高强度养殖活动下老爷海溶解氧的亏损及有机质成分的响应

Oxygen depletion and the response of organic matter in Laoyehai,a lagoon with strong aquaculture activities

老爷海是海南岛东岸的一处潟湖,受强烈人类活动(尤其是养殖活动)影响,其水体富营养化并伴随低氧.在选取的旱季和洪季(2010年4月和2011年8月),老爷海适值低氧期间,对老爷海开展了针对溶解氧和有机质的采样与观测.结果显示,春季潟湖低氧强烈,个别站位表层水溶解氧也仅为50%,夏季则在底层也存在低氧.在这样的背景下,春季有机质浓度明显高于夏季,颗粒有机质的C/N值(C与N的比值)也表现为春季高于夏季(平均值春季为9.7,夏季为7.7).氨基酸所指征的有机质成分暗示春季有机质有较强的细菌降解信号;夏季有机质的低C/N值和高氨基酸碳、氮归一化产量显示现场生产相对活跃,有机质主要来自海源浮游植物,表层水供氧充分.在水体发生氧亏损时,溶解和颗粒有机质的降解程度存在差异.整体而言,颗粒有机质的降解程度随着水体中溶解氧浓度的下降而增加,说明颗粒有机质的降解消耗氧气是造成潟湖低氧的重要驱动因素;溶解有机质成分的变化和溶解氧关联不显著.

Laoyehai is a lagoon located on the east coast of Hainan and is impacted heavily by human activities(especially those related to aquaculture).Laoyehai is characterized by its eutrophic and hypoxic waters.During previous dry and flood seasons(specifically,April 2010 and August 2011),when hypoxia occurred,field work was conducted to observe the dissolved oxygen(DO)and to collect organic matter.Hypoxia was significant in the spring season with surface DO as low as 50%,while the bottom hypoxic water prevailed in both seasons.In the spring season,the C/N ratio of particulate organic matter was higher than that observed in the summer season(C/N in the spring:9.7,C/N in the summer:7.7).Organic matter composition indicated by amino acids showed that there was strong in situ production in the spring relative to that in the summer.Lower C/N values and higher carbon and nitrogen yields of amino acids(AA C yield,AA N yield)in the summer showed active in situ production,suggesting that organic matter was mainly derived from phytoplankton.This also explains the sufficient surface DO in the summer.The degradation of particulate organic matter increased with the decrease of dissolved oxygen,indicating that the particulate organic matter and its degradation were the key driving factors for oxygen consumption in the lagoon.Meanwhile,we found that the relationship between dissolved organic matter components and DO was not significant.