高分辨率监测下的漓江省里断面生物地球化学特征分析

Biogeochemical Characteristics in Shengli Site of Lijiang River Under the High Resolution Monitoring

为了获得漓江流域不同季节生物地球化学昼夜动态变化过程、影响因素与规律,分别于2016年10月30日～11月1日(秋季)和2017年9月14～16日(夏季)对漓江流域省里断面进行了为期48 h的高分辨率在线监测和高频率取样工作,研究水体电导率(EC)、水温(T)、pH以及Ca^(2+)、HCO_3^-、NO_3^-等离子含量和溶解无机碳同位素(δ^(13)C_(DIC))等水化学参数的昼夜变化规律,并分析其影响因素,同时评估水生植物对输入岩溶水生生态系统中溶解无机碳的固定量.结果表明:①省里断面水化学参数表现出显著的昼夜变化规律,T、pH、DO、SIC白天上升夜间下降,Ca^(2+)、HCO_3^-、EC、p(CO_2)白天降低夜晚上升且秋季昼夜变化幅度大于夏季.②SO_4^(2-)、NO_3^-、Cl^-、Na^+、K^+和Mg^(2+)等营养元素含量昼夜变化主要受水生植物代谢过程(同化作用)控制,呈现白天降低夜间升高的变化规律.同时,省里断面夏季营养元素昼夜变化幅度小于秋季.③省里断面溶解无机碳同位素(δ^(13)C_(DIC))主要受水生植物光合作用和呼吸作用控制,表现为白天偏重晚上偏轻的动态变化.受土壤根系和土壤微生物呼吸作用强度和河流水文要素季节变化的影响,夏季省里断面δ^(13)C_(DIC)总体上偏轻于秋季,两者的平均值分别为-10. 08‰和-8. 90‰.④通过计算,实验期间省里断面水生植物光合作用岩溶碳汇量日平均值为2. 12 mmol·L^(-1)和0. 94mmol·L^(-1),秋季比夏季具有更高的固碳效率.

This study was done to understand the diel variation and factors influencing the hydrochemistry of the Lijing River in different seasons.This is a typical medium river located at Guilin City in the Guangxi Zhuang Autonomous Region,SW China.The Shengli site was selected for this study.Two-day monitoring work with a high resolution rate logger and high frequency sampling at 2 hour intervals was conducted at the Shengli site of the Lijiang River in summer and autumn separately.Physical and hydrogeochemical parameters including pH,dissolved oxygen(DO),water temperature(T),electrical conductivity(EC),dissolved inorganic carbon(DIC),isotopes,and other chemical parameters were examined.The results show that:①the physical and hydrochemical parameters[T,pH,DO,SIC,EC,p(CO2)]and major ions(HCO3-,Ca2+)at the Shengli site displayed regular diel variation during monitoring.The data for T,pH,DO,and SIC increased in daylight and decreased at night,while the data for Ca2+,HCO3-,EC,and p(CO2)decreased in daylight and increased at night.②The diurnal changes of nutrient elements(SO42-,NO3-,Cl-,Na+,Mg2+,and K+)at the Shengli site were mainly controlled by photosynthesis and respiration of aquatic plants,and showed the trend of decrease in daylight and increase at night.Due to the influence of a flood in mid-August 2017,the amount of diurnal variation in the nutrient element levels in summer was less than that in autumn.③Theδ13CDICincreased in daylight and decreased at night both in summer and autumn,reflecting the influences of photosynthesis and precipitation.Under the influence of different root systems,soil microbial respiration intensity,and seasonal variation of river hydrological factors,theδ13CDICin summer was generally lighter than that in autumn,with average values of-10.08‰and-8.90‰,respectively.④The daily average fixation amount of karst carbon sink caused by aquatic plants was calculated to be 2.12 mmol·L-1 and 0.94 mmol·L-1 for Autumn and Summer,respectively.To sum up,there is a higher efficiency of karst carbon sink caused by aquatic plants in Autumn than that in Summer.