Dissolved oxygen (DO) is one of the most important factors for maintaining a healthy marine ecosystem. The information of DO in large estuaries or bays with large entrances has been widely studied, while it is relatively limited for a bay with a narrow entrance which is vulnerable to human activities. The Zhanjiang Bay, located in the northwestern South China Sea, has a very narrow entrance and suffers from strong anthropogenic activities and obvious seasonal variations in environmental parameters. In this study, we analyzed the spatial and monthly variations of DO, apparent oxygen utilization (AOU), percent oxygen saturation (DO-saturation), and related environmental parameters in the surface water of Zhanjiang Bay to find out the factors controlling the dynamics of DO. Different from many other coastal ecosystems, DO concentrations in the Zhanjiang Bay reached minimum values in late spring and early autumn. The phytoplankton bloom in summer months, which was related to the high concentrations of nutrients brought by rainfall-induced terrestrial inputs, contributed to that phenomenon. Though high chlorophyll a (Chl a) concentrations were observed in both the summer months and December, the DO-saturation values were relatively low and AOU values were relatively high in summer months. Rainfall-induced terrestrial discharge in summer months, which had high concentrations of chemical oxygen demand, contributed much to that phenomenon. The average DO concentrations and DO-saturation values in a hydrological year decreased seaward, and AOU values increased seaward, indicating the anthropogenic influence from terrestrial input. The highest annual average Chl a concentration, relatively high annual average DO-saturation value and relatively low annual AOU value were observed near the Donghai Dam. This indicated that the construction of Donghai Dam has significant influences on the environment of Zhanjiang Bay.

中文翻译：

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湛江湾地表水中溶解氧的空间变化及影响因素

溶解氧（DO）是维持健康的海洋生态系统的最重要因素之一。大型河口或具有较大入口的海湾中溶解氧的信息已得到广泛研究，而具有狭窄入口的海湾相对容易受到人类活动的影响。湛江湾位于南海西北部，入口非常狭窄，人为活动强烈，环境参数也存在明显的季节性变化。在这项研究中，我们分析了湛江湾地表水中溶解氧的空间和月度变化，表观氧气利用率（AOU），氧气饱和度百分比（DO-饱和度）以及相关的环境参数，以找出控制水体动力学的因素。做。与许多其他沿海生态系统不同，湛江湾的DO浓度在春末秋初达到最小值。夏季，浮游植物的开花与降雨引起的地面投入带来的高养分含量有关，是造成这种现象的原因。虽然叶绿素a（Chla）在夏季和十二月都观察到浓度，夏季的DO饱和度值较低，AOU值较高。在夏季，由于降雨引起的陆地排放，其中化学需氧量的浓度很高，对这种现象起了很大作用。在一个水文年中，平均溶解氧浓度和溶解氧饱和度值向海减少，而AOU值向海增加，表明地面输入对人为的影响。最高年平均叶绿素一个浓度，相对高的年平均DO-饱和度值和相对低的年度AOU值附近的东海坝观察。这说明东海大坝的建设对湛江湾的环境有重大影响。