【作者】 白雪；

【导师】 朱琳；

【作者基本信息】 南开大学 ， 环境科学， 2022， 博士

【摘要】 氮(N)和磷(P)是合成用于细胞分裂和生长的核酸等物质的必要元素,但人类活动改变了淡水生态系统中N和P的含量,导致严重的富营养化,这是水生态系统最常见也是最大的威胁之一,预计在未来几十年由于人口增长以及对粮食生产和能源生产的更大需求,N和P含量还会继续增加。浮游植物是水环境的重要初级生产者,在营养元素生物地球化学循环和食物网结构中起着重要作用。浮游动物一方面通过捕食作用消耗浮游植物,另一方面又能为更高营养级生物提供食物来源,是微生物食物环与经典食物链能量传递过程中的重要枢纽。因此,阐明营养盐对浮游生物群落的影响对理解营养盐在整个水生态系统的生态效应至关重要。为提高生态现实性,其环境效应的评价应基于群落乃至生态系统水平。本研究以总氮(TN)和总磷(TP)为主要研究对象,结合水生态微宇宙技术评估了实际环境浓度范围内TN和TP的生态效应,以期为营养盐的环境管理提供科学依据。在本论文的第一部分中,我们利用人工微宇宙技术以《地表水环境质量标准》(GB3838-2002)为浓度设置依据,在包含复杂营养级联关系的体系内分析了环境浓度下TN和TP对浮游生物群落结构和功能的影响,并确定了淡水生态系统中的TN和TP阈值。获得的主要研究结果如下:(1)对于TN阈值分析,与对照相比,多数群落结构参数在TN≥1.0 mg/L处理组中发生显著变化(p≤0.05)。TN的潜在危害表现为浮游植物丰度的显著增加(p≤0.05),绿藻是受TN促进作用最明显的类群,小型绿藻优势种丰度的增加降低了浮游植物群落多样性,促进了浮游动物向小型化物种发展,即小型轮虫和无节幼体(copepod nauplius)丰度的增加。但浮游动物难以控制浮游植物的持续增长。主响应曲线(Principal Response Curve,PRC)分析结果表明,TN对浮游生物群落物种组成影响显著(p≤0.05)。在群落功能终点方面,浮游植物的光合活性对TN的响应并不敏感(p>0.05)。临界指示物种分析法(Threshold Indicator Taxa ANalysis,TITAN)表明,TN的负响应阈值为0.9 mg/L,正响应阈值为1.0 mg/L。(2)对于TP阈值分析,与对照相比,TP≥0.10 mg/L处理组的浮游生物群落结构和功能发生了显著变化(p≤0.05)。在群落结构方面,TP的潜在危害表现为促进蓝藻的持续增长。受浮游植物群落内部的种间竞争作用和浮游动物的捕食作用调控,绿藻和硅藻的丰度降低。TP通过浮游植物间接影响浮游动物群落,枝角类的丰度从42 d开始显著升高(p≤0.05)。TP持续抑制浮游生物群落多样性。PRC分析结果表明,TP对浮游生物群落物种组成影响显著(p≤0.05)。在群落功能终点方面,当TP浓度达到0.40 mg/L时,叶绿素荧光参数受到显著抑制(p≤0.05),浮游植物光合活性下降。TITAN分析表明,TP的负响应阈值为0.07 mg/L,正响应阈值为0.10 mg/L。本论文在第二部分对比分析了不同镉(Cd)污染条件下营养盐(TN+TP)对浮游生物群落结构和功能的影响,并阐明营养盐如何改变Cd在浮游生物食物链上的传递。主要结果表明:无论是在低Cd还是在高Cd条件下,营养盐都显著改变了浮游生物的群落物种组成(p≤0.05)。在低Cd条件下,营养盐促进了蓝藻和绿藻的生长,降低了群落多样性降低。这些效应传递给浮游动物群落,导致群落物种组成向小型化发展。群落结构的改变传递到群落功能,表现为微宇宙中可溶性有机碳(DOC)和pH增加。而在高Cd条件下,营养盐对几乎所有优势种都没有持续一致的效应。浮游动物物种组成受营养盐间接影响仍表现出小型化趋势。受Cd毒性影响,营养盐对浮游生物丰度和功能表现出轻微的抑制作用。叶绿素荧光参数总体来说对营养盐的响应并不敏感,更适合作为重金属毒性效应的长期评价指标。此外,高Cd污染下浮游生物表现出富集或潜在的富集效应,营养盐加剧了Cd沿食物链的生物放大效应。在此基础上,我们尝试构建了浮游植物-浮游动物-鱼微宇宙体系,评价了不同Cd污染下营养盐的生态效应。结果发现:在低Cd条件下,营养盐促进了浮游生物的生长。在物种水平,浮游动物物种向小型化发展。DOC和pH因浮游植物生物量的增加而升高,可作为评价营养盐长期生态效应的功能指标。高Cd情况下,与第二部分研究结果不同的是,营养盐在暴露后期(21-28 d)表现出了对浮游植物生物量的促进作用。杂食性鱼类对浮游动物群落的调控作用明显,具体表现为通过对枝角类和桡足类的捕食间接提高了轮虫在群落中的竞争优势,轮虫占比超过了90%。此外,无论低Cd还是高Cd情况下,营养盐均加剧了Cd沿浮游植物-浮游动物食物链的传递,但由于鱼的生物富集系数(BCF)低,Cd沿浮游动物-鱼的传递过程中不存在生物放大现象。更多还原

【Abstract】 Nitrogen(N)and phosphorus(P)are essential elements for the synthesis of nucleic acids and other substances used for cell division and growth.However,human activities have changed the contents of N and P in the freshwater ecosystems,leading to serious eutrophication,which is one of the most common and greatest threats to aquatic ecosystems.It is predicted that the content of N and P will continue to increase in the coming decades due to population growth,further development and greater demand for food production and energy production.Phytoplankton is an important primary producer of water environment and plays a key role in the biogeochemical cycle and the structure of food webs.Zooplankton can consume phytoplankton through predation and can provide food sources for higher trophic organisms.It is in a key position in the energy transfer process of microbial loop and classical food chain.Therefore,it is very important to clarify the effects of nutrients on plankton communities to understand the ecological effects of nutrients in the whole aquatic ecosystem.In order to improve the ecological reality,the evaluation of the environmental effects of N and P should be at community and ecosystem level.To sum up,we chose total nitrogen(TN)and total phosphorus(TP)as the main research objects.We used the freshwater microcosm technology to evaluate the ecological effects of TN and TP under environmental concentrations.We hope that this study can provide a scientific basis for the environmental management of TN and TP.In the first part of this paper,the effects of TN and TP under environmental concentrations on the structure and function of plankton community were analyzed through microcosm experiment containing complex trophic cascades.The test concentrations were based on the Chinese National Environmental Standard for Surface Water Quality GB3838-2002,and the thresholds of TN and TP in freshwater ecosystems were determined.The main results are as follows:(1)For TN threshold analysis,compared with the control,most community structure parameters changed significantly in the TN ≥ 1.0 mg/L groups(p ≤ 0.05).The potential harm of TN was the obvious increase of phytoplankton abundance(p ≤ 0.05).The abundances of Chlorophyta responded to nutrients most positively.The increase of the abundance of small-sized green algae resulted in the reduce of phytoplankton community diversity and promoted the development of zooplankton to miniaturized species,that was,the increase of the abundances of small rotifers and copepod nauplius.However,it was difficult for zooplankton to control the continuous growth of phytoplankton.The analysis results of Principal Response Curve(PRC)showed that TN had significant impacts on the species composition of plankton communities(p ≤ 0.05).In terms of community functional endpoints,the photosynthetic activity of phytoplankton was not sensitive to TN concentration(p > 0.05).Threshold Indicator Taxa ANalysis(TITAN)showed that the negative response threshold of TN was 0.9 mg/L and the positive response threshold of TN was 1.0 mg/L.(2)For TP threshold analysis,compared with the control,the plankton community structure and function in TP ≥0.10 mg/L groups had changed significantly(p ≤ 0.05).In terms of community structure,the potential harm of TP was its promotion effects on cyanobacteria.Due to the predation of zooplankton and interspecific competition of phytoplankton,the abundances of green algae and diatoms decreased.TP indirectly affected the zooplankton community through phytoplankton.The abundance of Cladocera increased significantly from 42 d(p ≤ 0.05).TP inhibited the plankton community diversity consistently.The results of PRC analysis showed that TP significantly affected the community composition of plankton(p ≤ 0.05).In terms of community functional endpoints,the addition of TP led to the decline of phytoplankton photosynthesis.When TP concentration reached 0.40 mg/L,chlorophyll fluorescence parameters were significantly inhibited(p ≤ 0.05).TITAN analysis showed that the negative response threshold of TP was 0.07 mg/L and the positive response threshold of TP was 0.10 mg/L.In the second part of this paper,the effects of nutrients(TN+TP)on the structure and function of plankton communities under different cadmium(Cd)pollution conditions were compared and analyzed.We also clarified the effects of nutrients on the transmission of Cd in the plankton food chain.The main results showed that nutrients significantly changed the community composition of plankton under both low and high Cd conditions(p ≤ 0.05).Under low Cd condition,nutrients promoted the abundances of cyanobacteria and green algae and declined the community diversity.These effects were transmitted to the zooplankton community,resulting in the development of community species composition towards miniaturization.The changes of community structure were transmitted to the community function,which were manifested by the increases of dissolved organic carbon(DOC)and pH in the microcosms.However,under the condition of high Cd,nutrients had no consistent effect on almost all dominant species.The species composition of zooplankton still showed a trend of miniaturization under the indirect influence of nutrients.Due to the toxicity of Cd,nutrients had a slight inhibitory effect on plankton abundance and function.Chlorophyll fluorescence parameters were generally insensitive to nutrients,and were more suitable for long-term evaluation of heavy metal.Our study also found that under high Cd pollution,phytoplankton and zooplankton showed bioconcentration effect or potential bioconcentration effect.The addition of nutrients intensified the biomagnification effect of Cd along the food chain.Furthermore,we tried to build the freshwater microcosm contained phytoplankton-zooplankton-fish,and evaluated the ecological effects of nutrients under different Cd pollution.The results showed that under low Cd condition,nutrients promoted the development of plankton.At the species level,the zooplankton species had been miniaturized.The DOC and pH increased with the development of phytoplankton biomass.The above indicators can be used to characterize the long-term responses of community function to nutrients.Under the high Cd condition,different from the results obtained from the second part,the nutrients showed a promoting effect on the biomass of phytoplankton from day 21 to 28.The omnivorous fish had obvious regulatory effect on the zooplankton community,which was manifested by the indirect improvement of the competitive advantage of rotifers in the community through the predation on cladocerans and copepods.The proportion of rotifers in community was more than 90%.In addition,in both low and high Cd condition,nutrients exacerbated the transfer of Cd along the phytoplankton-zooplankton food chain.However,due to the low bioconcentration factor(BCF)of fish,there was no biomagnification effect along the zooplankton-fish food chain.更多还原