A study of absorption characteristics of chromophoric dissolved organic matter and particles in Lake Taihu,China

Absorptions by non-phytoplankton particles and phytoplankton, and chromophoric dissolved organic matter (CDOM) were measured at 50 sites in large, shallow, Lake Taihu in winter and summer 2006 to study their seasonal and spatial variations, and their relative contributions to total absorption. The CDOM absorption was significantly higher in winter than in summer, due to degradation and release of fixed carbon in phytoplankton and submerged aquatic vegetation (SAV). The hyperbolic model was used to model the spectral absorption of CDOM, and the mean spectral slope of 6.38 nm⁻¹ was obtained. At most sites, the spectral absorption of non-phytoplankton particles was similar to that of the total particles, demonstrating that the absorption of the total particles is dominated by the absorption of non-phytoplankton particles. In summer, phytoplankton absorption increased markedly, due to frequent algal blooms especially in Meiliang Bay. In winter, the significant increase in non-phytoplankton particle absorption resulted from the increase of inorganic particulate matter caused by sediment resuspension. Strong linear relationships were found between a _d(440) and total suspended matter (TSM), organic suspended matter (OSM), and inorganic suspended matter (ISM). Strong linear relationships were also found between a _ph(440), a _ph(675) and chlorophyll a (Chl-a) concentration. The total relative contributions of non-phytoplankton particles over the range of photosynthetically active radiation (PAR) (400–700 nm) were 48.4 and 79.9% in summer and winter respectively. Non-phytoplankton particle absorption dominated the total absorption, especially in winter, in Lake Taihu, due to frequent sediment resuspension in the large shallow lake as a result of strong windy conditions. The results indicate that strong absorption by CDOM and non-phytoplankton particles at the blue wavelength has an impact on the spectral availability, and acts as a selection factor for the composition of the phytoplankton community, with cyanobacteria being the dominate species in Lake Taihu. Handling editor: L. Naselli-Flores     

Ecological restoration and factors regulating phytoplankton community in a hypertrophic shallow lake,Lake Taihu,China

A restoration program for the control of cyanobacterial blooms and the re-establishment of submerged macrophytes was conducted in Meiliang Bay of Lake Taihu since 2003. The effect of this ecological projects on plankton community and water quality, and factors regulating phytoplankton community were investigated in 2005. In general, some improvements of water quality occurred in the ecological restoration region, especially in the region of restoring aquatic macrophytes, where we detected significant reduction of nutrients. However, it seems the abundance of phytoplankton cannot be effectively control by the present ecological engineering. The phytoplankton abundance was high in the target restoration zone. Results of CCA and correlation analysis indicate that the phytoplankton community was mainly controlled by physico-chemical factors. Cyanobacteria species were positively related with pH, temperature, TP and TSS, while negatively related with TN, TN/TP and conductivity. The most discriminant variable was TN/TP, which explained 15% of the total variance of phytoplankton. However, TN was more important for the fluctuation of TN/TP than TP. It suggested that TN may be the ultimate factor controlling the phytoplankton community in Lake Taihu. Variation partitioning analysis showed that the pure contribution of crustacean was low for the variation of phytoplankton, suggesting that top-down control by crustacean zooplankton was weak in Lake Taihu. In general, this study suggested the reduction of nutrient load should be more important than top-down control using zooplankton for the ecosystem restoration in Lake Taihu.     

Relationship between bacterioplankton and phytoplankton community dynamics during late spring and early summer in Lake Taihu, China

The relationship between bacterioplankton and phytoplankton community compositions was investigated from April to June, 2005 with samples taken at five different stations in Lake Taihu, China. Bacterioplankton and phytoplankton community compositions as determined by denaturing gradient gel electrophoresis of polymerase chain reaction amplified bacterial 16S rRNA gene fragments (PCR-DGGE) and microscopic examination, respectively, revealed a high degree of diversity. In total, 43 unique bands were identified amongst the DGGE profiles, and 29 dominant phytoplankton populations were observed. The DGGE profiles were clustered into two distinct groups. These two clusters were closely associated with two dominant phytoplanktons, Ulothrix sp. and Microcystis spp., as observed on April 19, May 27 and June 27, 2005, respectively. The relationship between bacterioplankton and phytoplankton community compositions was investigated using Canonical Correspondence Analysis (CCA) with the Shannon-Wiener diversity index of phytoplankton community (Hp), the total cell abundance of phytoplankton (N) and the relative abundance of Microcystis spp. (M) as the variables. The CCA results indicated a 30.9 % correlation coefficient, suggesting a high degree of correlation between bacterioplankton and phytoplankton community compositions.     

Relationship between bacterioplankton and phytoplankton community dynamics during late spring and early summer in Lake Taihu, China

The relationship between bacterioplankton and phytoplankton community compositions was investigated from April to June, 2005 with samples taken at five different stations in Lake Taihu, China. Bacterioplankton and phytoplankton community compositions as determined by denaturing gradient gel electrophoresis of polymerase chain reaction amplified bacterial 16S rRNA gene fragments (PCR-DGGE) and microscopic examination, respectively, revealed a high degree of diversity. In total, 43 unique bands were identified amongst the DGGE profiles, and 29 dominant phytoplankton populations were observed. The DGGE profiles were clustered into two distinct groups. These two clusters were closely associated with two dominant phytoplanktons, Ulothrix sp. and Microcystis spp., as observed on April 19, May 27 and June 27, 2005, respectively. The relationship between bacterioplankton and phytoplankton community compositions was investigated using Canonical Correspondence Analysis (CCA) with the Shannon-Wiener diversity index of phytoplankton community (Hp), the total cell abundance of phytoplankton (N) and the relative abundance of Microcystis spp. (M) as the variables. The CCA results indicated a 30.9 % correlation coefficient, suggesting a high degree of correlation between bacterioplankton and phytoplankton community compositions.     

无机氮磷添加对太湖来源浮游植物和附着生物生物量的影响术

为了探讨富营养对太湖来源水体浮游植物的影响,对来源于太湖梅梁湾的水体进行氮磷营养盐添加实验.实验共3个处理(T0、T1和T2),T0不进行营养盐添加,处理T1和T2添加无机氮磷,T1中总氮、总磷净增加分别为10和0.5 mg·L-1,T2添加的量为T1的2倍.结果表明:T0的浮游植物叶绿素a含量明显低于添加营养盐的2个处理,而添加营养盐的2个处理之间没有显著差异,说明氮磷营养盐的添加在一定程度上能够促进浮游植物的生长,但并非营养盐添加越高浮游植物生物量就越高;添加处理与对照中附着生物叶绿素a含量的比较结果与浮游植物生物量的相同;T2中浮游植物的生长可能受到除氮磷之外的因素的限制;T1和T2中均没有出现期望的蓝藻水华,表明蓝藻水华的形成不只是与充足的氮磷供应有关.     

太湖流域湖西区城市化空间过程及其生态效应

我国快速推进的城市化进程正对周围生态系统造成现实或潜在的威胁.基于RS和GIS技术,从镇域尺度探讨1984～2004年太湖流域城市化空间过程及其生态效应.(1)城镇用地轴向扩展明显:沿路三级邻域带R1、R2、R3在1984～2004年期间新增城镇用地面积累积平均百分比分别为88.24%、90.23%、94.68%.(2)城镇用地扩展形态指数MFD与城镇公路连接数UR存在关系:UR=UR3时,扩展形态指数MFD>=1.5;UR＝UR1时,1.250高值区占全区面积的66.33%,形成两核两带:两核位于溧阳经济开发区和镇江谏壁镇-丹徒镇附近;两带分别是两核连线地带和溧阳城区-宜兴新街镇附件一带.     

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。     

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.     

太湖梅梁湾夏季水体组分光谱吸收特性

2006年8月16、17日对太湖梅梁湾湖区15个样点水体进行采样,利用分光光度计和定量滤膜技术测量了水体要素CDOM、非藻类颗粒物和浮游植物的吸收系数,同时进行水质参数的测定,分别对各水体要素的光谱吸收特性进行分析,并结合水质参数建立相应的区域模式.其中,分UV-C(250～290nm)、UV-B (290～320nm)、UV-A(320～400nm)和蓝光(400～500nm)4个波段建立CDOM光谱吸收的关系模式,同时发现曲线斜率值S与440nm处吸收系数存在很好的二次函数关系,在紫外和蓝光波段R2分别达到0.958和0.835;总悬浮物的光谱吸收特征在不同深度处有些相近,有些则存在明显差异,主要是由有机和无机颗粒物剖面分布的不确定性和总悬浮物浓度所引起;非藻类颗粒物吸收系数在400～700nm的指数函数拟合斜率值S的变化范围为0.0056～0.0090nm-1(平均值(0.0070±0.0008)nm-1),各样点指数函数拟合的R2在0.91以上.在可见光波段范围各水体要素对总吸收系数的贡献大小顺序是:浮游植物＞非藻类颗粒物＞CDOM.浮游植物在蓝、绿和红光波段的平均贡献率都在0.5以上,是水体吸收的主要贡献者;在蓝、绿和红光波段,非藻类颗粒物的平均贡献率分别为0.350±0.145、0.412±0.162和0.232±0.125,CDOM的分别为0.121±0.052、0.088±0.059和0.050±0.038.     

太湖湖岸带浮游植物初级生产力特征及影响因素

利用高频溶解氧监测,估算了太湖梅梁湾湖岸带浮游植物初级生产力的高频变化特征。结合同步气象监测及浮游植物、浮游动物和营养盐的周年逐周观测数据,分析了气象和环境条件对富营养化湖泊浮游植物初级生产力的影响。结果发现,高频溶解氧监测估算的初级生产力变化与浮游藻类生物量的变化一致,能够反映出浮游植物生产力的昼夜变化、季节变化等规律。统计分析表明,气温对太湖这一富营养化湖泊初级生产力影响很大;氮的供给与浮游动物的选择性牧食也是影响浮游植物初级生产力的重要因素。湖岸带的水华堆积过程对初级生产力影响巨大,气象、水文过程又加剧了蓝藻水华初级生产力的变化幅度,反映出富营养化湖泊初级生产力可能存在极大的时空不均一性。研究表明,溶解氧高频监测法估算初级生产力能够捕捉到湖泊初级生产力的快速变化过程,可以用于富营养化湖泊初级生产力监测、蓝藻水华灾害预警中。     

Distribution Characteristics and Risk Assessments of PAHs in Fish from Lake Taihu,China

The concentrations of PAHs in four species of fish (Common carp, Crucian carp, Bighead carp, and Topmouth culter) from Lake Taihu were tested, and the human health risks of PAHs by fish consumption were evaluated. Results showed that concentrations of PAHs in fish from Lake Taihu were 52.5–247.6 ng/g wet weight (ww), and the BaP equivalent concentrations of total PAHs (B[a]P_eq) were 0.2–0.6 ng/g ww, which were less than the screening value of 2.6 ng/g wet for human consumption. The concentration sequences of PAHs in fish from Lake Taihu from high to low were Bighead carp > Crucian carp > Common carp > Topmouth culter. The human health risk level of PAHs by fish consumption was 5.8 ± 2.5 × 10^?6, which was less than the maximum acceptable risk level of 1 × 10^?5 for human health set by the U.S. Environmental Protection Agency. The tissue residue guideline (TRG) of PAHs for protecting aquatic wildlife was 1.3 mg/kg diet ww, which was higher than the concentrations of PAHs in fish from Lake Taihu. The results indicated that fish consumption from Lake Taihu would not cause health risk or harmful effects on wildlife that consume aquatic biota.     

安徽沱湖夏季浮游植物群落结构特征与环境因子关系

为了揭示沱湖浮游植物群落结构特征及其与水环境因子的关系,于2016年7月(夏季),对沱湖流域上游至下游11个采样点浮游植物种类组成、细胞丰度、生物量等进行调查研究。结果显示,沱湖共有浮游植物96种(含变种),隶属8门48属,其中绿藻门(Chlorophyta)和硅藻门(Bacillariophyta)种类最多,绿藻门有23属39种,占总种数的40.63%,硅藻门有7属20种,占总种数的20.83%;其次为裸藻门(Euglenophyta),有5属17种,占总种数的17.71%,蓝藻门(Cyanophyta) 8属14种,占14.58%;甲藻门(Pyrrophyta) 2属2种,隐藻门(Cryptophyta) 1属2种,各占总种数的2.08%,黄藻门(Xanthophyta)与金藻门(Chrysophyta)均有1属1种,均占总种数的1.04%。绿藻和硅藻类物种在沱湖浮游植物群落结构中处于优势地位,沱湖夏季浮游植物种类组成表现为绿藻-硅藻型。沱湖夏季浮游植物细胞丰度与生物量从上游到下游呈逐渐增加趋势,细胞丰度与生物量平均值分别为4.022×106cells/L与3.046 mg/L,蓝藻门和绿藻门类群为沱湖浮游植物细胞丰度主体,硅藻门和裸藻门类群为沱湖浮游植物生物量的主体;上游浮游植物多样性指数与均匀度指数均略高于下游采样点,沱湖水质呈β中污型-无污染型,上游水质优于下游水质。浮游植物群落结构与水环境因子的典型对应分析(CCA)结果表明,电导率、透明度、水深及pH值等环境因子与沱湖夏季浮游植物群落结构有较强的相关性。     

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。     

Urea dynamics during Lake Taihu cyanobacterial blooms in China

Lake Taihu, the third largest freshwater lake in China, suffers from harmful cyanobacteria blooms caused by Microcystis spp., which do not fix nitrogen (N). Reduced N (i.e., NH₄⁺, urea and other labile organic N compounds) is an important factor affecting the growth of Microcystis. As the world use of urea as fertilizer has escalated during the past decades, an understanding of how urea cycling relates to blooms of Microcystis is critical to predicting, controlling and alleviating the problem. In this study, the cycling rates of urea-N in Lake Taihu ranged from non-detectable to 1.37 μmol N L⁻¹ h⁻¹ for regeneration, and from 0.042 μmol N L⁻¹ h⁻¹ to 2.27 μmol N L⁻¹ h⁻¹ for potential urea-N removal. The fate of urea-N differed between light and dark incubations. Increased ¹⁵NH₄⁺ accumulated and higher quantities of the removed urea-¹⁵N remained in the ¹⁵NH₄⁺ form were detected in the dark than in the light. A follow-up incubation experiment with ¹⁵N-urea confirmed that Microcystis can grow on urea but its effects on urea dynamics were minor, indicating that Microcystis was not the major factor causing the observed fates of urea under different light conditions in Lake Taihu. Bacterial community composition and predicted functional gene data suggested that heterotrophic bacteria metabolized urea, even though Microcystis spp. was the dominant bloom organism.     

太湖沉积物孔隙水无机氮空间变化特征

采集太湖不同生态类型湖区(草型湖区胥口湾;风浪大、水华较少的湖心区和水华较严重的梅梁湾)沉积物柱状样,研究沉积物理化性质以及孔隙水无机氮浓度垂直变化特征。结果显示,各点含水率、有机质、总氮均随深度增加而降低,而梅梁湾含量最高,湖心区最低。沉积物溶解氧随深度增加而降低,胥口湾最高,梅梁湾最低。孔隙水NH₄⁺-N随深度增加而增大,NO₃^--N、NO₂^--N均随随深度增加而减小。比较表层0-5cm沉积物孔隙水和上覆水无机氮浓度,发现各湖区NO₃^--N和NO₂^--N释放风险小,胥口湾(草型湖区)和梅梁湾(藻型湖区)NH₄⁺-N释放风险较大,湖心区较小。     

Chromophoric dissolved organic matter (CDOM) absorption characteristics in relation to fluorescence in Lake Taihu,China, a large shallow subtropical lake

Absorption measurements from chromophoric dissolved organic matter (CDOM) and their relationships with dissolved organic carbon (DOC) and fluorescence were studied in Lake Taihu, a large, shallow, subtropical lake in China. Absorption spectra of lake water samples were measured from 240 nm to 800 nm. Highest values of a(λ), DOC and F _n (355) occurred near the river inflow to Meiliang Bay and decreased towards the central lake basin. A significant spatial difference was found between Meiliang Bay and the central lake basin in absorption coefficient, DOC-specific absorption coefficient, exponential slope coefficient, DOC concentration and fluorescence value. The spatial distribution of CDOM suggested that a major part of CDOM in the lake was from river input. CDOM absorption coefficients were correlated with DOC over the wavelength range 280–500 nm, and a(355) was also correlated with F _n (355), which showed that CDOM absorption could be inferred from DOC and fluorescence measurement. The coefficient of variation between a(λ) and DOC concentration decreased with increase in wavelength from 240 nm to 800 nm. Furthermore, a significant negative linear relationship was recorded between S value and CDOM absorption coefficient, as well as DOC-specific absorption coefficient. S value and DOC-specific absorption coefficient were used as a proxy for CDOM composition and source. Accurate CDOM absorption measurements are very useful in explaining UV attenuation and in developing, validating remote sensing model of water quality in Lake Taihu.     

The bacterioplankton of Lake Taihu,China: abundance,biomass, and production

Abundance, biomass and production of pelagic bacteria were examined over one year at monthly sampling intervals across a trophic profile in Meiliang Bay, Lake Taihu. With the lowest density in the open lake, the bacterial abundance showed a clear trend in relation to trophic status. The carbon content per cell was higher in autumn and winter, and the opposite was true for bacterial biomass. Bacterial ³[H]-TdR and ¹⁴[C]-Leu incorporation rates, cell production, turnover times and carbon production varied during the annual cycle at different sites. The ratio of bacterial production to primary production was high, independently of the method used, indicates that the microbial food web in Lake Taihu is an important component of the total food web of the lake and dominated by external inputs. Electronic supplementary material Supplementary material is available for this article at and is accessible for authorized users     

Vegetation and soil properties in restored wetlands near Lake Taihu,China

Riparian wetlands are important components of the lake ecosystem, and they play essential roles in maintaining system health. Remediation of degraded lakeshore wetlands is an essential component of lake restoration. A study was conducted to investigate the restoration of lakeshore wetlands, which were converted to rice fields and then abandoned for 2, 5, 10 and 15 years, near Lake Taihu. Soil samples (0–20 cm and 20–40 cm) were taken and plant species were investigated. The carbon content in the soil had increased significantly, rising from 0.71% to 1.85% between 2 and 15 years. Organic matter accumulation improved soil texture, and water stable aggregate content (>0.25 mm) and soil porosity increased. Total nitrogen in the soil increased from 0.06% to 0.13%, and total Kjeldahl nitrogen increased from 124.4 mg kg⁻¹ to 351.5 mg kg⁻¹. Total phosphorus in the soil increased from 0.045% to 0.071%, and the Olsen-P value increased from 5.13 mg kg⁻¹ to 16.0 mg kg⁻¹. Results showed that phosphorous did not increase as much as nitrogen. In the vegetation restoration process, plant species composition moved towards a natural wetland community, and spatial heterogeneity and landscape diversity increased. The richness of plant biodiversity increased rapidly in the first 2 years, then more slowly in later restoration stages. The wetlands recovery process may be complicated by interactions of biota and soil and hydrological conditions.     

Response of bacterial communities to cyanobacterial harmful algal blooms in Lake Taihu,China

Cyanobacterial harmful algal blooms are prevalent around the world, influencing aquatic organisms and altering the physico-chemical properties in freshwater systems. However, the response of bacterial communities to toxic cyanobacterial blooms and associated microcystins (MC) remain poorly understood even though global concentrations of MC have increased dramatically in the past few decades. To address this issue, the dynamics of bacterial community composition (BCC) in the water column and how BCC is influenced by both harmful cyanobacterial blooms and environmental factors were investigated on a monthly basis from August 2013 to July 2014 in Lake Taihu, China. Non-metric multidimensional scaling (NMDS) revealed that seasonal variation in BCC was significant, and that the succession of BCC greatly depends on changes in environmental conditions. Redundancy analysis (RDA) results showed that the overall variation of BCC was explained mainly by dissolved oxygen (DO), nitrate nitrogen (NO₃⁻-N), and Microcystis. The alpha biodiversity of the bacterial community was different among months with the highest diversity in February and the lowest diversity in October. Furthermore, significant negative relationships were found between alpha biodiversity indices and Microcystis abundance as well as with intracellular MC concentrations, indicating that Microcystis and associated MC may influence the bacterial community structure by reducing its biodiversity. This study shows that potential associations exist between toxic cyanobacterial blooms and bacterial communities but more investigations are needed to obtain a mechanistic understanding of their complex relationships.