Spatial Distribution and Health Risk Assessment of Dissolved Trace Elements in Groundwater in southern China.

To understand the groundwater environmental quality and the impact of trace elements in the construction of urban agglomeration in China, this study collected 58 groundwater samples from the core area of the Chang-Zhu-Tan urban agglomeration (Changsha, Zhuzhou, Xiangtan) and quantitatively analyzed the content of 13 dissolved trace element and their spatial distribution characteristics. The health risk assessment model was further used to evaluate the human health risk caused by trace element pollution in groundwater. It was observed that Ba had the highest average concentration (0.28 mg·L-1), whereas Cd had the lowest (2.1 × 10-5 mg·L-1). Compared with China's groundwater environmental quality standard, the exceeding rates of Se, Mn, Zn, and Ni concentrations were 37.93%, 17.24%, 1.72% and 1.72%, respectively. Ba, Cd, Co, Cr, Cu, Fe, Mo, and Pb did not exceed the corresponding standards. The 13 trace elements were distributed in a scattered pattern in space and the trace elements in both banks of the Xiang River, Zhuzhou, Weishui River and surrounding areas were relatively high. Health risk assessments showed that the carcinogenic risk values of Cd, Cr, and Pb and the health risk values of 10 non-carcinogenic elements were less than the corresponding maximum acceptable risk level. The health risks associated with non-carcinogenic substances through ingestion were higher than those associated with dermal absorption. Among the non-carcinogenic substances, Ba and Mn posed the greatest health risks. With respect to drinking water exposure, Cr had the highest carcinogenic risk, followed by Pb. Furthermore, Cd had the lowest carcinogenic risk. This study recommended that continuous monitoring of Ba, Mn, and Cr in groundwater should be practiced by assessing the risk of these elements in the Chang-Zhu-Tan urban agglomeration.

Stable isotope evidence for identifying the recharge mechanisms of precipitation, surface water, and groundwater in the Ebinur Lake basin.

Arid areas cover more than one third of global land, and as such, water resources are vital for this fragile ecosystem. In order to reveal the recharge mechanisms among different water bodies in arid areas, precipitation, surface water, and groundwater were sampled in the Ebinur Lake basin, Xinjiang, China, and the isotopic values for hydrogen and oxygen were measured. The stable isotope values of precipitation showed significant seasonal variation, with minimum values in the winter, medium values in the spring and autumn, and maximum values in the summer. The slope and intercept of local meteoric water line were both lower than that of global meteoric water line, indicating subcloud evaporation effect. The vapor source of precipitation was dominated by the westerlies, but the regional re-evaporation vapor accounted for some proportions as well. In the Bortala River and Jinghe River, the stable isotopic values varied spatially, tending to be enriched with the river flow. The stable isotopic values for lake water were significantly higher than those of river water, which reflected a stronger evaporation and concentration effect of the lake water. The stable isotopic values of groundwater featured similar spatial variation compared to the river, and phreatic water evaporated to some extent. In the Bortala River, owing to its specific hydrogeological structure, the exchange rates between the groundwater and the river water were higher upstream than in the middle and lower reaches. In the Jinghe River, the deep groundwater aquifer received recharge from the shallow groundwater layers and from the river. At the edge of the Ebinur Lake, the interaction of groundwater and surface water was low and springs became the important recharge source for the lake. The results of this study provide insights into the determination of river hydrological processes and the management of water resources.

Stable isotope evidences for identifying crop water uptake in a typical winter wheat-summer maize rotation field in the North China Plain.

Better managing agricultural water resources, which are increasingly stressed by climate change and anthropogenic activities, is difficult, particularly because of variations in water uptake patterns associated with crop type and growth stage. Thus, the stable isotopes δ18O and δ2H were employed to investigate the water uptake patterns of a summer maize (Zea mays L.) and winter wheat (Triticum aestivum L.) rotation system in the North China Plain. Based on the soil water content, soil layers were divided into four groups (0-20cm, 20-40cm, 40-120cm, and 120-200cm) using a hierarchical cluster analysis. The main soil layer of water uptake for summer maize was from 0-20cm at the trefoil (77.8%) and jointing (48.6%) stages to 20-40cm at the booting (33.6%) and heading (32.6%) stages, became 40-120cm at the silking (32.0%) and milking (36.7%) stages, and then returned to 0-20cm at the mature (35.0%) and harvest (52.4%) stages. Winter wheat most absorbed water from the 0-20cm soil water at the wintering (86.6%), seedling (83.7%), jointing (45.2%), booting (51.4%), heading (28.8%), and mature (67.8%) stages, but it was 20-40cm at the flowering (34.8%) and milking (25.2%) stages. The dry root weight density was positively correlated with the contributions of the water uptake for winter wheat. However, no similar correlation was found in summer maize. Regression analysis indicated that the soil volumetric water content (SVWC) was negatively correlated with the contribution of the water uptake (CWU) for summer maize (CWU=-0.91×SVWC+57.75) and winter wheat (CWU=-2.03×SVWC+92.73). These different responses to water uptake contributions suggested that a traditional irrigation event should be postponed from the booting to flowering stage of winter wheat. This study provides insights into crop water uptake and agricultural water management.