Three-dimensional eutrophication model and application to Taihu Lake, China

Taihu Lake, the largest freshwater shallow lake in eastern China, has suffered from severe eutrophication over the past two decades. This research developed a three-dimensional eutrophication model to investigate the eutrophication dynamics. The model fully coupled the biological processes and hydrodynamics, and also took into account the effects of sediment release and the external loads from the tributaries. After sensitivity analyses, the key parameters were defined and then calibrated by the field observation data. The calibrated model was applied to study the seasonal primary productions and its regional differences. The comparisons between model results and field data in year 2000 indicated that the model is able to simulate the eutrophication dynamics in Taihu Lake with a reasonable accuracy. From the simulation experiments, it was found that the meteorological forcing have significant influences on the temporal variations of the eutrophication dynamics. The wind-induced circulation and sediment distribution play an important role in the spatial distribution of the algae blooms.     

反硝化脱氮对太湖蓝藻水华态势的影响

反硝化作用是水生生态系统的主要脱氮过程,与蓝藻生长之间存在对氮素的竞争作用,然而气候变化背景下反硝化脱氮对蓝藻水华发生动态的影响仍不清楚.基于2017~2021年北太湖为期5 a的水质监测历史数据,结合不同温度下蓝藻生长和沉积物泥浆培养实验,探究了湖体反硝化脱氮与蓝藻水华之间的相互影响.监测数据表明,太湖水体藻类生物量（以Chla表示）高值主要出现在夏秋季节,而总氮浓度季节变化规律与藻类生物量完全相反,冬春季较高,夏秋季显著降低,溶解态无机氮主要以硝态氮为主,并且硝态氮浓度在夏秋季节几乎接近于零.总磷浓度与Chla浓度变化一致.蓝藻培养实验结果表明,20℃以下蓝藻不能大量生长繁殖.泥浆培养实验结果发现,太湖反硝化作用的最高温度阈值为25℃,在10~25℃之间反硝化潜力与温度呈现显著的线性关系（R²=0.99）.反硝化作用发生的最高硝态氮浓度阈值为4 mg ·L^-1,远高于太湖水体的硝态氮浓度,反硝化潜力最高达到（62.98±21.36）μmol ·（kg ·h）^-1.太湖水体反硝化速率受到硝态氮浓度的限制,而气候变暖导致湖泊温度提前升高,会使蓝藻提前生长,蓝藻生长对硝态氮的同化吸收会和反硝化作用产生竞争,使得大量氮还未被反硝化作用脱除就被藻类吸收利用,从而加剧蓝藻水华暴发的态势.研究结果对于解释近年来气候变化背景下太湖蓝藻水华反弹的机制具有重要科学意义.     

Influence of sunlight on the proliferation of cyanobacterial blooms and its potential applications in Lake Taihu, China

To learn the relationship between sunlight intensity and cyanobacterial proliferations for the further control of the heavy blooms, enclosure experiment were conducted in Meiliang Bay, Lake Taihu by regulating the natural light intensities with different shading ratio （0% （full sunlight）, 10%, 25%, 50% and 75% of original natural sunlight intensities） from September to November in 2010. The results indicated that phytoplankton biomass （mean） decreased significantly when the shading ratios reached 50% or more. Higher shading ratios （e.g. 75%） were very efficient in controlling the average and total cyanobacterialbloom biomass, while 50% shading ratio was proven very effective either in controlling the peak value of phytoplankton biomass or postponing the occurrence of cyanobacterial blooms in Lake Talhu. In addition, phytoplankton composition and photosynthesis efficiency were also affected by altering the shading ratios, and in turn, they might also act on phytoplankton growth. Based on the results from the present study, intermediate shading strategies such as regulation of water level or turbidity through the hydrology regulations would probably be an effective and efficient method in controlling cyanobacterial blooms in large and shallow lakes.     

Eutrophication status and control strategy of Taihu Lake

The water quality and eutrophication status of Taihu Lake in recent years are presented and the pollution trends are analyzed. It is shown that because of unreasonable industrial structures, pollution discharge per GDP is high within the Taihu basin, and the pollution discharge from point and non-point sources exceed the basin’s environmental carrying capacity. Especially, excessive pollutants containing nitrogen and phosphorus are being discharged. Moreover, eutrophication may also result from internal pollution sources such as the release of nutrient elements from sediment. All these factors have resulted in the water quality deterioration of Taihu Lake. To solve this environmental problem, possible control strategies are summarized, including the control of internal pollution sources and inflow-river pollution, ecological restoration and reconstruction of the degraded lakeside zone ecosystem, clean water diversion, dredging, and manual algae removal.     

太湖出入湖河道与湖体水质季节差异分析

基于2016年太湖16条主要河道及对应湖体的水质逐月监测数据,深入探讨了太湖流域不同分区河道的外源营养盐输入对湖体水质影响及其季节变化.结果发现:(1)太湖流域河道总氮(TN)、溶解性总氮(DTN)、总磷(TP)和溶解性总磷(DTP)的月平均浓度均高于对应湖体,主要入流区河道与临近湖体的营养盐浓度呈现显著正相关,表明外源补给对湖体营养盐浓度产生巨大影响;(2)无论是河道还是湖体的营养盐浓度,均呈现明显的季节变化,且峰值产生月份不同:河道平均TN最高值出现在3月,为4.82 mg·L-1,平均TP最高值出现在12月,为0.218 mg·L-1;湖体TN、TP峰值均出现在蓝藻水华暴发期间(7月),分别为4.13 mg·L-1和0.255 mg·L-1;(3)极端降水过程短期内能明显降低河道营养盐浓度,但会引起湖体营养盐外源负荷的明显增高,不利于湖体富营养化控制.本研究表明,对于空间异质性较高的大型浅水湖泊,流域河道入湖污染对湖体营养盐时空格局具有重要的塑造作用,而湖体的污染物自净能力、蓝藻水华物质的空间堆积及风浪引发的底泥再悬浮作用等也都对湖体营养盐浓度、时空格局产生重要影响.     

基于太湖微囊藻毒素的叶绿素a阈值研究

以探讨叶绿素a(Chl-a)阈值为主要目的于2013年6~10月间每月在太湖采样,通过固相萃取超高效液相色谱串联质谱法对水体中3种微囊藻毒素(MC-LR、MC-RR、MC-YR)进行检测.利用SPSS软件分析各种形态的微囊藻毒素(MCs)与总氮(TN)、总磷(TP)、Chl-a、高锰酸盐指数等富营养指标的相关性,分析了MC-LR、MCs与Chl-a的关系.结果表明,太湖MCs污染较严重,其浓度的空间分布特征为:梅梁湾>贡湖、西部沿岸区>湖心区>胥湖区、南部湖区,并以MC-LR浓度最高;相关性分析表明MC-LR、MC-RR、MC-YR及MCs均与高锰酸盐指数、TN、TP、Chl-a呈极显著正相关(P<0.01).结合饮用水中MC-LR和MCs的标准限值分析得出,太湖Chl-a的阈值是12.26 mg·m-3,与美国北卡罗莱纳州湖泊的Chl-a标准值比较属于安全阈值,具有一定的科学性.     

Off-flavor compounds from decaying cyanobacterial blooms of Lake Taihu

The effect of cyanobacterial bloom decay on water quality and the complete degradation of cyanobacterial blooms in a short period were examined by an enclosure experiment in Gonghu Bay of Lake Taihu,China.Water quality parameters as well as taste and odor compounds during the breakdown of cyanobacterial blooms were measured.Results showed that the decay of cyanobacterial blooms caused anoxic water conditions,decreased pH,and increased nutrient loading to the lake water.The highest concentrations of dimethyl sulfide (DMS),dimethyl trisulfide (DMTS),and β-cyclocitral were observed in the anoxic water,at 62331.8,12413.3,and 1374.9 ng/L,respectively.2-Methylisoborneol was dominant during the live growth phase of cyanobacterial blooms,whereas DMS and DMTS were dominant during the decomposition phase.Dissolved oxygen,pH,and chlorophyll a were negatively correlated with DMS,DMTS,and β-cyclocitral,whereas total phosphorus,total nitrogen,and ammonium (NH4+-N) were positively correlated with DMS,DMTS,β-cyclocitral,and β-ionone.The experimental results suggested that preventing the anaerobic decomposition of cyanobacterial blooms is an important strategy against the recurrence of a malodor crisis in Lake Taihu.     

基于GIS下的太湖水质富营养化模糊综合评价

在地理信息系统和地统计学的支持下,探讨了模糊数学与层次分析法相结合的方法在水体富营养化评价中的应用.以太湖为研究对象,选取总磷、总氮、叶绿素、化学需氧量、5日生化需氧量、溶解氧和透明度7项指标进行评价.在对研究区域采样数据进行地统计分析后估算出整个区域评价指标的值,在此基础上建立不同指标的隶属度函数,并计算其隶属度;同时根据层次分析法的原理,确定了各项评价指标的权重,最终得到研究区域的综合结果,绘制出富营养化评价图.结果表明:北部、西北部湖区营养水平最高,属重富营养;中部湖区营养程度为中富营养;东南部湖区营养水平最低,属中营养.     

太湖水体富营养化中农业面污染源的影响研究

太湖流域地处长江三角洲核心部位,是我国的工业经济中心,但同时也是水体富营养化最严重的地区之一。文章通过实地调研、采集得到太湖流域污染的相关数据资料,运用结构解析模型(ISM)建模,通过研究太湖蓝藻各诱发因子的主次关系,对太湖蓝藻危机爆发的成因做了深入的分析。并以GIS为平台核算其耕地面积,结合当地土壤数据及作物特征,计算出了太湖流域农业每年磷的排放量,占总磷排放量的70.7%,得出农业面源产生的的氮、磷流失是引起太湖水体富营养化的重要原因。     

Impacts of algal blooms removal by chitosan-modified soils on zooplankton community in Taihu Lake, China

It is important to assess the e ect on zooplankton when perform the environmental protection or restoration technology, especially removing algal blooms, because algae were the major primary producer in algal lakes. The influence on zooplankton community after half a year of algal blooms removed by chitosan-modified soils in Taihu Lake was assessed and the rationality of carrying out the process semiannually was evaluated in the present study. Morphological composition and genetic diversity of zooplankton community were investigated by microscope checkup and polymerase chain reaction-denatured gradient gel electrophoresis (PCR-DGGE). A total of 44 zooplankton taxa (23 protozoa, 17 rotifers, 3 copepoda and 1 cladocera) were detected by microscope checkup, and a total of 91 bands (28 bands amplified by primers F1427-GC and R1616, 63 bands amplified by primers Fung-GC and NS1) were detected by PCR-DGGE. The results of cluster analysis or detrended correspondence analysis indicated that there was no considerable di erence in morphological composition of zooplankton and DGGE profiles between experimental and control sites, and DGGE profiles could represent the biologic diversity. The study showed that zooplankton community could recover original condition after half year of algal blooms removed by chitosan-modified soils and it was acceptable to apply this process semiannually. In addition, the results revealed that PCR-DGGE could be applied to investigate the impacts of the environmental protection or restoration engineering on zooplankton community diversity.     

太湖底泥的空间分布和富营养化特征

太湖是一个大型的浅水湖泊，周围有数十条入湖河流，陆地风化物质被携带入湖即形成了底泥，由于湖底地形的差异。底泥在湖中的分布并不均匀，根据浅地层剖面仪的测量，在湖的西部存在一条南北向分布，宽度不等的古河道，底泥主要分布于古河道，在湖的沿岸和东太湖也有分布，根据估算，太湖底泥的蓄积量约为13.5亿m^3。太湖周围人口密集，工农业发达，二十多年来经济的快速发展引起了湖泊的富营养化，太湖底泥中的营养元素不断增高，并在一定的条件下向水体释放，加剧了水体的富营养化，引起连续多年春夏季节的蓝藻爆发，经过政府的源头控制和治理。目前富营养化状况初步得到遏止，并有改善的迹象。但底泥中的营养元素可以在很长时间内释放，因此富营养化的治理将是一个长期的过程。     

太湖氮磷营养盐大气湿沉降特征及入湖贡献率

2009年8月—2010年7月在太湖流域不同区域10个采样点收集降水样品230多个,测定其中不同形态N,P营养盐的质量浓度,分析太湖大气湿沉降中N,P营养盐沉降特征,计算N,P营养盐湿沉降率及其占太湖河流入湖负荷的贡献率. 结果表明:湿沉降中ρ(TN)年均值为3.16 mg/L,DTN(溶解性总氮)占TN的70%以上,其中以NH₄+-N为主;湿沉降中ρ(TN)年均值最高值出现在南部湖区,最低值出现在北部湖区. 湿沉降中ρ(TP)年均值为0.08 mg/L,相对较低. 5个区域湿沉降中不同形态N的质量浓度均表现为冬季高、夏季低,而不同形态N,P的湿沉降量均为夏季最大. 南部、东部湖区TN的湿沉降率相对较大. 各采样点湿沉降中NH₄+-N沉降率约占DTN沉降率的30.4%～52.0%,NO₃--N沉降率约占DTN的31.6%;各区域间湿沉降中DTP(溶解性总磷)占TP的比例差异较大. 大气湿沉降中TN和TP的年沉降总量分别为10 868 和247 t,为同期河流入湖负荷的18.6%和11.9%,湿沉降对太湖富营养化的贡献及可能带来的水生态系统的影响不容忽视.      

太湖地区的水资源与水环境——问题、原因与管理

太湖目前主要存在的问题是:①1998年太湖达标排放以来北太湖地区与梅梁湾的水环境没有如预期的那样得到显著改善;②太湖地区的洪涝问题并没有消除,相反随着经济的发展,其易损性增加;③东太湖的沼泽化与富营养化日趋严重,极大地降低了湖泊泄洪能力与供水能力。东太湖的沼泽化与富营养化与养殖业的无计划发展有很大关系,主要是管理所造成的。洪涝问题则是由于流域下垫面的急剧变化导致洪峰提前和洪峰流量增大。     

太湖富营养化控制机理模拟

建立了一个将三维风生湖流模型,水质模型和富营养化模型耦合的数学模型,该模型不仅可以对太湖的风生湖流,总磷、总氮、COD等水质要素进行模拟,还可以模拟藻类在太湖中的生长和消亡情况以及其随风生湖流迁移的规律;在模型中,还考虑了水温、总氮、总磷和太阳辐射等环境生态因子对藻类生长率的影响,并且将模拟结果与1998年太湖的实测资料进行了对比,结果表明:该模型对风生湖流、总磷、总氮的模拟都是切合实际的,以叶绿素a浓度描述的藻类浓度的模拟值也能较好的拟合实测值。     

巢湖和太湖春季微囊藻毒素动态差异及与环境因子的关系

为探究春季巢湖和太湖水体中胞内微囊藻毒素(IMCs)动态变化时空差异及其关键影响因子,于2019年3—5月对两湖不同湖区进行采样分析。结果表明:春季巢湖和太湖的IMCs呈现明显的时空分布特征,IMCs浓度逐月增加,在富营养化水平高的湖区明显高于富营养水平低的湖区;两湖IMCs的异构体均以IMC-LR为主,占比分别为65.10%和58.10%;3—5月两湖IMCs浓度差异明显,巢湖月均IMCs浓度(0.077、0.238、0.632 μg/L)明显高于太湖(0.021、0.031、0.166 μg/L),单位生物量IMCs及其异构体LR的毒性(IMCs/Chla和IMC-LR/Chla)也明显高于太湖。相关性分析表明,总氮(TN)、总磷(TP)浓度和TN/TP是影响IMCs浓度和单位生物量IMCs毒性的关键环境因子,同时产毒藻的丰度和产毒能力也可能是造成此差异的重要原因。     

江苏省太湖水污染防治对策措施

太湖流域是我国城市化程度最高、经济最发达的地区之一;随着经济的发展和城市化进程的推进,流域水环境问题日益突出。太湖流域所跨省份之一的江苏省近年来采取了一系列措施对太湖水污染进行了防治,并取得了阶段性成效,本文从组织领导、规章制度、蓝藻应急治理、控源截污和长效治理5个方面总结了江苏省太湖水污染防治措施。     

太湖水域PH3的时空变化特征

以太湖为研究对象 ,考察了富营养化浅水湖泊中磷化氢的时空分布特征 .结果表明 ,湖面大气中PH3 由于受风向、天气等因素的综合作用 ,时空分布规律不太明显 .表层湖水和底层湖水由于受到风浪扰动 ,天气变化和船只等的影响 ,不同采样点PH3 的含量变化不大 .同时 ,PH3 浓度沿湖水垂直梯度方向的变化亦较小 .而过滤湖水与原始湖水中PH3 的时空变化在同一采样点位、同一采样时间 ,原始湖水中PH3 的浓度明显高于过滤湖水中PH3 的浓度 .底泥中PH3 含量的变化可能与湖底氧化还原环境和温度有关 ,对于水体污染比较严重的地方底泥PH3 含量较高 .     

2009~2018年太湖湖泛强度变化及其影响因素

基于2009~2018年的每年4~10月对太湖湖泛易发区的逐日巡查成果,以及相关太湖气象、水文、水质和水华监测资料的综合分析,揭示了太湖湖泛发生的环境条件及年际差异性特征,分析了影响太湖湖泛强度年际变化的因素及防控途径.结果表明,2009~2018年10 a中太湖共发生大小湖泛事件75次,平均湖泛面积1.35 km²,最大面积9.20 km²,平均持续时间3 d,最长持续16 d;湖泛发生引起了水体有机质、氮和磷等水质指标明显增高;湖泛的发生均在水温20℃以上,发生首日均处在5~9月;年际湖泛强度变化较大,2017年湖泛强度最大,2018年次之,而2014年湖泛强度最小;年际湖泛强度与蓝藻水华强度及5~9月的湖水平均温度显著正相关,而与水体营养盐等指标关系不密切,表明年际气候条件的波动对湖泛情势影响很大;湖泛的形成与河口区蓝藻水华的堆积关系密切：除了5次草源性湖泛外,70次藻源性湖泛均发生在入湖河口附近水域,河口区的底泥污染状况及底泥悬浮状况可能对湖泛的发生具有促进作用.根据形成湖泛的腐烂物质、来源、发生地点和持续时间的不同,可将湖泛分为藻源性湖泛和草源性湖泛这2种类型,藻源性湖泛又可分为港源型、迁移型和原发型这3种.结果表明,控制蓝藻水华强度是降低湖泛风险的根本途径,而避免河口区蓝藻水华过度堆积及厌氧分解的措施,如对蓝藻水华的及时打捞、工程措施形成的局部流场改变、蓝藻水华的离岸打捞工程和滨岸水华堆积区的应急曝气工程,以及河口区的污染底泥疏浚等工程措施,是降低湖泛发生风险的工程措施选项.     

太湖丘陵地区农田氮素迁移的时空分布特征

在太湖丘陵地区选择4种有代表性的土地利用类型进行野外原位试验,研究自然降雨条件下氮素随地表径流迁移的时空分布特征.试验结果表明,随地表径流迁移的农田氮素以氨氮为主,其“次降雨径流平均浓度”中位值占总氮的44.5%,亚硝态氮浓度最小,仅占1.8%.地表径流中的氮素浓度存在显著的季节性差异,其分布主要受降水量、气温等气象条件以及农事活动的影响.总氮、氨氮、硝态氮和亚硝态氮的“多场降雨径流平均浓度”的时间变异性依次减小.菜地径流中总氮、氨氮和硝态氮以及竹林亚硝态氮的SMC值最高,不同土地利用下氮素浓度的空间分布主要与施肥条件以及植被覆盖度有关.各氮素形态SMC值的空间变异性小于其时间变异性.旱地和菜地的氮素迁移通量大于板栗林和竹林,径流量是导致迁移通量存在显著差异的主导因素.     

Seasonal variation of Microcystis in Lake Taihu and its relationships with environmental factors

In order to monitor the changes of Microcystis along with temporal and spatial variations, seasonal variation of Microcystis in Lake Taihu was investigated by 16S-23S rRNA internal transcribed spacer denaturing gradient gel electrophoresis (16S-23S rRNA-ITS DGGE) and microscopic evaluation. Samples were collected quarterly at four sites (River Mouth, Meiliang Bay, Cross Area, and Lake Center) from August 2006 to April 2007. Results showed that Microcystis dominated total phytoplankton abundance at the four sites in all seasons except winter. The average annual abundance of Microcystis was relatively high at River Mouth and Meiliang Bay, reaching 81.22×106 and 61.32×106 cells/L, respectively. For temporal variations, Shannon-Wiener diversity index (H') according to DGGE profile revealed the richness of Microcystis in summer (H'=1.375±0.034) and winter (H'=1.650±0.032) was lower than that in spring (H'=2.078±0.031) and autumn (H'=2.365±0.032) (P<0.05). While for spatial variations, the richness of Microcystis at River Mouth (H'=2.015±0.074) was higher than at other sites during four seasons (P<0.01). Very few differences of Microcystis diversity in the same season were observed among the other three sites (P>0.05). Canonical correspondence analysis (CCA) was performed to elucidate the relationships between Microcystis operational taxonomic units (OTUs) composition and the environmental factors. Results of CCA revealed that temperature was strongly positively correlated with the first axis (r=0.963), while TSS was negative correlated with the second axis (r=-0.716). Phylogenetic tree based on the sequencing results of target bands on DGGE gel indicated that samples collected in summer and winter constituted two separated clusters.