泸沽湖水体溶解氧达标评价研究

Assessment of dissolved oxygen compliance rate in Lugu Lake,Yunnan Province

泸沽湖水质优良,但水体溶解氧常在冬末初春异常超标,引起多方关注。通过数据收集与统计分析,结合文献调研,探讨了泸沽湖水体溶解氧达标评价问题,并揭示了部分时段溶解氧超标原因。结果表明:①1999~2019年泸沽湖水体溶解氧浓度变化范围为5.2~9.5 mg/L,与水温因子呈显著负相关;根据海拔和实测水温计算的氧饱和率有一定年际差异,2018年均值最高,2012年均值最低;1999,2008年和2016年的氧饱和率误差线范围最小,2012,2014年和2015年的误差线范围较大;夏季7~8月氧饱和率较高,冬季2月氧饱和率最低,与水温变化规律较为一致。②根据GB 3838-2002《地表水环境质量标准》,以氧饱和率≥90%或溶解氧含量≥7.5 mg/L作为Ⅰ类标准限值,评价泸沽湖水体溶解氧达标情况,发现1999~2019年泸沽湖溶解氧达标率为88.5%,不达标主要集中于2009年和2019年,年内不达标主要集中于1~2月。③秋末冬初因水温分层而缺氧的下层水体在来年早春季节随水柱垂向混合而上升,是表层水体溶解氧在1~2月不达标的主要原因。

The water quality of Lugu Lake is excellent,but the dissolved oxygen in the waters often drops below the surface water quality standard in late winter and early spring,which results in many concerns.Through data collection and statistical analysis,combining with literature investigation,we discussed the compliance rate of dissolved oxygen in Lugu Lake,and revealed the reasons for the exceeding the standard concentration of dissolved oxygen in some periods.The results showed that:①the concentration of dissolved oxygen varied from 5.2 to 9.5 mg/L in 1999 to 2019,with significant negative correlation with water temperature.The oxygen saturation percent calculated according to the altitude and water temperature had demonstrated a little interannual variation feature in recent 20 years,with the largest mean value in 2018,and the smallest in 2012.The varied ranges of error bars of the oxygen saturation percent were smaller in 1999,2008 and 2016,and relatively larger in 2012,2014 and 2015.The oxygen saturation percent values were higher in July and August in summer,and the least was in February in winter,which were consistent with the variation of water temperature.②According to the Surface Water Environmental Quality Standard in China(GB 3838-2002),when the oxygen saturation percent was greater than or equal to 90%,or the concentration of dissolved oxygen was greater than or equal to 7.5mg/L,the surface water body would be classified into the first class I in the view of water quality.The standard was used to evaluate the dissolved oxygen condition in the plateaued Lugu Lake.The results showed that the compliance rate of the dissolved oxygen was 88.5%in the recent 20 years.The un-attainment times mainly appeared in 2009 and 2019,and usually in January and February within the year.③The upwelling and mixing of the anoxia water in the water column due to water stratification during the last late autumn and early winter,was supposed to be the main reason leading to the low content of oxygen in the surface water in January and February in those years.