The Temporal-spatial Distribution Characteristics Of Cu、Zn And Their Pollution Assessment In Hyporheic Zone Of Weihe River

Hyporheic zone is the connection between groundwater and surface water, it is of great importance in the ecological process and the pollutants transformation. It plays an important role in the interaction of groundwater and surface water. Therefore the exploration of the spatial and temporal distributions of heavy metal in both river sediments and interstitial water has the significance for the pollution research and its controlling management. The Weihe River is the mother river in Guanzhong Area and is the pivotal for the development of ecology in this region. Which takes the leading position in the economic and social development in the west regions. With the rapid development of industry and growth of population along the Weihe River, the ecological environment is getting worse and worse in the Weihe River Basin. Thus, the pollution problems need to be solved immediately. To analyze the spatial and seasonal distribution of Cu and Zn in the hyporheic zone, and to estimate the heavy metal pollution degree of the Weihe River, both laboratory experiments (determination of Cu, Zn in hyporheic zone and analysis of sediment grain size) and field measurements (determination of pH, dissolved oxygen, water temperature, electrical conductivity, and organic content) were conducted in five typical test sites along the Weihe River in summer (June) and winter (December) in 2013. The spatial and seasonal distributions of Cu and Zn in river sediments and interstitial water are analyzed by the metal concentration variations from content graph. Statistical methods like correlation analysis, multivariate analysis of variance, calculation of variable coefficient and diffusion flux were used to analyze the main environmental factors and the driving mechanisms influencing the special and temporal distribution of Cu and Zn in the hyporheic zone. Several evaluation methods are used to estimate the pollution status of these two heavy metals in the Weihe River. The results show that:(1) The concentration of Cu and Zn in different layer of the hyporheic zone in same research site, in the same depth of different research sites or the at same time indifferent research sites are all different; for the seasonal changes, the concentration of Cu and Zn of five test sites in winter are all higher than in summer. (2) The concentration of Cu and Zn in river sediments could be from the same pollution source; the factors including the pH, dissolved oxygen, water temperature, electrical conductivity and organic matter content are all the main factors influencing the concentration of Cu and Zn in the hyporheic zone. (3) The vertical distribution of Cu and Zn in the hyporheic zone is influenced by water exchange and human activity disturbance, and this disturbance strength in interstitial water is stronger than in river sediments. (4) The content variations of Cu and Zn in different sites and different seasons are more obvious than in different depth of the hyporheic zone. (5) The most values of diffusion flux are negative which indicates that river sediments of five test sites have strong absorbability. (6) The evaluation results indicate that river sediments are slightly polluted by Cu and Zn based on the method of geoaccumulation index and the potential ecological risk index. However, the concentrations of Cu and Zn have a little toxicity on aquatic organism through the evaluation from the environment quality criterion. (7) In the most of the test sites, the concentration of Cu has chronic or acute toxic effect on interstitial water, but for Zn, it has no toxic effect.