生物地球化学过程是地球关键带的三大过程之一.在全球变化与岩溶碳循环研究领域,了解生物地球化学过程、影响因素与机制,对解决岩溶作用时间尺度与碳汇稳定性问题具有至关重要的作用.以广西桂林漓江支流潮田河为例,通过高分辨率在线监测与高频率自动化取样分析,研究了溶解无机碳(DIC)及其同位素、电导率与其他离子含量的昼夜变化规律,并分析了其影响因素.pH、溶解氧、电导率、Ca2+和HCO3-离子含量均呈现显著的昼夜动态变化,反映水生植物和藻类光合作用及钙沉积的影响.鸟岭桥与两河沟两个监测点的电导率、Ca2+和HCO3-离子含量具有白天下降、夜间上升的变化规律,鸟岭桥白天下降幅度分别为10％、11.5％～12.5％和10％～12％.48小时监测期间鸟岭桥光合作用DIC平均转化速率为0.64×10-5 mmol/L·s,日转化HCO3-的量约为1484kg/d(相当于292kg C/d),占总DIC输入量的4％;平均钙沉积速率为0.38× 10-5 mmol/L·s,较小的速率可能与水体中较高的溶解有机碳含量产生的抑制作用有关.Ca2+与HCO3-离子含量夜间的快速上升主要是上游来自岩溶含水层的地下水直接补给造成的.在年际尺度上潮田河DIC中75％～80％来自于岩溶地下水.%Biogeochemistry process is one of three key processes in Earth's critical zones.In the research field of karst carbon cycle and global change,the study of biogeochemical processes,mechanism and their influence factors can help to understand better of the short-time scale property of karst processes and the carbon sink stability in karst systems.Taking Chaotian River (a tributary of Lijiang River),about 20km east of Guilin,China as an example,the diurnal fluctuation of dissolved inorganic carbon (DIC),isotope,specific conductivity and other chemical parameters were examined by conducting high resolution field monitoring and high frequency sampling.The monitoring and sampling work was deployed from 9 to 13,August,2013 at the two sites of the reach near hydrological station (25°11'41.8"N,110°28'59.5"E) of Chaotian River,i.e.Niaolingqiao site (NLQ) (25° 11'37.3"N,110°29'22.7"E) and Lianghegou site (LHG) (25° 11'44.7"N,110°28'27.4"E),representing gravel and muddy bed respectively.Auto data logger (YSI 6920) and auto water sampler (Teledyne ISCO 6700) were installed at two sites.pH,dissolved oxygen,specific conductivity (SpC),HCO3-and Ca2+ all showed diurnal variations,reflecting influence of photosynthesis and calcite precipitation.The SpC,Concentrations of Ca2+ and HCO3-at NQL and LHG monitoring sites showed a diel cycle of daytime decrease and nighttime increase,with an amplitude of 10％,11.5％ ～ 12.5％ and 10％ ～ 12％ respectively at Niaolingqiao site.Conversely,the δ13CDIC values presented a diel cycle of daytime increase and nighttime decrease.Using the diurnal amplitude of DIC and calcium concentrations,the mean conversion rate of DIC by aquatic vegetation photosynthesis at Niaolingqiao site is calculated to be 0.64× 10-5mmol/L·s during a 48-h period,daily DIC transform magnitude is about 1484kg/d (be equivalent to 292kg C/d),accounting for 4％ of total DIC input;the average Ca precipitation rate is estimated to be 0.38× 10-5mmol/L · s.The small rate for Ca precipitation could be related to the presence of inhibiting solute of dissolved organic carbon in water of Chaotian River.The nighttime increase in DIC and calcium could be explained by groundwater input from the upstream karst aquifer.Hydrochemical data of water samples collected in different seasons from October 2010 to April 2012 showed that the concentrations of Ca2+ and HCO3-of karst water are much higher than that of reservoir water and surface water draining from silicate-rich rock areas upstream.The values of δ'3CDIC of different water bodies exhibit remarkable differences,for example,the δ'3CDIC values of Si'anjiang reservoir and Zhaidi underground stream range-8.39‰～-13.52‰ and-11.57‰～-15.67‰ respectively,with an average of-10.69‰ and-13.78‰ respectively.The values of δ13CDIC at Chaotian hydrological station are between the surface water and the groundwater,ranging from-10.47‰ to-15.57‰ with an average of-13.15‰.It suggested that DIC could be sourced by the mixture process of surface water in silicate-rich system upstream and carbonate system groundwater.DIC-supply from groundwater is estimated using isotope constraint end-member method,roughly 75％ ～ 80％ of DIC at Chaotian station is contributed by karst underground water on a yearly basis.
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