Variation characteristics of dissolved oxygen and metabolic rate in lakes during the ice-covered period

Abstract

冰封期湖泊与大气的气体交换受冰盖阻碍，影响湖泊溶解氧含量，进而影响湖泊水质.为探究冰封期湖泊溶解氧和新陈代谢速率变化特征及影响因素，本研究通过监测典型季节性冰封湖泊不同深度的溶解氧（DO）、水温和光合有效辐射（PAR），结合水质检测结果，分析冰封期湖泊DO变化及代谢速率影响因素，对湖泊日新陈代谢速率计算方法进行改进并估算冰封期湖泊新陈代谢速率.结果表明：2021年1—3月间，岱海DO浓度平均值为15.49 mg/L，并出现昼夜变化和分层现象.DO在冰封期变化趋势呈现出先逐渐升高，然后保持稳定，进入消融期（2021年3月2—11日）分层现象逐渐消失的规律.岱海冰封期净初级生产力和生态系统呼吸速率平均值分别为0.11和0.10 mg/（L·d），在水温未出现分层时净初级生产力呈现较高水平；之后水温沿水深方向出现分层，净初级生产力明显下降；当冰层融化后，PAR显著上升，净初级生产力又逐渐恢复至0.10 mg/（L·d）.统计分析表明，岱海冰封期DO与水温、PAR、总氮等变化具有一定相关关系，且由于湖泊流域生态环境条件及冰封期物候特征不同，岱海与内蒙古其他湖泊相比，冰封期DO变化趋势存在一定差异.;In ice-covered periods, the gas exchange between lakes and the atmosphere is blocked by ice sheets. The dissolved oxygen concentration and consequently the water quality of the lakes are thus affected. To explore the metabolic rates and variation characteristics of the dissolved oxygen, and its influencing factors in typical seasonal ice-covered lakes, dissolved oxygen concentration, water temperature and photo-synthetically active radiation (PAR) were monitored at different depths of the lakes. In combination with the water quality monitoring results, the variations of the dissolved oxygen and the influencing factors of the metabolic rates were analyzed to optimize the calculation methods of the everyday metabolic rates, thus to estimate the metabolic rates of the ice-covered lakes. The results showed that the average dissolved oxygen concentration in Lake Daihai was 15.49 mg/L, and diurnal variation and stratification had appeared. The dissolved oxygen concentration initially increased gradually and then stabilized from Jan. to Mar. 2021, the ice-covered period. The stratification phenomena disappeared from Mar. 2nd to 11th, 2021, the thawing period. The average net primary productivity and ecosystem respiration rate of Lake Daihai were 0.11 mg/(L·d) and 0.10 mg/(L·d) respectively in the ice-covered period. The net primary productivity appeared to be higher when the water temperature was not stratified. Along with the rise of the water temperature, the water temperature began to stratify along the depth of water, and the net primary productivity decreased significantly. After the ice had melted, the PAR increased significantly, and the net primary productivity gradually increased back to 0.10 mg/(L·d). Statistical analysis demonstrated that water temperature, PAR and total nitrogen had exerted significant effects on the dissolved oxygen concentration during the ice-covered period in Lake Daihai. Due to the different ecological environment conditions and phenological characteristics of the ice-covered period in the lake basin, compared with other lakes in Inner Mongolia, Lake Daihai has certain differences in the trend of DO changes during the ice-covered period.