北仑河口及其邻近海域物质输运滞留时间研究

Transport Time Scale in the Beilun River Estuary and Its Adjacent Area

河口、近岸物质的输运时间尺度是将海洋物理过程与生态过程联系起来的一个重要指标，反映了水体内物质更新速率。为有效控制北仑河口及其临近海域环境污染和促进海岸线资源的合理开发，开展近岸物质输运的时间尺度研究具有重要意义。基于此目的，本文建立了平面二维高分辨率物质输运数学模型，对北仑河口至珍珠湾海域滞留时间的空间变化及其对于径流、潮差、地形等因素的响应进行了研究。结果显示，在北仑河口外部海域，滞留时间一般不超过20h，在口门附近，在不同的径流量、潮差的情况下，滞留时间变幅较大，约为30-200h；在珍珠湾海域，滞留时间的空间及随潮差的变化亦很大，珍珠湾内的Z1区域最大可达413．7h，湾口处的Z4区域，最小仅为3．5h。在空间上，北仑河口及其邻近海域的滞留时间在纵向上的变化呈现明显的白口门向外海逐渐减小的趋势，减小的幅度逐渐变小，说明径流的影响逐渐减小，在横向上滞留时间自深槽向浅滩逐渐增大。珍珠湾海湾边缘的浅水区，滞留时间明显大于深水区域的滞留时间。北仑河口区域滞留时间与径流量呈现明显的二次函数或线性函数关系，径流的影响向外海逐渐减弱，在深槽处大于浅滩处。滞留时间随潮差的增大而减小，变幅在口门处大于外海。北仑河口滞留时间主要受潮汐的影响。

Transport time scale of estuary and nearshore areas is an important agent connecting the marine physical processes and the ecological processes which reflace the exchange of water and materials in it. It is of vital importance to investigate the transport time scale in the Beilun River estuary to control marine environmental pollutions efficiently and to promote the reasonable shoreline development. A high-resolution 2-Dimensional numerical model is established and applied in the Beilun River estuary to calculate the residence times and their reactions to river discharge, tidal range and topography. The results show that the residence times in the outer areas adjacent to the Beilun River estuary are less than 20h. Near the river mouth, the residence times exhibit great variations with a range between 30h to 200h under different conditions of river discharges and/or tidal ranges. In the Zhenzhu Gulf, the residence times show great spatial variations as tidal range changes. In the inner subzone Z1, the residence time is 413.7h, while in the outer subzone Z4, the residence time is only 3.5h. The residence time decreases gradually from the river mouth to outer areas and from the channel to the shoal. In the Zhenzhu Gulf, the residence time is much longer than those in the marginal shallow zones. The residence time can be fitted satisfactorily with the river discharge by quadratic polynomials, the influences of river discharge to residence time become weaker from river mouth to the outer zones and from channel to shallow areas. The residence time increases as the tidal range decreases and the changes are larger near river mouth than that in the outer seas. In the Beilun River estuary, the dominate influence on residence time is due to tidal flushing rather than river dischange.