[Analysis of Regional Differences in Cadmium Ecological Risk in Surface Waters of the Yangtze River Basin].

This study primarily focused on the regional disparities in both water quality criteria and ecological risks attributed to cadmium presence within the surface waters of the Yangtze River Basin. In the initial phase, the long-term water quality criteria for cadmium were recalibrated in accordance with the guidelines outlined in China's "Water Quality Criteria for Freshwater Aquatic Organisms-Cadmium," accounting for the prevalent hardness distribution within the Yangtze River Basin's surface water. Subsequently, a more refined revision was undertaken considering the specific characteristics of the species residing within the Yangtze River Basin. This undertaking led to a comprehensive interpretation of the regional variations in both the distribution of long-term water quality criteria values and the risk quotient distribution of cadmium throughout the Yangtze River Basin. The incorporation of hardness and species-specific attributes resulted in a revised range of long-term water quality criteria for cadmium across different urban locales within the Yangtze River Basin. Notably, the recalibrated values ranged from 0.08 µg·L-1 as the lowest threshold to 0.75 µg·L-1 as the upper limit, signifying a tenfold differentiation. Correspondingly, the urban average annual risk quotient associated with cadmium exposure demonstrated a variation from 0.035 to 1.12, marking a significant 32-fold discrepancy between the lowest and highest values. It is essential to highlight that regions of paramount importance, such as the confluence area connecting the upper and middle stretches of the Yangtze River Basin and the intricate Dongting Lake system, exhibited noteworthy ecological risks attributed to cadmium presence. Consequently, further in-depth investigations into these critical regions are imperative for a comprehensive understanding of the associated risks.

[Study on the growth characteristics and root exudates of three wetlands plants at different culture conditions].

Wetland plants are the important component of constructed wetlands and their root exudates provide the interior hydrocarbon for denitrification. In this study, the growth characteristics and root exudates of Canna indica, Zizania caduciflora and Lythrum salicari in different culture conditions were researched. The results showed that the average biomass initial/biomass in 120 days growth of Canna indica, Zizania caduciflora and Lythrum salicari were 9.1, 3.7, and 4.7, respectively. There was a positive correlation between the root exudates and the biomass of plants, but the release rate of root exudates decreased with the biomass increase. The root exudates release rates of unit biomass were 0.92, 0.47, 0.43 mg x (g x d)(-1) for Lythrum salicari, Canna indica and Zizania caduciflora, respectively. And the root exudates of those three plants are mainly organic acids and arylprotein based on the three-dimensional fluorescence spectrum analysis. The results ofthis study also indicate that Canna indiea and Lythrum salicari are befitting wetlands plants.