Phosphorus release from cyanobacterial blooms in Meiliang Bay of Lake Taihu, China

To investigate the relationship between cyanobacterial density and phosphorus release into a lake aquatic environment, in situ experiments with 2.5 L microcosms were conducted in Meiliang Bay, located in the northern part of Lake Taihu, China. The effects of different environmental factors on phosphorus release and the ways changes of water quality indexes are involved in phosphorus release were further examined. It was found that total dissolved phosphorus (TDP) concentration kept to low levels (around 0.488 mg L⁻¹) in the microcosm with the low cyanobacterial density (8.85 × 10⁷ cell L⁻¹) throughout the experimental period, whereas first-order kinetics of TDP release was observed in microcosms with intermediate (7.60 × 10⁸ cell L⁻¹) and high cyanobacterial density (3.65 × 10⁹ cell L⁻¹). Accordingly their TDP release rate constants were both approximately 0.8930 d⁻¹ in the latter two treatments. The dissolved inorganic phosphorus (DIP) concentrations also increased with the increase of cyanobacterial density in 4 days. However, the DIP decreased from 35.52 mg L⁻¹ on day 4 to 6.72 mg L⁻¹ on day 6 in microcosm with the high cyanobacterial density during the experiments. Temperature could remarkably improve phosphorus release, while disturbance and illumination had negative effects on it. In addition, both TDP and DIP concentrations were positively correlated with electronic conductivity, salinity and total dissolved solid, but negatively correlated to chlorophyll-a and cyanobacterial density when cyanobacterial density was more than 7.60 × 108 cell L⁻¹. Thus, more phosphorus can be released from cyanobacterial blooms at higher cyanobacterial densities in Meiliang Bay, which is also determined by high temperature. Higher dissolved phosphorus concentration in cyanobacteria-dominated lakes (regions) is mainly due to the decomposition of cyanobacteria during the outbreak of cyanobacterial bloom in Lake Taihu, especially in Meiliang Bay.     

Environmental changes in Lake Taihu during the past century as recorded in sediment cores

The Lake Taihu drainage basin is an economically developed area with some of the highest population densities in China. The lake has deteriorated due to ecological destruction and eutrophication. Three short sediment cores from eastern, northeastern and southwestern Lake Taihu were collected. Total organic carbon (TOC), total nitrogen (TN), pigments, elements and particle size were analyzed for the purpose of understanding past trophic status and pollution levels. Sedimentation rates were based on ¹³⁷Cs or ²¹⁰Pb methods. Results indicated that sediment particle size became coarser since the 1920s, and the lake was contaminated by heavy metals, such as Cu and Zn, since the 1970s. A remarkable increase in eutrophication since the 1980s due to increased loading of untreated effluents from industry, agriculture and urbanization is reflected by total organic carbon, total nitrogen and pigments in the studied cores. However the onset times of eutrophication in different parts of Lake Taihu were not synchronous.     

The effect of wave-reduction engineering on sediment resuspension in a large, shallow, eutrophic lake (Lake Taihu)

Frequent resuspension of sediments is recognized as an important process in large shallow lakes, impeding the recovery of eutrophic lakes. A large-scale project, including a wave barrier (3.3 km long) and a soft enclosure, was implemented to reduce wave energy and sediment resuspension in Lake Taihu, eastern China. The effects of the wave-reduction engineering on sediment resuspension and internal nutrient loading were investigated. Results showed that sediment resuspension rates as well as suspended solids (SS) in the areas protected by the wave barrier and the soft enclosure were significantly lower than in the unprotected areas. There was a positive relationship between total phosphorus (TP) and SS; thus internal loading of phosphorus was significantly reduced by the wave-reduction structure. High nutrient levels and phytoplankton biomass persisted during the experiment period, suggesting that additional measures, such as re-establishment of the macrophyte community, must be included to help restore the water quality in such a large, shallow and eutrophic lake.     

Floating-leaved macrophyte (<Emphasis Type="Italic">Trapa quadrispinosa</Emphasis> Roxb) beds have significant effects on sediment resuspension in Lake Taihu,China

Trapa quadrispinosa Roxb is a common floating-leaved macrophyte in China. In this study, the effects of Trapa on sediment resuspension in Lake Taihu, a large, shallow, eutrophic lake in eastern China, were investigated using sediment traps. The study was conducted at stations with and without Trapa beds from 7 September to 18 October, 2003. Results showed that sediment resuspension rates at the station without Trapa were significantly higher than those at the station with Trapa. During the study period (41 days), 10,970 g dw m⁻² of surface sediment was resuspended within the Trapa beds and 29,903 g dw m⁻² in the pelagic zone. These equate to phosphorus fluxes of 7.4 g m⁻² to the water column at the station with Trapa and 16.1 g m⁻² at the station without Trapa. Floating-leaved macrophytes, such as Trapa, may be important in sediment resuspension and internal phosphorus loading in shallow lakes.     

泥浸汁对太湖沉积物中的好氧可培养细菌多样性的影响

【目的】研究添加泥浸汁与否对太湖沉积物中可培养细菌的影响。【方法】采用R2A培养基和添加泥浸汁R2A培养基对沉积物中细菌进行分离培养,16S r RNA基因系统发育分析比较种群结构。【结果】培养基中添加泥浸汁,可使可培养细菌的种类数量增加到1.6倍。16S r RNA基因序列分析表明,培养的优势细菌类群存在明显差别。R2A培养基上生长的细菌主要为厚壁菌门(52%)、放线菌门(24%)、变形菌门(20%)和拟杆菌门(4%),其中大部分细菌与芽孢杆菌属、假单胞菌属、节杆菌属等关系密切;而添加泥浸汁的R2A培养基上生长的细菌则主要为变形菌门(40%)、放线菌门(35%)、厚壁菌门(22.5%)和拟杆菌门(2.5%),与鞘脂单胞菌属、芽孢杆菌属、副球菌属、节杆菌属等关系密切。【结论】添加泥浸汁原始营养因子可提高沉积物中可培养细菌的多样性,提高菌种可培养效率。     

Impacts of the Yangtze River water transfer on the restoration of Lake Taihu

In order to improve the water quality and to abate the jeopardy of water bloom in Lake Taihu, China, two experimental water transfers from the Yangtze River to Lake Taihu were conducted in winter–spring 2002 and in summer–autumn 2003. In this study, an ecological model (EcoTaihu) was introduced to assess their environmental effects. First, the model was re-calibrated and reverified for the periods of the water transfer, then numerical calculations with and without the water transfer were carried out. The percentage of the area where water quality was improved by the water transfer was calculated in seven sub-zones of the lake. The results show that the experimental water transfers in both of the periods have notable positive effects on debasing the concentration of phytoplankton, total nitrogen and dissolved oxygen in some sub-areas. The positive effects fluctuated with the duration of the water transfer, and were different for different water quality parameters and in different sub-zones. Among the five water quality parameters considered, chlorophyll a achieved the most significant improvement. There are no notable positive effects on the total phosphorus in any sub-zones. Meiliang Bay, Gonghu Bay and Northwest Zone had more positive effects than the east epigeal zone and Dongtaihu Bay. As the water transfer results in net input of nitrogen and phosphorus to Lake Taihu, it can only be used as an emergency measure to abate the jeopardy resulting from water bloom. Otherwise, the water transfer would increase the risk of eutrophication in Lake Taihu if the concentration of phosphorus and nitrogen in the influent water was not cut down to a reasonable level.     

Modeling impacts of Yangtze River water transfer on water ages in Lake Taihu, China

To improve water quality and alleviate eutrophication in Lake Taihu, the third largest freshwater lake in China, a Yangtze River water transfer project was initiated in 2002 to bring water from the Yangtze River to Lake Taihu to dilute and divert pollutants out of the lake. We used a three-dimensional numerical model, Environmental Fluid Dynamics Code, to study the impacts of water transfer on the transport of dissolved substances in the lake by using the concept of water age. In particular, the influences of inflow tributaries and wind forcing on water age were investigated. Model results showed that the effect of water transfer on transport processes in the lake is strongly influenced by hydrodynamic conditions induced by wind and inflow/outflow tributaries. During the simulation year (2005), the water ages in Lake Taihu were highly variable both spatially and temporally, with a mean of approximately 130 days in summer and 230 days in the other seasons. Southeasterly winds—dominant in the summer—could improve the quality of water by reducing the water age in the eastern areas of the lake, which are used as a drinking water source, and in Meiliang Bay, the most polluted bay. In terms of dilution, the most efficient flow rate for transferred water was predicted to be approximately 100 m³/s. The spatial distribution of water ages showed that water transfer may preferentially enhance exchanges in some areas of the lake unless nutrient concentrations in the transferred water are reduced to a reasonable level. This study provides useful information for a better understanding of the complex hydrodynamic and mass transport processes in the lake, which is important for developing and implementing effective ecological restoration strategies in the region.     

太湖五里湖生态修复示范区水质改善效果分析

鱼类清除和沉水植被恢复常是富营养化浅水湖泊生态系统修复的重要手段。为探讨这种生态系统修复方式对亚热带富营养化浅水湖泊太湖五里湖水质的改善效果,论文研究了五里湖生态修复区与未进行任何修复的对照湖区为期6个月(2010年7～12月)的水质监测数据。数据分析结果表明,生态修复区总氮(TN)、总磷(TP)、叶绿素-a(Chl-a)以及悬浮质(TSS)浓度显著降低,分别比对照区低43.4%、48.3%、65.5%和78.9%,透明度则明显升高,约为对照区的3倍。本研究表明以鱼类清除和沉水植被恢复为主要手段的生态系统修复措施能够有效改善亚热带富营养化浅水湖泊水体的水质。     

The influence of water quality and sediment geochemistry on the horizontal and vertical distribution of phosphorus and nitrogen in sediments of a large,shallow lake

Distinct horizontal water column concentration gradients of nutrients and chlorophyll a (Chl a) occur within large, shallow, eutrophic Lake Taihu, China. Concentrations are high in the north, where some of the major polluted tributaries enter the lake, and relatively low in the south, where macrophytes generally are abundant. It is not clear, however, whether these water column concentration gradients are similarly reflected in spatial heterogeneity of nutrient concentrations within the bottom sediments. The main objective of this study was therefore to test if horizontal and vertical variations in the phosphorus and nitrogen content in bottom sediments of Lake Taihu are significantly related to (1) horizontal variations in overlying water column nutrient concentrations and (2) other sediment geochemical constituents. We measured the concentration of total phosphorus (TP) and total nitrogen (TN) in surficial sediments (0–2 cm) and TP, TN and Chl a concentrations in water column samples, collected from 32 sites in 2005. In 2006 sediment, TP, TN, carbon, iron and manganese concentrations were measured vertically at 2 cm intervals, extending to a depth of approximately 20 cm, at an additional eight sites. Linear correlation analysis revealed that surficial sediment TP concentrations across the 32 stations were related significantly, though weakly, to annual mean water column concentrations of TP, TN as well as Chl a. Correlations of surficial sediment TN with water column variables were, however, not significant (P > 0.05). Amongst the geochemical variables tested, the vertical variability of sediment TP concentrations was most strongly related to sediment manganese and carbon concentrations. A multiple stepwise linear regression revealed that the combination of sediment manganese and carbon concentrations explained 91% of the horizontal variability in sediment TP concentrations and 65% of the vertical variability. Handling editor: Luigi Naselli-Flores     

Lipid biomarker evidence for determining the origin and distribution of organic matter in surface sediments of Lake Taihu,Eastern China

Lipid biomarkers from surface sediments of Lake Taihu (Eastern China) were analyzed in order to determine the origin and spatial distribution of sediment organic matter (OM), which is necessary to understand the regional carbon cycles and design environmental management strategies for lake systems. The results indicated significant heterogeneity in the distribution of autochthonous (algae-, photosynthetic bacteria- and macrophyte-based) and allochthonous (terrestrial plant-based) OM in sediments across the lake. Allochthonous OM inputs, indicated by long-chain n-alkane and long-chain n-alkanol biomarkers, generally declined in abundance from northwestern (Zhushan Bay and Meiliang Bay) to southeastern (East Bays) parts of the lake, suggesting a critical influence of hydrology, and in particular of inflowing rivers, which mainly enter the lake from the west and drain from the east. Autochthonous OM, on the other hand, appeared to reflect variations in overall nutrient status and habit type across the lake. Cyanobacterial OM inputs, identified by short-chain n-alkanes, were most abundant in sediment from the most severely polluted zones in Lake Taihu, namely Zhushan Bay and Meiliang Bay. OM derived from diatoms, indicated by brassicasterol and highly branched isoprenoids (HBIs), was most abundant in sediments from the East Bays, a clear-water zone with relatively low levels of nutrient input. Macrophyte OM input, indicated by the middle-chain n-alkanes and Paq ((n-C23 + n-C25)/(n-C23 + n-C25 + n-C29 + n-C31)), was only identified in sediments from the East Bays. The lowest recorded inputs for both autochthonous and allochthonous OM were in sediments from open areas with significant sediment resuspension, including Gonghu Bay, Central and Western Region. This finding might reflect degradation mineralization of OM in the water column during sediment resuspension.     

Selection of benthic macroinvertebrate-based multimetrics and preliminary establishment of biocriteria for the bioassessment of the water quality of Taihu Lake, China

To develop benthic macroinvertebrate-based multimetrics for the bioassessment of the water quality of Taihu Lake, benthic macroinvertebrate assemblages were sampled at 60 sites in 8 subareas of Taihu Lake. A total of 24 species of benthic macroinvertebrates were obtained: 14 species of Mollusca, 5 species of Arthropoda and 5 species of Annelida. A comprehensive evaluation of the metrics was carried out. The results showed that 7 metrics (i.e., total number of taxa, the number of Mollusca & Crustacea taxa, % Mollusca & Crustacea, % Gastropoda, Goodnight-Whitley index, Hilsenhoff biotic index and % Collector-gatherers) were sensitive. A score of 5, 3 or 1 was assigned to every metric for standardization of the metrics, and a multimetric on a scale ranging from 7 to 35 for bioassessment was developed. Four-level discriminatory biocriteria for water quality were eventually proposed by quartation: 7–14, very poor; 15–21, poor; 22–28, fair; 29–35, good. The re-scored results from the 60 sites showed that the water quality of southeastern Taihu Lake was relatively good, whereas that of northwestern Taihu Lake was relatively poor. Basically, the discriminatory biocriteria are suitable for the assessment of the water quality of Taihu Lake.     

Ecological Risk Assessment of DDT Accumulation in Aquatic Organisms of Taihu Lake,China

DDT (Dichlorophenyltrichloroethane) is a toxic, ubiquitous, and persistent bioaccumulative pollutant in the global environment. Although its use as an insecticide has been banned in China since 1983, residual DDT levels in the Taihu Lake are evident. Aimed at the protection of fish resources, three species of high-value fish in the Taihu Lake (Protosalanx hylocranius (Abbott), Salangichthys tangkahkeii (Wu), and Coilia nasus Temminck et Schlegel) were selected and an ecological risk assessment was used to estimate the DDT threats to fish populations. Based on a food web model, a bioaccumulation model was used to estimate the DDT concentration in zooplankton, benthos, and fish and the Monte Carlo (MC) simulation method was used to analyze the uncertainty in the bioaccumulation process. Then the chronic toxicity dose-response relationship of DDT on the Protosalanx hyalocranius (Abbott) population, estimated by ICE and ACE software, was used to calculate the mortality rates in different fish stages with the DDT concentrations. Last, the demographic modeling (Leslie matrix) was used to assess the ecological risk of DDT damage on the Protosalanx hyalocranius (Abbott) population. The results show that the estimated DDT concentrations in benthos and zooplankton were 0.14–16.56 μ g/kg, 2.15–99.30 μ g/kg, respectively. The fish DDT concentration results are a series of increasing curves and the maximal values reach 266, 101, and 211 μ g/kg for Protosalanx hylocranius (Abbott), Salangichthys tangkahkeii (Wu), and Coilia nasus Temminck et Schlegel, respectively. In the process of ecological risk quantization, a 4.06–7.25% reduction in the biomass of the Protosalanx hyalocranius (Abbott) population was estimated in 10,000 MC imulations and 4.21%, 4.89%, and 5.69% reductions were estimated in 75%, 50%, and 25% probability, respectively.     

太湖水体溶解性氨基酸的空间分布特征

为探索氨基酸(DAAs)组分特征对生物可利用性溶解有机质(DOM)的示踪及定量表征可能性, 对太湖3个湖区(北太湖: 藻型湖区,东太湖: 草型湖区, 南太湖: 农业污染湖区)水体DAAs浓度、组分特征及其空间变化进行了调查研究,并对控制其量、质空间分布的因素加以讨论。结果表明夏季太湖水体DAAs的浓度范围为0.27-3.95 μmol/L,平均值为(1.38±1.17)μmol/L,与湖泊、海洋中研究中报道结果相近。北太湖、南太湖、东太湖3个湖区的DAAs浓度平均值分别为(2.59±0.71)μmol/L,(0.48±0.14)μmol/L,(0.48±0.16)μmol/L,北太湖DAAs浓度及对有机碳氮的贡献都明显高于其他湖区,DAAs组分中以苯丙氨酸和赖氨酸为主,而在南太湖和东太湖,赖氨酸都是最主要的DAAs组分。表明水体的DAAs组分特征能对湖泊营养状态及生态类型的变化做出响应,可以作为指示湖泊营养状态的生物标记物。DAAs也可以作为DOM 生物降解性的评价参数,反映湖泊水体中与生物活性相关的DOM 动态变化。根据氨基酸对有机碳的贡献估算出北太湖的活性溶解性有机碳相对含量为(17.65±17.84)%,显著高于南太湖和东太湖。但由于太湖高度的空间异质性,还需要在今后的研究工作中进行相关的室内实验,建立适用于太湖的经验公式。     

太湖流域景观空间格局动态演变

基于2000、2010和2015年的土地利用数据集,利用景观格局指数、动态变化模型、景观转移矩阵及CLUE-S模型预测的研究方法,对太湖流域景观空间格局动态演变进行分析.结果表明: 2000—2015年间,流域景观类型始终以耕地、建设用地为主,景观破碎化程度加强,分布呈现均匀趋势.从动态转移变化来看,耕地和建设用地变化显著,分别以2.1%和8.4%的速度减少和增加了6761和6615.33 km²;由景观转移可见,耕地减少部分主要转变为建设用地,有7866.30 km²的耕地转变成建设用地,占耕地变化量的91.6%,对建设用地增加的贡献率达到96.5%.各县市的耕地、建设用地变化趋势与整个太湖流域相同,其中,上海市中心城区、浦东新区、临安市、宝山区、闵行区、嘉定区和常州市的耕地和建设用地面积变化尤为突出.结合总量变化与CLUE-S模型模拟2030年景观格局动态演变表明,自然发展情景下耕地和建设用地的变化幅度最大;在生态保护情景下草地面积猛增,动态度达到54.5%;在耕地保护情景下耕地和建设用地的变化幅度骤减.     

太湖西岸湖滨带水生生物分布特征及水质营养状况

对太湖西岸湖滨带入湖河口区浮游生物和底栖动物的种类、单位体积数量以及物种多样性调查的基础上,分析了该区域水生生物分布特征。研究表明,在调查到的5个浮游植物门类中,蓝藻和绿藻门种类占到46.81%和36.17%。单位水体中的物种数量分别占到总藻类的60.97%和34.49%,而硅藻门仅占到总藻类数量的3.07%。Shannon-Wiener物种多样性及均匀度指数基本在1.3~1.6和0.14~0.22之间波动。在调查到的71种浮游动物中,耐污染的桡足类和枝角类占36.62%。单位水体中的物种数量分别达到7.07×104个/L和7.76×104个/L;底栖动物群落结构趋于单一化,敏感种大量减少或消失,物种多样性指数值低下,H′及其均匀度值J仅分别为1.59和0.581左右。同时,部分耐污染和广布种大量繁殖,其单位水体中的物种数量平均占到底栖动物总量的84.76%。对入湖河口区24个点位的水质监测结果也表明,水体中的TN、TP浓度分别为3.50mg/L和0.28mg/L,分别高于国家湖泊水环境质量Ⅴ类水质(TN≤2.0mg/L,TP≤0.2mg/L)标准。结合优势种和多样性指数水质分析方法,太湖西岸湖滨带水体水质已近严重富营养化程度。     

大镜山水库底泥磷释放模拟研究

通过模拟实验,研究了从耗氧到厌氧转变过程中期间大镜山水库底泥磷的释放特征。结果表明:两处底泥均表现为磷的释放,大坝区底泥释放速率高于库中区的底泥;两个点底泥的磷释放速率均先升高后缓慢降低,在第2周达到最大值;大坝区域底泥总磷和可溶性总磷释放的最大速率分别为6.64mg·m^-2·d^-1和1.37mg·m^-2·d^-1,库中区底泥的总磷和可溶性总磷的释放速率最大值分别3.24mg·m^-2·d^-1和0.62mg·m^-2·d^-1;底泥上覆水的氧化还原电位和pH均趋下降趋势,它们是影响底泥磷释放的重要影响因子。     

Evaluation of chronic toxicities from sediments before and after ecological project in Meiliang Bay, Lake Taihu, using cell bioassays

An ecological project for water purification was conducted in Meiliang Bay, Lake Taihu, which supplies one-third of the drinking water for Wuxi City, China. Sediment dredging was employed. The floating-leaf and floating macrophytes were planted, combined with wave-attenuating, algal bloom blocking to improve the water quality. At the same time, large amounts of fish net were placed in the experimental zone, to which massive periphytes adhere. To evaluate the effectiveness of remediation, many studies were based on chemical analysis or acute toxicity test. In this study, chronic toxicities before and after the ecological project in Meiliang Bay, Lake Taihu, China, were evaluated based on a battery of in vitro bioassays, including EROD bioassay, recombined yeast assay, as well as umu test for detection of Ah-receptor (AhR) agonists, estrogenic chemicals and genotoxic chemicals, respectively. Before remediation, AhR effect, estrogenic effect and indirect genotoxicity were all detected in sediments of Meiliang Bay, Taihu Lake. After amelioration, levels of AhR agonists decreased by 42.3–80.7%, estrogenic chemicals decreased by 71.6–93.9% and indirect genotoxic chemicals decreased by 23.2–75.0%. Results showed that the ecological project effectively removed the chronic toxicants from the sediments.     

Water quality improvement and phytoplankton response in the drinking water source in Meiliang Bay of Lake Taihu, China

Water quality experienced changes throughout the 3-year ecological engineering experiment in the drinking water source in Meiliang Bay of Lake Taihu. Average concentrations of TN, TP, NH₄⁺, BOD₅ and transparency in the drinking water source during the period of July–December 2005 were 1.85, 0.13, 0.23, 3.03 mg L⁻¹ and 27.5 cm, respectively, decreasing by 47.9%, 21.2%, 83.3%, 54.4% and 24.2%, compared to concentrations from the same period in 2003. Concentrations of chlorophyll a and COD were 89.9 μg L⁻¹ and 6.45 mg L⁻¹, increasing by 27.9% and 17.7%, compared to the values in 2003. Cyanobacteria (mainly Microcystis) dominated the phytoplankton community in the ecological engineering area during July–December 2005. Densities of cyanobacteria and Microcystis were higher in 2005 than in 2004 and higher inside the engineering area than outside. Density percentages of cyanobacteria and Microcystis to total algae were above 90% and 60% during the bloom period. Average density of flagellate algae was higher during July–December 2005 than in 2004. Changes in water quality in the engineering area resulted mainly from the weakening of waves, decrease in concentrations of suspended solids, and assimilation of mass algae and periphytons. In spite of initial improvement of water quality, cyanobacterial bloom still determined the phytoplankton dynamics and variations. Additionally, nutrient concentration still remained at a high level without control of external loading. Therefore, a more holistic approach and long-term management should be adopted in Lake Taihu.     

环太湖复合型生态网络构建

生态网络构建的定量化研究已在生态规划中发挥了重要作用,但复合型生态网络构建却仍旧停留在理论探索与创新阶段。以环太湖地区为例,基于RS和GIS软件平台,采用最短路径分析方法模拟研究区潜在的生态廊道;然后叠加景观、游憩图谱网络,进行无标度网络的构建和检测,构建空间效能好的环太湖复合型生态网络图谱,并据此有针对性地提出复合型生态网络结构和框架优化的建议。研究结果表明,环太湖区域的生态网络和景观、游憩网络可以通过图谱分析和无标度网络检测进行整合,构建出空间效能好的复合型生态网络模型,从而指导环湖生态、景观、游憩资源的耦合发展与廊道建设;通过对不同分区的图谱形态和指标分析,具有小世界网络特征的太湖北部的苏州段和无锡段应以保护和连接为重点,南部的湖州段无标度网络特征明显,成长潜力较好,需要进行高质量的规划保护和开发。