Vertical distribution of phytoplankton and physico-chemical characteristics in the lacustrine zone of Xin'anjiang Reservoir(Lake Qiandao) in subtropic China during summer stratification

Abstract

The investigation on vertical distribution of phytoplankton and physical-chemical characteristics was conducted in the lacustrine zone during summer stratification in Xin'anjiang Reservoir(Lake Qiandao).The Water-PAM Chlorophyll Fluorometer was used to obtain vertical profiles of phytoplankton photosynthesis.The results showed that depth of thermocline appeared between 10-20m.Besides,the vertical profiles of pH,dissolved oxygen and turbidity were in agreement with chlorophyll-a.In summer,the phytoplankton was dominated by Bacillariophyta,C.meneghiniana was dominant in surface layer,while F.crotonensis was absolutely dominant below the surface layer.High-density of phytoplankton was found around 5-10m below the water surface.However,a sharp decline was observed for phytoplankton density below thermocline layer.Therefore,the thermal stratification might affect the vertical distribution of phytoplankton population.Phytoplankton maximum photosynthetic efficiency had a negative relationship with water depth and the actual maximum value of photosynthetic efficiency was determined at 10m depth.