Effects of thermal discharge on the spatial distribution of bacterioplankton community near a power plant in Xiangshan Bay

The thermal discharge of coastal power plants has resulted in serious environmental problems,such as the increasing frequency of disease in marine biota and red tides at a global scale. For this reason,previous studies have largely focused on the effects of thermal discharge on the diversity of zooplankton and phytoplankton species,whereas the study of the response and feedback of ecologically important planktonic microorganisms to thermal discharge is lacking. The ecosystem feedback response to elevated seawater temperature is dependent on the balance between primary production and heterotopic bacterial respiration. Therefore,we integrated Illumina sequencing technique and geochemical variables of seawater to investigate the spatial pattern of bacterioplankton communities,and identify the key factors shaping the pattern along a thermal gradient caused by the discharge from a power plant at Xiangshan Bay,Ningbo. Elevated temperature was significantly related to increased nitrate concentration( NO-3,P = 0.041,one-way analysis of variance),chemical oxygen demand( COD,P 0.001),oil( P = 0.004),and residual chlorine( Cl-,P 0.003),whereas the levels of dissolved oxygen( DO,P = 0.034) and chlorophyll a( Chl a,P = 0.045) significantly decreased along the temperature gradient. In addition,an analysis of similarity( ANOSIM) revealed that thermal discharge significantly( r = 0.338,P = 0.042) altered the structure of bacterioplankton communities,whereas the spatial distribution of the bacterioplankton communities followed a distance-similarity decay relationship in that the similarity between the bacterioplankton communities linearly decreased( r=-0.582,P= 0.026) with increasing geographic distances,with a turnover rate of 0.0013. Multivariate regression tree showed that bacterial diversity was primarily affected by the levels of DO,COD,and seawater temperature,which respectively constrained 34.6%,20. 1%,and 10. 0% of variation in bacterial diversity. A redundancy analysis( RDA)revealed that the environmental variables( including seawater temperature,oil,DO,and Chl a) explained 55.6% of the variation in the bacterioplankton communities. Thus,it appeared that the diversity and structure of bacterial communities were shaped by different factors. Notably,the direct effect of temperature only explained 4. 8% of the variation. This is consistent with the premise that temperature increases have a moderate direct impact on bacterial community structure; however,water tempera