不同生长阶段凤眼莲净化不同程度富营养化水体的效果研究

通过模拟实验,比较不同生长阶段凤眼莲对不同程度富营养化水体氮、磷去除效果,研究植株吸收氮、磷能力对去除水体营养盐的贡献,以及对底泥营养盐含量的影响。结果发现随着富营养化水体初始氮浓度增加,不同生长阶段凤眼莲吸收氮量占水体可溶性总氮(TDN)去除量的比例呈现明显下降趋势,但不同生长阶段凤眼莲吸收作用在净化不同浓度氮的效率和贡献方面存在一定差异。在低浓度富营养化水体中,三个生长阶段凤眼莲对水体TDN、TDP去除效果和效率的影响无显著差异。在净化中、高浓度水体氮时(TDN浓度约为7、13 mg·L-1),生长初期凤眼莲对水体TDN在实验前期的净化效率明显高于生长后期,而生长中期净化效率最慢,但在实验中、后期各生长阶段凤眼莲净化速率趋于一致。在中等氮浓度水体中(TDN浓度约为7 mg·L-1),凤眼莲吸收氮量占水体氮损失量百分比为生长后期生长中期生长初期。种植凤眼莲水体中底泥总氮、总磷含量均显著降低;凤眼莲对磷吸收量高出水体可溶性总磷(TDP)损失量,不同生长阶段凤眼莲吸收作用对消减水体磷的贡献无显著差异。综合分析说明生长初期凤眼莲通过主动吸收净化高浓度水体氮的速率最快、贡献最高,而通过凤眼莲根系调节的生物脱氮途径理论上较弱,凤眼莲不仅能够快速去除上覆水体中的磷,而且能够吸收底泥中的磷。

Nutrient Removals from Eutrophic Water by Eichhornia Crassipes at Different Growth Stages

The capability of floating macrophyte, water hyacinth(Eichhornia crassipes), to clean up eutrophic water has been widely recognized, but there is still lack of information on the effect of E. crassipes at different growth stages on nutrient removal from eutrophic water with various concentrations of nitrogen(N) and phosphorous(P). A series of simulated experiments were conducted comparing the efficiency of N and P removals from eutrophic water by E. crassipes at different growth stages. The proportion of N accumulated by E. crassipes to the total dissolved nitrogen(TDN) removal from the water declined as the initial concentrations of N in the water increased. However, E. crassipes at different growth stages showed different efficiencies of TDN removal from the water with the various concentrations of N and P. In water with relatively low concentrations of N and P, the effects of E. crassipes on the removals of TDN and total dissolved phosphorous(TDP) were not significantly different among the different growth stages; whereas in water with relatively high concentrations of N(TDN ~7 mg·L^-1 or ~13 mg·L^-1), the efficiency of TDN removal from the water at the initial phase of the experiments was significantly higher at the early stage of plant growth than the middle and late growth stages, but became closer among the different growth stages as the experiments progressed. In water with TDN levels of ~7 mg·L^-1, the proportion of plant N accumulation to N removals from water was in order of the late growth stageE. crassipes significantly reduced the contents of N and P in sediments. The amount of P assimilated by E. crassipes exceeded the amount of P removed from the water. The contribution of plant assimilation to the removals of TDP was not significantly different among the different stages of plant growth. These results showed that nitrogen assimilation by E. crassipes at the early growth stage contributed greatly to N removals from water; while N removal via the root biological processes was small, and E. crassipes not only removed P from the water, but also assimilated P released from the sediments.