Reference evapotranspiration (ET0) plays an irreplaceable role in regional dry/wet conditions under the background of climate change. Based on the FAO Penman-Monteith method and daily climate variables, ET0 was calculated for 22 stations in and around Songnen Grassland, northeast China, during 1960-2014. The temporal and spatial variations of ET0 and precipitation (P) were comprehensively analyzed at different time scales by using the Mann-Kendall test, Sen’s slope estimator, and linear regression coupling with break trend analysis. Sensitivity analysis was used to detect the key climate parameter attributed to ET0 change. Then, the role of ET0 in regional dry/wet conditions was discussed by analyzing the relationship between ET0, P and aridity index (AI). Results shown a higher ET0 in the southwest and a lower in the northeast, but P was opposite to that of ET0. Evidently decreasing trend of ET0 at different time scales was detected in almost the entire region, and the significant trend mainly distributed in the eastern, northeastern and central. For the whole region, sensitivity analysis indicated decreasing trend of ET0 was primarily attributed to relative humidity and maximum air temperature. The positive contribution of increasing temperature rising to ET0 was offset by the effect of significantly decreasing relative humidity, wind speed and sunshine duration. In addition, the value of ET0 shown higher in drought years and lower in wet years.

In recent decades the Yinma River Basin has been receiving increasing pollution from industrial and domestic wastewater, agriculture, and livestock production – which are all potential 4-NP pollution sources. Thus, this work investigated spatial-seasonal distribution, risks, and seasonal variations of 4-nonylphenol in the aquatic environment of the Yinma River Basin. The results indicated that the highest concentrations in water and sediment occurred in livestock-production, industrial, and domestic-wastewater areas, and the lowest occurred in agricultural areas; a seasonal variation in 4-NP concentrations in water was observed, with the highest concentrations occurring in the dry season and the lowest concentrations in the wet season. The results for risk quotient indicated that in three water seasons, low ecological risks of 4-NP in water primarily occurred in agricultural areas, and high ecological risks occurred downstream of domestic-wastewater drainage; the ecological risks of 4-NP in sediment from all the sampling sites were exposed to moderate or high ecological risks. Based on the results for hazard quotient, a seasonal variation in human health risks of 4-NP in water was observed; except for a sampling site located downstream of domestic wastewater drainage, human health risks of 4-NP in water were low.

Bioflocculation is a promising method of removing GO from the water as it is safe, biodegradable, and non-secondary pollution, but few studies on effective and economic bioflocculant of GO have been reported. Accordingly, this work evaluated flocculation efficiency of an extracellular bioflocculant named MBF-21 produced by Enterococcus faecalis. Optimum culture conditions for bioflocculant production were initial medium pH of 7 and incubation temperature of 40ºC. The optimum carbon and nitrogen sources for bioflocculant production were glucose and beef extract. Results of Fourier transform infrared (FTIR) indicated the presence of carboxyl, hydroxyl, and amide groups on the MBF-21. The Zeta potential of MBF-21 analysis revealed that MBF-21 was mainly negatively charged. MBF-21 showed a significant ability in flocculation of GO, and flocculation efficiency was over 90% under neutral, acidic, and alkaline conditions, indicating that flocculation of GO was ion-independent. The conditions for flocculation of GO were optimized by response surface methodology (RSM) and determined to be an 11.57 mg/L dose and flocculation time of 75 min.