In recent decades，coastal zones have experienced many ecological changes owing to climate change and human activities.The objective of this postdoctoral research report is to gain understanding of and quantify the key mechanisms driving the environmental changes in Jiaozhou Bay,China.To accomplish this goal，statistical analysis of abrupt climate changes and model study on water age and nutrients transport were conducted to lay a good foundation for future study and reveal the response of water quality variability in Jiaozhou Bay to natural and anthropogenic stresses.The statistical analysis involves developing a new technique to pinpoint the regime shifts and analyze the long-term change of physical parameters and its ecological potential consequence.The new technique based on Haar wavelet transform can effectively identify multiple timescales regime shifts，quantitatively describe their corresponding confidence levels，and is strongly resistant against random signal components.The large scale climate anomalies in the Northern Hemisphere have impacted the decadal change in Jiaozhou Bay physical environment．Particularly,the significant abruptness of precipitation，temperature and salinity is consistent very well with the 1976-78 and 1988-89 shifts in the Arctic Oscillation and ENSO events.Precipitation and temperature jump at decadal scales might play an important role in the decrease of benthic diatom cell abundance.The mean water age and residence time pattern is closely related to the geomorphology and structure of the tidal residual currents。This residence time.derived from the view of Lagrangian theory,ranges from less thanlO days in the bay channel to greater than 130 days in the western part．Comparison of this residence time from Lagrangian and Euler theory revealed that the east(west)region，suggesting that water parcel there has left(still remains inside)JZB when its original place is filled by YS water.The water age for the pollutant released from the surrounding rivers shows longitudinal gradient in the north and latitudinal gradient in the south.The interaction and combination of the rivers around JZB leads to the complex reasons for the eutrophication processes.If the advection is overwhelmed during the material transport process，the water age Can be calculated by in situ measurement of the concentrations of the conservative tracers and radioactive isotopes.A 3-D biological model was developed and coupled to a hydrodynamic model，i.e.,Princeton Ocean Model，for simulating the seasonal variation and budget of dissolved inorganic nitrogen，phosphate and silicate，in Jiaozhou Bay.The modelled nutrients distribution pattern is consistent with observation.Silicate，the most important limiting element for phytoplankton growth，is characterized by consumption in spring，increase in summer and autumn，and accumulation in winter,while dissolved inorganic nitrogen and phosphorous keep increasing trend with low rates in spring，owing to excessive river loads.Phytoplankton plays an important role in nutrient renewal through photosynthesis and respiration processes.During an annual cycle，7.83×103 t N，0.28×103 t P and 3.93×103t Si are transported to the bays outer sea，i.e.，the Yellow Sea，suggesting that Jiaozhou Bay is a significant nutrients source for the Yellow Sea.The spatial distribution of nutrients is characterized by verticallv homogeneous profiles，high concentration inside the bay and low concentration toward the bay channel.These features are mainly governed by s~ong turbulent mixing，fluvial influx，water exchange rate and Yellow Sea water intrusion.Numerical experiments suggest that the government should pay enough attention to proper layout for sewage drainage.