Spatiotemporal Variation And Spatial Autocorrelation Of Nutrient And Environmental Factors In Maowei Sea At Monthly Scale

Affected by the interaction between the sea and the land,the seawater environment of the estuary is complex and changeable.The multi-site and high-frequency characterization of the temporal and spatial distribution of nutrients and environmental factors,and discussing their spatial correlation,is useful for revealing the migration,transformation and interaction of nutrients and environmental factors.Analyzing the contribution of the land and sea is of great significance to achieve precise monitoring of the marine environment.The Maowei Sea is a semi-enclosed bay that integrates the estuary of the Haihe River,the mangrove reserve,the breeding base,the marine park,and the port.It has diverse production and ecological functions.This also leads to a wide range of environmental material sources and strong temporal and spatial heterogeneity.The monitoring and management of the marine environment in the tail sea and the assessment of marine productivity have brought great difficulties.Based on this,according to the actual situation of the Maowei Sea,this study set up 16 monitoring stations in the Maowei Sea from May 2017 to April 2018 to monitor the surface seawater nutrients of the Maowei Sea with high frequency on a monthly scale for the first time(DIN,NO₃-N,NO₂-N,NH₄-N,PO₄-P,Si O₃-Si)and environmental factors(chemical oxygen demand(COD),dissolved oxygen(DO),p H,transparency,water temperature and salinity),In order to reveal its temporal and spatial distribution law,explore the spatial correlation between the two,and comprehensively evaluate the quality of the seawater environment,it provides a scientific basis for the division,stage,classification,grading monitoring,treatment and protection of the Maowei seawater environment.The main conclusions drawn in this article are as follows:1.During the study period,the surface seawater nutrients and environmental factors of the Maowei Sea have obvious temporal and spatial variability.In terms of time,the high-value periods of the nutrient indicators DIN and PO₄-P are concentrated in winter and spring,and the low-value periods are summer and autumn.The opposite is true for Si O3-Si,and the concentrations of DIN and PO₄-P are up to 0.430 mg/L and 0.041 mg/L.Belongs to the fourth category of sea water quality standards;the high value periods of environmental factors COD and water temperature are distributed in spring and summer,and the high value periods of DO,p H,transparency and salinity are distributed in autumn and winter.Spatially,the nutrient indicators show a decreasing distribution law from the estuary to the estuary.The COD,DO and water temperature in the environmental factors also decrease from the estuary to the estuary,but the p H,transparency,and salinity,on the contrary,decrease from the estuary to the estuary the trend of.The research results on a monthly scale support the predecessor's view that the surface seawater nutrients of the Maowei Sea are mainly derived from land sources,and DIN and PO₄-P are the main pollutants.2.The hot spots for the spatial variation of the nutrient indicators in Maowei Sea are mainly the estuary area,and the cold spot area is the bay mouth area;the distribution of environmental factors COD,DO,water temperature and nutrient salt cold and hot spots are the same,but p H,transparency,and salinity are opposite.The bay mouth is a hot spot,and the estuary is a cold spot.In terms of time change,the seasonal change hotspot of each nutrient indicator is the estuary area(except for the NO₂-N change hotspot is the Baykou area),and the annual change hotspot of DIN,NO₃-N,NO₂-N,and NH₄-N is Qinjiangkou The annual hot spots of PO₄-P and Si O₃-Si are Qinjiangkou and Maolingjiangkou.It shows that the estuary area is a concentrated area of nutrient salt changes in time and space,and should be used as a key monitoring area for the seawater environment of Maowei Sea.3.The results of the bivariate global spatial autocorrelation analysis showed that each nutrient index was significantly positively correlated with COD and DO,and significantly negatively correlated with p H,transparency,water temperature,and salinity.The results of bivariate local space autocorrelation analysis show that the spatial autocorrelation between each nutrient index and COD,DO had three main types:"high-high"in estuarine area,"low-low"in bay mouth area and"insignificant"in central area,and the spatial autocorrelation between each nutrient index and p H,transparency,temperature,salinity were"high-low"in estuary area,"low-high"in bay area and"insignificant"in central area;The spatial autocorrelation characteristics of nutrients and environmental factors had an obvious spatial-temporal variation,including the transfer of spatial autocorrelation type and area increases and decreases.It shows that the interaction between nutrients and environmental factors in the mouth and bay mouth of Maowei Sea is complex and time fluctuations are strong.The simultaneous monitoring of nutrients and environmental factors in the sea area should be strengthened,and the density and frequency of monitoring points should be increased.Set up monitoring points at the junction of types.4.The environmental quality results of Maowei seawater showed that the water environment of the bay was mainly polluted by DIN,PO₄-P,COD.Among them,DIN,PO₄-P,and COD pollution at the Qinjiang Estuary were more serious,and the Maoling Estuary p H influence was serious.The Maowei Sea has serious organic pollution,and the level of eutrophication has reached moderate or above pollution.Among them,the eutrophication pollution in the estuary area is the most serious in spring,and the area of eutrophication pollution during the flood season is relatively wide.In autumn and winter,the potential of phosphorus is moderately restricted.The period of high incidence of eutrophication,spring and summer is the period of high incidence of eutrophication.The comprehensive water pollution in this area is relatively light,but it shows an upward trend in spring and summer,especially in the estuary area.In terms of space,the environmental pollution of Maowei seawater has a decreasing distribution pattern from the estuary to the bay mouth.The results show that DIN and PO₄-P are still the main pollutants in the sea area,the estuary is the most polluted area,and the water body eutrophication pollution types have obvious seasonal differences.In summary,the environmental quality of Maowei seawater is poor,DIN and PO₄-P are the main pollutants,and the estuary area is the main polluted sea area and nutrient change hotspot.The estuary should be set as a key monitoring area;nutrients and environmental factors have high values The period is different,and the key monitoring time can be divided according to the high value period.There are many types of pollution in the seawater environment of Maowei,and different pollution types have seasonal differences.Corresponding monitoring and management strategies should be formulated according to different types of pollution and pollution periods;water environment The spatial pattern of pollution shows a decreasing distribution law from the estuary to the estuary,and monitoring and control plans can be formulated according to the pollution level;in addition,the interaction between nutrients and environmental factors at estuary and estuary is complex and changeable,and the types of spatial autocorrelation transform each other,which should be increased The location and intensity of monitoring points in two sea areas.