Comparative Analysis Of Ecological Characteristics Between Two Typical Reservoirs For Drinking Water Supply In Zhuhai City, China

Reservoirs supply the main part of drinking water in the South China, specially, in the coastal regions. For example, all of the drinking water in Zhuhai city is provided by 18 reservoirs. To understand the basic features of reservoir ecosystems and provide suitable strategies for water quality management, two typical reservoirs, Dajingshan reservoir and Meixi reservoir, were selected for ecological study. As the two reservoirs were fed by different water sources, there was a significant difference in hydrodynamics and water quality. From last Decemeber, the two reservoirs were sampled every two weeks for water quality and phytoplankton.The pH value was obviously different between the two reservoirs. The water in Dajingshan Reservoir was alkaline and its pH value was over 8, but that of the Meixi Reservoir showed acidity and its pH value was below 7. There was a strongly correlation between pH value and cyanobacteria density in the Dajingshan Reservoir and high pH value may favore growth of cyanobacteria.The concentrations of TN , TP, chlorophyll-a ranged from 0.86 to 2.37 mg/l, 0.04 to 0.07 mg/l, 19 to 50μg/l, respectively, in the Dajingshan Reservoir, and 0.4 to 0.8 mg/1, 0.01 to 0.03 mg/l, 3.4μg/l in the Meixi Reservoir. The chlorophylla concentration in the surface water was much higher than near the bottom in the Dajingshan Reservoir, but the concentration chlorophylla was vertically equal in the Meixi Reservoir.In the Dajingshan Reservoir, 62 species of phytoplankton was found in the collected samples, 14 species in Cyanophyta, 30 species in Chlorophyta, 11 specie in Bacillariophyta, 2 species in Pyrrophyta , 2 species in Chrysophyta and 2 species in Euglenophyta, and 1 species in Cryptophyta. The dominant species in the Dajingshan Reservoir were Pseudarabaena and Synedra ulna and the secondary dominant species were Microcystis marginata , Dactyloccopsis rhaphidioide , Limnothrix , Achnanthes , Cyclotella. The phytoplankton community in the Dajingshan Reservoir was a type of Cyanophyta- Bacillariophyta- Chlorophyta. In the Meixi Reservoir 26 species of phytoplankton were identified, 13 species in Chlorophyta had, 11 species inBacillariophyta, 2 species in Pyrrophyta, 2 species in Chrysophyta and 2 species in Euglenophyta, and 1 species in Cryptophyta. The dominant species in the reservoir were Ceratium hirundinell and Peridinium. The phytoplankton community in the Meixi Reservoir was a type of Pyrrophyta - Bacillariophyta- Chlorophyta. The cell density of phytoplankton was high in the Dajingshan Reservoir, it ranged from 2.86 X 106 to 3.95X 107 cells/1. Cyanophyta accounted for 36%to 81 % in cell abundance. In the Meixi Reservoir the phytoplankton cell density ranged from 3.15 X104 to 26.6 X 104 cells/1, Pyrrophyta accounted for 16.6% to 55.8% in density. In the Dajingshan Reservoir, the phytoplankton biomass was dominated by Cyanophyta and Bacillariophyta. There was a strongly correlation between phytoplankton biomass and Cyanophyta biomass, which indicated that the phytoplankton biomass was contributed mainly by the cyanobacteria. Cyanobaterial biomass is significantly related to total phosphorus concentration, this relation showed the growth of phytoplankton was limited by phosphorus. In the Meixi Reservoir, the phytoplankton biomass was relatively low, it ranged from 0.22 to 1.9mg/l, mainly contributed by Pyrrophyta.In the Dajingshan Reservoir, the Shannon-Weaver index ranged from 1.2 to3.5, the evenness index ranged from 0.313 to 0.9695. In the Meixi Reservoir, the Shannon-Weaver index was similar to that in the Dajingshan reservoir, and the evenness index ranged from 0.779 to 0.887.