中文摘要：

河流水化学昼夜动态变化的研究有助于揭示水体中相对快速的生物地球化学过程（河流内过程）,同时也有助于判别上游补给区流域过程。已有的研究表明生物过程（光合作用与呼吸作用）、地球化学过程（碳酸盐平衡、碳酸钙沉积）是控制河流pH、SpC、Ca^2＋和HCO3^-含量昼夜变化的主要因素。不同级别、类型及河床微环境均会对水化学昼夜变化产生影响,与气温密切相关的光合作用是产生河水pH值和DO昼夜变化的主控因素。在偏碱性与富含钙离子的岩溶河流,有机体的钙化作用与酸分泌可能对光合作用具有重要作用,从而导致水体中Ca^2＋和HCO3^-出现白天下降-夜间回升的昼夜动态变化,下降幅度达20%～30%。水生植物通过光合作用产生DIC（主要为HCO3^-）的原位沉降,是真正意义上的净碳汇。昼夜生物地球化学循环及效应研究有助于全面认识岩溶区碳循环特征及岩溶含水层源汇关系,尤其是岩溶碳汇稳定性与净碳汇估算;同时对长时间尺度河流监测计划的制定具有重要意义。

英文摘要：

Study on diel cycling of stream hydrochemistry can help to reveal relatively rapid biogeochemical processes in natural water（processes of in stream flows）and discriminate drainage basin processes in recharge areas.Existing research shows that biological processes（photosynthesis and respiration）,geochemical processes（bicarbonate equilibrium,and calcite precipitation）are the main controlling factors on diel variations of pH values,specific conductivity（SpC）,concentrations of Ca^2＋ and HCO3^- in streams.Furthermore,stream orders and types and even microenvironments of the riverbed all have remarkable influence on diel aqueous chemistry.The pH value and dissolved oxygen（DO）are mainly controlled by photosynthesis which is closely related to air temperature.In high-alkalinity and calcium-rich streams,representing carbonate-rich basins,calcification and acid secretion of organisms may play an important role in aquatic plant photosynthesis,thus resulting in diel hydrochemical cycling with daytime decrease（up to a 20% to 30% decline）and nighttime increase of concentrations of Ca^2＋ and HCO3^-.Diel DIC cycling downstream caused by photosynthesis and its changes along the stream flow indicate that the stream is losing inorganic carbon along its flow path.It converts to organic carbon,such that inorganic C storage in streambeds will be an important net DIC sink in small productive streams.The effect of diel cycling of biogeochemistry on interpretation of carbon cycling,sink and source,especially on clarification of karst carbon sink stability and net carbon sink estimation trends becomes increasingly important in karst aquifer systems.Diel variability has implications for the design of long-term surface water monitoring programs and interpretation of water quality trends.