[Research Progress on Remote Sensing Monitoring of Lake Water Quality Parameters].

Lakes are an important component of the hydrosphere and are important freshwater resources. The water environment of lakes has become increasingly polluted, and monitoring the dynamic changes in lake water quality is of great significance for ecological environment protection. Remote sensing can provide technical support for lake water quality monitoring, overcoming the low-cost and poor timeliness characteristics of manual sampling; thus, it has been widely used in lake water quality monitoring. Remote sensing can be used to monitor many indicators, including suspended solids, chlorophyll a, soluble organic matter, dissolved oxygen, transparency, etc. Although remote sensing provides a new method for lake water quality monitoring, there are still some problems in practical application. ① It is difficult to accurately retrieve the component changes in different substances in lake water from the signals received by remote sensing, resulting in the limitation of remote sensing accuracy. Atmospheric correction can eliminate the images reflected by factors such as atmosphere and light. In order to improve the accuracy of water quality monitoring, higher-accuracy atmospheric correction algorithms are needed. However, at present the atmospheric correction algorithm is not mature enough and lacks the portability between sensors. Therefore, atmospheric correction is still a difficult problem of remote sensing retrieval in lake water quality. ② Due to seasonal and spatial constraints, there are differences in surface optical properties of different lakes and biological optical properties, resulting in changes in remote sensing reflectance. There is also a lack of portability of the model established by using limited measured data. ③ The interference of aquatic plants and external forces (wind, fish, etc.) causes the error between the measured data and the model estimation, and the synchronization of the data is difficult to guarantee, which will introduce large errors to the lake water quality model, resulting in a decrease in the reliability of the model. ④ The spatio-temporal scale of measured data and remote sensing data do not match, and it is difficult to capture dynamic and fine changes in water quality. More precise observation of water quality is needed that can capture rapid changes in lakes. However, it is still challenging to obtain real-time measured data that meet the requirements. Therefore, it is necessary to further understand the spectral characteristics of water quality parameters, combining multi-source data and other hydrological models. In the future, a retrieval algorithm with low dependence will be developed, and migrated models will be constructed to break the regional limitations of the model. Additionally, remote sensing promotes the operational development and early warning for the water quality of lakes.

[Long-term Variation Characteristics of Zooplankton Community Structure in Meiliang Bay, Lake Taihu].

Zooplankton, as an important part of the water food chain, plays an important role in lake ecosystems. It is an important monitoring indicator for water bodies. However, due to the lack of long-term monitoring data of zooplankton community structure, there is a lack of understanding about its long-term characteristics. Based on monthly monitoring data from 1997 to 2017 of Meiliang Bay in Lake Taihu, the long-term trends of zooplankton community structure and its relation to the environment were examined. The results showed that the abundance and biomass of zooplankton in Meiliang Bay significantly decreased from 1997 to 2017 (P<0.05). In particular, the abundance and biomass of rotifer and copepod slowly declined, and the abundance of cladocerans fluctuated but its biomass presented a significant decreasing trend (P<0.05). The cladocerous biomass contributed the most to the zooplankton biomass in Meiliang Bay. The dominance of smaller cladocerans and copepods increased with decreasing rotifer density, significantly decreasing the average body size of zooplankton (P<0.05). This study indicated that zooplankton were becoming smaller, potentially weakening the top-down control on phytoplankton. In addition, zooplankton abundance and biomass showed an upward trend in spring and decreased in autumn and winter, and reached maximum values of 1406.70 ind.·L-1 and 25.64 mg·L-1, respectively, in September. In the summer, their changes were the opposite. Pearson correlation analysis showed that zooplankton community structure was significantly related to water physical characteristics (alkalinity, electrical conductivity, water depth, suspended substance, and water temperature), chlorophyll a, and nitrogen (P<0.05). This indicated that the eutrophication of Meiliang Bay in Lake Taihu had a significant impact on the community structure of zooplankton.

[Influence of Cyanobacterial Blooms on Denitrification Rate in Shallow Lake Taihu, China].

Denitrification is the most important nitrogen removal process in lake waters, and is of great significance for mitigating nitrogen pollution and controlling eutrophication in lakes. The outbreak and decline of cyanobacterial blooms may promote denitrification directly in the water column by changing the nitrogen circulation pathway and microenvironment of the water body, and accelerate the removal of nitrogen. In order to verify this hypothesis, the cyanobacteria with different biomass and the NO3--N, PO43--P nutrient for 10 days were taken from Taihu Lake water to simulate the effects of cyanobacteria growth and degradation on denitrification. The dynamic changes of algal biomass and various forms of nitrogen concentration were simultaneously determined by 15N isotope addition culture combined with membrane inlet mass spectrometer (MIMS) for real-time quantitative determination of denitrification rate. The results showed that cyanobacteria absorbed nitrogen into particle nitrogen during the growth period. During the decay period, algae cells released a large amount of NH4+-N by degrading mineralization, which was then converted into NO3--N to provide a substrate for denitrification. That is the key to promoting denitrification in water; the denitrification rate (as N2) reaches (1614.52±301.57)µmol·(m2·h)-1, which is three times higher than the denitrification rate[ (534.45±242.18)µmol·(m2·h)-1]of the lowest concentration cyanobacterial group at the same time. At the end of the experiment, the highest rate of TN removal was highest in the group with the highest initial biomass of cyanobacteria (40.02%), which was 2.26 times of the TN removal rate (17.72%) in the control, indicating that cyanobacterial accumulation can significantly promote the intensity of denitrification and accelerate the removal of nitrogen in water. The rate of denitrification in the decline of cyanobacteria is significantly affected by the concentration of NH4+-N, indicating that the coupling of nitrification-denitrification of microorganisms attached to algae is the main route of nitrogen removal. The results study indicate that the cyanobacteria bloom rapidly during the growth period. Nitrogen is converted into particle nitrogen. The degradation of cyanobacteria is accelerated by coupled nitrification-denitrification, which may be one of the reasons for the decrease of nitrogen concentration in Taihu Lake.

[Efficacy of Phoslock® on the Reduction of Sediment Phosphorus Release in West Lake, Hangzhou, China].

Famous as the world cultural heritage, West Lake in Hangzhou city has plenty of soft sediments with high organic matter content. To search the countermeasures for internal phosphorus release reduction from the sediment, the sediment core incubation was conducted to understand the efficacy of Phoslock® on internal phosphorus release in spring, summer and winter, respectively. The results showed that the internal phosphorus release fluxes in winter and spring were relatively low, with averaged values in the entire lake of 0.13 mg·(m2·d)-1 and 0.29 mg·(m2·d)-1, respectively, while the release flux was 3.29 mg·(m2·d)-1 in summer, more than ten times higher than those in spring and winter. It was estimated that 23.7 kg of phosphorus could be released from sediment in the entire lake every day in summer. Spatially, the phosphorus release flux was related to organic matter contents in sediments, but not the phosphorus or bioavailable phosphorus contents in sediments in West Lake. With Phoslock® added at the rate of 630 g·m-2, sediment phosphorus release was successfully controlled, which reduced the phosphorus concentration in the lake water to less than 0.010 mg·L-1. Especially during summer time, the sediment phosphorus release was reduced by 98% after Phoslock® application. The research suggested that Phoslock® is powerful for phosphorus control even for sediments with high organic matter content, which could be considered in ecological restoration of WEst Lake.

[Source analysis of urea-N in Lake Taihu during summer].

To study the effect of urea nitrogen on the ecosystem of Lake Taihu, we conducted urea and various nitrogen analysis for the water samples collected from the lake and surrounding rivers during summer. The ecological index analysis of 82 sites in rivers and lake yielded the following results: (1) The urea nitrogen contents in Taihu ranged from 0.011 to 0.161 mg x L(-1), which was high in the northwest and low in the southeast, related to the main pollution sources distribution of its drainage basin. (2) The dissolved nitrogen was dominated by inorganic nitrogen and the ratio between ammonia nitrogen and nitrate nitrogen was 5: 1. The average percentage of urea nitrogen in total nitrogen, dissolved nitrogen, dissolved organic nitrogen and bioavailable nitrogen was respectively 2.28%, 5.91%, 15.86%, and 6.22%, which showed a significant ecological function in Taihu. (3) Urea nitrogen concentration in river was more than twice that in lake, and the lake river concentration was slightly higher than the river into the lake. (3) In Taihu, there was a transformation relationship between urea nitrogen and the nitrogen in other forms. It showed that urea nitrogen had a significant positive correlation with permanganate index and the other forms of nitrogen, and a significant negative correlation with dissolved oxygen. In addition, urea nitrogen was weakly and positively correlated with chlorophyll a, while closely related to the spatial distribution of benthos and zooplankton species. All the results above showed that urea nitrogen was the bridge of organic and inorganic nitrogen transformation, and was the sign of nitrogen cycle of Lake Taihu, which was controlled by the circulating rate. High nitrogen content (especially the organic nitrogen) and low dissolved oxygen content were the key contributors to the increased urea nitrogen content. In Taihu, the urea nitrogen content was affected by both exogenous input and endogenous release.

[Physiological response of Vallisneria natans to nitrogen and phosphorus contents in eutrophic waterbody].

The response of Vallisneria natans to the increase contents of nitrogen and phosphorus were studied under laboratory conditions by measuring chlorophyll fluorescence parameters of V. natans using a pulse-amplitude modulated fluorometer (Diving-PAM), combined with measuring some other physiological indexes of V. natans. The results showed that V. natans responded quickly to water nitrogen and phosphorus concentration changes, the maximum quantum yield decreased significantly after 2 h and 6 h, the maximum quanta yield returned to normal levels 12 h after the treatment. There was no significant difference between treatment groups for the maximum quantum yield. Inhibitory effect of light intensity on photosynthesis of V. natans was more obvious under higher (treatment D) or lower (treatment A) concentrations of nitrogen and phosphorus. The average quantum yields of four measurements in the treatment B or C was significantly higher than that of A or D (p < 0.05). Within a certain range, chlorophyll content increased significantly with the nitrogen and phosphorus concentrations. When nitrogen and phosphorus concentrations further increased and reached the level of D treatment, chlorophyll content of V. natans decreased. Malondialdehyde (MDA) content of V. natans changed in the different treatment groups, MDA content of treatment B was the lowest while treatment D was the highest. It shows that V. natans is more suitable for growing in eutrophic waterbodies, but excessive nitrogen and phosphorus could inhibit the physiological activities of V. natans.

[Photosynthetic fluorescence characteristics of floating-leaved and submersed macrophytes commonly found in Taihu Lake].

Some aquatic macrophytes commonly found in Taihu Lake, including Trapa bispinosa, Nymphyoides peltatum, Vallisneria natans, and Hydrilla verticillata were collected, and their maximal quantum yield of photosystem II (Fv/Fm) as well as the rapid light curves (RLCs) under conditions of light adaptation and dark adaptation were measured in situ by using a submersible and pulse-amplitude modulated fluorometer (Diving-PAM). The results showed that floating-leaved plants T. bispinosa and N. peltatum had higher potential maximum photosynthetic capacity than submerged macrophytes V. natans and H. verticillata. The measured maximal quantum yield of T. bispinosa, N. peltatum, V. natans, and H. verticillata was 0.837, 0.831, 0.684, and 0.764, respectively. Both the maximal relative electron transport rate and the half saturation point of light intensity of T. bispinosa and N. peltatum were higher than those of V. natans and H. verticillata, especially under the condition of light adaptation.

[Variation of spectrum of photosynthesis available radiation absorbed by underwater optical medium with depth in Lake Taihu in summer].

Normalized spectrum of photosynthesis available radiation (PAR), which was absorbed by all kinds of medium per unit volume of water at different depths, was calculated by the data from downward and upward irradiance and absorption coefficients of phytoplankton, non-algae particles and chromophoric dissolved organic matter (CDOM) in 41 locations in Lake Taihu from July 29 to August 1, 2006. The results showed that there were two peaks at about 450 nm and 675 nm in the normalized spectrum of PAR absorbed by phytoplankton per unit volume of water, respectively. With the increasing of the depth, the peak at about 450 nm gradually weakened, and red-shift appeared from 450 nm. The above phenomena were much more obvious in the algae-type zone and the center of Lake Taihu. The PAR absorbed by phytoplankton per unit volume of water was shift to 600-700 nm which mainly originated from 400-500 nm to 600-700 nm. The transitional speed was slower in the grass-type zone but it was faster in Meiliang Bay(algae-type zone)and the center of Lake Taihu. In the above water, the PAR absorbed by non-algae particles per unit volume of water mainly originated from 400-500 nm, but energy source gradually shifted to 500-600 nm with the increasing of depth. The variable characteristics of normalized spectrum of PAR absorbed by CDOM per unit volume of water were similar to that of non-algae particles. However, the advantage in grass-type zone which CDOM per unit volume of water absorbed PAR between 500 and 600 nm was less significant than that of non-algae particles per unit volume of water.

[Spatial distribution of COD and the correlations with other parameters in the northern region of Lake Taihu].

Spatial variation of chemical oxygen demand (COD) concentration was documented and significant correlations between COD concentration and chromophoric dissolved organic matter (CDOM) absorption, fluorescence, DOC concentration were found based on a cruise sampling in the northern region of Lake Taihu in summer including 42 samplings. The possible source of COD was also discussed using every two cruise samplings in summer and winter, respectively. The COD concentration ranged from 3.77 to 7.96 mg x L(-1) with a mean value of (5.90 +/- 1.54) mg x L(-1). The mean COD concentrations in Meiliang Bay and the central lake basin were (6.93 +/- 0.89) mg x L(-1) and (4.21 +/- 0.49) mg x L(-1) respectively. A significant spatial difference was found between Meiliang Bay and the central lake basin in COD concentration, CDOM absorption coefficient, fluorescence, DOC and phytoplankton pigment concentrations, decreasing from the river mouth to inner bay, outer bay and the central lake basin. Significant correlations between COD concentration and CDOM absorption, fluorescence, DOC concentration, suggested that COD concentration could be estimated and organic pollution could be assessed using CDOM absorption retrieved from remote sensing images. Significant and positive correlation was found between COD concentration and chlorophyll a concentration in summer. However, the correlation was weak or no correlation was found in winter. Furthermore, a significant higher COD concentration was found in summer than in winter (p < 0.001). Our results indicated that degradation of phytoplankton blooms was the main source of COD in summer, except for river terrestrial input.

[Vertical distribution of physicochemical characteristics and the microbial diversity in different spatial sediments samples in Lake Taihu].

The physicochemical characteristics, nutritions and the microbial community diversity of sediment core samples of three different space locations in the Lake Taihu were studied by fumigation-digestion and PCR-DGGE analysis respectively. The results indicated that below the surface of sediments Eh declined rapidly with increase of sediment depth and it was under anaerobic condition except the top layer of sediment. pH value changed silightly in the profile of sediments, which ranged from 7.2 to 7.8. TN and TP concentrations in sediments of Lake Taihu were high,and the maximum concentrations reached 2.436 mg/g and 0.731 mg/g, respectively. Their vertical profiles showed that TN and TP concentrations in surface sediments were much higher than in deeper layers and decreased with the increase of the depth of sediment layers. OM concentrations declined rapidly at the top 15 cm of sediment layers. There were prominent difference spatially in microbial diversity and the comparability and dynamics of community structure between different sediment samples of different space locations and different depth. The little significant correlation at alpha < or = 0.05 level was observed between the Eh, pH, percentage organic matter, TN concentration and TP concentration and microbial community structure diversity index except of TN concentration and percentage organic matter.

[Comparative study on seasonal variations of community structure of rotifer in different lake areas in Lake Taihu].

A comparative study on seasonal variations of rotifer in different lake areas, including the riverine zone, Meiliang Bay, the central open water area and Gonghu Bay in Lake Taihu, was conducted from Jul. 2006 to Jun. 2007. Twenty-three rotifer species were identified in the riverine zone, 15 in Meiliang Bay, 14 in the central open water area and 21 in Gonghu Bay. The annual average density of rotifer was 475 individuals x L(-1) in the riverine zone, 164 individuals x L(-1) in Meiliang Bay, 189 individuals x L(-1) in the central open water area and 338 individuals x L(-1) in Gonghu Bay. The dominant species were different in the four different Lake areas.In the riverine zone, B. calyciflorus was the dominant species. In Meiliang Bay, B. angularis was the dominant species. However, in Gonghu Bay and the central open water area, P. trigla was the dominant species. The foods and suppression by large crustaceans are both important factors in determining the structure of rotifer community among the four differential lake areas in Lake Taihu. There were significant negatively correlations between the abundance of rotifer and the abundance of cladoceran, the biomass of cladoceran and copepod. The number of rotifers was positively related to Secchi transparency. Results indicate that the structure of rotifer community differs from the four differential lake areas in lake Taihu.

[Release of colloidal N and P from sediment of lake caused by continuing hydrodynamic disturbance].

The course of continuing hydrodynamic disturbance and succeeding long time settlement of lake water was simulated to study the release of nitrogen (N) and phosphorus (P) from lake sediment. It was showed in the experiment that the hydrodynamic disturbance caused abundant release of particulate and colloidal phosphorus and nitrogen. The concentration of total nitrogen (TN) and total phosphorus (TP) in water reached the highest values of 2.106 mg/L and 0.272 mg/L, respectively, when the water was disturbed for 0.5 d, and the concentration of colloidal nitrogen (CN) and colloidal phosphorus (CP) in water reached the highest values of 0.452 mg/L and 0.052 mg/L, respectively, when the water was disturbed for 1 day. Then, the concentration of TN, TP, CN and CP turned to decrease despite the continuing disturbance, for the particles and colloid deposited exceeded that suspended. During the settling phase after disturbance, the bigger suspended particles deposited quickly while the tiny colloid deposited much slower, and the concentration of CN and CP did not decrease until the water was settled for 1 day. The concentration of ultra-filtrated dissolved nitrogen (UDN) and ultra-filtrated dissolved phosphorus (UDP) increased much more in the settling phase than in the disturbing phase. It can be drawn that the adsorption of colloid limited the increase of dissolved N and P in lake water in the disturbing phase and prolonged the time of suspended N and P stayed in water. And the N and P adsorbed by colloid could also be released into water in the settling phase after disturbance, which delayed the elimination of nutrition and improvement of water quality.

[Effect of wind-induced wave on concentration of colloidal nutrient and phytoplankton in Lake Taihu].

In order to find out the characteristics of colloidal nutrient and phytoplankton under different wind conditions in Lake Taihu, observation were carried out and samples were collected. Colloid was collected by using cross-flow ultrafiltration system. Organic carbon, nitrogen, and phosphorus in colloidal, dissolved and other fractions of water samples were determined, and concentration and biomass of phytoplankton were also determined. The result showed that the concentration of colloidal nitrogen (CN), colloidal phosphorus (CP) increased with the increasing of wind speed when the wind speed was less than 4 m/s, and did not increase or even decreased with the increasing of wind speed when the wind speed was more than 4 m/s. The concentration of Chl-a, phytoplankton, cyanobacteria, and biomass of cyanobacteria increased with the increasing of wind speed when the wind speeds was less than 4 m/s, and decreased with the increasing of wind speeds when the wind speed was more than 4 m/s. It was indicated that the small wind-induced waves are of advantage to the float or growth of cyanobacteria while the big wind-induced waves are of disadvantage to the float or growth of cyanobacteria. Concentration of CN and CP are significantly correlated with concentration of phytoplankton and cyanobacteria, indicating that algae and their production are main sources of CN and CP in summer in Lake Taihu.

[Effects of epiphyte on submerged macrophyte in Taihu Lake].

With the eutrophicated Meiliang Bay and macrophyte-dominated Gonghu Bay of Taihu Lake as test areas, this paper studied the biomass of epiphyte and its effect on submerged macrophyte during the vigorous growth season (May-June) of submerged macrophyte in 2005. The results showed that the biomass of epiphyte attached on macrophyte was higher in Gonghu Bay than in Meiliang Bay, and varied within different macrophyte species. The epiphyte inhibited the photosynthetic rate of submerged plant significantly, which could be up to 91.9% in June, and this effect increased with increasing epiphyte biomass but varied with different host plants.

[Quantitative retrieval of phytoplankton pigment based on water inherent optical properties in Lake Taihu].

Total 92 sampling waters were collected from different lake regions in Lake Taihu from May to August in 2005. Absorption coefficients of total particles and chromophoric dissolved organic matter (CDOM), beam attenuation coefficient, scattering coefficients, backscattering coefficients were measured and calculated. Spatial distributions of chlorophyll a, pheophytins concentrations, spectral features of total absorption coefficients and backscattering coefficients were also discussed. Chlorophyll a, pheophytins concentrations were in the range of 3.9 - 149.8 microg x L(-1) with a mean value of (38.14+/-28.89)microg x L(-1) ; 0 - 45.8 microg x(L-1) with a mean value of (8.49+/-7.24) microg x L(-1), respectively. A significant spatial difference was found for chlorophyll a, pheophytins concentrations with lower values in lake center, and typical macrophyte lake regions such as East Lake Taihu, Xukou Bay and Gonghu Bay. Similar significant spatial difference was found for total absorption coefficients and backscattering coefficients with lower values in typical macrophyte lake regions such as East Lake Taihu, Xukou Bay and Gonghu Bay. at(440) and bt(550) ranged from 0.86 to 23.25m(-1) with a mean value of (6.21+/-33.31)(m1)', from 0.05 to 2.25(m-)1 with a mean value of (0.72 +/-0.52)m(-1). Total absorption coefficients increased from 00 to 650nm with a peak near 680nm and increased from 720 to 750nm due to pure water absorption. Total backscattering coefficients generally decreased from 400 to 750nm An optimum band combination of reflectance R (706)/R (682) was selected to model chlorophyll a, pheophytins concentrations in Lake Taihu. Determination coefficients retrieving chlorophyll a concentrations, sum of chlorophyll a and pheophytins concentrations were 0.823, 0.864 5 based on reflectance ratio R (706) /R (682), respectively. Retrieval model of phytoplankton pigment can be used to all the lake including macrophyte lake regions with leaving-water reflectance affected by lake sediment and submerged plants.

Heavy-metal contents in suspended solids of Meiliang Bay, Taihu Lake and its environmental significances.

Surface water was taken from river mouth to the central area of Meiliang Bay, Taihu Lake, a large shallow eutrophic lake in China. Suspended solids were condensed by centrifugation 25 L surface water samples from each selected site. Suspended solids and surface sediments were further freeze-dried and microwave digested before determining the metals by ICP-AES. Among the metals analyzed in suspended solids and sediments, contents of Cr, Cu, Mn, Ni, and Zn in suspended solids were significantly higher than those in sediments while contents of Al, Ba, Be, Ca, Co, Fe, K, Mg, Pb, and V in suspended solids were 10%-30% higher than those in sediments. Sr and Ti contents in suspended solids and sediments were very similar. Na content in suspended solids was lower than that in sediments. Heavy metals were significantly accumulated in suspended solids. From the river mouth to the center of Meiliang Bay, contents of Cr, Cu, Pb, and Zn in suspended solids showed a gradual decreasing trend indicating the river (Zhihugang River) still discharged large quantity of heavy metals to Meiliang Bay. The study suggests that the geochemical behaviors and ecological effects of heavy metals in suspended solids may serve as a good indicator for the pollution of lake.

[Chromophoric dissolved organic matter absorption characteristics with relation to fluorescence in typical macrophyte, algae lake zones of Lake Taihu].

Chromophoric dissolved organic matter (CDOM) represents one of the primary light-absorbing species in natural waters and plays a critical in determining the aquatic light field. CDOM shows a featureless absorption spectrum that increases exponentially with decreasing wavelength, which limits the penetration of biologically damaging UV-B radiation (wavelength from 280 to 320 nm) in the water column, thus shielding aquatic organisms. CDOM absorption measurements and their relationship with dissolved organic carbon (DOC), and fluorescence are presented in typical macrophyte and algae lake zone of Lake Taihu based on a field investigation in April in 2004 and lab analysis. Absorption spectral of CDOM was measured from 240 to 800 nm using a Shimadzu UV-2401PC UV-Vis recording spectrophotometer. Fluorescence with an excitation wavelength of 355 nm, an emission wavelength of 450 nm is measured using a Shimadzu 5301 spectrofluorometer. Concentrations of DOC ranged from 6.3 to 17.2 mg/L with an average of 9.08 +/- 2.66 mg/L. CDOM absorption coefficients at 280 nm and 355 nm were in the range of 11.2 - 32.6 m(-1) (average 17.46m(-1) +/- 5.75 m(-1) and 2.4 - 8.3 m(-1) (average 4.17m(-1) +/- 1.47 m(-l)), respectively. The values of the DOC-specific absorption coefficient at 355 nm ranged from 0.31 to 0.64 L x (mg x m)-1. Fluorescence emission at 450 nm, excited at 355 nm, had a mean value of 1.32nm(-1) +/- 0.84 nm(-1). A significant lake zone difference is found in DOC concentration, CDOM absorption coefficient and fluorescence, but not in DOC-specific absorption coefficient and spectral slope coefficient. This regional distribution pattern is 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 East Lake Taihu. The values of algae lake zone are obvious larger than those of macrophyte lake zone. In Meiliang Bay, CDOM absorption, DOC concentration and fluorescence tend to decreasing from inside to mouth of the Bay. The results show a good correlation between CDOM absorption and DOC coefficients during 280 - 500 nm short wavelength intervals. The R-square coefficient between CDOM absorption and DOC concentration decreases with the increase of wavelength from 280 to 500 nm. The significant linear regression correlations between fluorescence, DOC concentration and absorption coefficients were found at 355 nm. The exponential slope coefficients ranged from 13.0 to 16.4 microm(-1) with a mean value 14.37microm(-1) +/- 0.73microm(-1), 17.3microm(-1) - 20.3microm(-1) with a mean value 19.17microm(-1) +/- 0.84microm(-1) and 12.0microm(-1) - 15.8microm(-1) with a mean value 13.38microm(-1) +/- 0.82microm(-1) over the 280 - 500 nm, 280 - 360 nm and 360 - 440 nm intervals.

Growth and phosphate uptake kinetics of Microcystis aeruginosa under various environmental conditions.

Growth and uptake of exogenous phosphate by Microcystis aeruginosa in batch culture under different temperature, photoperiod, and turbulence were studied by the method of phosphate isotope tracer. Relatively high temperature, long photoperiod and strong turbulence increased the cell density of M. aeruginosa in these batch cultures. The initial rapid uptake of phosphate by M. aeruginosa was independent of the temperature, photoperiod, and turbulence. Similarly, maximum exogenous phosphate uptake was not related to these environmental factors. However, elevated temperature and turbulence shortened the time, required to obtain maximum P accumulation. The growth of M. aeruginosa could alleviate the phosphorous leakage. Total amounts of exogenous phosphate uptake to M. aeruginosa and the phosphorus leakage of M. aeruginosa were significantly influenced by the growth state of M. aeruginosa closely correlated with the environmental factors. The maximum volume of exogenous phosphate uptake to M. aeruginosa was 46% of added exogenous phosphate in water with 16 hours of photoperiod. Thus, total amounts of exogenous phosphate uptake to M. aeruginosa were more strongly affected by the photoperiod length than temperature and turbulence.

Sediment distribution pattern mapped from the combination of objective analysis and geostatistics in the large shallow Taihu Lake, China.

Investigation was made into sediment depth at 723 irregularly scattered measurement points which cover all the regions in Taihu Lake, China. The combination of successive correction scheme and geostatistical method was used to get all the values of recent sediment thickness at the 69 x 69 grids in the whole lake. The results showed that there is the significant difference in sediment depth between the eastern area and the western region, and most of the sediments are located in the western shore-line and northern regimes but just a little in the center and eastern parts. The notable exception is the patch between the center and Xishan Island where the maximum sediment depth is more than 4.0 m. This sediment distribution pattern is more than likely related to the current circulation pattern induced by the prevailing wind-forcing in Taihu Lake. The numerical simulation of hydrodynamics can strong support the conclusion. Sediment effects on water quality was also studied and the results showed that the concentrations of TP, TN and SS in the western part are obviously larger than those in the eastern regime, which suggested that more nutrients can be released from thicker sediment areas.

Divergence of carbon dioxide fluxes in different trophic areas of Taihu Lake, China.

Carbon dioxide partial pressures (pCO2) and CO2 fluxes on air-water interface in different trophic-level areas of Taihu Lake were calculated and corrected using alkalinity, pH, ionic strength, active coefficient, water temperature and wind speed on the basis of the data sets of monthly sampling in 1998. The mean values of pCO2 in the hypertrophic, eutrophic, and mesotrophic areas are 1807.8 +/- 1025.8 (mean +/- standard deviation) microatm, 416.3 +/- 207.8 microatm, and 448.5 +/- 194.0 microatm, respectively. A maximum and minimum pCO2 values were found in the hypertrophic (4053.7 microatm) and the eutrophic (3.2 microatm) areas. There was about one magnitude order of difference in mean CO2 fluxes between the hypertrophic area (27.3 +/- 17.4 mmol/(m2 x d)) and the eutrophic (1.99 +/- 4.50 mmol/(m2 x d)) and mesotrophic (2.22 +/- 4.31 mmol/(m2 x d)) areas. But there was no significant difference between eutrophic and mesotrophic areas in pCO2 and the flux of CO2. In respect to CO2 equilibrium, input of the rivers will obviously influence inorganic carbon distribution in the riverine estuary. An exponential relationship between the pCO2 values and chlorophyll-a concentrations was obtained (r = 0.8356, n = 60) in eutrophic bay. Results suggested that lake ecosystems, also may be considered as unique aggregation, which can contain and be patient of different components that have their relative independence so long as its size enough to large. A productive lake, though it has positive fluxes of CO2 to atmosphere during the most of time, is a huge and permanent sink of carbon in terrestrial ecosystems through receiving a great quantity of carbon materials via rivers, precipitation, and biological production.