Migration of two antibiotics during resuspension under simulated wind-wave disturbances in a water-sediment system.

In this study, the migration of antibiotics (norfloxacin, NOR; and sulfamethoxazole, SMX) under simulated resuspension conditions across the sediment-water interface were quantified for two locations in China: point A, located in Meiliang Bay of Lake Taihu, and point B, located in Dapukou of Lake Taihu. The concentrations of suspended solids (SS) in the overlying water amounted to 100, 500, and 1000 mg/L during background, moderate, and strong simulated wind-wave disturbances, respectively. At each SS level, the initial concentrations of the two antibiotics were set to 1, 5, and 10 mg/L. The results showed that both resuspended SS and the initial concentration of antibiotics could influence the migration of NOR in the water-sediment system. Specifically, both higher SS and initial antibiotic concentrations were associated with higher rates of migration and accumulation of NOR from water to sediment. In contrast, the migration of SMX in the water-sediment system was not impacted by SS or initial antibiotic concentration. The adsorption capacities of sediments for NOR and SMX were significantly different at both locations, possibly reflecting differences in cation exchange capacity (CEC) and organic material (OM) contents. In general, higher CEC and OM values were found in sediments with a higher adsorption capacity for the antibiotics. When CEC and OM values of sediments were higher, the adsorption capacity reached up to 51.73 mg/kg. Large differences in the migration from water to sediment were observed for the two antibiotics, with NOR migration rates higher than those of SMX. The accumulation of NOR in surface sediment during resuspension was about 14 times higher than that of SMX. The main reason for this is that the chemical adsorption of NOR is seldom reversible. Overall, this study demonstrates that resuspension of NOR and SMX attached to sediments under simulated wind-wave disturbances can promote the migration of the antibiotics from water to sediment; these results could be useful for assessing the migration and fate of commonly used antibiotics in water-sediment systems.

[Statistical analysis of factors influencing N2O emission from paddy fields in Asia].

Most previous studies attributed variation in N2O emission from paddy fields to water managements and fertilizer input. In this study, we compiled a database of N2O emission from paddy fields in Asia, including water management, type and amount of nitrogen fertilizer, soil property, climate and rice types. After screening the influencing factors with statistical significance (p < 0.01) such as different water managements, N input, different organic N types, interaction of soil total nitrogen content and different pH levels, different annual temperature levels, and different rice types, a linear model was established to link N2O emission to those factors, which could totally explain up to 60.7% of the observed variation in N2O emission. The most important influencing factor was the amount of N fertilizer input, which had significantly positive correlation with N2O fluxes. Relative emission fluxes of continuous flooding, intermittent irrigation and wet irrigation were 0.17:0.56: 1. The soil total nitrogen content had significantly positive effect on N2O fluxes while the optimum pH for N2O emission was pH > 8. Straw of N-fixing crop had much higher fluxes than other organic fertilizers while manure had no significant effects on increasing N2O emission. Application of other crop straws actually reduced N2O emission by 36%, as compared with fields without organic N input. The relative fluxes for early rice and later rice were 71% and 48% of that for single rice, respectively. Inclusion of more influencing factors such as soil property, climate and rice type helped explaining more of the variations in the observed N2O emission from paddy fields.