封冻期高纬度湖泊底层溶解氧浓度的变化特征分析

The Characteristics Analysis of Dissolved Oxygen Concentration at the Bottom Layers During Ice-Covered Period in a High-Latitude Lake

溶解氧是评价水质好坏的重要参数，对水中生物的生存状况影响很大，而封冻后的湖泊，水中溶解氧的变化更加值得关注．对于高纬度地区的湖泊冬季封冻时间比较长，光照时间比较短，湖泊中的溶解氧与水温相对封冻前变化比较大．通过对2013—2014冬季芬兰Valkea-Kotinen湖封冻期底层水中的溶解氧浓度与水温数据的研究，讨论了在整个封冻期该湖3-6m深度溶解氧浓度的时空变化情况，其随着封冻时间持续下降，在融化前有比较大的跃升．得到了不同深度的溶解氧浓度与水温变化的回归方程，在最底层溶解氧浓度与水温的拟合优度最差，因此在最底层影响溶解氧浓度的变化因素更为复杂一些，不仅仅受水温变化的影响．通过对溶解氧的功率谱分析，可见在3m深度的周期是24h，但是4-6m深度日变化周期并不明显．通过对底部无氧层的分析，发现在封冻后的第36天，底部6m深度的溶解氧耗尽，得到了底部无氧层厚度随冰封持续时间变化的对数表达式．

Dissolved oxygen is a good index of the health of the lake and has a great impact on living conditions in the water. Changes of dissolved oxygen in the water of the ice-covered lake during ice season are more worthy of attention. During the winter period, there are relatively long ice season and relatively short illumination time for the high-latitude lakes, so in lakes change of dissolved oxygen is larger than that before freezing. Presently, the mathematics as a tool can not completely solve the complex phenomena of physical synthesis, but it can describe the main characteristics of the problem. This paper aims at describing the main characteristics of dissolved oxygen under ice in the lake water. Based on the measured data of Lake Valkea-Kotinen （Finland） during the frozen period in the water of 2013-2014, we analyze temporal and spatial variation of dissolved oxygen concentration at the depths from 3m to 6m during the whole ice-frozen period. Dissolved oxygen concentration continues to decline as the frozen time, and they have a relatively large jump until ice broken up, which mainly because the exchange with the outside oxygen gradually restores and photosynthesis of aquatic plants in water are strengthen with ice melting. And Convection begins when sunlight penetrates the ice and thus deeper water gets oxygen from upper layers by mixing. Through the study of the relationship of dissolved oxygen and water temperature, we get the regression analysis equations at different depths. The goodness of fit of dissolved oxygen concentration and water temperature at the bottom layer （6m） is lower than that of 4-5m depth, so it is more complicated to affect the change of dissolved oxygen concentration in the bottom layer, not only affected by water temperature. And based on power spectrum analysis of dissolved oxygen concentration, we find that the cycle at depth 3 m is 24h, but diel variation do not obviously at the depth of 4--6m. Finally dissolved oxygen depletion at the depth of 6m occurs on the 36th day after the ice is frozen, and the logarithmic expression type about thickness of anoxia layer changing with frozen time is modeled, which is more consistent with the dissolved oxygen change of the lake.