[Effects of ultrasound on the physiological characteristics and competitive growth between Microcystis aeruginosa and Chlorella pyrenoidosa]. / è¶ å£°æ³¢å¯¹é“œç»¿å¾®å›Šè—»ä¸Žè›‹ç™½æ ¸å°çƒè—»ç”Ÿç†ç‰¹å¾åŠç«žäº‰ç”Ÿé•¿çš„å½±å“.

Microcystis aeruginosa is a common bloom-forming cyanobacterium, which generally coexists and competes with Chlorella pyrenoidosa in lakes. Sonication can be used for emergency management of algal blooms. Ultrasound influences algal growth and physiological parameters, as well as interspecific competition in algal community. To explore the effects of ultrasonic stress (35 kHz, 0.035 W·cm-3) on physiological characteristics and interspecific competition of algae, M. aeruginosa and C. pyrenoidosa were sonicated in mono- and co-cultures (1:1 mixture, according to cell concentration). Results showed that M. aeruginosa was more sensitive to ultrasonic stress. After the sonication for 600 s, both photosynthetic activity (Fv/Fm) and esterase activity of M. aeruginosa showed significant changes, with Fv/Fm values in mono- and co-cultures being decreased by 51.8% and 64.7%, respectively. In comparison, Fv/Fm values of C. pyrenoidosa changed slightly. M. aeruginosa released more chromophoric dissolved organic matter (CDOM, including tryptophan-, tyrosine-, and fulvic-like substances) than C. pyrenoidosa. The cell concentration of C. pyrenoidosa showed little changes regardless of sonication time, while the cell concentration of M. aeruginosa decreased at different degrees. The cell concentration of M. aeruginosa in co-cultures decreased by 42.6% after sonication for 600 s, which might be responsible for the dominance of C. pyrenoidosa during 8 days after sonication. M. aeruginosa inhibited C. pyrenoidosa in other treatments, but mutual inhibition appeared in the 600 s sonication treatment. After ultrasonic treatment, the activity of M. aeruginosa could recover gradually. The treatment should be conducted again within a week to improve the persistence of algal control.

[Impact of Enclosure Culture on Heavy Metal Content in Surface Sediments of Hongze Lake and Ecological Risk Assessment].

In order to explore the concentrations of heavy metals and the influence of fencing on Hongze lake, the content, source, and spatial distribution characteristics of heavy metals in surface sediments and ecological risks were analyzed in 2018 after part of the fence around Hongze Lake was removed. The results showed that the average contents of Cr, Ni, Cu, Zn, As, Cd, and Pb in the surface sediments in Hongze Lake were 66.78, 33.89, 25.35, 74.77, 16.55, 0.23, and 27.20 mg·kg-1, respectively. Cr, Ni, Cu, Zn, and Pb contents were at non-polluting levels, with As and Cd at the lowest level, based on the accumulation index evaluation. Except for Cd, all the elements showed low potential ecological risk. The results showed that the heavy metal content in the fenced, dismantled, and peripheral areas increased and accumulated towards the center of the lake. The removal of the fence did not significantly reduce the heavy metal content in the short-term. Overall, Hongze Lake presented a state of low ecological risk. In the future, environmental policies should include surface sediment accumulation areas and fencing culture in the north and northeast of Hongze Lake.

[Distribution and Risk Assessment of OCPs in Surface Water, Sediments, and Fish from Lake Gucheng and Inflow and Outflow Rivers].

To investigate the distribution, source, and ecological risk of organochlorine pesticides (OCPs) residues in Lake Gucheng, surface water, sediment, and biological samples were collected from 12 sampling sites of Lake Gucheng and its inlets and outlets during summer and winter, and the concentrations of 19 OCPs were analyzed. The results showed that the concentration (dry weight) of OCPs in Lake Gucheng ranged from 26.74 to 48.12 ng·L-1 in surface water, 9.01 to 35.34 ng·g-1 in sediment, and 13.39 to 124.29 ng·g-1 in organisms. The pollution characteristics of OCPs in surface water showed that the concentration was much higher in summer than in winter, and much higher at inflow and outflow rivers than in farming ponds and the central region of Lake Gucheng; the seasonal pollution characteristics in sediment were not obvious. All 19 kinds of OCPs in water, sediment, and organisms were detected in different degrees, and the dominant contaminants were HCHs and DDTs. α-HCH was the main pollutant at all sites in both surface water and sediment, with 21% to 42% of total HCHs in two seasons. p,p'-DDD was the main pollutant in surface water with 30% to 76% of total DDTs, whereas p,p'-DDT was the main pollutant in sediment with 68% to 93% of total DDTs in two seasons. Source analysis based on ratios of HCHs isomers and DDTs isomers indicated that there was a new input of OCPs under anaerobic conditions in the study area. The ecological risk assessment showed that the OCPs in surface water did not lead to significant health risks, but the OCPs in sediments might pose ecological risks to the Lake Gucheng ecosystem. The organisms were within the acceptable potential carcinogenic risk range.

[Pollution distribution and potential ecological risk assessment of heavy metals in sediments from the different eastern dredging regions of Lake Taihu].

In order to investigate the distribution characteristics of nutrients and heavy metals in sediments from different eastern dredging regions of Lake Taihu, the surface and core sediment samples at 5 sites (in East Taihu Lake and Xukou Bay) were collected in 2012. Contents of nutrients (TOC, TN and TP) and heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) in the sediments were measured and the pollution degrees of heavy metals were evaluated with the potential ecological risk method. The results showed that the heavy metal contents in Xukou Bay were generally higher than those in East Taihu Lake, whereas the nutrients contents showed the reverse trend. There were significant differences between the phytoplankton-dominated and culture lake regions. The concentrations of both nutrients and heavy metals decreased with increasing profile depth. Moreover, the contents of nutrients and heavy metals in the sediments of all dredged areas were lower than those in the un-dredged areas, suggesting that dredging may be a useful approach for decreasing nutrients and heavy metals loading in sediments, but its effectiveness decreased with time. Significant positive correlations were found among different heavy metals and nutrients, indicating that they were from the same pollution source. The Hakanson potential ecological risk index was applied for assessing the status of sediment heavy metal enrichment and the result indicated that sediment dredging could reduce the extent of potential ecological risk. The risk index in different sites followed the order: X1 > D1 > D3 > X2 > D2, while the risk index in site X1 of Xukou Bay was higher than that in site D1 of East Taihu Lake. And the comprehensive ecological risk grades in sites X1 and D1 were in the moderate range, while the sites D2, D3 and X2 were low.

[Hydroacoustic assessment of fish resources in reservoirs with different fishery management].

By using Biosonics DT-X echosounder (208 kHz), a hydroacoustic investigation was conducted on the fish resources in three mesotrophic reservoirs (Daxi Reservoir, Shahe Reservoir, and Jinniushan Reservoir) with different fishery management in late autumn and early winter 2011, and a GIS model was constructed to assess the fish resource distribution in the reservoirs. No significant difference was observed in the average size of fish in the three reservoirs, but the distribution curves of fish target strength (TS) showed that the fish size distribution proportion was different, and had close correlation with fishery management. The fish density in Daxi Reservoir (averagely 0.0183 ind x m(-3)) had no significant difference with that in Shahe Reservoir (averagely 0.0124 ind x m(-3)), but the fish density in Jinniushan Reservoir (averagely 0.0085 ind x m(-3)) was significantly lower than that in Daxi and Shahe reservoirs. There was no significant correlation between the horizontal distribution of fish density and the water depth in the three reservoirs. The fish in the three reservoirs were in group distribution, and fish aggregation was found in Daxi and Shahe reservoirs. In the three reservoirs, the fish biomass was the highest in downstream, and there was a greater biomass near the dam, except in Shahe Reservoir which was affected by fish catch activity. Based on the raster data obtained from GIS fish distribution model and the surface water area of each grid, the total amount of fish resources with the TS > -60 dB in the Daxi, Shahe and Jinniushan reservoirs was estimated as about 480000, 610000 and 520000 individuals, and that with the TS > -40 dB was about 50400, 52900 and 90700 individuals, respectively.

[Experimental study on the environmental fate of nitrogen in snail-macrophyte ecosystem for water purification].

A snail-macrophyte simulation system was built and isotope tracer technique was adopted to study the environmental fate of nitrogen in snail-macrophyte purification system, the results showed that: Vallisneria spiralis increased its wet weight by 580% and its number by 6.6 ramets, moreover, Vallisneria spiralis absorbed 1.07% 15N by the roots and 7.74% by stems and leaves, while Bellamya only absorbed 0.06%. And 5.73% 15N was retained in the sediment. Through analyzing of the results, it indicated that: in such simulation system, sediment was the main nutrition source for the growth of Vallisneria spiralis, which absorbed only few dissolved nitrogen from water; ammonium nitrogen in water was transformed mainly in the sediment-water interface, most of which was absorbed by Vallisneria spiralis, a small amount was removed through nitrification and denitrification, and the rest was kept by sediment; Vallisneria spiralis was final vector for removing nitrogen in the system, and Bellamya could also boost the growth of Vallisneria spiralis and strengthen the processes of nitrification and denitrification, thus promoting the nitrogen removal from the system indirectly. So, during the period of culture, rational allocation of snail-macrophyte structure in different stages plays an important role in controlling water quality in ponds.

[Comparison of overwintering and rrecruitment of cyanobacteria in Taihu Lake and Chaohn Lake].

Dynamics of overwintering and recruitment of cyanobacteria were studied in Taihu Lake and Chaohu Lake. The results demonstrated that cyanobacteria sank to the sediment in autumn (November) and recruited to water column in May in Taihu Lake. From November to next May, the cyanobacteria kept growing with an increased growth rate from March to May in the sediment. A similar pattern of overwintering and recruitment of cyanobacteria was found in Chaohu Lake, which showed the cyanobacteria sinking in November and recruitment in spring with the cyanobacteria growing in the sediment, while the cyanobacteria recruited to water column from March to April. Our results showed there was typical overwintering and recruitment of cyanobacteria in Taihu Lake and Chaohu Lake. The numbers of cyanobacteria in sediment represented by the almost same pigments content in different lake areas of Taihu Lake according to nutrient levels probably implied the little relationships of the numbers in sediments with the summer bloomed biomass of cyanobacteria.

[Effects of anthropogenic organic matter inputs on stable carbon and nitrogen isotopes in organisms from microbial food chain in Taihu Lake].

Stable isotope analyses of carbon and nitrogen were used to evaluate autochthonous versus allochthonous contribution to the main microbial food loop components in the four sampling sites based on different trophic status in Taihu Lake. On average, the delta13 C and delta15 N values of organic matter (OM) sources (bacteria, cladocera, particulate and sedimentary organic matter) and the delta13 C of dissolved inorganic carbon (DIC), which are the main components in microbial food chain, showed the lowest values at estuary location compared with the other three sites, reflecting a strong influence by terrestrially derived nutrients and organic matter. The mean delta13 C value of dissolved organic matter (DOM) that we measured was close to the estimated terrestrial delta13 C - 26 per thousandd, suggesting an allochthonous-derived organic C pool. Particulate organic matter (POM) was supposed to be mainly dominated by algae under the assumption of a constant fractionation from DIC to phytoplankton of 22 per thousand. Cladocera had a lower delta13 C than the average delta13 C of POM (0.2 per thousand) and bacteria (2.5 per thousand), supposing a lipid accumulation or selective feeding a more delta13 C-depleted algal fraction (pico- and nano-plankton, < 50 microm) of POM. The contribution of autochthonous versus allochthonous carbon to the bacterial biomass was estimated by applying a two-member mixing model using a delta13 C of - 26 per thousand as the allochthonous end member. The bacterial biomass consisted of 61.2% allochthonous carbon at estuary point with large terrestrial effluents, while in the large open lake area, bacteria was mainly supported by autochthonous OM (58.5% - 92.9%). The results substantiate the finding that the analysis of carbon and nitrogen stable isotopes can help to elucidate sources and sinks of organic matter in Taihu Lake, which are characterized by a great spatial variability and complexity.