胶州湾大沽河水龄及其对径流变化响应的数值研究

A Numerical Study on the Water Age of the Dagu River and Its Response to Runoff Change in Jiaozhou Bay

水龄是表征海域水动力系统环境效应的重要参数。本研究利用三维普林斯顿海洋模式模拟的胶州湾水动力场,驱动水龄模型计算了多年平均(1964—2008年)径流下胶州湾内大沽河水龄,并定量分析了不同径流条件下大沽河水龄的差异。结果表明:多年平均径流下大沽河水龄约为42d,丰水年(2007年)和枯水年(2006年)分别为40和47d。水龄空间分布表现为大沽河口附近水龄最低,小于30d;从河口向湾口呈递增趋势,湾口处约为40d;东北部湾顶最高,可达60d以上。水龄季节性变化表现为冬季(48.1d)>秋季>春季>夏季(31.8d)。胶州湾内水龄空间分布与拉格朗日余流形态密切相关,春、冬两季湾内存在多个余流涡,阻碍了水交换,是导致湾东西两侧水龄差异较大的可能原因。径流量变化可显著影响水龄的时空分布:丰水年较枯水年水龄减小16%,冬季差异最大,河口以外海域可达10d以上,变幅超过20%,夏季影响最小,大部分海域不足5d,变幅约为10%;空间上径流变化对东北部湾顶影响显著,差异可达10d以上,河口附近差异不大。

Water age is a valid tool to explore the environmental effects of hydrodynamics in coastal waters.Driven by the hydrodynamics of Jiaozhou Bay simulated by three dimensional Princeton Ocean Model,the water age of the Dagu River was calculated with the constituent-oriented age and residence time theory(CART).Then the temporal and spatial distribution of the water age under different runoff conditions was quantitatively analyzed.The results show that the mean water age of Dagu River is 42 days in the normal year while the water ages in the high flow year(2007)and low flow year(2006)are 40 and 47 days,respectively.In the normal year,the water age is lowest in the western region near the Dagu River estuary(<30 days),and increases gradually to 40 days around the bay mouth.The water age in the northeast bay can reach as high as more than 60 days.The descending order of seasonal variations of water age is winter(48.1 days)>autumn>spring>summer(31.8 days).The spatial distribution of water age is closely related to the pattern of Lagrangian residual flow.During spring and winter,several lagrangian residual vortexes in Jiaozhou Bay obstruct the water exchange progress and lead to an age discrepancy between the eastern and western side of Jiaozhou Bay.Runoff change can significantly affect the spatial and temporal distribution of water age.The mean water age in the high flow year decreases by 16%compared with that in the low flow year.Seasonal variations of water age change due to the runoff change shows that the influence is heaviest in winter which is more than 10 days with 20%change range and the influence is smallest in summer which is less than 5 days with 10%change range.The variation is largest in the northeast corner of the Bay(>10 days)and least near the estuary.