千岛湖水体稳定度和热分层结构对溶解氧垂向分布的影响

Effects of water stability and thermal stratification on the vertical distribution of dissolved oxygen at Lake Qiandao

基于2017年1月—2020年2月千岛湖大坝前水质高频监测数据与湖心区气象数据,使用Lake Analyzer(LA)软件计算了水体稳定度指标(“施密特稳定度”和“浮力频率”)和热分层指标(“温跃层深度”和“温跃层厚度”),并与溶解氧垂向分布指标(“氧跃层深度”和“氧跃层强度”)结合分析。结果表明千岛湖存在时间长且稳定的热力分层和溶解氧分层,分层期为每年4—12月,根据结构变化可分为形成期(4—6月)、稳定期(7—9月)和减弱期(10—12月)三个阶段。水体稳定度指标、热分层指标和溶解氧垂向分布指标间相关分析结果表明:水体混合状态是影响溶解氧垂向分布的重要因素,湖体存在热分层则是氧跃层出现的根本原因,水体稳定度升高与热分层结构形成均阻碍溶解氧的垂向交换,促进氧跃层的形成。基于回归分析,发现温跃层深度与氧跃层深度具有良好的线性关系,拟合精度高(R^(2)=0.81,N=25),说明在千岛湖可通过温跃层深度推断氧跃层态势。研究结果同时证明LA在千岛湖的可适用性,以及在其它湖泊的可推广性,提供了水体稳定度和热分层指标定量化计算的工具。

To provide substantial information of vertical distribution of dissolved oxygen(DO)at Lake Qiandao,oxycline depth(OD)and oxycline intensity(OI)were defined and calculated for January 2017 to February 2020.Lake Analyzer(LA)was used to calculate Schmidt Stability(St),Buoyancy frequency(N_(2)),thermocline depth(thermD)and thermocline thickness(thermT)based on the high-frequency monitoring water quality(WQ)data and the meteorological data at Lake Qiandao for the same period.The results demonstrated that there were long-lasting thermal stratification and DO stratification from April to December through the year.Thermal stratifications showed obvious seasonality with stratifications initially formed during April-June,strengthened during July-September,and weakened during October-December.According to Spearman correlation analysis among the parameters for water stability,thermal stratification and vertical DO distribution,water stability was a key factor for vertical DO distribution,and the thermal stratification was a key factor for oxycline formation.Intensive thermal stratification decreased vertical DO exchange between the upper and lower layers,and promoted the oxycline formation.ThermD and OD was closely correlated with R^(2) of 0.81(N=25).Successful application of LA to Lake Qiandao showed that LA was a reliable and adaptive tool for quantitatively estimating the parameters for thermal and oxycline stratifications and water stability not only for Lake Qiandao but also for other lakes.