热冲击和加氯后亚热带海区浮游植物细胞数量的动态变化

DYNAMIC CHANGE OF PHYTOPLANKTON CELL DENSITY AFTER THERMAL SHOCK AND CHLORINATION IN A SUBTROPICAL BAY IN CHINA

近年来,随着电厂在河口和港湾等生态脆弱区和敏感区的急剧增多,电厂冷却系统热冲击和加氯对浮游生物造成的伤害已成为沿海地区非常严峻的生态安全问题。为探明冷却系统升温和加氯联合作用对亚热带海区浮游植物的影响程度,针对滨海电厂的实际运作情况,在室内对采自浙江省乐清湾海域的四季浮游植物进行了不同水平的热冲击和加氯胁迫,并观察了这些浮游植物细胞数量在15d内的动态变化。结果表明,热冲击、加氯和季节均显著影响浮游植物细胞数量的恢复(p<0.001),其中,加氯的影响最大,季节次之,热冲击影响最小,但热冲击增强了氯对浮游植物的毒性。自然水温越高、升温幅度越大,细胞数量恢复越慢。春、秋、冬季自然水温较低时,升温4～12℃后,细胞数量仅需1～6d即可恢复到对照组水平;夏季自然水温较高,升温4～8℃后,细胞数量需4～9d恢复到对照组水平,但升温12℃后,细胞数量在15d内未能恢复到对照组水平。加氯浓度越高,细胞数量恢复越慢。加氯1.0～1.8mg·L?1后,浮游植物生长虽受影响,但大多能在15d内恢复;而加氯5.6mg·L?1后,其生长受到完全抑制,细胞数量在15d内未恢复到对照组水平。

Aims With the drastic increase in number of power plants adjacent to estuaries and bays, damage to plankton caused by thermal shock and chlorination in cooling systems has become a serious ecological problem in coastal areas. Presently, there are no criteria for temperature increment （AT） and chlorine dosage （CD） for coastal cooling systems in China. Our objectives are to 1） determine under which AT and CD that the phytoplankton biomass has potential to recover after passage through a cool- ing system and 2） supply a scientific basis for environmental risk assessment and standard formulation of AT and CD in cooling water. Methods In four seasons from August 2006 to May 2007, we collected phytoplankton from the Yueqing Bay. In the laboratory, we stressed the phytoplankton at different AT （0, 4, 8, 12 ℃） and CD （0, 1.0, 1.8, 3.2, 5.6 mg-L-1）. We then recorded the phytoplankton cell density （PCD） every 24 h in a stable culture for 15 d. Important findings Both thermal shock and season significantly affected PCD recovery （p〈0.001）. The recovery period was longer with rising acclimation temperature （AT） and AT. When AT was low in spring, autumn and winter, PCD could recover to the control level in 1-6 d at the ATof4-12 ℃. How- ever, thermal shock would affect PCD more severely when AT was high in summer, as 4-9 d was needed for recovery at the AT of 4-8 ℃ and the resilience was lost at the AT of 12 ℃. Chlorination also significantly affected the PCD recovery （p〈0.001） and had a greater impact than thermal shock. The PCD recovery period was longer with increasing CD. Though PCD could generally restore during 15 d at the CD of 1.0-1.8 mg·L-1, it could not at the CD of 5.6 mg·L-1 in all seasons. Also, there was a synergistic effect between AT and CD that the effect of chlorine on PCD recovery was enhanced under temperature increase in the four seasons. Based on these data, current AT （6-12 ℃）, CD （1-2 mg.L-1） and residual chlorine discharge level （0.15-0.25 mg.L-1） in coastal power plants do not severely affect subtropical phytoplankton biomass.