To explore the effects of sedimentation plants on water quality in different water environments,the decomposition processes of Vallisneria natans were respectively investigated in the manipulated environment of high pure water,overlying water and sediment suspension under laboratory conditions.Moreover,the differences of N and P content between sediment and overlying water environment were discussed.The results showed that,during the decomposition process of V.natans,the pH of the overlying water and sediment decreased first then increased,and the DO concentration was simultaneously sharply down.In the overlying water enviromnent,the pH increased to 8.7 after decreasing from 7.8 to 7.2 with about 56％ reduction of DO concentration in the 10th day compared with the beginning of the experiment.The pH of the sediment suspension decreased from 7.8 to 7.3 and then rose to 8.3 with a decrease of 60％ of DO concentration in the 10th day.In the overlying water and sediment suspension,the nitrogen in the process of the decomposing of V.natans was mainly organic nitrogen,followed by ammonia nitrogen.The concentration of total phosphorus (TP) showed a trend of an initial increase followed by a decrease in the early stage of the experiment;nevertheless,the TP concentration showed a dynamic balance in the middle stage of the experiment,around 1 mg/L in the sediment suspension.In addition,variation of the biomass density of 0.1,0.2 and 0.4 g/L resulted in a change of nutrient content.The concentrations of CODcr and TP were positively correlated with biomass,while the concentrations of TN and NO2--N increased along with the peak value in the early stage of the experiment.The results showed that decomposition of V.natans had a similar effect on the physicochemical properties of the two kinds of water environment,and there was a significant difference in the forms of nitrogen and phosphorus.%为探究沉水植物在不同水环境下的腐解对水质的影响,在实验室条件下分别模拟不同生物量沉水植物苦草在高纯水、上覆水及底泥悬浮液环境下的腐解过程及其对水体水质的影响,并分别讨论了N、P等含量在底泥和上覆水环境下的差异性.结果表明:①随着时间的推移,苦草腐解均会导致上覆水及底泥悬浮液中pH先降后升,ρ(DO)急剧降低,在上覆水环境中,pH自7.8降至7.2,再增至8.7;与试验初期相比,ρ(DO)在第10天降低了56％.在底泥悬浮液中,pH自7.8降至7.3,再增至8.3;在第10天ρ(DO)降低了近60％.②在上覆水及底泥悬浮液中,苦草腐解以释放有机氮为主,NH3-N次之;ρ(TP)在试验前期呈先升后降趋势,但在试验中期底泥悬浮液环境中ρ(TP)则呈动态平衡,约为1 mg/L.③不同生物量(0.1、0.2、0.4 g/L)的苦草腐解后水环境中的营养盐含量有所不同,其中ρ(CODCr)、ρ(TP)与生物量呈正相关,在试验前期ρ(TN)、ρ(NO2--N)随着峰值的增大而增大.研究显示,苦草腐解对两种水环境的物化性质有着相似的影响,而对其主要营养盐氮、磷形态的变化有着显著性的差异.
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