三峡水库典型支流底泥-水-气系统的碳转化过程及其驱动机制

Carbon is essential biogenic matter in rive ecosystems, the transport and transformation of carbon plays vital role for human being as well as the earth systems. In this study, on the purpose of interpreting the transport and transformation process of carbon in river systems and the mechanisms underlying it, we devote to study carbon behavior in a tributaries (Yulin river) of Three Gorge Regions from the view of sediment-water-atmosphere integrated systems using the multi-disciplinary knowledge including hydrodynamic, water chemistry and aquatic ecosystems, during which the long-term in-site and laboratory study is conducted, the high-throughput sequencing technology, microelectrode, GC-MS are employed. We particularly attempt to study the impact of the present water-lever regulation activities of Three Gorges Reservoir (TGR in short) on 1) the transport and transformation characterize of carbon in sediment-water interface, 2) the transport and transformation of carbon, the water chemistry associate with the utilization pathway of carbon by phytoplankton in overlying-surface water system in response to annually variation of hydrodynamic conditions, and 3) the flux of CO2 and CH4 in water-atmosphere interface, as well as the physical-chemistry-ecology response involves in it. The results of this study can extend our knowledge on the impact of TGR operation on carbon behavior, and may assist TGR operators as they seek to prompt the bio-utilization of carbon meanwhile reduce the emission of green house gas, through the alternation of TGR regulation.

碳是河流生态系统重要的生源物质，碳迁移转化对人类生存环境乃至整个地球系统的稳定起着重要作用。本研究以三峡库区库尾支流-御临河为对象，围绕河流水动力学、水化学、水生态学响应，结合长期原位监测及室内模拟试验，应用微生物高通量测序、微电极、气相色谱串联质谱等分析手段，从底泥-水-气系统角度研究三峡水库现有调度方式下：①库尾支流底泥-水界面碳素的迁移转化特征；②上覆水-表层水碳素迁移转化规律、水化学特点和浮游植物在变化碳素行为特征下的碳利用机制；③水-气界面CO2 和CH4的释放通量，以及上述研究中涉及的物理-化学-生物学耦合机理，来阐明现有调度方式下三峡水库支流底泥-水-气系统的碳行为与驱动机制。研究结果将补充深化现有对三峡库区调度方式下支流碳素多介质环境行为、效应及其驱动机制的认识，为制定基于削减含碳温室气体减排和强化碳素生物捕捉的水库调度方式的优化提供理论依据与数据支撑。

针对筑坝对河流碳素在迁移转化过程的内在影响机制，该项目以三峡库区库尾筑坝支流御临河为研究对象，通过原位调研，解析了在三峡库区水位周期性变动情况下，筑坝对其上下游河段CO2、CH4的产生、迁移、转化、排放全过程的影响机制；通过室内实验，模拟了铜绿微囊藻水华的自然和快速衰亡过程，探究了藻类衰亡中影响碳行为的主导因子和机制。研究发现研究蓄水稳定期水体CO2分压的主要影响因子是沉积物CO2浓度水平与水体微生物代谢强度，水体CH4浓度的主要影响因子是N、P营养盐和有机质浓度；水体CO2、CH4均以水-气界面分子扩散的形式排放至大气，排放量的主要影响因子是水温和表层水体CO2、CH4浓度。泄水稳定期间CO2主要以水气界面分子扩散形式（diffusion）排放至大气，排放量主要受沉积物CO2浓度水平与水体微生物代谢强度影响；而CH4主要以冒泡释放形式（ebullition）排放至大气，排放量受河流水深、流速及沉积物CH4浓度共同影响。御临河CH4环境排放通量（Flux(CH4)）总体变化范围为0.14 ~ 253.76 mmol/(m2•d)，平均值为120.08±102.10 mmol/(m2•d)。铜绿微囊藻的衰亡具有阶段性，且衰亡对河流CH4和CO2的产生具有显著的促进作用，具体表现为自然衰亡和快速衰亡下CH4累积释放量分别为对照组的22.80倍和37.72倍，CO2的累积释放量分别为对照组的5.36倍和4.03倍。此外，藻类在衰亡中释放大量新鲜AOM，其中的不稳定组分，主要是芳香类蛋白物质和溶解性微生物代谢产物，为微生物代谢提供了底物，同时也为产CH4微生物创造了合适的厌氧环境，促进了CH4和CO2的产生。铜绿微囊藻不同衰亡模式下总碳释放量无明显差异，但快速衰亡下AOM的迅速释放显著改变了藻源碳素的归趋，使得快速衰亡释放的碳素中CH4的占比达27.49%，是自然衰亡的1.86倍。结果提升了对水利工程生态环境效应的认识。