沙海蜇（Nemopilema nomurai）消亡过程中海水溶解氧变化的模拟研究

摘要

To understand the influence of the decaying process after a large jellyfish bloom on marine environment, laboratory simulation experiments were performed to study the variations of dissolved oxygen （DO） during the decompo- sition process of Nemopilema nomurai at different temperature, pH, salinity, and N/P ratios. The results suggested that the decomposition ofN. nomurai needed a great deal of oxygen, and the extents of DO decrease were not significantly differ- ent under different temperature, pH, salinity, and N/P ratio conditions. Complete decomposition of N. nomurai generally took about 6--7 days and more time was needed under high N/P conditions. The decomposition of N. nomurai caused se- vere hypoxia of the seawater and the oxygen concentration was below 20% of saturation. Oxygen consumption in the simulation experiments dramatically increased from the second day to the third day and it peaked on the sixth or the sev- enth day. However, the high DO consumption rates under different N/P conditions appeared in the second day and contin- ued to the seventh day. Different temperature, salinity, pH and N/P ratios in the seawaters caused variations in the extents of DO consumption during the decomposition process. The extents of DO consumption were in the order of temperature （23--30℃） 〉 pH （5.0--9.0） 〉 salinity （21--33） 〉 N/P ratio （16：1--240：1）, and the values of 39.9, 39.7, 38.0, and 35.9 mg/（kg·d）, respectively. Consequently, the influence of temperature and pH on the DO consumption was more significant and the influence of N/P ratio and salinity was relatively small.%采用实验室模拟的方法，研究了不同海水温度、盐度、pH、N／P比下，沙海蜇消亡过程中海水溶解氧的变化特征，这对探讨水母灾害性暴发后消亡的环境影响有重要的科学意义。研究结果表明，沙海蜇的消亡可引起海水溶解氧浓度的显著降低，不同海水温度、盐度、pH、N／P比条件下沙海蜇消亡引起的海水溶解氧浓度的降低无显著差异，但与没有沙海蜇消亡时，海水溶解氧的变化相比则差异显著。沙海蜇消亡一般需要6—7天时间，在高N／P比的海水中，沙海蜇的消亡时间延长。沙海蜇的消亡造成水体的严重缺氧，水体氧饱和度低于20％，从第2天到第3天，本底海水、不同过程温度、盐度、pH条件下，消耗水体氧的量剧增，第6天达到峰值，但不同N／P比条件下，水体溶解氧的降低在第2天即可达到一个耗氧的高值，一直持续到第7天出现峰值；海水温度、盐度、pH、N／P比变化，可导致沙海蜇的消亡过程中水体氧消耗量的变化，就这四种影响因素而言，其平均最大耗氧量从大到小的顺序是：温度（23—30℃区间段）〉pH（5．0—9．0区间段）〉盐度（21～33区间段）〉N／P比（16：1—240：1区间段），分别为39．9、39．7、38．0和35．9mg／（kg·d），相对而言，水体温度和pH对沙海蜇消亡过程中氧消耗量影响较大，水体N／P比和盐度影响较小。所以，沙海蜇消亡过程中，由于海水温度和pH的变化形成的低氧区更为严重，而且在当今富营养化（高N／P比）的近海水域中，水母的消亡高耗氧的时间加长，对海水环境造成的影响更为严重。