Enhua Li

Soil-Based Treatments of Mechanically Collected Cyanobacterial Blooms from Lake Taihu: Efficiencies and Potential Risks

In China, mechanical collection of cyanoblooms followed by soil-based treatments has been widely used as emergency strategies in many eutrophicated freshwaters. This study was to evaluate both efficiencies and potential risks of typical soil-based technologies. Results from this study indicated that over 90% of cyanobacterial biomass and 96% of dissolved microcystins (MCs) could be restrained in soils via three-level systems, which were much better than single-level systems. High concentrations of MCs, ranged from 65 to 276 ng g⁻¹ and from 2.12 to 6.6 ng g⁻¹, were found in soils around treatment systems and croplands, respectively. In the soil solutions, MCs ranged from 0.35 to 2.0 μg L⁻¹, showing a potentially high leaching risk. In the samples from shallow groundwater near the treatment systems, MC concentrations were detected as high as 1.2 μg L⁻¹. Moreover, bioaccumulations of MCs varied between 22 and 365 μg kg⁻¹, and 19-222 μg kg⁻¹ were found in 13 kinds of crops and 7 kinds of wild grass, respectively. Our results indicated for the first time that current soil-based technologies were effective but could pose potential environmental, ecological, and public health risks. Further improvements of these technologies were also proposed based on our findings.

Occurrence and ecological hazard assessment of selected antibiotics in the surface waters in and around Lake Honghu, China

The occurrence and temporal-spatial distributions of 13 antibiotics (tetracyclines, sulfonamides, and fluoroquinolones) in the water of a high-intensity aquaculture lake, Honghu Lake, and its associated river network and ponds were investigated. Tetracycline, oxytetracycline, chlortetracycline, and sulfadiazine are the four dominant antibiotics in this region, with maximum and median concentrations of 1454.8 and 304.8ng/L, 2796.6 and 161.9ng/L, 1431.3 and 349.9ng/L, and 499.5 and 106.5ng/L, respectively. The median concentrations of the other nine antibiotics are lower than 57.1ng/L. The highest contaminated sites are located in the Four-lake main canal and its lake inlets. Antibiotic concentrations were higher in November than in May and the concentrations were strongly correlated with water temperature, dissolved oxygen, and nitrates according to redundancy analysis. The source analysis indicated that besides untreated domestic and husbandry sewage, the aquaculture in the lake and ponds is a main source of antibiotics in the study region. The environmental hazards posed by the selected antibiotics were assessed by using the methods of hazard quotient and mixture hazard quotient. The results suggested that tetracycline, oxytetracycline, sulfadiazine, and ciprofloxacin pose medium to high ecological hazard to algae in almost all of the water samples, and the high combination ecological hazards of antibiotics are mainly posed by the high individual hazard quotient of tetracycline in the study area.

Analysis of nutrient transport and ecological response in Honghu Lake, China by using a mathematical model

A two-dimensional (2D) water quality model was established to determine the response of water quality variables and submerged aquatic vegetation biomass to load reduction from watershed inflows and enclosure aquaculture in Honghu Lake in China. Results showed that the total nitrogen (TN) and total phosphorus (TP) loads from upstream discharge were the major external loads in the lake, accounting for 70% and 63% of the total loads, respectively. Scenario simulation results indicated that 93.2% of the lake area in summer (August) and 89.5% in autumn (November) could reach the protective targets (TN<1.0mg/L) under 50% reduction of inflow TN loads. Meanwhile, 58.7% of the lake area in summer and 63.1% in autumn could reach the protective targets (TP<0.05mg/L) under 50% reduction of aquaculture areas. The mass budget results of TN and TP showed that TP immobilisation was larger than TN immobilisation. The immobilisations for TN and TP from July to September were higher than those of other months under the combined impacts of increasing runoff during the wet period, phytoplankton bloom and water residence time. The 2D water quality model provided a relevant example for assessing the effects of runoff and aquaculture activities and served as scientific support for lake management to improve water quality in large shallow macrophytic lakes.

Combined toxic effects and mechanisms of microsystin-LR and copper on Vallisneria Natans (Lour.) Hara seedlings

Microcystin-LR (MCLR) and copper are commonly found in eutrophic water bodies because of eutrophic run-offs, cyanobacterial blooms, and copper algicide applications. However, the ecotoxicological risk of their combination remains unknown. This study investigated the effect of MCLR, Cu, and their mixture on the growth and physiological responses of Vallisneria natans. Results showed that the combined toxicity of them was concentration dependent. Synergistic effects were elicited at low concentrations of MCLR and Cu exposure (≤0.25+0.64mg/L). Additive or antagonistic effects were induced at higher concentrations. Single and combined exposures could induce oxidative stress, such as increased superoxide anion radical levels. To cope with oxidative stress, V. natans could activate their antioxidant defense systems, such as enhanced superoxide dismutase production and changes in peroxidase activities. Exposure to combined MCLR and Cu (even only with 0.005+0.041mg/L) adversely affected their antioxidant defense systems. As a consequence, malondialdehyde levels significantly increased. The interaction of MCLR and Cu could also significantly increase the bioaccumulations of MCLR and Cu. This increase could be accounted for their synergistic toxic effects on V. natans. Our results suggested that the exacerbated ecological hazard of MCLR and Cu with environmental concentrations may harm aquatic ecosystems.