【作者】 念宇；

【导师】 杨再福；

【作者基本信息】 东华大学 ， 环境科学， 2010， 硕士

【摘要】 在现状调查的基础上,探讨了淡水生态系统（包括水质、淡水藻类、河湖岸带、水生动植物、沉积物等因子）的退化现状、退化原因与机制,建立了退化评价标准体系和方法,评估淡水生态系统退化水平。通过建立水生态AQUATOX模型,定量化模拟预测了淡水生态系统的退化演变和生态恢复方案的效果。研究结果表明,目前退化淡水生态系统水质均已退化至地表水Ⅳ—Ⅴ级质量水平,浮游藻类结构简单,以蓝—绿藻结构为主,且多为富营养化指示种类,藻类多样性指数低。着生藻类主要以硅藻群落为主,藻类细胞小型化趋势严重,优势种多为耐污种,大型丝状绿藻仅出现在春季。河（湖）岸带宽度狭窄,水生植被以挺水植物和浮叶植物为主,沉水植物多为高冠型种类且有退化演替趋势;水泥垂直陡岸带隔离水陆生态系统,大量植物残枝和淤泥在枯水期淤积河岸,造成裸露环境,沉积物厚度加深,为有机质丰富淤泥型,底栖动物种类稀少单一,且分布不均。通过参照体系法建立了淡水生态系统退化评价指标体系,利用主成分析法筛选出了BOD₅、CODcr、DO、NH₃-N、C_P、TP、DDA、B-IBI、F-IBI、HQI等10个指标,作为淡水生态系统退化程度指示指标。按照理论参照标准将淡水生态系统退化程度分为5个等级:微退化、轻度退化、中度退化、强度退化、极度退化。灰色关联度法综合评价得出张家浜河生态系统退化水平为轻度—中度退化等级,镜月湖生态系统退化等级为轻度退化,部分区域为强度退化。通过建立张家浜河AQUATOX生态模型,模拟和预测该河流5年后生态演替趋势,结果表明,在无外来干扰的情况下,张家浜河生态环境因子演替会年复一年按照各自的生长变化规律进行,呈现出重复演替规律。通过对可能引起生态系统退化的营养盐负荷、有机污染负荷、沉水植物量、沉积物碎屑输入量等条件设置不同干扰,模拟其对淡水生态演替可能产生的后果。结果表明,水体有机污染负荷BOD₅增加10倍,可以导致水生态系统的全面退化;而分别增加氮磷面源和污染负荷的10倍,则会引起水质和藻类不同程度的退化;沉水植物生物量的降低可使着生藻类生物量全面提高;沉积物碎屑输入量增加5倍,不但可造成水质变差,还可引起大型底栖动物生物量的下降。基于AQUATOX模拟不同生态恢复方案的作用效果,结果表明除了控制有机污染源以外,恢复河岸带生态环境,改建自然河道,能够降低水体总磷含量40%左右,有效恢复沉水水生植生物量20%以上,对营养盐降低和底栖动物多样性恢复均有明显作用;通过分别控制氮磷污染负荷50%的模拟研究,发现水质变化不大,沉水植物和底栖动物生物量均有升高,控制磷比控制氮更能有效防止蓝藻水华发生;控制沉积物全部外源负荷,能够大量削减水体营养盐含量,改善水质状况,有益于大型沉水植物生长,减少蓝藻生物量,但是对于底栖动物生长不利。因此对于淡水生态系统的恢复研究,必须结合水文条件改善,营养盐负荷削减和控制沉积物碎屑负荷等三方面共同考虑,从不同层次上考虑整个生态系统的恢复。本文研究了淡水生态系统退化的现状和原因、退化生态系统定量化评价方法,退化过程与机理以及恢复与重建的理论方案,对于保护淡水生态环境,促进人类与自然环境可持续发展具有重要的意义。更多还原

【Abstract】 Based on the investigation research of the status quo, analysis and evaluation on the present situation, the causes and the mechanisms of the degradation in the freshwater ecosystems were studied including factors like water quality, freshwater algae factor, river shore zone factor, aquatic plant and animal factor and sediment factor. Degradation evaluation criteria systems and methods were established to assess the level of degradation in the freshwater ecosystems. Through aquatic ecological AQUATOX modeling, the degradation and evolution of the freshwater ecosystems were quantitatively simulated and predicted and the effect of its restoration measures.The simulation results showed that the current degradation level is high. The water quality of the ecosystems has degraded toⅣ～Ⅴclass quality level; phytoplankton algae had a simple, blue-green algae（many of which are instructions for the eutrophication） dominated structure and the algae diversity index is also at a low level. The periphyton algae is mainly diatom community-based and the algae cell miniaturization become a serious problem of which the dominant species are mostly large filamentous algae with Fog kinds that appears only in spring. The River shore has a narrow width as well as the lake. The aquatic vegetation is dominated by floating-leaved and Ting plants, while the submerged plant is dominated by the topped species which shows degradation and succession trend. The vertically steeping cement isolated the water ecosystem from the land coast causing a large number of broken branches and mud siltation near river bank during its dry season resulting in their exposure to environment.The sediment thickness deepens and is of organic matter-rich mud type. The zoobenthos species is rarely single and unevenly distributed.According to the reference system, the degradation evaluation index system of freshwater was established by using principal component analysis and 10 main indicators were extracted and screened out as the direction indicators of degradation level including BOD₅, COD_cr, DO, NH₃-N, CP, TP, DDA, B-IBI, F-IBI, HQI. The degradation of freshwater ecosystems has five levels: micro-degradation, light degradation, moderate degradation, strong degradation, extreme degradation in accordance with the references from the theory. After comprehensive evaluation using gray correlation degree method, results was obtained that the ecosystem degradation level in Zhangjiabang River ranges from light to moderate. The degradation level in Mirror Lake ecosystem is mainly mild but in some part it is strong.Through the AQUATOX ecological modeling of Zhangjiabang River, the 5-year-trend of ecological succession was simulated and predicted. The results showed that in the absence of external interference, the succession of eco-environmental factors of Zhangjiabang River will be in a cycle repeated pattern which can be explained by succession law in accordance with the changes of the environment periodic growth. The external interference factors includes nutrient load, organic pollution load, the amount of submerged vegetation, sediment detritus input, which may cause degradation. By changing these factors, the possible consequences of ecological succession were simulated. The results showed that the BOD5 would increased by 10 times, which may lead to overall degradation of aquatic ecosystems; the non-point source nitrogen and phosphorus may also 10 times, which can cause varying degrees of degradation to the water quality and algal. The reduction of submerged plant biotechnology can increase the amount of algal biomass. The clastic sediment input increase by five-fold, not only can cause water quality deterioration, but also a large decline in benthic biomass.Based on AQUATOX, the effects of different ecological restoration methods were simulated. The results show that the organic input control, riparian environment restoration and alteration of natural river can reduce the TP by 40% and restore aquatic plant biomass by 20% which can have significant effect on nutrient reduction and zoobenthos diversity recovery. Through the respective control of nitrogen and phosphorus pollution Ioad（50% off）, the simulation study found that little changes occurred in water quality, meanwhile the biomass of submerged plants and zoobenthos increased. It is more effective to control nitrogen to prevent algal blooms than to control phosphorus. The control of all the exogenous sediment load can lead to a substantial reduction of water nutrient thus to improve water quality. This method is conducive while promote the large-scale submerged plant growth and reduce blue-green algae biomass, but it cannot help the growth of the zoobenthos. Therefore, the restoration of freshwater ecosystems research must take into account the followings combined: hydrological conditions improvement, nutrients load reduction and sediment control. They should be considered together from different levels in the whole ecosystem recovery process.The current status of the degradated freshwater ecosystem and its cause, process and mechanism, its quantitative evaluation method and its rehabilitation & reconstruction theory method were studied in this paper so as to protect the freshwater ecological environment and promote the sustainable development of human beings and the natural environment.更多还原