Extraction and characterization of bound extracellular polymeric substances from cultured pure cyanobacterium (Microcystis wesenbergii).

Preliminary characterization of bound extracellular polymeric substances (bEPS) of cyanobacteria is crucial to obtain a better understanding of the formation mechanism of cyanobacterial bloom. However, the characterization of bEPS can be affected by extraction methods. Five sets (including the control) of bEPS from Microcystis extracted by different methods were characterized using three-dimensional excitation and emission matrix (3DEEM) fluorescence spectroscopy combined chemical spectrophotometry; and the characterization results of bEPS samples were further compared. The agents used for extraction were NaOH, pure water and phosphate buffered saline (PBS) containing cationic exchange resins, and hot water. Extraction methods affected the fluorescence signals and intensities in the bEPS. Five fluorescence peaks were observed in the excitation and emission matrix fluorescence spectra of bEPS samples. Two peaks (peaks T1 and T2) present in all extractions were identified as protein-like fluorophores, two (peaks A and C) as humic-like fluorophores, and one (peak E) as a fulvic-like substance. Among these substances, the humic-like and fulvic-like fluorescences were only seen in the bEPS extracted with hot water. Also, NaOH solution extraction could result in strong fluorescence intensities compared to the other extraction methods. It was suggested that NaOH at pH10.0 was the most appropriate method to extract bEPS from Microcystis. In addition, dialysis could affect the yields and characteristics of extracted bEPS during the determination process. These results will help us to explore the issues of cyanobacterial blooms.

[Variation and Driving Factors of Black Water Event Intensity in Lake Taihu During 2009 to 2018].

Using daily survey and monitoring "black water event" (BWE) results in the sensitive area of Lake Taihu from April to October, 2009-2018, as well as the BWE analyzed data for relative meteorological, hydrological, chemical, and algal bloom conditions, the characteristics and yearly differences of BWEs were summarized. A BWE control strategy was suggested. There were 75 BWE occurrences detected in the past 10 years. The average area of a BWE was 1.35 km2, with a maximum area of 9.20 km2. The BWEs lasted for an average of three days, while the longest lasted 16 days. The BWEs significantly increased organic matter, total nitrogen, total phosphorus, ammonia, and sulfate, among others. All the BWEs occurred at water temperatures over 20℃. All the BWE occurrences started between May and September. The yearly BWE intensity (BWEI) varied significantly among years, with the strongest intensity in 2017 and the second strongest in 2018. The BWEI was significantly positively related to yearly algal bloom intensity (ABI) and average daily water temperature from May to September, while there was no significant relationship with major nutrient indicators. This suggests that climatic variation among years will significantly influence the risk of a BWE in Lake Taihu. The occurrence of a BWE was significantly influenced by a polluted river mouth. Almost all the BWEs occurred near river mouths, except for five macrophyte-related BWEs. This suggests that sediment pollution and its resuspension could be strongly related to the occurrence of a BWE. When considering degradation factors, a BWE could be classified as an algal-related BWE and a macrophyte-related BWE. The algal-related BWE could be further classified into three types:river-related BWE, bloom transport BWE, and local origin BWE. This research suggests that algal bloom control will be the fundamental countermeasure to decrease the risk of a BWE. Bloom abatement treatments, including mechanical bloom cleaning, water current adjustment engineering, coast-away bloom cleaning engineering, mechanical aeration treatment, and sediment dredging near river mouths would be effective methods to abate the risk of a BWE.

[High-Frequency Dynamics of Water Quality and Phytoplankton Community in Inflowing River Mouth of Xin'anjiang Reservoir, China].

The tail of the reservoir is the unstable zone regarding water quality and phytoplankton community. Therefore, it is the crucial zone in aquatic ecosystem transitions. To understand the transition characteristics and driving mechanisms of water environment dynamics, high-frequency monitoring of the water environment and phytoplankton community in the tail of a deep and large reservoir, the Xin'anjiang Reservoir in southeast of China, was conducted using a water quality monitoring buoy and three-day interval water sampling during 18 months. Results show clear seasonal thermal and oxygen stratification in the river mouth of the reservoir. The nutrient and chlorophyll-a concentrations also show stratifying phenomena during the thermal stratification period. Heavy rain and inflow quickly consume the stratification. Nutrient concentrations were highly dynamic in the river mouth. The total phosphorus ranges from 0.011 mg·L-1 to 0.188 mg·L-1, and total nitrogen ranges from 0.75 mg·L-1 to 2.76 mg·L-1. Dissolved phosphorus comprised 56% of total phosphorus, and dissolved nitrogen occupied 88% of total nitrogen, respectively. Nutrient concentrations were influenced strongly by rainfall intensity and inflow rate. Total phosphorus and nitrogen concentrations were significantly related to the three-day accumulated rainfall. Nutrient concentrations in the flood season (March to June) were significantly higher than in the non-flood season (P<0.001). Seasonal phytoplankton proliferation also significantly influenced by total phosphorus concentration. The phytoplankton community changes significantly with seasons and flood events. Bacillariophytea was generally dominant throughout the year, with the predominant genus of Fragilaria spp., Cyclotella spp., Synedra spp., and Melosira spp. Cyanophyta biomass peaked in July, August, and September, with the dominant genus of Aphanizomenon spp., Microcystis spp., and Oscillatoria spp. Apart from the high temperature, storm inflow events also triggered Cyanophyta proliferation. The proliferation of Chlorophyta was similar to Cyanophyta, with the predominant genus of Pediastrum spp. and Closterium spp.. While the Cryptophyta biomass peaked during March to May, with the predominant genus of Cryptomonas spp.. Redundancy analysis shows that the influence factors of phytoplankton community dynamics include the inflow rate, temperature, water level, water transparency, total nitrogen, total phosphorus, and nitrogen to phosphorus ratio. The meteorological and hydrological factors were major factors for phytoplankton dynamics during later autumn and winter, while the nutrient will be the co-driving factors of phytoplankton community dynamics during summer and early autumn. The research confirmed the huge influence of the intensity rainfall event on the water environment in reservoirs and described the key environmental conditions for phytoplankton community dynamics. The research is useful for the design of the monitoring and forecasting system for water safety in drinking water source reservoirs.

Inflow rate-driven changes in the composition and dynamics of chromophoric dissolved organic matter in a large drinking water lake.

Drinking water lakes are threatened globally and therefore in need of protection. To date, few studies have been carried out to investigate how the composition and dynamics of chromophoric dissolved organic matter (CDOM) in drinking water lakes are influenced by inflow rate. Such CDOM can lead to unpleasant taste and odor of the water and produce undesirable disinfection byproducts during drinking water treatment. We studied the drinking water Lake Qiandao, China, and found that the concentrations of suspended particulate matter (SPM) in the lake increased significantly with inflow rate (p < 0.001). Similarly, close relationships between inflow rate and the CDOM absorption coefficient at 350 nm a(350) and with terrestrial humic-like fluorescence C3 and a negative relationship between inflow rate and the first principal component (PC1) scores, which, in turn, were negatively related to the concentrations and relative molecular size of CDOM (p < 0.001), i.e. the concentration and molecular size of CDOM entering the lake increased proportionately with inflow rate. Furthermore, stable isotopes (δD and δ(18)O) were depleted in the upstream river mouth relative to downstream remaining lake regions, substantiating that riverine CDOM entering the lake was probably driven by inflow rate. This was further underpinned by remarkably higher mean chlorophyll-a and in situ measured terrestrial CDOM fluorescence (365/480 nm) and apparent oxygen utilization (AOU), and notably lower mean PC1 and CDOM spectral slope (S275-295) recorded in the upstream river mouth than in the downstream main lake area. Strong negative correlations between inflow rate and a(250):a(365), S275-295, and the spectral slope ratio (SR) implied that CDOM input to the lake in rainy period was dominated by larger organic molecules with a more humic-like character. Rainy period, especially rainstorm events, therefore poses a risk to drinking water safety and requires higher removal efficiency of CDOM during drinking water treatment processes.

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.

Influence of algal bloom degradation on nutrient release at the sediment-water interface in Lake Taihu, China.

Algal bloom could drastically influence the nutrient cycling in lakes. To understand how the internal nutrient release responds to algal bloom decay, water and sediment columns were sampled at 22 sites from four distinct regions of China's eutrophic Lake Taihu and incubated in the laboratory to examine the influence of massive algal bloom decay on nutrient release from sediment. The column experiment involved three treatments: (1) water and sediment (WS); (2) water and algal bloom (WA); and (3) water, sediment, and algal bloom (WSA). Concentrations of dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), ammonium (NH (4) (+) -N), and orthophosphate (PO (4) (3-) -P) were recorded during incubation. The decay of algal material caused a more rapid decrease in DO than in the algae-free controls and led to significant increases in NH (4) (+) -N and PO (4) (3-) -P in the water. The presence of algae during the incubation had a regionally variable effect on sediment nutrient profiles. In the absence of decaying algae (treatment WS), sediment nutrient concentrations decreased during the incubation. In the presence of blooms (WSA), sediments from the river mouth released P to the overlying water, while sediments from other regions absorbed surplus P from the water. This experiment showed that large-scale algal decay will dramatically affect nutrient cycling at the sediment-water interface and would potentially transfer the function of sediment as "container" or "supplier" in Taihu, although oxygen exchange with atmosphere in lake water was stronger than in columns. The magnitude of the effect depends on the physical-chemical character of the sediments.

[Influence of scum of algal bloom on the release of N and P from sediments of Lake Taihu].

Sediment cores were sampled in macrophyte dominated zone, phytoplankton dominated zone and river mouth in Lake Taihu and incubated with one half of them added algae in laboratory in August to reveal the influence of algal accumulation on the release of nitrogen and phosphorus in sediments. Concentrations of dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), ammonium, phosphate and other parameters were determined during cultivation of the sediment cores in dark. There were differences in release of TN and TP in sediments and significant variations in changes of DO, ammonium, phosphate in overlying water after adding algae. When DO declined to nearly zero, the changes of release of TN, TP in sediments differed from different ecological types of Lake Taihu with minus numbers of -0.1, -3.01 mg x (m2 x d)(-1) in macrophyte dominated zone, larger numbers of 31.1, 0.75 mg x (m2 x d)(-1) in phytoplankton dominated zone and 9.5, 2.46 mg x (m2 x d)(-1) in river mouth. The concentrations of ammonium in overlying water increased 3.62, 5.10, 6.57 mg/L and phosphate increased 53, 219, 418 microg/L in macrophyte dominated zone, phytoplankton dominated zone, river mouth, respectively. The changes of nutrients have good correlations with the decrease of DO and duration. The release of nutrients from sediments caused by accumulation and decay of algae may be the way that algal bloom satisfied itself.

[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.

[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.