Analysis On Variation Characteristics And Drivers In Chlorophyll-a In Xiamen Bay Based On Marine Water Quality Buoy Observations

Marine water quality buoy system has become an effective means to understand the state and various of Marine ecological environment,study the mechanism and early warning methods of algal bloom/red tide according to its advantages of all-weather and long-term continuous observation.Under the quality control,observation data of two water quality buoys were selected at Baozhu island and Tongan bay in Xiamen bay from 2008 to 2016..Combined with meteorological and tidal data,the relationship between chlorophyll-a and environmental factors was preliminarily analyzed.Then the Generalized Additive Models(GAM)was further used to explore the main driving factors that affect the change of chlorophyll-a in Xiamen bay.The main conclusions are as follows:1.The variation of chlorophyll-a and water quality factors at Baozhu island and Tongan bay were consistent.In the annual variation of chlorophyll-a,There are three peaks occur in winter,spring and summer respectively.In Tongan bay,the higher peak value is in winter,lower in summer.In Baozhu island the higher peak value occur in summer,lower in winter.At the same time,the annual variation of each factor is significant.Correlation analysis shows that the relationship between chlorophyll-a and environmental factors is very complex and difficult to be explained by a linear model.2.In this paper,chlorophyll-a was taken as the response variable,and environmental factors such as water temperature,salinity,air temperature,air pressure,dissolved oxygen,tidal range,wind speed,and wind direction were taken as the initial explanatory variables to build a generalized additive model.Then single-factor analysis,concurity diagnosis and interaction analysis were used to optimize the initial GAM model.Finally,a GAM model was built with the interaction between wind speed and wind direction,water temperature and air pressure,dissolved oxygen saturation and salinity as explanatory variables.The models can explian the variance of 43.8%in Baozhu island and 65.7%in Tongan bay,indicating that chlorophyll-a in Tongan bay is more affected by water quality,meteorological than in Baozhu island.In oeder to explor the difference from the two chlorophyll-a peak value in winter and summer.the generalized additive model in winter and summer is further built in Tongan bay as an example.The explanatory variables of the model in winter include the interaction between water temperature and air pressure,salinity,wind speed,and dissolved oxygen saturation,which can explian the variance of 94.5%.and the explanatory variables of the model in summer include the interaction between water temperature and air pressure,salinity,wind speed,dissolved oxygen saturation,and tidal range,which can explian the variance of 90.2%.3.The results of the GAM model show that chlorophyll-a concentration in Xiamen bay is affected by many environmental factors.The influence mechanism of chlorophyll-a in Baozhu island and Tongan bay is similar,but the influencing factors of chlorophyll-a in winter and summer are different.The results of model show that with the increase of dissolved oxygen saturation,the concentration of chlorophyll-a all showed a rising trend,but it will decreased while reached a certain high value.The effect of salinity on chlorophyll-a is complex,which needs to be determined in different situation.The effect of meteorological on the various of chlorophyll-a in winter and summer is different.Low wind speed,high temperature,and low pressure promote the growth of chlorophyll-a in summer,while low temperature,high pressure and weak increase of wind speed promote the growth of chlorophyll-a in winter.Also,the tidal range has no significant effect on chlorophyll-a in winter,but smaller tidal range is conducive to chlorophyll-a growth in summer.