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Six decades field observation data series on submerged aquatic vegetation (SAV), water level and water quality from Lake Taihu were compiled to reveal the dynamics in coverage and species composition of SAV and their anthropogenic drivers. We found that both SAV species composition and coverage area declined significantly in Lake Taihu during the period, and the increasing nutrient levels and water level as well as decreasing water clarity were responsible for these change trends. Specifically, the decrease in species richness could be particularly well predicted by total nitrogen (TN) and the ratio of water clarity (i.e., Secchi disk depth (SDD)) to water level (WL), contributing 47.3 % and 32.3 %, respectively, while the coverage of macrophytes was most strongly related to the water level, accounting for 70.1 % of the variation. A classification tree analysis revealed a threshold of TN of 3.2 mg/L and SDD/WL of 0.14 that caused a shift to a eutrophic low-macrophyte dominated state. Our results highlight that SDD/WL must be improved for SAV recolonization, rather than merely reducing nutrient input and regulating water level. Our findings provide scientific information for lake managers to prevent plant degradation in macrophyte-dominant lakes and facilitate a shift to a macrophyte-dominant state in eutrophic lakes.

化学需氧量是衡量水体中有机物量及污染程度的综合性指标，也是我国《地表水环境质量标准（GB 3838—2002）》的重要评价指标.然而，由于测定过程缓慢和使用了有毒有害试剂易于形成二次污染，现行标准的高锰酸钾和重铬酸钾化学需氧量测定方法无法做到环境友好，也不能反映当前快速和实时监测的技术需求.因此，迫切需要发展操作简便、快速高效、灵敏可靠、环境友好和环保绿色的化学需氧量替代检测方法.本文首先从文献计量学视角比较我国与世界上发达国家化学需氧量研究主题论文发文量，剖析了我国发展化学需氧量替代检测方法的迫切性.基于全国大范围65个湖库706个样本有色可溶性有机物吸收系数、化学需氧量和其他水质参数同步调查数据，构建广覆盖范围的有色可溶性有机物特征波长吸收系数和化学需氧量间高精度线性关系模型，确定了地表水环境质量评价的吸收系数阈值，模型可以广泛应用于不同类型（深水、浅水、大型、中型、小型）和不同营养状态（贫、中、富营养）湖库水体有机物浓度的定量表征，具有一定普适性.通过对比有色可溶性有机物吸收系数和传统的高锰酸钾、重铬酸钾法优势和不足，明确了有色可溶性有机物吸收系数替代化学需氧量用于湖库水体开展有机物表征和污染程度评价的可行性和应用前景.

风浪扰动是影响湖泊生态系统的重要环境因素之一.为了解扰动方式对微囊藻群体大小的影响，在实验室可控条件下，模拟不同扰动方式（持续扰动和间歇扰动）对太湖水华微囊藻（Microcystis flos-aquae）群体大小的影响.结果显示，间歇扰动组水华微囊藻群体从35.09 μm迅速增大至43.73 μm，实验第17天时为59.00 μm；而持续扰动组水华微囊藻群体大小先从35.07 μm增大到43.51 μm，实验第17天时减小至13.95 μm；不扰动组整个实验期间群体大小相对稳定，实验初为35.38 μm，实验第17天时为33.67 μm.方差分析显示，间歇扰动组群体大小显著大于持续扰动组和不扰动组，持续扰动组显著小于不扰动组.实验第17天时间歇扰动组藻细胞密度（1.675×106 cells/ml）显著高于持续扰动组（0.344×106 cells/ml）和不扰动组（1.461×106 cells/ml）.研究结果表明，适当强度下的间歇扰动能促使水华微囊藻群体显著增大和生长，而长时间的持续扰动则会抑制水华微囊藻群体的聚集和生长，该结果有助于人们对太湖微囊藻水华暴发机理的认识.

In order to restore the aquatic vegetation and improve local water quality,reconstruction of two ecological types of aquatic plants were carried out in two large enclosures in the Kangshan Bay demonstration area of Lake Taihu.By annual investigation,results showed that floating-leaved aquatic plants such as Limnanthemun nymphoides and Trapa bicorni,and submerged plant such as Potamogeton macckianus grew better than other plants under controlled conditions.Their coverage was quite high during the growing season.Results also showed that,controlling wind-driven wave disturbance and improving water transparency were the prerequisite for aquatic vegetation restoration;there was no difference about N and P contents between submerged macrophyte and floating-leaved aquatic plants,but floating-leaved aquatic plants performed better than submerged macrophyte in removing water N and P content.Concerning the economic and environmental benefit,aquatic plants including L.nymphoides,T.bicorni and P.macckianus with powerful anti-wave ability could be selected as the pioneering species to rebuild the aquatic vegetation in the open area of Lake Taihu.This research provided theoretical basis for ecological restoration in the open littoral area of Lake Taihu.

In order to understand the effects of the ingestion of metazooplankton on the formation of Microcystis blooms in summer in Lake Taihu,a field simulation experiment had been carried out by taking water samples from the Meiliang Bay in Lake Taihu from July 15 to August 14,2009.During the period,visible Microcystis blooms floating on the water surface were found in the controls which did not filter out metazooplankton,but Microcystis blooms were not found in the treatments which had filtered out metazooplankton.Nine species of metazooplankton were found in the controls and three species of metazooplankton in the treatments during the whole experiment.Metazooplankton were found in the treatments in the sixth days of the experiment.The zooplankton biodiversity(H) analysis showed that the value of H in the controls was significantly higher than that in the treatments.During the later stage of experiment(21-30 days),the average density of Microcystis spp.in the controls was significantly higher than those in the treatments.During the experiment,the density of Microcystis wesenbergii and Microcystis flos-aquae in the controls were significantly higher than those in the treatments,and Microcystis wesenbergii contributed 60.79% of the total Microcystis abundance in the controls.The results showed that the ingestion of metazooplankton could not control the Microcystis blooms,on the contrary,metazooplankton,especially large metazooplankton,promoted the formation of Microcystis blooms.The experiment also suggested that the community structure of metazooplankton was an important factor in affecting the formation of Microcystis blooms.

Concentration of chlorophyll-a(Chl.a),total phosphorus(TP),total nitrogen and water temperature are the four main driving factors resulting in eutrophication in Meiliang Bay,Lake Taihu.Based on the observation data in the period of 1992-2010,the temporal pattern characteristics of the four factors in different temporal scales were analyzed respectively using wavelet analysis.Results showed that the temporal patterns of the four factors were obvious in the inter-annual and inter-decadal scales and the primary periods were different,but the real parts of wavelet coefficients of Chl.a and TP were consistent.The distributions and the periodic oscillation were analyzed and it was predicted that the eutrophication condition in Meiliang Bay would keep stable in the future 3-5 years.This method will provide reliable scientific evidence to the management of Lake Taihu.

In September 2008,a meteorology-hydrology-water quality simultaneous observation was conducted to study the influences of prior wind field on hydrodynamic characteristics and cyanobacterial bloom in northern bays(Meiliang Bay and Gonghu Bay) of Lake Taihu.The results showed that exposed to prior wind field,the surface,middle and bottom water layers flowed out of the bays.There was no compensation current in the two bays.Surface current field was sensitive to real wind field,but middle and bottom current fields lagged behind the wind changing.Influenced by southeast wind,a clockwise circulating current could be rapidly formed in the surface water layer of Meiliang Bay.In Gonghu Bay,the flow direction of surface current field did not change under the action of Westerlies,but its magnitude decreased obviously so that the current velocity increased with the water depth.The observation proves that hydrodynamic is very important for the stratification of chlorophyll-a concentration and drift of cyanobacterial bloom in northern bays of Lake Taihu.Cyanobacteria tended to accumulate and form bloom on water surface in low-hydrodynamic area.Under the condition of high-intensity disturbance,cyanobacteria mixed along the water depth.This can greatly decreased the risk of cyanobacterial bloom.Comparing with the influence of hydrodynamic,that of nutrients on the distribution of chlorophyll-a concentration was less important.

Vallisneria natans from oligotrophic water body(Daxi Reservoir,Jiangsu) and eutrophic bay of Lake Taihu(Meiliang Bay) was studied to observe morphological characteristics of roots and anatomical structures of leaves and stolons.The results showed that root morphological characteristics,including total root length,root surface area,projected root area,total root volume,average root diameter,and total forks of V.natans from oligotrophic Daxi Reservoir,were significantly higher than that of V.natans from eutrophic Meiliang Bay.Leaf surface was glabrous of this species from Daxi Reservoir,which implied less influence by epiphytes than leaf of V.natans from Meiliang Bay.The leaf and stolon anatomical structures of V.natans from Daxi Reservoir developed well.Leaf had obvious veins and rounded cells and stolon was composed by epidermis,parenchymatous cell,number air chambers and several vascular bundles from external to internal,and there were great numbers of starches in cells.Anatomical structures of V.natans implied growth was inhibited in Meiliang Bay.That morphological and anatomical structure changed along with the lake eutrophication,which would be a great threat to its existence.

A nine-day observation on the process of vertical stratification of physicochemical variables was taken from 24th July to 1st August,2010 in Lake Taihu,a large shallow lake of China.Frequent stratification processes occurred during the 9 days.But the stratifying state was unstable,and normally last less than 1 day.The main factors causing stratification were water temperature and its diel variation,cyanobacterial bloom scum and wind-induced wave disturbance.The vertical difference of water temperaturemay reached 3.94℃,which was mainly influenced by diel variation of air temperature and solar radiation.And the stratification of water temperature was the basic factor causing the stratification of dissolved oxygen,electric conductivity,and pH.Cyanobacterial bloom scum could cause the strongest stratification,which could cause vertical difference of 8.67mg/L of dissolved oxygen,48μC/cm of electric conductivity,1.49 of pH,9.1μg/L of chlorophyll-a and 26.5NTU of turbidity.Besides turbidity,stratification of physicochemical variables became weaker with the increase of wind speed.No stratification happened during strong wind period in which of wind speed over 6m/s,while it often happened during weak condition in which of wind speed less than 2m/s.The study indicated that,stratification processes could frequently short-term occurred in large shallow lakes,and might have potential influences on the processes of biological activities and exchange on air-water interface and water-sediment interface.

Experiments were carried on by using four dominant species of Microcystis of Lake Taihu, including Microcystis aeruginosa 905 (toxic), M. aeruginosa 469 (non toxic), M. flos-aquae 1028 and M. wesenbergii 929, grazing by Ceriodaphnia cornuta cultured in a modified BG-11 medium (TN=10mg/L, TP=0.4mg/L) with over 12 day tests. No large colony (above 10 cells) formations in M. aeruginosa 905, M. aeruginosa 469 and M. wesenbergii 929 were observed in the controls and treatments except for M. flos-aquae 1028. The cells proportion of large colony of M. flos-aquae to total cells was significant different between controls and treatments, contributing 22% in controls and 53% in treatments. There were significant differences between controls and treatments in M. flos-aquae in density of different units of unicell, two-cells, small colony (3-10 cells) and large colony. Significant differences were found between controls and treatments in the number of cells per large colony of M. flos-aquae from day 6 to day 12 in the experiment. Our results showed that large colony of M. aeruginosa 905, M. aeruginosa 469 and M. wesenbergii 929 can not be obtained by grazing in the C. cornuta, but C. cornuta is one of important factors in enlarging colony formation of M. flos-aquae.

Using absorption and three-dimensional excitation-emission matrix spectra (3DEEMs), concentration and source of chromophoric dissolved organic matter (CDOM) were studied at the river inlet and open water area of the Lake Taihu in summer of 2007. Significantly spatial difference was recorded for CDOM absorption coefficient at the areas (ANOVA, P0.001), with the highest value in the river inflows of Dapu and Caoqiao and with the lowest value in East Lake Taihu and Xukou Bay. CDOM absorption coefficients are significantly correlated with dissolved organic carbon (DOC) and with chemical oxygen demand (COD) concentrations. Four EEMs peaks were identified in every samples, including a humic acid fluorescence peak (C) in visible range, a humic acid fluorescence peak in UV range (A) and two protein-like fluorescence peaks (B and D). Strong humic acid fluorescence was identified in the samples from the river inflows, with a significant spatial difference from humic acid fluorescence (Peaks A and C) at the river inlet and the open lake area (ANOVA, P0.05). However, there was no significant decrease for protein-like fluorescence (Peaks B and D) from the river inlet to the open area due to the dilution of lake water, showing that the dilution effect is increasing from internal source of phytoplankton degradation to protein-like fluorescence. The ratio of peak B over peak C (r(B/C)) was lower than 1 with the average value of 0.62±0.14, but was larger than 1 at sample 12 with the average value of 1.12±0.13. The r(B/C) can be preliminary used to distinguish the composition and source of CDOM. Significantly positive correlations were found between CDOM absorption coefficient and the fluorescence intensities of peaks A, C, D, but no significant correlation found with peak B.

This paper reviews three hot topics associated with Lake Taihu environmental and ecological researches in the recent ten years, i.e. hydrodynamics and its effects on the lake environment and ecosystem, lake sediment and internal pollution loadings, lake ecological structure and functions related to algal bloom. In the aspect of hydrodynamics and its effects, a field approach to investigate the relationships between hydrodynamic parameters and environmental factors was developed. We found hydrodynamical intensity quantitatively related to sediment erosion and suspension, and further related to the transparency, internal loading and oxidation-deoxidization conditions at water-sediment interface. The internal structure of hydrodynamics in Lake Taihu has been achieved, so that the necessity of three dimensional hydrodynamic model has been built instead of two-dimensional hydrodynamic model for this large shallow lake. Relation functions of light penetration and intensity distribution as well as transparency related to seston have been established. Primary production estimate model of Lake Taihu based on the seston has been developed. In aspect of sediment and internal loading, the distributions of sediment and the pollutant in sediment have been clearly revealed. The main force which makes sediment resuspension was identified. The effects of hydrodynamics on the sediment resuspension and further on the nutrient releasing were investigated. A conceptual mode of nutrient releasing for large shallow lake was proposed and the criteria for internal loading control were put forward. In aspect of lake ecosystem and algal bloom, based the hypothesis of algal bloom formation, the understanding of algal bloom formation has been improved via the findings of nutrient thresholds and restoration ofdormancy algal spores. Investigations also revealed the phenomena that eutrophication leads to degradation of ecosystem and biota tends to small sizes. The nutrient cycling will speed up and more available nutrient will be imported which in turn enhances the eutrophicating. After investigation of periphyte effects on the submerged macrophyte, the mechanism on macrophyte disappearance was clarified. Based on these findings, new idea on eutrophic lake control and ecosystem restoration was proposed, i.e. reducing the nutrient loading firstly and restoring ecosystem secondarily. Finally, the paper made perspective for the future development of these aspects.

According to MONERIS,three models were established to estimate the nutrient emissions into the river systems of the southwestern Taihu Basin,i.e,a nutrient balance model of the agricultural land,an emission model that was used for the estimation of nutrient emissions from catchments to river systems,and a riverine retention model that was used for the estimation of nutrient loads from emissions.The comparison of the calculated loads with the observed loads shows a deviation as low as 10% and 30% for nitrogen and phosphorus,respectively.It was es- timated that the nitrogen input into the river system amounts to about 5645 t/a in the period 1997-2001.These e- missions have decreased since the former five years by about 827 t/a.For phosphorus the emissions have reduced by 45 t/a and amount 554 t/a in the period 1997-2001.Analysis of the results show that the decrease of the nu- trient emissions are mainly caused by the great reduction of nutrient surpluses from the agricultural land and the e- missions from point sources.

It is generally considered that nitrogen is one of the major factors regulating the trophic status of lakes, and the biogeochemical cycling of nitrogen serves the most important function in lake systems.Lakes often receive large anthropogenic inputs of nitrogen that cause eutrophication,and the exchange of nitrogen-compounds between sediment and water has a profound effect in all kinds of lakes.Such increased nutrient loading promotes the growth of phytoplankton while rooted plants and benthic are suppressed due to reduced light availability,the transfer of the nitrogen through the food chains in algal lake and macrophytic lake is different accordingly.Meanwhile,in this re- view progresses made on the processes such as nitrification,denitrification,nitrogen fixation and anammox(anaero- bic ammonium oxidation)are emphasized.Methods and techniques applied in the research of biogeochemical cyc- ling of nitrogen are also summarized,and the development of molecular techniques has contributed enormously to the rapid recent progress in the field.Current insufficiencies are pointed out and future directions are recommended in the end.

The effects of nutrients on periphytton and phytoplankton in the condition with and without macrophyte were studied.The results show:1) When the nitrogen concentration was 5 mg/L,the effects of the nitrogen vs phosphorus ratio on phytoplankton were more sensitive than periphyton.While the nitrogen concentration was 2 mg/ L,this effect was no significant different between the periphyton and phytoplankton.2) When the ratio of nitrogen vs phosphorus was 15,the periphyton biomass increased significantly following the increasing of nitrogen,but hyto- plankton biomass was relatively stable.When this ratio was 25,the biomass of both periphyton and phytoplankton were increased significantly following the increment of nitrogen.3) The periphyton biomass was higher and in- creased more fast following the increasing of nitrogen in the condition without macrophyte than with macrnphyte, while it was reverse for the phytoplankton.

Surface water was taken from the east shore of the mouth of Meiliang Bay,Lake Taihu.The lake water was sampled under weak (2 m/s),modest (7 m/s) and strong wind-wave (11 m/s),respectively.Suspended solids (SS) were obtained by centrifuging 25L surface water.SS were further freeze-dried and microwave digested, and the contents of Co,Cr,Cu,Ni,Pb,Zn,AI,Ca,Fe,Mn in SS were determined by ICP-AES.It was found that the particulate metal amounts increased gradually with wind speed.Moreover,different metal contents in SS showed different variation trend with wind speed.The contents of Zn in SS decreased with wind speed;the contents of Mn and Cu were highest at middle wind speed;and contents of AI,Fe,Ni,Pb,Co,Cr were lowest at the mid- dle wind speed.These results suggested the metal contents in the shallow lake water were mainly influenced by wind-wave disturbance.

Based on the absorption coefficients at 16 sampling sites in Meiliang Bay on July 17 2004, the absorption coefficients of algal particles were discriminated from those of nonalgal particles by the method of spectral criteria, and compared with those by methanol-extractions. The results were as follows. Discriminated from absorption coefficient of nonalgal particles by methanol-extractions, the absorption coefficient of alga particles shows the absorption characters of nonalgal particles when the concentration of nonalgal particles is high. The absorption coefficients of algal particles are overestimated especially in short wave band. By the method of spectral criteria, the absorption coefficients of nonalgal and algal particulates can be successfully separated. Compared with the partition by methanol-extractions , the limear correlation coefficients between absorption coefficient of algal particles at 440 nm and 675 nm and the concentration of chlorophyll a significantly increase. The limear correlation coefficients increase to 0. 8901 and 0. 8401 from 0.66 and 0. 75 at 440 and 675 nm, respectively. As far as the method of melhanol-extractions is concerned , the spectral shape of absorption coefficient of particles matter significantly affects the degree of over-estimating the absorption coefficient of algal particles. When the spectral shape of absorption coefficient of particles matter is much more similar to that of alga particles, the error is lower; on the contrary, the error is bigger.

The variations of the spectral absorption coefficient of natural water can be attributed to three principal factors-alga particles, nonalga particles and CDOM. Based on the absorption coefficients of the three factors in Mei-liang bay, the variations in spectral absorption coefficient was analyzed. The result shows That the spatial variations of normalized spectral absorption coefficients of total particles are caused by the difference in alga particles; nonalga particles ratio ,and the variance centralize between 400 -425 nm and 600 -690 nm. As far as the spectral shape is concerned , there is prominent characteristic of nonalga particles in spectral absorption coefficients of total particles. Namely nonalga particles dominant the spectral absorption coefficients of total particles. The spatial variations in absorption coefficient of alga particles, nonalga, particles and CDOM are caused by the difference of their concentration. Namely,in the time of sampling, there is no evident difference in their constitutes of pigments for alga particles, and. humic and fulvic acid for nonalga particles and CDOM of the water in Meiliang bay. In addition, the absorption characteristic of alga particles separated by the method based on spectral criteria was analyzed and compared with that by methanol - extractions. We found that the absorption coefficients of latter exhibits significant fluctuation.

The nitrogen surplus of the upstream agricultural land have a great impact on the eutrophication of the Lake Taihu. Based on the suburban agricultural data of the year 2002, the nitrogen surplus was calculated for the agricultural land of the upstream Taihu. The calculation results show that the agricultural land has a total surplus of 134. 8×103 t/a, and the kilogram surplus per hectare agricultural land is 178. 9 kg per year. The east and west Tiaoxi catchments have lower surplus values less than 130 kg/(hm2·a) , but the other regions have higher values. According to the long calculated series of the N-surplus in the case-study region, the long-term N-surplus changes for the whole upstream area of the Lake Taihu are analyzed in the paper. At last, the authors discuss the relationship of the eutrophication trend of the Lake Taihu and N-surplus changes in the upstream agricultural land.

Chromophoric dissolved organic matter (CDOM) is the light absorption fraction of dissolved organic carbon (DOC) that absorbs light in both the ultraviolet and visible ranges. The spatial and temporal distribution of CDOM in aquatic ecosystems can have important effects on ecosystem productivity, negatively impacting primary productivity due to CDOM absorbs light at both ultraviolet and visible wavelengths while positively impacting secondary productivity by fueling of microbial respiration by photo-degraded CDOM. In water color remote sensing, o-verlaps of pigment absorption spectra with CDOM absorption at blue wavelength generally complicate the use of chlorophyll a retrieval algorithms that are based on remotely sensed ocean color and lead to overestimated chlorophyll a concentration. In addition, high concentrations of CDOM can also act as a photoprotectant against UV damage for aquatic organisms. However, the protection against UV radiation provided by dissolved humic material for a-quatic biota may be diminished if photodegradation of CDOM by UV radiation and acidification increase the UV transparency in lakes. CDOM absorption measurements and their relationship with DOC, and fluorescence are presented in Meiliang Bay of Lake Taihu based on a field investigation and lab analysis to show the spatial distribution of CDOM. Absorption spectral of CDOM was measured from 240 to 800 nm. Concentrations of DOC ranged from 10. 48 to 19. 72 mg/ L with an average of 13. 20±2. 78 mg/L. CDOM absorption coefficients at 280 nm and 355 nm were in the range 18.73-31.91 m-1(average 23. 19±4.36m-1) and 4. 63 -7. 14 m-1 ( average 5. 76±0. 90 m-1) , respectively. The values of the DOC-specific absorption coefficient at 355 nm ranged from 0. 34 to 0. 57 L/(mg·m). Fluorescence emission at 450 nm, excited at 355 nm, had a mean value of 1. 69±0. 77 nm-1. A significant lake zone difference is found in DOC concentration, CDOM absorption coefficient and fluorescence. This regional distribution pattern was in agreement with the location of sources of yellow substance; highest concentrations close to river mouth under the influence of river inflow, lower values in outlet of Meiliang bay. CDOM fluorescence and absorption coefficient were significantly and positively correlated. The results show a good correlation between CDOM absorption and DOC coefficients during 280 -500 nm short wavelength intervals. The coefficient of variation between CDOM absorption and DOC concentration decreased with the increase of wavelength from 280 to 500 nm. The linear regression equations between fluorescence, DOC concentration and absorption coefficients at 355 nm are: Fn(355) = 0.692(±0. 135)a(355) -2.297(±0.786), a(355) =0.233(±0.061)DOC +2.690(±0.816), respectively. The exponential slope coefficient ranged from 11.0 to 14.9μm-1 with a mean value 13. 86±0.91μm-1 , 15.8-20.7μm-1 with a mean value 18.54±1. 11μm-1 and 9.9-13.9μm-1 with a mean value 12.93±0.92μm-1 over the 280 -500 nm, 280 -360 nm and 360 -440 nm intervals. A significant negative linear correlation was found between spectral slope coefficient and DOC specific absorption coefficient, but a significant positive linear correlation for spectral slope coefficient and the ratio of a( 250)/a (365). Larger specific absorption coefficient corresponds to smaller a(250)/a(365) and spectral slope coefficient, which shows higher ratio humic in CDOM.

Concentration of colloidal phosphorus in Lake Taihu, China, was determined in this paper. Lake water was sampled in April, 2005. Cross-flow filtration technique was applied to extract colloid from the water. The result shows that colloidal phosphorus concentration in Lake Taihu varied from 0. 017 to 0. 029 mg/L. In Meiliang Bay, an algae type zone, it is 0. 023 -0. 029 mg/L; while in Gonghu Bay, a grass type zone, it is 0. 017 -0. 022 mg/L. The colloidal phosphorus account for 28. 6% of total phosphorus (TP) in Meiliang Bay, and account for 39.3% of total phosphorus (TP) in Gonghu Bay, respectively. The true-dissolved phosphorus in Meiliang Bay is four times of that in Gonghu Bay.

Bacterioplankton are not only decomposers of organic material but also secondary producers in water ecosystems. They are abundant and dynamic members of remobilization of organic carbon and regeneration of inorganic nutrients in water environments. This paper presents the seasonal variation in the abundance of bacterioplankton and the difference in different zone, the relationship between the environmental factors and the abundance of bacterioplankton in the North Lake Taihu from January to December in 2003 ,the results showed that the number of bacte-rioplankton changes with the seasons. With the increase of water temperature, the number of bacterioplanklon in the water increases, the smallest value in winter, and the largest value in summer. The number of baclerioplankton was closely correlated with the concentration of chlorophyll a ( r2 = 0. 8301 ,n = 12, P 0.01 ) and water temperature (r2 =0. 463 , n = 12, P 0. 01 ) respectively, but has no correlation with the nutriment. The results indicate that the nutrimental substance is very high in Lake Taihu, and is not be the limiting factrs for bacterioplankton ; the DOC is an important source for bacterioplankton which comes from the phytoplankton.

The effect of wave disturbance on the nutrient release from lake sediments was simulated in flume experiments. The sediments were sampled from Lake Taihu, China, which is a large, shallow, eutrophic lake with a mean depth of 1. 9 m and an area of 2447 km2. The water flume was 30 m long, 0. 5 m wide and 0. 7 m deep. The sediments was 10 cm thick in the bottom of water flume in flume experiments. In a "little-wave" experiment, which means the wave height just a bit higher than the critical wave height for sediment resuspension, the depth of overlying water was 40 cm, the critical wave height for sediment resuspension was 8. 45 cm, and the wave height for sediment resuspension experiments was 8.77 cm. In a "strong-wave" experiment, the depth of o-verlying water was 30 cm, the critical wave height for sediment resuspension was 5. 93 cm, and the wave height for sediment resuspension experiments was 12. 31 cm and 13. 29 cm. In the "little-wave" experiments, contents of suspended solids (SS) was increased to 13. 6 mg/L, while in strong-wave experiments, the SS content was increased to 245. 2 mg/L. The equilibrium of the concentration of nutrients and SS in overlying water was lag more than 1 h than the change of wave height. Strong wave disturbance significantly increased the concentrations of ammonia nitrogen and soluble reactive phosphorus in overlying water. In both the little-wave experiment and strong-wave experiment, concentrations of dissolved oxygen in overlying water was increased and concentrations of dissolved organic carbon in overlying water decreased. The study indicated that strong wave might caused significant increase of internal loading of nutrients. However, flocculation and adsorption of resuspended sediments and the oxygenate action accompany by the wave disturbance may district the increasing of reactive nutrients in overlying water.

In this study, underwater light field and optical properties in Lake Longgan were studied by applying in situ measurement data from 2002 to 2003. Incident downwelling photosynthetically available irradiance (PAR, 400 -700 nm) at the water surface and at different depths were measured using a 192SA light sensor connected to a Li -1400 datalogger. Underwater spectral irradiance was measured with a high-resolution spectroradiometer ( SR -9910; Macam Photometries, Livingston, Scotland) equipped via a 4 - m light guide with a cosine-corrected light collector. The spatial distribution of light attenuation, the spectral distribution of attenuation coefficients, and the effect of different wind and wave on underwater light field were assessed. The ultraviolet light was most strongly attenuated and its attenuation decreased with the increase of wavelength. The downward attenuation coefficients were larger than upward attenuation coefficients. The ranges of spectral attenuation coefficient from 400 to 700 nm were 0. 71 - 3. 60, 1.06 -3.72 and 0.78 -2.89 m-1 at sampling station L1, L2 and L3, respectively. There were insignificant spatial differences in the optical properties, only attenuation coefficients being larger at sampling station L2 than those at sampling station station L1, L3. No significant differences of spectral irradiance ratio at sampling station L2, L3, being minimal values during blue wavelength and maximal values during550 -600 nm. In open, wind-exposed lake region with silty sediment, the increase in total suspended solids resulted from the wind and wave would increase the attenuation of light. The attenuation coefficients of PAR increased from 1. 74 to 2. 02, 2. 45 m-1 under three different wind and wave processes. The most significantly positive correlation was found between transparency, attenuation coefficient and total suspended solids. Light attenuation was predominantly correlated to the concentration of total suspended solids and dissolved organic carbon, chlorophyll a. Multiple linear regression equation at 440 nm was listed: Kd(440) =0.514-0.075SS+0. 125DOC+0. 100Chl. a

Accumulation characteristics of heavy metals in sediment cores from three lake areas of Lake Taihu, a typical large-shallow freshwater lake in China, were studied with 210 Pb and 137 Cs isotope dating method. Meiliang Bay of Lake Taihu, a eutrophic shallow bay with a deepest depth of less than 2.6m, occurred cyanobacterium algae-bloom every year and received large amount of municipal sewage and industrial wastewater since the middle of 1980s, has a significant increas trend of the contents of Cd, Cr, Cu, Ni, Pb, and Zn in sediment since the recent 25 years. Jiapu District of Lake Taihu, located in the upper reach of Lake Taihu with a disturbed and yellow water, have a significantly low but also drastically varied contents of heavy metals in sediments of 1 -10cm layer from top to bottom, and a largest sedimentation rate and a largest median particle size at the same layer. Xukou Bay of Lake Taihu, a shallow bay located in the lower reaches of Lake Taihu and gradually become macrophyte-dominant lake in recent 10 years, have a decreasing trend of the contents of heavy metals in sediment from bottom to top except the top 3 cm layer, which the contents of heavy metals abruptly increased. The difference of the content of heavy metals among different sediment time was significant higher than the difference of the mean value of the contents of heavy metals among different sediment cores, which resulted in the different evaluating conclusion of heavy metal pollution in different periods. For example, in the middle of 1980s, it was concluded that no Cd pollution of sediment in Meiliang Bay but there was Cd pollution of sediment in Xukou Bay. However, in 2000, it was concluded that Meiliang Bay was the most serious Cd polluted area in Lake Taihu by sediment quality evaluation. Hydrodynamics also could drastically affect the heavy metals sediment in the large-shallow and frequently wind-induced wave disturbing lake by dynamical size differentiation.

Lake Taihu is one of the five largest freshwater lakes and also one of the most-studied and better-understood water bodies in China. There have been many studies on nutrient distribution and concentrations in the water body; however, the amount and chemical forms of nutrients input from the atmosphere to Meiliang Bay are largely unknown. To fully understand and assess the impact of atmospheric P on water quality of Meiliang Bay, we have quantified the atmospheric input of P by measuring its concentrations in aerosols during spring of 2003. Aerosol samples were collected at eastern part of the lake for determination of phosphorus concentrations in the atmospheric aerosols. The aerosol P was speciated into soluble inorganic phosphorus, insoluble inorganic phosphorus, and organic phosphorus. The average concentrations of the total aerosol P in spring are 0. 157 μg/m3. And about 15. 6% - 51. 0% of atmospheric phosphorus is soluble inorganic phosphorus. Through estimating the flux of aerosol phosphorus to Meiliang Bay, we found that dry deposition of P has an important impact on the water quality of Meiliang Bay.

Aquatic ecosystem restoration is a wide-used term at present, and it has gradually aroused the attention of the public and government due to serious environmental problem of lake in China. In fact, as a systematic work, ecosystem restoration makes the ecosystem towards the good state or prestine status. It comes true through the decreasing or amelioration of environmental press combining with single or multi introduced measures of plants and animals. At present, lake ecosystem restoration is usually considered as simple planting grass and cultivating fish etc. or explained as the man-made re-arrangement or incrustation of biocommunity. These bias in cognition result in less successful examples during the long time of the ecosystem restoration practices. Here we put forward an alternative technological way to purify the lake water in part area of Lake Taihu through ecosystem restoration, including three mutual-connected phases, viz,improving the lake condition→restorating aquatic macrophyte→ecosystem transformating from algae-typed to grass-typed lake→improving water quality. Whether this idea directing the restoration of aquatic macrophyte and lake ecosystem is successful will be tested by future practice.

Based on the collected wave and current data in July,2002 and April, 2003, Lake Taihu, the wave stress (Tw) and the current stress (Tc) were calculated for better understanding of sediment re suspension mechanism. The results show that Tc is much larger than Tw with the water surface slightly disturbed but no re suspension can be found. Under stronger disturbance, Tw is so much larger than Tc that the current effects can be ignored in the bottom stress calculation. The wave effect is more important than the current effect although Tc is slightly smaller than Tw when the water surface is forced by a moderate wind. In this case, the non linear wave current interaction was favored to be considered for the bottom stress calculation in Lake Taihu. The conclusion can benefit the coming research on nutrients release from sediment and suspended sediment concentration (SSC) response to the surface disturbance.