降雨对香溪河库湾主要藻种原位生长的影响

Influence of Rainfall on the in situ Growth of Dominant Algae Species in Xiangxi River

为明晰蓄水期降雨对三峡库区香溪河支流主要藻种原位生长的影响因素,本文在三峡水库降雨前后采用原位培养装置(培养笼)对铜绿微囊藻、小球藻和栅藻生物量变化特征进行原位培养实验.结果表明:①研究期间(2017年10月4~18日)降雨期与非降雨期水动力条件存在显著性差异(ANOVA,P<0.05),降雨期间3种主要藻种Chl-a总量、比生长速率均显著小于非降雨期(ANOVA,P<0.05),表明降雨对藻类生长起一定的抑制作用;相关分析结果指出,表征垂向掺混的4个水动力参数与3种藻种比生长速率呈显著/极显著负相关关系,表明水动力条件中剪切力τ、垂向紊流黏性系数Vr和垂向紊流扩散系数Vt的改变是导致藻类迅速衰亡的关键因素;②降雨前培养装置内混合层深度较低(1~2 m),降雨后(10月10~18日)混合层深度明显上升(大于5 m),同时降雨期叶绿素a(Chl-a)浓度显著低于非降雨期(ANOVA,P<0.05).相关分析结果表明,光混比与3种藻种的比生长速率呈显著/极显著正相关,表明降雨导致水体垂向扰动增强,混合层不断扩大,打破了水体原有的水温分层从而抑制藻类的生长增殖;③降雨量、水温、光照强度、总氮(TN)和溶解性总氮(DTN)在降雨期与非降雨期均存在显著差异(ANOVA,P<0.05),相关分析表明,降雨带来降雨量、水温、光照强度、总氮(TN)和溶解性总氮(DTN)改变是影响3种主要藻种比生长速率的关键环境参数.

To understand the influence of rainfall on the in situ growth( in a culture cage) of dominant algae species in the Xiangxi River tributary of the Three Gorges Reservoir,culture experiments were carried out to measure the biomass of Microcystis aeruginosa,Chlorella vulgaris,and Chlorella aeruginosa before and after rainfall. The results showed that ① during the study period( October 4-18,2017),there were significant differences in hydrodynamic conditions between the rainfall period and the non-rainfall period( ANOVA,P < 0. 05). Total Chl-a and the specific growth rate of the three main algae during rainfall period were significantly lower than during the non-rainfall period,which inhibited algae growth to some extent. The results of correlation analysis showed that the four hydrodynamic parameters characterizing vertical mixing had a highly significant negative correlation with the specific growth rate of the three dominant algae species. Meanwhile,the changes of shear force τ,the vertical turbulent viscosity coefficient Vr,and the vertical turbulent diffusion coefficient Vtwere the key factors leading to the rapid decline of algae;② the depth of the mixed layer was lower( 1-2 m) before rainfall,but increased(> 5 m) markedly after rainfall( October 10-18). At the same time,the concentration of Chla during the rainfall period was significantly lower than that during the non-rainfall period. The results of the correlation analysis showed that there was a highly significant positive correlation between the ratio of eutrophic depth to mixing depth( Zeu/Zmix) and the specific growth rate of the three dominant algae species. This indicated that the vertical disturbance of water was enhanced by rainfall,and mixing layer expanded continuously,which reduced the water temperature stratification and thus inhibited the growth and proliferation of algae;③ there were significant differences in rainfall,water temperature,light intensity,total nitrogen,and dissolved total nitrogen between the rainfall period and non-rainfall period( ANOVA,P < 0. 05). Correlation analysis showed that changes in rainfall,water temperature,light intensity,total nitrogen,and dissolved total nitrogen caused by rainfall were the key environmental parameters affecting the in situ growth rate of three dominant algae.