极端干旱水文年(2011年)夏季珠江口溶解氧的分布特征及影响因素研究

Distribution Characteristics of Dissolved Oxygen and Its Affecting Factors in the Pearl River Estuary During the Summer of the Extremely Drought Hydrological Year 2011

气候变化背景下,极端气候事件对河口生态环境的影响已引起许多研究者的关注.基于2011年夏季的调查资料,分析了珠江口在极端干旱情况下溶解氧的分布特征及其与海水稳定性、营养盐和浮游植物分解之间的关系,并对河口底层低氧区的成因进行初步探讨.调查结果发现,在珠江特低径流量的情况下,珠江口邻近海域底层明显出现低氧状态,DO的最低值仅为1.38 mg.L-1.相关性分析显示,表层水和底层水之间的ΔDO与ΔT、ΔS、ΔDIN、ΔSS和ΔPOC都达到显著相关的水平,其中ΔDO与ΔT和ΔPOC呈极显著的正相关,而与ΔS呈极显著的负相关关系.研究表明,与1999年和2009年夏季不同,2011年夏季珠江口底层低氧环境的形成主要与极端干旱气候下低径流导致河口水体滞留时间延长及颗粒态有机物质在沉降过程中的分解耗氧有关.另外,从最低DO值的角度分析,珠江口季节性缺氧程度在过去20 a间并未呈现显著的变化趋势.

More and more attention has focused on assessing impacts of extreme hydrologic events on estuarine ecosystem under the background of climate change.Based on a summer cruise conducted in the Pearl River Estuary in 2011（extreme drought event）,we have investigated the spatial distribution of dissolved oxygen（DO） and its relationships to water column stability,nutrient concentrations,and organic matter;besides,the major reason which caused the oxygen depletion was discussed.Under the influence of the extreme drought event,low bottom water dissolved oxygen was apparent in regions characterized by great depths,with an oxygen minimum value of 1.38 mg·L^-1.Statistical analysis shows significant correlations among ΔDO,ΔT,ΔS and ΔPOC.A comparison was conducted to show the mechanisms of oxygen depletion during the summers of 1999,2009 and 2011,respectively.The result indicates that prolonged residence time of water due to the extremely low discharge and the subsequently decomposition of organic substance are major factors causing the formation of hypoxia during the summer drought in 2011.Despite the changing nutrient and organic matter regime in the Pearl River Estuary,there was no apparent trend in the minimum values of DO over the past 2 decades.