Xuanwu Lake Research Articles

Spatial distribution of bacterial communities in sediment of a eutrophic lake revealed by denaturing gradient gel electrophoresis and multivariate analysis

Bacterial community structure and the effects of several environmental factors on the microbial community distribution were investigated in the sediment of the eutrophic Lake Xuanwu. Profiles of bacterial communities were generated using denaturing gradient gel electrophoresis (DGGE), and the results were interpreted with multivariate statistical analysis. Five major variables in sediment were examined in a principal component analysis, which indicates notable differences of physicochemical parameters among different sites of the lake. To assess changes in the genetic diversity of bacterial communities of different sampling sites, DGGE band patterns were analyzed by multidimensional scaling analysis, which indicated that sampling sites having similar environmental characteristics also have the similar microbial communities. Canonical correspondence analysis demonstrated that pH and redox potential had significant effects on the bacterial community composition in the sediments. Analysis of DNA sequences revealed that the dominant bacterial groups in Lake Xuanwu belonged to Proteobacteria, Actinobacteria, Verrucomicrobia, and Nitrospirae, which are commonly isolated from freshwater ecosystems.

Vertical distribution of bacterial community structure in the sediments of two eutrophic lakes revealed by denaturing gradient gel electrophoresis (DGGE) and multivariate analysis techniques

Vertical distribution of bacterial community structure was investigated in the sediments of two eutrophic lakes of China, Lake Taihu and Lake Xuanwu. Profiles of bacterial communities were generated using a molecular fingerprinting technique, denaturing gradient gel electrophoresis (DGGE) followed by DNA sequence analysis, and the results were interpreted with multivariate statistical analysis. To assess changes in the genetic diversity of bacterial communities with changing depth, DGGE banding patterns were analysed by cluster analysis. Distinct clusters were recognized in different sampling stations of Lake Taihu. Canonical correspondence analysis (CCA) was carried out to infer the relationship between environmental variables and bacterial community structure. DGGE samples collected at the same sampling site clustered together in both lakes. Total phosphorus, organic matter and pH were considered to be the key factors driving the changes in bacterial community composition.

Study on vertical distribution and activity factor of P forms in sediments of three urban shallow lakes in People’s Republic of China

The vertical variation of P forms in sediments of urban shallow lakes in China, Xuanwu Lake, Daming Lake and Mochou Lake, were sequentially extracted and measured with the method of SEDEX. The results indicated the TP content in the sediment profiles ranged from 371.94 to 777.25 mg kg−1 for Xuanwu Lake, 1,308.14 to 4,632.63 mg kg−1 for Daming Lake, and 995.49 to 1,860.71 mg kg−1 for Mochou Lake. The results of sequential extraction showed that Ca-P and Fe-P were the main fractions. Meanwhile, the proportions of Bio-P to TP were 35.24% for Xuanwu Lake, 29.57% Daming lake, and 25.26%, for Mochou Lake, indicating a high potential of P releasing. The content of Bio-P was significantly and positively correlated with TP (r = 0.978, P < 0.01). Lake hydrations conditions played an important role in the distribution and contents of Bio-P and TP. In the region with macrophytes, the contents of TP and Bio-P were relatively low. Physicochemical properties of sediments were significantly related to the fraction distribution and P contents, and might play an important role in controlling P activity and mobility. Moreover, Fe showed an evident influence on P fraction and the ratio Fe/P might be good indicator to the contents and composition of active P in sediments.

The Effect of a Microcystis aeruginosa Bloom on the Bacterioplankton Community Composition of Lake Xuanwa

ABSTRACT To understand the influence of a Microcystis aeruginosa bloom on the bacterioplankton community composition in Lake Xuanwu, water samples were collected during the outbreak and decline of the bloom. Traditional microbial methods and denaturing gradient gel electrophoresis were used to characterize the bacterioplankton community. During the outbreak of bloom, the proportions of firmicutes, bacteroidetes, and α-, β-, and γ-proteobacteria were respectively 31.3%, 25.0%, 18. 8%, 12.5%, and 12.5% of the total bacteria. At the decline of the bloom, the total abundance of bacterioplankton increased, and the proportion of γ- proteobacteria increased to 50%. Pseudomonas and Bacillus were always the principal genera but with changing species. Sixteen genera of bacteria were predominant in the community during the outbreak of bloom, but some species of Hydrogenophaga, Vogesella, Sphingomonas, and Exiguobacterium disappeared at the decline of the bloom, and only six predominant genera remained.

Microbial diversity in lake sediments detected by PCR-DGGE

In this study, PCR-denaturing gradient gel electrophoresis (DGGE) was applied to analyze the microbial communities in lake sediments from Lake Xuanwu, Lake Mochou in Nanjing and Lake Taihu in Wuxi. Sediment samples from seven locations in three lakes were collected and their genomic DNAs were extracted. The DNA yields of the sediments of Lake Xuanwu and Lake Mochou were high (10 μg/g), while that of sediments in Lake Taihu was relatively low. After DNA purification, the 16S rDNA genes (V3 to V5 region) were amplified and the amplified DNA fragments were separated by parallel DGGE. The DGGE profiles showed that there were five common bands in all the lake sediment samples indicating that there were similarities among the populations of microorganisms in all the lake sediments. The DGGE profiles of Lake Xuanwu and Lake Mochou were similar and about 20 types of microorganisms were identified in the sediment samples of both lakes. These results suggest that the sediment samples of these two city lakes (Xuanwu, Mochou) have similar microbial communities. However, the DGGE profiles of sediment samples in Lake Taihu were significantly different from these two lakes. Furthermore, the DGGE profiles of sediment samples in different locations in Lake Taihu were also different, suggesting that the microbial communities in Lake Taihu are more diversified than those in Lake Xuanwu and Lake Mochou. The differences in microbial diversity may be caused by the different environmental conditions, such as redox potential, pH, and the concentrations of organic matters. Seven major bands of 16S rDNA genes fragments from the DGGE profiles of sediment samples were further re-amplified and sequenced. The results of sequencing analysis indicate that five sequences shared 99%–100% homology with known sequences (Bacillus and Brevibacillus, uncultured bacteria), while the other two sequences shared 93%–96% homology with known sequences (Acinetobacter, and Bacillus). The study shows that the PCR-DGGE technique combined with sequence analysis is a feasible and efficient method for the determination of microbial communities in sediment samples.

Assessing indicators for water diversion based on improving water quality of shallow lakes

Based on the goal of water diversion for shallow lakes, taking the requirement of ecological hydraulics and economic factor into consideration, an attempt to establish an assessing indicator system for water diversion scheme of shallow lakes is put forward in this paper. The indicators are consisted of lake quality-improving indicators, hydraulic indicators and economic indicator. By the case of Lake Xuanwu, a 2-D water-quality model is adopted to simulate different schemes of water diversion for Lake Xuanwu with different flow flux, diversion mode, flow distribution of inlets, and flow distribution of outlets. Detailed assessing indicators of statistic results are obtained, and then the optimum water diversion scheme is assessed. The method can be applied to the assessment of water diversion on similar shallow lakes.

Improved AHP method and its application in lake environmental comprehensive quality evaluation—a case study of Xuanwu Lake, Nanjing, China

The relative importance of each pollution factor in analytical hierarchy process (AHP) method comes from pooling expert opinions in general. Because expert opinions are based on information and judgment criteria, determining their weight may lead to uncertainty.. Therefore, an improved AHP method had been developed. The process of the improved AHP method involved four key procedures. The weights of pollution factors were completely related to the objective monitoring data through the standardization of these procedures. The environmental comprehensive quality of water and sediment of Xuanwu Lake, Nanjing, China had been evaluated. The environmental quality comprehensive indices (EQCI) of the water in 1991-1995 and 1996-2000 were 3.32 and 1.85, respectively, indicating that the water quality improved. The EQCI of the sediment in 1995 and 2000 indicates that the sediment contamination decreased from 1995 to 2000. Such results agreed with the fact that the lake had been under comprehensive control. However, with the classical AHP method, the EQCI of the sediment in the northwestern part of the lake may have indicated that sediment contamination increased from 1995 to 2000. The discrepancy may have resulted from the judgment difference of the experts. The improved AHP method can avoid arbitrariness of subjective judgment and can reflect the real influential factors of environment pollution in different periods or regions.

In situ study on the photochemical vitality of overwintering phytoplankton

水体中浮游植物在越冬期间数量少，关于湖泊中越冬浮游植物如蓝藻、绿藻、硅藻等浮游植物的光合作用活性情况少见报道．本实验通过Phyto-PAM(Pulse Amplitude Modulation)对最大光量子产量F_v/F_m(可变荧光和最大荧光之比)和快速光曲线的测定，结合显微镜镜检结果，并在室内进行了硫酸铜处理以及鲁哥氏液处理实验，对太湖、巢湖和玄武湖处于越冬期间的浮游植物进行了原位光合作用活性的研究．显微镜镜检结果表明太湖和玄武湖水体中以绿藻和硅藻为主，而蓝藻很少，巢湖水体中有大量蓝藻、绿藻和硅藻，Phyto-PAM在对玄武湖和太湖水样原位测定时未检测出蓝藻，而绿藻和硅藻有光合作用活性，其F_v/F_m在0．5左右；对巢湖的水体检测到的蓝藻、绿藻、硅藻都具有光合作用活性，其中绿藻和硅藻的F_v/F_m在0 5左右．蓝藻的n／Fm在0．3左右:用硫酸铜处理实验在巢湖水样中发现水体仅有硅藻活性(F_v/F_m下降至0．2左右)，而用鲁哥氏液处理后无任何藻类光合作用活性，上述实验结果表明，即使处于越冬期间，以较多数量出观在水体中的蓝藻、绿藻和硅藻仍然具有较高的光合作用活性．;Photochemical vitality of overwintering phytoplankton including cyanobacteria chlorophyta and bacillariophyta was not known because of the general small blomass. In present study, Phyto-PAM ( Pulse Amplitude Modulation) was applied to measure F_v/F_m (ratio of variable to maximal fluorescence) and rapid light curves of phyto-plankton to study the photochemical vitality in situ of overwintering phytoplankton sampled from LakeTaihu, Lake Chaohu and Lake Xuanwu. Both microscopic determination of cyanobacteria, chlorophyta and bacillariophyta and treatment of copper sulfate and Lugol's solution to water samples were performed. The results from microscopy determination showed that there were ehlorophyta and baeillariophyta but without eyanobaeteria in Lake Taihu and Lake Xuanwu. However, a large amount of cyanophyta was detected in Lake Chaohu besides chlorophyta and bacillariophyta. F_v/F_m and rapid light curves from Phyto-PAM showed that there was no photochemical vitality of cyanobacteria in Lake Taihu and Lake Xuanwu but presented with photochemical vitality of chlorophyta and bacillariophyta ( F_v/F_m was about 0. 5 ). In Lake Chaohu, all the three kinds of phytoplankton showed photochemical vitality ( F_v/F_m was about 0. 5 in chlorophyta and bacillariophyta;F_v/F_m was about 0. 3 in cyanophyta). Samples treated with copper sulfate only showed the bacillariophyta photochemical vitality, while even this disappeared when treated with Lugol's solution. The results from Phyto-PAM combined with chemical treatment experiments suggested that the photochemical vitality of phytoplankton was still active in overwintering period.

Speciation of heavy metals in sediments from Lake Xuanwu and their environmental significance

通过对玄武湖12个底泥样品采用连续提取的方法, 分别获得湖中6种金属的总量和形态分布数据, 并用因子分析的方法对金属总量进行统计分析.金属总量结果表明, 部分样点的Ni和大部分样点的Cr、Pb、Zn超过背景值, 显示有轻度污染, 这与玄武湖周围的地理环境和人类活动对底泥重金属的影响有关.对金属形态分析的结果表明, 在所测金属中残渣态是主要的存在形式, 其次比例较高的是有机物和硫化物结合态, 而Pb、Zn有潜在的生物危害性.;Six elements (Ni, Cu, Cr, Pb, Mn, Zn) in twelve sediment samples from Lake Xuanwu were studied by BCR sequential extraction method to obtain their distribution features in this region and the data were analyzed with Factorial Analysis method.The results showed that the metal concentrations of Ni, Pb, Zn in some sediments of Lake Xuanwu exceeded the background levels, revealing slight pollution, which were affected by the geological setting and the anthropogenic input.Metals detected was mainly associated with the residual fraction in the lake, and the oxidable fraction was followed.The acid soluble fraction of Pb, Zn had higher percentages in total contents than other four metals, so their potential risk to aquatic organisms must be considered.

Environmental effects of &lt;i&gt;Potamogeton crispus&lt;/i&gt; population in Lake Xuanwu, Nanjing

为了解玄武湖菹草种群的环境效应, 对玄武湖2006年春季水质变化、菹草区内外水质差异进行了监测, 并分析了2003-2006年春季水质监测资料, 结果表明:菹草区DO高于菹草-水交界区及开阔水域;从菹草区到菹草—水交界区、开阔水域TP、TN逐渐升高, TP均值分别为0.062、0.098、0.105mg/L, TN均值分别为1.674、2.202、2.412mg/L;与2003-2005年同期均值相比, 2006年3-5月份TP分别下降了15.4%、45%、43.3%, TN分别下降58.2%、43.9%、51.3%, SD保持在65cm以上;说明菹草在改善湖泊环境和净化水质方面有重要作用。最后提出了改善、维持玄武湖健康稳定水生生态系统的措施和建议。;To investigate the environmental effects of Potamogeton crispus population in Lake Xuanwu, water quality in and out Potamogeton crispus population area were monitored from January to June of 2006, and were compared from 2003 to 2006 in Lake Xuanwu. The results showed :1) From P. crispus population area to open water area, concentration of DO gradually decreased; 2)From u P. crispus population area”, “transition area” to “open water area”, concentration of TP and TN increased gradually. Average concentration of TP in those area were 0.062, 0.098 and 0.105 mg/L respectively, and average concentration of TN in those area were 1.674, 2.202 and 2.412mg/L respectively; 3) TP concentration from March to May in 2006 decreased by 15.4%, 45% and 43.3%, compared with the same months from 2003 to 2005; these told us that Potamogeton crispus population had vital roles in improving lake environment and purifying water quality. Finally, some suggestions about improving and maintaining stable aquatic ecosystems of Lake Xuanwu were put forward in the article.

Molecular detection of &lt;i&gt;Microcystis &lt;/i&gt;(Cyanobacteria) from sediments by DNA amplification

通过改进裂解温度和延长裂解时间并增加苯酚/氯仿洗脱次数的DNA提取方法获得南京玄武湖底泥中的DNA, 通过PCR法来扩增微囊藻的16SrRNA基因。结果表明在所有采样点中均得到微囊藻基因组DNA, 并且纯度较高, OD₂₆₀/OD₂₈₀均高于1.54, 最高值达到1.89。PCR的扩增结果显示所有样点的DNA都得到212bp大小的微囊藻16SrRNA基因片断, 表明这种方法可以有效的从底泥中提取微囊藻的DNA, 从而为研究底泥微囊藻生理生态及其越冬、上浮、形成水华的机理提供更有利的方法。;A method for DNA extraction from sediment samples of Lake Xuanwu, Nanjing, China was developed, and purification and efficience of extracted DNAs were evaluated through ultraviolet spectrum OD₂₆₀/OD₂₈₀ ratios and PCR ampliilcation of 16S rDNA specific for Microcystis. The results showed that sediment samples from all sites in the study obtained quite purified genomic DNAs with OD₂₆₀/OD₂₈₀ ratios from 1.54 to 1.89, and Microcystis 16S rRNA gene fragments have been detected in all sampling sites, which indicating this method can be used for molecular detection of Microcystis cells in sediments.

Release fluxes estimate of phosphorus in a urban shallow lake:Lake Xuanwu, Nanjing

以南京玄武湖为研究对象,通过静态条件下5℃、10℃、15℃、25℃、35℃玄武湖底泥释磷室内实验计算玄武湖释磷速率,得出底泥释磷速率与上覆水温度的关系,进而算出玄武湖北湖每年磷释放量为0.815 t,东南湖每年磷释放量为 1.013t,西南湖每年磷释放量为0.266t.玄武湖每年底泥释磷总量为2.094 t.根据费克定理,建立了间隙水扩散模型,利用模型计算玄武湖北湖每年磷释放量为0.799 t,东南湖每年磷释放量为0.983 t,西南湖每年磷释放量为0.232 t.玄武湖每年底泥释磷总量为2.014t.在不考虑外源污染的情况下,由底泥磷释放造成的内源污染使玄武湖磷浓度年均维持在 0.101 mg/L,超过湖泊富营养化磷标准,因此,在切断外源污染的情况下应采取措施治理磷的内源污染.;The phycial and chemical characteristics of the surface sediment of Lake Xuanwu, Nanjing were investi-gated in April-September, 2004 and April-July, 2005. After simulating the phosphorus release in laboratory fromthe surface sediments samples under static conditions under 5, 10, 15,25,35℃, respectively, the release fluxes ofphosphorus across the water-sediment interface in different sub-lakes of Lake Xuanxu were calculated, i. e.0.815 t/a, 1.013 t/a and 0.266 t/a for northern, southeastern and southwestern sub-lakes, separately. The totalrelease flux for Lake Xuanwu could be 2. 094 t/a. Based on the Fick's Law, a pore water dispersion model wasbuild up, and the phosphorus release for the whole Lake Xuan could be calculated as 2. 014 t/a to the water, with0.799 t/a, 0. 983 t/a and 0. 232 t/a for northern, southeastern and southwestern sub-lakes. Such a net releasefrom lake sediment for phosphorus makes an appropriate 0, 101 m/L in lake water-a value exceeding threshold forlake eutrophication-on the year run when excluding the diffusion pollution to the lake. As a result, additional meas-ures should be taken to reduce internal phosphorus pollution even when external pollutants are under control.

Isolation and identification of five microcystin degrading bacterial strains

有毒蓝藻产生的蓝藻毒素导致地表水的污染已是全球普遍的现象,最常见的毒素是能导致肝癌的肝毒素微囊藻毒素(MC),迄今为止尚无适用的MC驱除技术,微生物降解MC可能是-条有效的途径.本研究以铜绿微囊藻(Microcystis aeruginosa PCC 7806)所产生的MC为底物,从多个形成微囊藻水华的水体中分离获得能显著降解MC的细菌18株,相对降解能力从18.4%到48.2%.对其中5株MC相对降解能力较强的菌,通过形态特征和生理生化特征分析,鉴定出5株菌分别为:不动细菌属(Acinetobacter)、肠杆菌属(Enterobacter)、微杆菌属(Microbacterium)、芽孢杆菌属(Bacillus)和弗拉特氏菌属(Frateuria),均不同于已报道的属种.;Cyanotoxins produced by cyanobacteria have caused pollutions in land surface water around the world.The most common toxin is microcystin(MC),a cancer inducing hepatoxin. No effective technology could be used to remove it up to now. Microbiulogical degradation should be a suitable way. In this study, we used BG-ll rnedium to culture Mi.crocystis nerngiraosa PCC 7806 in the library.MC was extracted by 70% methanol, then concenteafed and purified by C}fl solid-phase extraction collum. The relative contents of MC-LR and MC-RR were 68.2% and 9.3%, respectively, on the basis of high performance liquid chromatography(HPLC) analysis. We used this MG as seleraive substrate to isolate MC degradable bacaeria. From cyanobacterial bloom forming water body such as Xuanwu Lake,Qinhuai Rever, we got eighteen bacterial strains, which could degrade MC-LR obviously. The relafive efficiencies were from 18.4%to 48.2%.Five more effective strains of them were identified as rlcinetaLncter,Enterahacter, Microhacteriu.m, Bacillus and, Fratetcria, respectively by there morphology and biochemical characteristics. These strains were all different from the published ones up to now.

Processes and mechanism of effects of sludge dredging on internal source release in lakes

Simulated research of internal loading and collecting and analyzing the samples from the lakes were carried out before and after dredging in polluted suburb lakes, Wuli Lake (Wuxi City) and Xuanwu Lake (Nanjing City). The research results showed that dredging can inhibit internal loadings in a certain degree in a short term. The discrepancy of dredging effect and technical level, namely dredging quality, by different dredging methods will result in a difference of control of lake internal loadings. The internal loadings’ reversion will gradually appear along with the biogeochemical processes, including suspended particle precipitation, hydrodynamic disturbance and microbio-transformation. The reversion rate mainly depends on the dredging method and the change of interfacial processes on the newborn surface layer. The higher nutrient contents and organic matter in the sediment will enhance water-sediment interfacial processes and nutrients regeneration. It is very important to study the physicochemical and biological character of lacustrine sediments before dredging for determining the dredging methods and predicting their environmental effect.

Investigation into the cause of eruptive death of fish occurring in Xuanwu Lake, Nanjing

The dominant population, Merismopedia, is not a preference bait for fish. On the contrary, it makes fish struggle along on the verge of starvation during the summer. In addition, terrible pollution of water and sediment may not only destroy the antibody systems of fish but also effect the dynamic of pathogenic bacteria. Therefore, that bacteriosis is an environmental disease.

SEASONAL CHANGES OF NUMBER AND BIOMASS OF ZOOPERIPHYTON IN XUANWU LAKE

用挂片法研究玄武湖周丛动物数量和生物量季节性变动,其优势种为褶累枝虫,钟形钟虫,沟钟虫,壶状臂尾轮虫和花箧臂尾轮虫。周丛原生动物数量和生物量在夏、秋季出现高峰,Ⅰ站数量最高达19952ind./cm²,生物量为296.6μg/cm²。Ⅱ站数量最高达16393ind./cm²,生物量为246.5μg/cm²。周丛轮虫在秋、冬季出现高峰,10月初Ⅰ站周丛轮虫数量为873ind./cm²,生物量为958.3μg/cm²。2月初Ⅱ站周丛轮虫数量为201ind./cm²,生物量为257μg/cm²。Ⅰ站年平均周丛动物数4661ind./cm²,年平均生物量为量为391μg/cm²;Ⅱ站周丛动物年平均数量为3037ind./cm²,年平均生物量为150.6g/cm²,因此Ⅰ站周丛动物数量和生物量都比Ⅱ站高。从指示生物的角度得出玄武湖水体富营养化程度是很严重的。;Seasonal changes of number and biomass of zooperiphyton on suspended substrates in' Xuanwu Lake were studied. The main species are Epistylis plvcatdis,VoHicella convallaria, V orlicella campanula, Brachionus urceus and Brachionus cap suliflous. The number and the biomass of perihytic protozoan are large in summer and fall with their maximum number being 19952 ind. /cm² and the maximum biomass 296.6/ig/cm² in Station I, and with maximum number being 16393 ind. /cm² and the maximum biomass 246.5pg/cm² in Station II. The number of periphytic rotifera is large in fall and winter,with their maximum number being 873 ind. /cm² and the maximum biomass 958.3 ng/cm² in Station I in October and with their maximum number being 201 ind. /cm² and the maximum biomass 257 p.g/cm² in Station II in February. The yearly mean number for zooperiphyton is 4661 ind. /cm² and the yearly mean biomass is 391 /ig/cm² in Station I. The yearly mean biomass is 3037 ind. /cm² and the yearly mean biomass is 150.6jxg/cm² in Station II. So both the number and the biomass are larger in Station I than in Station II. According to indicative organism, the eutrophication has been very serious in Xuanwu Lake.

Evidence of Recent Eutrophication of an Urban Lake in Nanjing, China

Abstract There is very little known about urban lakes in China, and for this reason this paper provides a synthesis of palaeolimnological and past and present phytoplankton studies of Xuanwu Lake, an urban lake near the center of Nanjing, in Jiangsu Province, China. Documented changes in biotic species diversity and water chemistry in this urban lake over the last thirty years have been attributed to progressive eutrophication associated with lake in-filling, commercial harvesting of plants and fish and intense industrial and urban activities within the lake's watershed. During the last decade, phytoplankton biomass in Xuanwu Lake has increased ten fold. This has resulted in a steady shallowing of the lake's photic zone to a depth of less than 0.7 m with Secchi transparencies of 0.3 to 0.4 m. Wind-generated currents prevent anoxia from occurring in this shallow wind-swept lake no matter how eutrophic the lake. As a result, many of the negative impacts of hypertrophication, such as anoxia, fish kills and noxious odors, are avoided. Thus, shallow lakes like Xuanwu Lake can become eutrophic without producing long periods of hypolimnetic anoxia such as those frequently reported for deeper eutrophic lakes. It was concluded that it is important to treat deep urban lakes differently from shallow urban lakes as the latter systems rarely display extended periods of anoxia, fish kills and noxious odors.

Studies on the plankton and sediment diatoms in Xuanwu Lake, Nanjing, China

The sediment diatom data based on a 16 cm long sediment core removed from near the center of the lake indicated that nutrient pollution tolerant diatoms have replaced pollution intolerant taxa which were common near the base of the core (about 35 years before present). These observations support the hypothesis that there is progressive eutrophication in Xuanwu Lake. This conclusion is corroborated by direct comparisons of the present day phytoplankton and zooplankton species composition within the lake and published accounts of its species composition during the mid 1970s.

The limnology and paleolimnology of a shallow eutrophic lake in Eastern China

Xuanwu Lake (3.7 km2) is a shallow (mean depth 1.4 m) hypereutrophic lake (annual productivity greater than 600 g cm−2) located in East China's flood plain near the N end of Nanjing, China's ninth largest city. Paleolimnological data based on a 16 cm long sediment core removed from near the center of the lake indicated that nutrient pollution tolerant diatoms have replaced pollution intolerant taxa which were common near the base of the core (approximately 35 years before present). These paleolimnological observations support the hypothesis that progressive eutrophication is occurring in Xuanwu Lake. This conclusion is corroborated by direct comparisons of the present day phytoplankton and zooplankton species composition within the lake and published accounts of its species composition during the mid 1970's.