| 其他摘要 | 随着我国社会经济的高速发展，出于对农业灌溉、防洪、抗旱、供水、发电的多重需求，近几十年来，我国规划和修建了大量的水库大坝。这些水库大坝不仅对区域生态环境产生了深刻的影响，也对物质的全球循环产生不可估量的影响。水坝拦截的“蓄水河流”表现出不同于天然河流的水环境特征，也产生了天然河流所没有的“湖沼学反应”。从河道变为水库，碳、氮、磷、硅等生源元素的循环过程发生了极为显著的改变，循环的通量、路径、速率等都会发生变化。乌江流域作为一个梯级水库开发的典型流域，前期对这些梯级水库营养元素的截留效率、水气界面温室气体交换通量、水-沉积物界面碳埋藏等都有比较深入的研究。但这些研究对通量的分析较多，对碳的来源重视不够，导致研究成果的系统性不足。特别是对有关水库内部有机碳与无机碳的相互转变重视不够，进而造成对水库碳循环过程与通量的分析不够准确。为此，本论文立足于对乌江流域梯级水库水体DIC、POC、沉积物有机碳三者浓度和δ13C的综合分析，探讨梯级水库水体POC、DIC及沉积物有机碳三者的来源以及三者之间的迁移转化，揭示梯级水库碳的生物地球化学循环过程。另外，从流域整体性出发，选择典型的河流流域为研究对象，充分阐释上、中、下游梯级水库碳循环的空间连续性，进一步揭示流域梯级水库中碳来源、迁移、转化的空间变化规律。期望论文的研究结果能对水库区域碳效应等科学问题提供数据支持。主要研究结果如下：1) 普定、引子渡、东风和乌江渡水库夏季丰水期的DIC平均浓度分别为2.21±0.13mmol/L、2.43±0.25mmol/L、2.47±0.22mmol/L和2.62±0.28mmol/L，普定、东风和乌江渡水库冬季枯水期的平均DIC浓度分别为2.76±0.11mmol/L、2.77±0.18 mmol/L、2.86±0.12 mmol/L。乌江流域梯级水库DIC浓度季节变化明显，夏季浓度低于冬季浓度。在夏季丰水期，水库表层DIC浓度低于深部水体浓度，在冬季枯水期，水体垂直剖面DIC浓度差异缩小。流域空间尺度上，由上游源头水库至中游水库，水中DIC浓度均值逐级增加。2) 普定、引子渡、东风和乌江渡水库夏季丰水期的δ13CDIC平均值分别为（-7.7±0.7）‰，（-7.4±0.8）‰，（-7.4±1.1）‰和（-8.3±0.7）‰，普定、东风和乌江渡水库冬季枯水期的的δ13CDIC平均值分别为（-7.6±0.3）‰，（-8.8±0.7）‰，和（-8.8±0.3）‰。乌江流域梯级水库δ13CDIC值存在明显的季节变化，夏季丰水期δ13CDIC值较冬季枯水期偏负。乌江流域梯级水库在夏季丰水期的δ13CDIC值表现出“上偏正，下偏负”的趋势，冬季枯水期剖面变化较小。在空间流域尺度上，由上游源头至中游水库，水体δ13CDIC值逐级减小。3) 普定、引子渡和东风水库夏季丰水期的POC平均浓度分别为（0.06±0.04）mmol/L，（0.05±0.01）mmol/L，（0.04±0.02）mg/L。乌江流域梯级水库在夏季丰水期的POC浓度表现出“上层高，中间低，下层有回升”的趋势。流域空间尺度上，上游水库水体POC浓度高于下一级水库的POC浓度，4) 普定、引子渡和东风水库夏季丰水期δ13CPOC平均值分别为（-29.3±1.0）‰，（-29.7±1.6）‰，（-29.4±1.4）‰。三个水库的δ13CPOC值相对接近。乌江流域梯级水库夏季丰水期δ13CPOC值均呈现“上层0~10m先降低后增加，底部较表层偏正”的趋势。5) 普定水库坝前、普定水库入库口和乌江渡水库坝前沉积物的δ13Corg平均值分别为（-24.8±0.6）‰，（-24.7±0.6）‰，（-27.6±1.8）‰。在垂直剖面上，普定水库入库口沉积物与乌江渡水库坝前沉积物的δ13Corg值变化趋势大致相同，即随深度的加深而逐渐偏正，然而，普定坝前沉积物的δ13Corg变化则与之相反，即随深度增加而渐趋偏负。6) 通过对沉积物C/N和δ13Corg值的端元分析，普定入库口处受陆源植物的贡献大，普定坝前则以内源水生植物贡献为主。乌江渡水库受内源有机质影响较多，受外源有机质的影响较少。7) 乌江流域梯级水库水体溶解无机碳、颗粒有机碳及沉积物有机碳迁移转化过程受以下几个因素的影响：水温分层等水动力条件、植物光合和呼吸分解作用、表层沉积物再悬浮、外源有机质输入和河流输出。8) 藻类等浮游植物的光合呼吸作用是控制乌江梯级水库DIC、POC浓度及其稳定碳同位素组成的主要因素，同时在此过程实现有机碳和无机碳的转化。9) 乌江流域水库POC、DIC浓度呈现梯级变化，即由上游至中游，POC含量逐渐降低，DIC含量逐渐增加.; With the rapid development of China's social economy, China has planned and built a large number of reservoir dams to satisfied the multiple needs of the agricultural irrigation, flood control, water supply, power generation in recent decades. These dams not only have a profound impact on the regional eco-environment, but also have an immeasurable impact on the global cycle of material. The "water-storing rivers" intercepted by dams show the characteristics of the aquatic environment different from the natural rivers, and also produce the "Limnology reaction" which the natural rivers do not. From river turn into reservoir, the cyclic process of the elements of carbon, nitrogen, phosphorus, silicon and other element has changed dramatically, and the flux, the path and the rate of material cycle will change. As a typical watershed in the development of Cascade Reservoirs, Wujiang River basin has more in-depth study on the interception efficiency of nutrient elements, the gas exchange flux, and the water-sediment interface of greenhouse gases, and so on. However, these studies have more analysis of flux, and the source of carbon is insufficient, which leads to the systemic deficiency of the research results. In particular, there is insufficient attention to the transformation of organic carbon and inorganic carbon in reservoirs, and the analysis of reservoir carbon cycling process and flux is not accurate.For these reasons, this thesis bases on the. comprehensive analysis of the concentration and carbon isotope of DIC POC and sediment organic carbon and δ13C, will be measured, and the source of the water POC and DIC and the organic carbon of the sediments in the cascade reservoirs and the migration transformation among the three will be discussed, so that, revealing the biogeochemical cycling process of the carbon in cascade reservoirs. In addition, from the whole watershed, selecting typical river basin as the research object, will fully explain the spatial continuity of the carbon cycle of upstream, middle and downstream cascade reservoirs, and further reveal the spatial variation regularity of carbon source, migration and transformation in cascade reservoirs. It is expected that the research results can provide data support for the regional carbon effect of reservoirs. The main results are follows:(1) In summer (June, 2015), the average concentration of DIC of Puding, Yinzidu, Dongfeng and Wujiangdu Reservoir were 2.21±0.13mmol/L, 2.43±0.25mmol/L, 2.47±0.22mmol/L and 2.62±0.28mmol/L respectively. In winter (January,2016), the average concentration of DIC of Puding, Dongfeng and Wujiangdu reservoirs were 2.76 ± 0.11mmol/L, 2.77 ± 0.18 mmol/L, 2.86 ± 0.12 mmol/L respectively. The seasonal variations of DIC concentration in cascade reservoirs of Wujiang River basin was obvious, and the concentration of summer was lower than winter. In summer(abundant water period), the concentration of DIC in the reservoir surface is lower than the deep water concentration, and the difference of the concentration of DIC in vertical section of water is narrowed in winter(dry season). On the spatial scale of watershed, the concentration of DIC in water is increased by the upstream to the midstream reservoir, that is, the concentration of DIC in cascade reservoirs gradually increases with the extension of the river.(2) The δ13CDIC average value of DIC of Puding, Yinzidu, Dongfeng and Wujiangdu Reservoir in summer(abundant water period) were(-7.7 ± 0.74) ‰, (-7.4 ± 0.75) ‰, (-7.4 ± 1.13) ‰ and (-8.3 ± 0.72) ‰ respectively. And the average of δ13CDIC value of Puding, Dongfeng and Wujiangdu Reservoir in the winter dry season were (-7.6 ± 0.31) ‰, (-8.82 ± 0.65) ‰, and (-8.76 ± 0.26) ‰ respectively. There were obvious seasonal variations of δ13CDIC value of cascade reservoirs in Wujiang River basin, and δ13CDIC value of summer water is more negative than winter water. The δ13CDIC value of those cascade reservoirs shows the trend of the upper water was positive while the lower water was negative in Wujiang River basin in the summer. The variation in vertical section of the winter water was smaller. On the spatial scale of watershed, the δ13CDIC value is decreased progressively by the upstream to the midstream reservoir, that is, the δ13CDIC value of Cascade Reservoir is gradually negative with the extension of the river.(3) In summer, the average POC concentration of Puding, Yinzidu and Dongfeng Reservoir were (0.72 ± 0.44) mg/L, (0.57 ± 0.17) mg/L, and (0.52 ± 0.26) mg/L respectively. The concentrations of POC showed the trend of the upper water was higher, the middle was lower and the bottom had a tendency to rebound in the summer. On the spatial scale of watershed, The concentration of POC of the upstream reservoir is higher than that of the next-level reservoir, that is, with the extension of the river length, the POC concentration of the cascade reservoir was decreased.(4) The δ13CPOC average value of POC of Puding, Yinzidu and Dongfeng Reservoir were(-29.32 ± 0.96) ‰, (-29.74 ± 1.58) ‰, (-29.42 ± 1.42) ‰ in the Summer abundance period ,respectively. The δ13CPOC value of these reservoirs is relatively close. The δ13CPOC value of these cascade reservoirs shows the trend of the upper 0~10m was firstly decreased and then increased, meanwhile, the bottom was more positive than the surface water in Wujiang River basin in the summer.(5) The δ13Corg average value of sediments in the PDS-1, PDS-3 and WJDS-2 were (-24.78 ± 0.55) ‰, (-24.73 ± 0.55) ‰, (-27.58 ± 1.80) ‰, respectively. In the vertical section, there was similar trend of the δ13Corg value of the PDS-3 sediments and the WJDS-2 sediments, that is gradually being positive with the deepening of depth. However, the δ13Corg value variation of the PDS-1 sediments was contrary to that, which is gradually negative with the increase of depth.(6) The Puding reservoir , which was the upstream of Wujiang River, was obviously influenced by exogenous organic matter and endogenous organic matter, through the element analysis of C/N ratios and δ13Corg value of sediments. The effect of the Terrestrial plants on the sediments is greatly contributed at the entrance of Puding reservoir. And the effect of the endogenous aquatic plant is mainly to the sediments of Puding dam. Wujiangdu Reservoir , which was the midstream of Wujiang River, was more influenced by endogenous organic matter and less affects by exogenous organic matter.(7) There were some factors having impact on the process of transformation among DIC, POC and sediment organic carbon , including Water temperature stratification and other hydrodynamic conditions, Photosynthesis and respiration of phytoplankton, Suspension of surface sediments, Exogenous organic matter Input and River output.(8) Photosynthesis and respiration of phytoplankton were the main factors to control the concentration of DIC, POC and stable carbon isotope composition of wujiang cascade reservoirs, and the transformations of organic carbon and inorganic carbon were realize in this process. (9) The concentration of POC and DIC in the reservoirs of Wujiang River basin showed the cascade change, that is, from upstream to midstream, the concentration of POC was decreasing gradually, and the concentration of DIC was increasing gradually. |
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