Research On The Response Mechanisms Of Ulva Prolifera Decay Process To Key Ecological Environment Factors In The Southern Yellow Sea

Since 2007,the South Yellow Sea has been affected by U.prolifera disaster every summer.In order to control U.prolifera,the Chinese government has spent a lot of human,material and financial resources.Based on this,this paper studies the dissipaton process of U.prolifera in the South Yellow Sea and its impact on the coastal environment through the combination of remote sensing technology and field measurement data.First,we used MODIS,HJ-1A/B CCD and GF-1 data,then combined with normalized vegetation index?NDVI?,extracted the distribution information of U.prolifera in the Southern Yellow Sea from 2011 to 2018.We analyzed the process of U.prolifera disaster from emergence to extinction,and also explored the influence of sea surface temperature on U.prolifera;then analysied the temporal and spatial distribution of chlorophyll-a concentration in the Southern Yellow Sea within the life cycle of U.prolifera;finally,based on the data of Haiyang marine monitoring station,the influence of U.prolifera on chlorophyll-a and other environmental factors was analyzed by multiple regression analysis.The conclusions are as follows:?1?Based on the distribution information of U.prolifera in the Southern Yellow Sea from 2011 to 2018,it is found that the coverage area of U.prolifera is increasing on the whole.In late June 2015,the coverage area reached the maximum value of 8 years,with an area of 1714.21 km².The influence area of U.prolifera showed a wave like trend.In mid July 2014,the influence area of U.prolifera reached the maximum value of 8 years,with an area of 39020.63 km².Based on the remote sensing image,the distribution of Ulva prolifera was first detected in the sea area near the Jiangsu Shoal in early May,and then it began to drift northward into the sea area near Shandong Peninsula.?2?SST is the key environmental factor affecting the outbreak of U.prolifera.And the SST anomaly and average growth rate of U.prolifera were positively correlated in May?R²=0.62?.The variation trends of PAR and SST are approximately the same,and the PAR in this time period maintained a range of 40–50 mol m^-2d^-1.The energy provided by illumination was suitable for the growth and outbreak of U.prolifera.In addition,because of the abundant nutrients and suitable temperatures in the sea area near northern Jiangsu shoal,high growth rate of U.prolifera was observed in May.?3?In terms of spatial distribution,the concentration of chlorophyll-a in the sea area near Jiangsu shoal is higher than that in the sea area of Shandong Peninsula from May to August,2011-2018.And the concentration range is about 4-5 mg/m³,while the concentration of chlorophyll-a in the sea area is higher than that in the open sea.In the time distribution,from May to June,the concentration of chlorophyll-a in the study area showed a general downward trend;from July to August,the concentration of chlorophyll-a in the study area showed an overall upward trend.The concentration of chlorophyll-a in the surface layer of the South Yellow Sea generally shows a trend of"overall rise-sharp decline-slow rise-tend to be stable".?4?Multiple regression analysis demonstrated that chlorophyll-a concentration was related to sea surface temperature,salinity,phosphate and DIN.Among them,DIN and phosphate content are important environmental factors that affect chlorophyll-a.There is a significant positive correlation between chlorophyll-a concentration and DIN,but a significant negative correlation between chlorophyll a and phosphate.The concentration of chlorophyll-a in the sea area of Dingzi Bay was mainly affected by the input from the Baisha River and the Wulong River,while it is mainly affected by the dissipation of U.prolifera in the sea area outside Dingzi Bay.Compared with the average chlorophyll-a concentration in May,it increased from 1.398?g/L to 2.819?g/L in Haiyang City.In addition,human activities,land-based input and the YSCWM increased eutrophication of the coastal area in Haiyang City.These factors increase the risk of secondary algal disasters such as red tides.