The Effect Of Sediment Resuspension On Phytoplanktonic Communities

A comparative limnological investigation and an artificial simulated experiment were carried out to analyze the variations of transparency and nutrient levels caused by sediment resuspension and to evaluate the effect of resuspension on phytoplanktonic communities.The intensity of sediment resuspension was weakened by a large-scale enclosure in the demonstration area of water quality restoration in Meiliang Bay, Lake Taihu. The mean increment of water transparency was 41.3% and decrement of TSS concentration was 25.7% inside the enclosure, respectively. The concentration of TN, TDN, TP, TDP, NH₄⁺-N, PO₄^3--P, NO₂^-N and NO₃^-N were declined by 39.8%, 36.1%, 8.3%, 18.2%, 34.2%, 20.0%, 50.0% and 38.1% inside the enclosure, respectively.Biological diversity was higher and phytoplanktonic species were raised by 31.8% inside the enclosure, on average. The mean biomass of phytoplankton was 9.33 mg/L and 7.30 mg/L inside and outside the enclosure, respectively. Microcystis spp, Aulacoseira granulata and Cryptomonas erosa were the dominant species during the period of June to December, 2004。CyclotelIa spp, Anabaena circinalis and Aphanizomenon flos-aquae were the dominant species inside the enclosure and Ulothrix sp was the dominant species in June outside the enclosure, too. The mean biomass of Microcystis spp were 1.87mg/L and 2.70mg/L inside and outside the enclosure and decreased by 30.7% inside the enclosure, on average.The changes of physical and chemical variables and phytoplanktonic communities were studied in an artificial simulated experimental series which comprised of a control group, a weak resuspension group and a strong resuspension group. Water transparency was declined and the concentration of suspended substance was raised and underwater light intensity was weakened when artificial simulated sediment resuspension happened. The nutrients were enhanced and the concentration of TN, TP, PO₄^3--P were raised by 8.5%, 83.5%, 131% and 21.8%, 135%, 409% in the weak and strong resuspension Group, respectively. The growth of phytoplankton was accelerated due to the increment of nutrients caused by the simulated sediment resuspension. The mean biomass of phytoplankton were 11.50mg/L, 28.96mg/L and 20.18mg/L in the control Group, weak and strong resuspension Group, respectively. It was raised by 152% in the weak resuspension group and 75.5% in the strong resuspension group than the control group, respectively.Simulated sediment resuspension changed the succession pattern of phytoplanktonic communities and the composition of dominant species. Phytoplanktonic communities were dominated by Chlorophyta and Cryptophyta at the beginning of the experiment (April 22, 2006) in all of the three groups. The dominate communities of the control group varied to Bacillariophyta and Chlorophyta on May 2; and to Chlorophyta on May 12; and finally changed to Bacilladophyta and Chlorophyta on May 22. The dominant species involved Ulothrix sp, Fragilaria ulna var acus, Cyclotella spp, Cryptomonas erosa, Chlamydomonas sp, Aulacoseira granulata and Asterionella formosa. The predominated communities in the weak resuspension group were shifted to Chlorophyta and Bacillariophyta on May 2; Cryptophyta was abundant on May 12, finally Chlorophyta prevailed on May 22. The dominant species were Ulothrix sp, Cryptomonas erosa, Cyclotella spp, Microcystis spp and Eudorina eIegans. The strong resuspension group experienced a relatively simple variation, Cryptophyta occurred in large numbers on May 7 and became dominant towards the end of the experiment. The dominant species included Ulothrix sp, Microcystis spp, Cryptomonas erosa and Chroomonas acuta.Simulated sediment resuspension accelerated the growth of Microcystis; compared to the control group, the biomass of Microcystis increased by 198% and 300% in the weak and strong resuspension Group, respectively.Our study suggests that sediment resuspension can impose a significant effect on phytoplanktonic communities.