[Analysis of Influencing Factors of Chlorophyll-a in Lake Taihu Based on Bayesian Network].

Global warming has aggravated the problem of lake eutrophication. As a typical large, eutrophic, shallow lake in China, the issue of cyanobacterial harmful algal blooms (cyanoHABs) was particularly prominent in Lake Taihu. We took Lake Taihu as the study area, using the meteorological (temperature, wind speed, rainfall, and sunshine hours), water quality (total nitrogen, total phosphorus, conductivity, pH, and chemical oxygen demand), and biological (chlorophyll-a in phytoplankton) monitoring data from 1992 to 2020. We built a simulation model of chlorophyll-a based on the Bayesian network model with continuous variables to study the chlorophyll-a level of Lake Taihu under different meteorological and water quality conditions. The 75th percentile of chlorophyll-a concentration was used as the threshold to judge the risk of cyanobacterial bloom. When the probability of chlorophyll-a concentration below this threshold was greater than 75%, it was regarded as "low risk" of cyanobacterial bloom outbreak. The results showed that the average level of "temperature wind ratio" (ratio of air temperature to wind speed) in spring was 6.67℃·s·m-1, and the probability of high chlorophyll-a was less than 75% when the total phosphorus concentration was less than 0.130 mg·L-1. The average "temperature wind ratio" level in summer was 10.52℃·s·m-1, and the probability of high chlorophyll-a was less than 75% when the total phosphorus concentration was less than 0.257 mg·L-1. The average level of total phosphorus concentration in autumn was 0.154 mg·L-1, and the probability of high chlorophyll-a was less than 75% when the "temperature wind ratio" was less than 6.30℃·s·m-1. Based on the above research, the chlorophyll-a model constructed by the Bayesian network model with continuous variables was further used to simulate the nutrient control objectives under different climate change backgrounds. In order to control chlorophyll-a in Lake Taihu at the:"low risk" level of cyanoHABs, the target concentration thresholds of total phosphorus needed to be controlled under the climate level background from 1992 to 2000, 2001 to 2010, and 2011 to 2020 were given. From 1992 to 2000, the threshold value of total phosphorus concentration was 0.135 mg·L-1 in spring, 0.174 mg·L-1 in summer, and 0.171 mg·L-1 in autumn. From 2001 to 2010, the threshold value of total phosphorus concentration was 0.115 mg·L-1 in spring, 0.164 mg·L-1 in summer, and 0.162 mg·L-1 in autumn. From 2011 to 2020, the threshold value of total phosphorus concentration was 0.059 mg·L-1 in spring, 0.145 mg·L-1 in summer, and 0.145 mg·L-1 in autumn. The results showed that the control of cyanoHABs in eutrophic lakes required more stringent nutrient control strategies with global warming. It provided a reference for preventing and controlling cyanoHABs and eutrophication in Lake Taihu. Previous studies have used multiple regression models, hydrodynamic numerical models, and other methods to predict chlorophyll-a concentrations or cyanobacterial blooms in lakes. However, there has been no study on the prediction of cyanoHABs in lakes based on the Bayesian network model with continuous variables and the "dynamic" evaluation of nutrient thresholds. Therefore, based on the seasonal meteorological, water quality, and biological monitoring data of Lake Taihu from 1992 to 2020, the chlorophyll-a model of Lake Taihu was constructed for the first time based on the Bayesian network model with continuous variables to simulate the chlorophyll-a concentration of Lake Taihu under different climate indicators and total phosphorus concentrations. The weight of its influencing factors was also analyzed, and the nutrient control objectives under different climate scenarios were "dynamically" evaluated.

[Spatio-temporal Characteristics of Organic Aggregates and the Driving Factors in Typical Lakes].

Organic aggregates (OA) are the important circulation hub of matter and energy in aquatic ecosystems. However, the comparison studies on OA in lakes with different nutrient levels are limited. In this study, spatio-temporal abundances of OA and OA-attached bacteria (OAB) in oligotrophic Lake Fuxian, mesotrophic Lake Tianmu, middle-eutrophic Lake Taihu, and hyper-eutrophic Lake Xingyun were investigated in different seasons during 2019-2021 using a scanning electron microscope, epi-fluorescence microscope, and flow cytometry. The results showed that:① the annual average abundances of OA in Lake Fuxian, Lake Tianmu, Lake Taihu, and Lake Xingyun were 1.4×104, 7.0×104, 27.7×104, and 16.0×104 ind·mL-1, whereas the annual average abundances of OAB in the four lakes were 0.3×106, 1.9×106, 4.9×106, and 6.2×106 cells·mL-1. The ratios of OAB:total bacteria (TB) in the four lakes were 30%, 31%, 50%, and 38%, respectively. ② OA abundance in summer was significantly higher than that in autumn and winter; however, the ratio of OAB:TB in summer was approximately 26%, which was significantly lower than that in the other three seasons. ③ Lake nutrient status was the most important environmental factor that affected the abundance variations of OA and OAB, accounting for 50% and 68% of the spatio-temporal variations in OA and OAB abundances. ④ Nutrient and organic matters were enriched in OA, especially in Lake Xingyun; the proportions of particle phosphorous, particle nitrogen, and organic matters in this lake were as high as 69%, 59%, and 79%, respectively. Under the circumstance of future climate change and the expansion of lake algal blooms, the effects of algal-originated OA in the degradation of organic matters and nutrient recycling would be increased.

[Effect of a Comprehensive Improvement Project on Water Quality in Urban Lakes: A Case Study of Water Quality Variation in Lihu Lake Over the Past 30 Years].

In order to improve water quality, many urban lakes in China have undergone environmental restoration since the introduction of China's tenth five-year plan. To understand the effectiveness of improvement projects on eutrophic urban lakes, we analyze the changes in water quality of Lihu Lake over the past 30 years, i.e., before and after comprehensive remediation. We use long-term monitoring data from TLLER and from two regional investigations undertaken in 2017. The results were as follows. ① Concentrations of total nitrogen (TN) and total phosphorus (TP), the permanganate index, and chlorophyll-a (Chl-a) in Lihu Lake all increased dramatically since the 1990s and reached the worst levels during the period from 1997 to 2003. After comprehensive improvement measures for the lake undertaken by the local government in 2003, the water quality improved remarkably year by year, but reduced slightly in the past two years assessed here. There was no obvious improvement in water transparency when comparing data from before to after the remediation. ② Before the improvement measures, the water quality fluctuated greatly with season, however, water quality sampled during the winter post remediation was significantly better than during the summer. ③ Spatially, the water quality in the western region of Lihu Lake was significantly better than of that in the eastern region. When comparing government measures in different eutrophic urban lakes, we found that engineering management measures can improve the water quality of urban lakes over a relatively short time period. However, after the water quality has been improved, it is necessary to restore the macrophyte-dominated ecosystem, which should be supplemented by ecological restoration based on biological regulation. By improving species diversity, the aquatic ecosystem can be successfully transformed from being phytoplankton-dominated to macrophyte-dominated, thereby enabling the service functions of a lake ecosystem to be truly restored.

[Effects of wind-induced wave on organic aggregates physical and chemical characteristics in a shallow eutrophic lake (Lake Taihu) in China].

The physical and chemical characteristics were continually monitored during a wind course one time per day, which continued for 10 days, and other water physical and chemical parameters were concomitantly monitored. Organic aggregates (OA) abundance was significantly higher during wind period than calm stage and the maximum of OA abundance, which occurred the same day when wind speed was highest, was 29 times higher than that in the calm stage. Although OA-C, OA-N and OA-P concentration were decreased during wind period, the total C, N and P contend in OA were increased for the increased OA abundance. Additionally, suspended soil (SS), total nitrogen (TN) and total phosphorus (TP) concentration during wind period were significantly higher than that of clam stage, but total dissolved phosphorus (TDP), total dissolved nitrogen (TDN) and soluble reactive phosphorus (SRP) were insignificantly different. During the wind, OA alkaline phosphatase activity (OA-APA) and OA enzymatically hydrolyzable phosphorus (OA-EHP) both increased significantly, which accelerated organic phosphorous mineralization and SRP release. The results indicate that SRP release induced by wind in shallow lakes may comes from suspended matter, especially OA release rather than directly comes from sediment.

[Effects of ecosystem structure on the organic aggregates physical and chemical parameters of Lake Taihu].

The abundance, organic matter content and chemical composition of organic aggregation (OA) were monitored in Lake Taihu in different ecotype sites from January to December in 2007, and other water physical and chemical parameters were concomitantly monitored. The OA abundance was increasing along regional and P-enrichment gradients, and there were significant differences in OA characteristic in different ecotypes. Moreover, wind is one important factor that contributes to OA characteristic in Lake Taihu. OA maybe one potential important nutrient source in lake water for its high enrichment factors of nutrition: the concentrations of P and N in the OA were much higher than that of in the water; more than one third (43.3%) of TP could be attributed to the OA-P, and that number of OA-N is 16.5%.

[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.

Production and characterization of a bacterial single-chain antibody fragment specific to B-cell-activating factor of the TNF family.

An active form of a single-chain antibody fragment (scFv) from the murine monoclonal antibody ABL-1, which is specific for B-cell-activating factor of the TNF family, was produced in Escherichia coli. The complementary DNAs encoding the variable regions of the heavy chain (VH) and light chain (VL) were connected by a (Gly4Ser)3 linker, using an assembly polymerase chain reaction. The construct VH-linker-VL was placed under the control of highly efficient T7 promoter system. The cloned scFv was expressed in E. coli BL21(DE3) as inclusion bodies. After extraction from the E. coli cells, the inclusion bodies were solubilized and denatured in the presence of 8M urea. The expressed scFv fusion proteins were purified by Ni(2+)-IDA His-bind resin and finally renatured by dialysis. The purity and activity of the purified scFv were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and enzyme-linked immunosorbent assay. The result revealed that the ABL-1 scFv retains the specific binding activity to BAFF with an affinity constant of 0.9x10(-8)molL(-1).