威海市天鹅湖海洋牧场底层海水溶解氧浓度时间变化特征

依据威海市天鹅湖海洋牧场2016年7—10月海洋生态环境海底有缆在线观测系统的长期连续观测数据,研究了该牧场底层海水溶解氧浓度的时间变化特征,并探讨了其可能的影响因素。结果表明:观测期间海水溶解氧浓度平均值为6.65mg/L,呈先下降后上升的变化趋势,月平均值最小为6.36mg/L,出现在9月。溶解氧月浓度标准差呈先减小后增大的变化趋势,而溶解氧日浓度标准差总体变化趋势与月浓度标准差相反。底层海水基本上处于不饱和状态,月均溶解氧消耗量在观测期间逐月增大。海水温度是影响溶解氧浓度变化的主要因素。7月1日至8月24日期间,牧场海域存在季节性温跃层。7月1日至17日与8月11日至24日期间,溶解氧浓度下降可能受季节性温跃层和海水温度上升的共同影响;7月18日至8月1日期间,溶解氧浓度变化不受季节性温跃层控制。大风过程会增强表、底层海水交换,使溶解氧浓度上升。月均溶解氧浓度日变化均表现出双峰双谷的特征,与月均水深日变化对比, 7—8月0—13时无显著正相关性, 7—8月1—23时及9—10月相位变化基本一致,涨潮时海水溶解氧浓度升高,而落潮时降低,说明研究区域外海水溶解氧浓度很可能高于近岸,而潮流输运过程使得近岸海水溶解氧浓度随潮汐过程变化。

Feature research for temporal variability of the bottom water dissolved oxygen concentration in the marine ranch of Swan Lake, Weihai

This studyinvestigated the temporal variability of bottom water dissolved oxygen (DO) in the marine ranch of Swan Lake in Weihai, with a discussion about its influencing factors, using the long-term and continuous observation data obtained by a real-time online marine ecosystem observation system laid at themarine ranch from July 1, 2016, to October 25, 2016.Results showed that during the study period, the mean DO content was 6.65 mg/L, which initially decreased and then increased. Regardingthe monthly mean value, the minimum was 6.36 mg/L, which was observed in September. The monthly standard deviation of DO initially decreased and then increased. The bottom water maintained an almostunsaturated situation, and the consumption of DO increasedover time. The primary influencing factor for DO variation was temperature. From July 1 to August 24, seasonal thermocline existed at the ocean of the marine ranch. From July 1 to July 17 and from August 11 to August 24, the decline in DO was possibly affected by the seasonal thermocline and the increasing temperature of seawater. From July 18 to August 1, the seasonal thermocline could not control the variation in DO. A strong wind process intensified the exchange of seawater, which increased the DO content. Furthermore, after the strong wind process, the DO content decreasedshortly. There wasa possibility that the strong wind process affected the bottom water biochemical reaction. The monthly mean diurnal variation in DO exhibited dual peaks and valleys. Compared to the monthly mean diurnal variation of depth, at 0-13 o''clock in July and August, both had no obvious positive correlation; however, at 14-23 o''clock in July and August and the whole day in September and October, both had the same phase variation, which implies that when the tide rises(falls), the DO content increases(decreases), and the DO content in the open sea was higher than that in the inshore area. The variation inthedaily standard deviation of DO was opposite to the variation in the monthly standard deviation of DO.