http://www.paper.edu.cn Estuarine, Coastal and Shelf Science 61 (2004) 25e35 Simulation of water exchange in Jiaozhou Bay by average residence time approach ) Zhe Liua, , Hao Weia,b, Guangshan Liuc, Jing Zhangd aInstitute of Physical Oceanography, Ocean University of China, 5 Yushan Road, Qingdao 266003, China bKey Lab of Physical Oceanography, State Education Department, 5 Yushan Road, Qingdao 266003, China cOceanography Department, Xiamen University, 422 Siming Road South, Xiamen 361005, China dState Key Lab of Estuarine and Coastal Research, East China Normal University, 3663 Zhongshan Road North, Shanghai 200062, China Received 29 November 2003; accepted 4 April 2004 Abstract A dispersion model coupled with the Princeton Ocean Model was used to estimate the average residence time of the water in Jiaozhou Bay. The tidal simulation agreed quite well with drift experiments and water elevation observations at the Dagang tide station in the east coast of the bay. In particular, in situ measurements of 228Ra and salinity were carried out to calibrate the dispersion model. The modelled average residence time was about 52 days, ranging from less than 20 days in the deep part near the bay channel, the only passage connecting the bay to the Yellow Sea, to over 100 days in the shallow area in the northwest. The spatial difference of average residence time was controlled by tidal residual currents and the distance to the bay channel. The modelled tidal exchange rate was uneven in the bay, and consistent with 228Ra observations. The temporal evolution of the passive tracer accords with the evolution of the rain fraction after the rainstorm in August 2001. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: water exchange; dispersion model; average residence time; Jiaozhou Bay 1. Introduction Water exchange in coastal areas can be studied by box, parcel-tracking, and dispersion models (e.g., Cheng Water exchange plays a critical role in coastal and Casulli, 1982; Luff and Pohlmann, 1996; Kitheka, ecosystems (Kraufvelin et al., 2001). Coastal areas with 1997; Dong and Su, 1999a,b), with dispersion model active water exchange usually have good self-purifica- being characterized by major physical processes (i.e., tion capability. For instance, despite increased loading advection and diffusion). Some simulation results (e.g., of contaminants, rapid water exchange transports water elevation and currents) calculated from the model nutrients to the Iroise Sea and thus maintains the could be calibrated by comparison with observations. steadiness of the ecosystem in Brest Bay (Le Pape and Other aspects of model output, such as the water Menesguen, 1997). On the other hand, flow fields favor exchange curve, cannot be easily calibrated due to lack bringing in and accumulation of pollutants, and of observations. consequently deteriorate water quality. In Koljo Fjords, In this study, a dispersion model was developed and coastal eutrophication has been building up and the used to simulate the exchange processes of Passive environment is becoming worse because of slow water Dissolved Conservative Matter (PDCM) in Jiaozhou exchange, although there are no significant local sources Bay (JZB), based on the average residence time ap- of pollutants in the adjacent land-region (Rosenberg, proach (Takeoka, 1984). The model was calibrated by 1990; Lindahl et al., 1998; Nordberg et al., 2001). observations of tidal water elevation and drift experi- ments. Data were collected from intensive measurements of a natural radiotracer (228Ra) and the salinity change ) Corresponding author. after a sudden rainstorm in the region was also moni- E-mail address: [email protected] (Z. Liu). tored. The comparison between the two datasets and the 0272-7714/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2004.04.009 转载 中国科技论文在线 http://www.paper.edu.cn 26 Z. Liu et al. / Estuarine, Coastal and Shelf Science 61 (2004) 25e35 model outputs helped us to directly estimate the tidal (Ding, 1992), resulting in nearly homogeneous vertical exchange rate and obtain the curve of water exchange profiles of temperature and salinity. JZB receives limited in the area. The flow chart of analysis and computation river discharge from land regions around. On the JZB is shown in Fig. 1. west coast is the Dagu River (Fig. 2) with annual mean discharge of about 7:2 ! 108 m3 (1952e1979) (Editorial Board of Annals of Bays in China, 1993), accounting for 2. Study area 84% of the total riverine discharge into JZB (Marine Environmental Monitoring Center, 1992). The stratifi- JZB is located at the west coast of the Yellow Sea cation is weak even in summer when land-source (e.g., (YS) (35(58#e36(18#N, 120(04#e120(23#E), has aver- river) input reaches its maximum (Weng et al., 1992). In age water depth of about 7 m (Fig. 2), and is a partly- recent decades, the total amount of freshwater discharge enclosed waterbody with a narrow channel between from rivers into JZB decreased considerably, according Xuejiadao and Tuandao that connects the bay with the to data from the State Oceanic Administration of China YS (Fig. 2). JZB tides induce strong turbulent mixing and the Qingdao Aquiculture Bureau (SOA and QAB, Start M2 tidal force at open boundary Input Elevation Cali Drift data from bration experiments tidal gauge Princeton Calibration Ocean Model Input Input Output Grids scheme Elevation; Topography velocities; diffusivity Input Input Input Dispersion Initial Input Model Input Open boundary concentration condition field Output Salinity Modelled Calibration Calibration Measurement recovery concentration of of 228Ra process passive tracer Stop Fig. 1. This study’s flow chart of analysis and computation showing the main processes such as the coupling of hydrodynamic and dispersion models, and the integration of simulation results and observations. The details are discussed in Sections 3e5. 中国科技论文在线 http://www.paper.edu.cn Z. Liu et al. / Estuarine, Coastal and Shelf Science 61 (2004) 25e35 27 N 36.20° A1 A2 A3 A4 A5 Dagu River B1 B2 B3 B4 B5 Jiaozhou Bay DG 36.10° C1 C2 C3 C4 D1 Channel N T D2 H E3 Shandong Peninsula D3 37° D4 E2 D5 E1 36.00° 36° XJ Yellow Sea 35° Yellow Sea 120° 121° 122° E 35.90° 120.10° 120.20° 120.30° 120.40° E Fig. 2. Topography (m) of JZB, together with the sampling stations for field observation in August 2001. Insert is the location map (lower left). The interval of water depth is 10 m. There were two stations (B3 and C2) for 228Ra isotope measurement. Around JZB, T is Tuandao, XJ is Xuejiadao, H is Huangdao, and DG is Dagang tide station (solid triangle). The dotted areas indicate the mud tidal flat. The dashed line between XJ and T indicates the channel connecting the bay to the Yellow Sea. 1998). Qingdao city with total population of about 7.1 calibrating the hydrodynamic model (Fig. 3a). The million surrounds JZB. Due to the rapid economical and sampling interval of 1 h yielded 720 valid records. social developments in this region, JZB is greatly influenced by human activities, leading to increasing 3.2. Drift experiments amount of industrial, agricultural, and aquicultural input into JZB (Fan and Zhou, 1999). Red tide has Three drift experiments, Z1, Z2, and Z3, started at become a frequent event, as the bay water is eutrophied different places (Fig. 3b), yielded the Lagrangian (Environmental Bureau of Qingdao, 1999). The de- trajectories of water mass that were used to calibrate terioration of water quality in JZB led to such serious the modelled current field. The drifter, made of iron bar- ! concern of social and scientific communities that several framed 1 m 1 m sail at 3 m depth, was attached to research projects were carried out to investigate the a buoy with a nylon cable. A thin bamboo pole was mechanisms of the water exchange in this area (e.g., Sun fixed to the top of the buoy with a flashlight and a flag. et al., 1988; Zhao et al., 2002). These projects provided The trajectories of the drifter were recorded by Model the scientific background of the present work. GPSMAP230 Global Position System. In Case Z1, the drifter was launched in the bay channel at flood tide and its trajectory was recorded for 6 h. The Z2 experiment, conducted in the north of Huangdao (H in Fig. 2), was 3. Field observations, data and methods discontinued after 9 h due to severe weather conditions. In Case Z3, the drifter was deployed at high tide in the Local historical records of tidal elevation were center of the bay and the experiment lasted for 6 h. All collected in this study. Three cruises for drift experi- the trajectories are shown in Fig. 3b. ments, observing salinity and measuring 228Ra, were ac- complished during August 13e28, 2001. 3.3. Salinity recovery 3.1. Observations of tidal elevation Typhoon Taozhi that passed over JZB in August 2001 brought heavy precipitation of over 120 mm within The September 9 to October 8, 1993 tidal elevation 9 days, which accounted for nearly 1/6 of the annual data series measured by WLR7 Aanderaa tide recorder mean rainfall (732.7 mm) in this region (Editorial Board at the Dagang tide station (DG in Fig. 2), were used for of Annals of Bays in China, 1993). In the field 中国科技论文在线 http://www.paper.edu.cn 28 Z. Liu et al. / Estuarine, Coastal and Shelf Science 61 (2004) 25e35 2.4 Tidal Elevation at Dagang tide station 2.0 observation a 1.6 simulation 1.2 0.8 0.4 0.0 -0.4 -0.8 Tidal Elevation (m) -1.2 -1.6 -2.0 -2.4 0 48 96 144 192 240 288 336 384 432 480 528 576 624 672 720 Time (hour) N b 36.20° date: 08-23 Z2 time: 20:20 date:08-23 time:11:35 DG 36.10° Z3 date:08-23 date:08-24 time:02:35 time:02:20 H T Z1 date:08-15 Observation time:16:30 Simulation date:08-15 time:10:30 XJ 36.00° 120.15° 120.20° 120.25° 120.30° 120.35° E Fig.