Aimin Hao

Occurrence and Distribution of Microcystins in Lake Taihu, China

The occurrence and distribution of microcystins were investigated in Lake Taihu, the third largest lake in China. An extensive survey, larger and broader in scale than previous studies, was conducted in summer 2010. The highest microcystin concentration was found at southern part of Taihu, which was newly included in this survey. In northern coastal areas, total cellular concentrations of 20 to 44 μg/L were observed. In northern offshore waters, levels were up to 4.8 μg/L. Microcystin occurrence was highly correlated with chemical oxygen demand, turbidity, and chlorophyll-a. Extracellular/total cellular microcystin (E/T) ratios were calculated and compared to other water quality parameters. A higher correlation was found using E/T ratios than original microcystin values. These results show that algal blooms are having a severe impact on Lake Taihu, and further and extensive monitoring and research are required to suppress blooms effectively.

Oxidative stress responses of submerged macrophyte Vallisneria asiatica to different concentrations of cyanobacteria

In a 10-day aquarium experiment, this investigation examines macrophyte restoration in eutrophic Lake Taihu, the physiological effects of different plant biomass levels and of increasing natural cyanobacterial concentrations on a submerged macrophyte, Vallisneria asiatica. Cyanobacterial stress suppressed the superoxide dismutase (SOD) activity of the plant’s leaves and induced the catalase (CAT) and peroxidase (POD) activities of its roots. The soluble protein content in V. asiatica decreased with an increase in natural cyanobacterial concentrations, whereas the malonaldehyde (MDA) increased significantly at chlorophyll a (Chl a) concentrations of 222 and 262 μg/L in water. V. asiatica adapted to the stress caused by cyanobacterial concentrations by adjusting its antioxidant defense system to remove the excessive reactive oxygen species when the algal Chl a concentration was >109 μg/L. Additionally, high biomass of V. asiatica (2 222 g FW/m2) can inhibit the reproduction of cyanobacteria more significantly than low biomass (1 111 g FW/m2). High biomass of V. asiatica increased the oxidative stress in an individual plant when the initial Chl a concentration in the water reached 222 and 262 μg/L, as expressed by the increased MDA in leaves, compared with low biomass of V. asiatica. This provides a basis for controlling cyanobacterial concentrations and V. asiatica biomass for the recovery of V. asiatica in eutrophic Lake Taihu.

Water Quality Monitoring at Lowland Creek Area by GIS and Improvement Trials Using Fallow Paddy Fields

Lowland area at seacoast of the Arikake Bay in Japan is famous for rotational use of creek water for rice production. About 40 years ago, almost whole area was covered with rice paddy in summer season. For the purpose of regulating the rice production, about 40 % of rice fields have been used for upland crop production. In addition to the changes of agricultural style, the inflow of the contaminated drainage water has been increased by the development of urbanization. To keep the sustainable agriculture in this area, it is requested to establish the regional control system to keep the creek water clean. The objective of this study is to evaluate the effect of the rice paddy, upland crop, and greenhouse cultivations on the water quality. First, the effects of water management, fertilizer management, crop management on the nitrogen and phosphate loads to creek water were studied experimentally at the study site about 10 ha. Water purification functions of rice paddy were evaluated quantitatively. From this result, it was advocated to prepare water ponded fallow fields through out the year for cleaning creek water. Additionally, the effectiveness for water purification by some vegetables planted in the fallow paddy are introduced. Second, daily changes of creek water qualities were monitored with the automatic sampler at the end of creek networks. Using the data, the relationships between land use condition and water quality along the main creek were simulated with the support of GIS.