hydraulic resident time, stable water environment and so on. |
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