DDT对池塘模型生态系统的影响

运用微宇宙实验方法研究了浓度为0.2、2.0、20.0和200.0μg·L-1的DDT对池塘模型生态系统结构和功能的影响.结果表明,整个实验过程(4周)中对照组和浓度为0.2、2.0、20.0和200.0μg·L-1的DDT暴露组水体pH均值分别比实验前下降了0.28、0.19、0.15、0.38和0.37,电导率均值分别下降了6.3%、3.1%、4.7%、6.6%和8.6%;对照组和0.2、2.0、20.0μg·L-1组水体溶解氧(DO值)分别上升了27.3%、28.1%、26.4%和14.4%,而200.0μg·L-1组的DO值下降了7.2%.各组中总磷浓度在实验中后期即下降到较低的水平,总氮的浓度也大幅度下降.和对照组相比,200.0μg·L-1的DDT对大型水生植物优势种类浮萍(Lemna minor)的生长繁殖具有抑制作用,而其它浓度的DDT具有促进作用;DDT对菹草(Potamogeton crispus)的生长影响不明显.DDT可使浮游动物种类减少.2.0μg·L-1的DDT对方形网纹溞(Ceriodaphnia quadrangula)、枝角类和桡足类密度均具有促进作用,20.0和200.0μg·L-1的DDT使轮虫和介形亚纲动物数量在实验后期上升,除此以外,随时间的推移,各浓度的DDT使各类浮游动物密度下降的幅度均大于对照组.与实验前相比,对照组以及浓度为0.2、2.0和20.0μg·L-1的暴露组中凸旋螺(Cyraulus convexiusculus)重量分别增加了12.8%、5.3%、102.2%和219.9%,而200.0μg·L-1组中凸旋螺重量下降了33.8%.随着DDT浓度的升高,微宇宙中的细菌总数总体呈现出下降的趋势.整个实验过程中,对照组的群落总生产量/群落呼吸量(P/R比值)的平均值接近于1,表明生态系统成熟稳定;而各暴露组P/R比值均大于1.1,这可能与DDT对浮游动物具有较强的毒性作用,而对水生植物没有明显影响有关.

Effects of DDT on Model Ecosystems of Ponds

Effects of different concentrations (0.2, 2.0, 20.0 and 200.0μg·L-1 of DDT on structure and function of model ecosystems of ponds (microcosms)were investigated. Results showed that compared with the parameters measured before the experiment was commenced, the average values of pH in the control and the treatments with DDT at 0.2, 2.0, 20.0 and 200.0μg·L -1 decreased by 0.28, 0.19, 0.15, 0.38 and 0.37, and the average values of conductivity decreased by 6.3%,3.1%, 4.7%, 6.6% and 8.6%, respectively. The average concentrations of dissolved oxygen in the control and the treatments with DDT at 0.2, 2.0 and 20.0μg·L -1 increased by 27.3%,28.1%,26.4% and 14.4%,respectively, but that in the treatment with 200.0μg·L-1 decreased by 7.2%. The concentrations of TN in all the treatments decreased to lower levels at the middle and latter periods of the experiment, and those of TP also decreased at larger extents. Compared with the control, DDT at 200μg·L-1 inhibited growth and reproduction of the dominant macrophyte Lemna minor, but the reverse was found for DDT at other concentrations. DDT at all the concentrations did not affect the growth of Potamogeton crispus, but decreased the number of species of zooplankton. DDT at 2.0μg·L -1 increased the densities of Ceriodaphnia quadrangula, cladoceran and copepods, and which at 20.0 and 200.0μg·L-1 increased the densities of rotifers and ostracods at the latter period of the experiment. However, the decline of zooplankton density in the treatments with DDT at the other concentrations was higher than that in the control. Compared with the weight measured before the experiment was commenced, the weight of Cyraulus convexiusculus in the control and the treatments with DDT at 0.2, 2.0 and 20.0μg·L-1 increased by 12.8%,5.3%,102.2% and 219.9%,respectively, but which in the treatment with DDT at 200.0μg·L -1 decreased by 33.8%.With the increase of DDT concentrations, the bacterium density in the microcosms had a decline tendency. During the experiment, the ratio of production/respiration (P/R)of the community in the control was close to 1.0, indicating that the aquatic ecosystem was mature and stable. However, the P/R ratios in all the treatments were bigger than 1.1, which might attribute to the toxic effect of DDT on zooplankton and non-significant effect on aquatic plants.