春夏季大亚湾核电厂温排水对海洋浮游植物群落结构的影响

Impacts of thermal effluent on the phytoplankton community structures nearby Dayawan Nuclear Power Station in spring and summer

在2008年4～8月温升季节,对大亚湾核电厂进水口和排水口附近水体4个测站浮游植物种类组成进行了逐月调查,以评估温排水对海区浮游植物群落结构的影响.结果表明获得的网采浮游植物有117种,其中硅藻为该海区的主要种类,其次是甲藻;甲藻与硅藻的种数比为64∶36.比较分析了核电厂进水口和排水口外水体浮游植物群落差异,结果显示温排水区水体浮游植物密度有增加趋势,在4～8月份增加的细胞密度总平均值为17 492×103cells/m3,平均密度是排水口站位的2.73倍,没有迹象表明温排水导致排水口站位上浮游植物细胞密度降低.不相似性分析结果表明导致核电厂进、排水口水体浮游植物细胞密度差异的主要贡献种是硅藻;在排水口外水体中甲藻种数减少,但其细胞密度未见明显变化,显示冷却水系统对甲藻的损害.调查结果表明:除6月份外,核电厂排水口外水体的浮游植物均匀度指数和种类多样性指数普遍降低,其降幅分别达到0.15(0.03～0.22)和0.54(0.23～0.92);水温和盐度测定结果表明核电厂温排水区调查站位水体平均温升不高于2℃,且各站间盐度差不大.但是,6月份特大暴雨后各调查站位水温、盐度结构出现很大变化,各站之间表层水温温差缩小,仅在0.1℃左右,站位间盐度差拉大,最大差值达6.9;同时,核电厂温排水对浮游植物群落的影响随之减弱,排水口站位上的浮游植物均匀度和种类多样性指数均高于进水口站位的对应值.

According to surveys in warm-up seasons of April to August in 2008 changes of phytoplankton communi- ties at 4 sites in waters near the outlet of Dayawan Nuclear Power Stations （DNPS） were studies for evaluation of thermal effects on the phytoplankton community structure. As results, 117 species from net samples were recorded and the most dominant species were identified as diatoms and dinoflagellates with ratio of diatoms to dinoflagellates 64： 36. The phytoplankton communities between the waters near inlet and outlet of DNPS were compared and it showed that phytoplankton densities had increased in waters near the discharge outlet where monthly phytoplankton density increment was averaged 17 492 x 103 cells/m3, i. e. 2.73 timed as high as that of waters near the inlet. No evidence showed that thermal discharge had dropped the phytoplankton densities at the sites near the discharge out- let. Dissimilarity analyses showed that discriminating species contributing to the density increment in the outlet wa- ters were diatoms. However, the proportion of dinoflagellate species decreased and their densities increased insig- nificantly, suggesting the damage by the cooling system to the dinoflagellates. With no consideration of particular case in June, it is evident that the species diversity indexes （J＇ and H＇ ） had generally decreased at sites near the outlet, where the decrements accounted for 0. 15 （0.03 -0. 22）and 0.54 （0. 23 -0. 92 ）, respectively, against the background temperature increment around 2 degree centigrade with little salinity difference. However, great chan- ges in temperature and salinity distributions occurred after severe rainstorms in June when surface water temperaturedifference suddenly narrowed to a minimum 0. 1 degree centigrade and salinity widened to a maxima of 6.9 among the sites. At the same instant, the effects of thermal influents on phytoplankton communities dispatched and in- dexed of J＇ and H＇ increased in waters near the thermal discharge outlet.