Effects Of Plant Floating Beds On Water Quality And Phyplankton Community Structure In Intensive Culture Ponds

Water quality and phyplankton community structure of intensive culture ponds in an experimental area in Yaowan Town, Jingzhou, Hubei Province were investigated during the period of May to October 2009. The regulating effects of planted floating beds on water quality and their impacts on algae balance in culture ponds were analyzed. In addition, the feasibility of optimization of phytoplankton community strucuture and control of cyanobacterial biomass via floating beds were discussed. The main results were as follows:1. The effects of planted floating beds on water quality were explored. After buliding floating beds in ponds, The floating beds obviously induced phosphorus, nitrogen, improved water transparency (SD), kept pH value gently fluctuate and made dissolved oxygen (DO) stay at about 3.42mg/L, while had less or weak impact on electrical conductivity (EC) and temperature (T) in the culture ponds. A descending trend for total phosphorus (TP), orthophosphate (PO43-P), total nitrogen (TN), chlorophyll a (Chla) and chemical oxygen demand (CODMn) was found with the increasing plant coverage rate of the floating beds, while an opposite trend for ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and nitrite nitrogen (NO2--N).2. The dynamics of phytoplankton community structure in culture ponds were studied. During the period of the investigation, a total of 142 genera/species of phytoplankton belonging to 7 phyla were identified. In detail, they were as follows: 67 genera/species of Chlorophyta,32 Cyanophyta,19 Euglenophyta,18 Bacillariophyta,3 Pyrrophyta,2 Cryptophyta and 1 Xanthophyta. In culture ponds with planted floating beds (Hereafter abbreviated as floating-bed pond), water color was light green, tan or cyan, etc. implying these ponds were in good conditions; simultaneously, phytoplankton community was mainly composed of Chlorophyta and Bacillariophyta, among which the dominant species were Chlorococcum, Scenedesmus, Pediastrum, Cyclotella, Nitzschia, Synedra, Melosira and dinoflagellate. All these species displayed obvious seasonal succession and the species composition was also in a dynamic state. There was no obvious difference in algal composition between the control and floating-bed ponds in the early experimental stage(May), whereas significant distinctions appeared during the medium and later stages (June-September) in the control pond. The water color of the control pond was maintaining blue or cyan over a long period of time and the algal composition was predominated by Cyanophyta, among which the dominant species were Microcystis, Oscillatoria, Anabaena and Phormidium. The Shannon-Wiener and Pielou evenness index of phytoplankton of the control pond were both lower than those of the floating-bed ponds.3. The phytoplankton density of the floating-bed ponds ranged from 55.4×106 to 201.2×106 ind./L and the biomass ranged from 12.8 to 65.9 mg/L. Correspondingly, the phytoplankton density of the control pond ranged from 73.0×106 to 250.0×106 ind./L and the biomass ranged from 16.6 to 126.8 mg/L, Statistical analysis showed that there were significant (p<0.05) differences in algal biomass between the control and floating-bed ponds. Phytoplankton density or biomass did not differ among the floating-bed ponds, but they decreased with the increasing plant coverage rate with the minimum abundance occurred at a rate of of 15%. Moreover, there were significant differences (p<0.05) in cyanobacterial density and biomass between the control and floating-bed ponds. The abundance of cyanobacteria fluctuated heavily in the control pond and accounted for a large fraction of total phytopkankton abundance. The highest proportion was even up to 63.5%, which was much higher than that of the floating-bed ponds (Mean less than 25.0%). Hereby, conclusions could be reached that, through the construction of floating beds in culture ponds, water quality could be effectively regulated, phytoplankton community structure optimized, cyanobateria reproduction controlled, and algal biodiversity and uniformity increased. All these resulted in a proper maintenance of algae balance in culture ponds and benefited pond aquaculture.