Seasonal Water Quality Changes in the Huoditang Forest Region of the Qinling Mountain Range
秦岭火地塘森林水质的季节性变化特征

This study was conducted in the Huoditang forest region of Shaanxi Province. The region is located in the Qinling Mountain range. We collected stream water samples at the outlets of two small watersheds and two tributaries each month across an eight year period. The samples were analyzed for pH and water chemistry. Changes in pH and water chemistry with season were studied by using contributing factor analyses. The results of the study showed that stream water was slightly alkaline, with the pH ranging from 7.1 to 8.4 throughout the year. Stream water pH was higher in winter and spring and lower in summer and autumn. The NO3- concentrations in stream water were highest in spring and early summer, while NH4+ concentrations were highest in winter and early spring, and PO4(3-) concentrations were highest in winter and summer. K+ concentrations were highest in spring. Na+ concentrations were highest in September and lowest in August. Ca2+ concentrations in stream water were highest in June and September and ranged from 19.4 mg x L(-1) to 44.3 mg x L(-1) during the year. Mg2+ concentrations were highest in March and ranged from 2.18 mg x L(-1) to 5.25 mg x L(-1) during the year. Cd concentrations were highest from January to April, while Pb concentrations were highest in November and January. The concentration of both Cd and Pb was lowest in autumn. The concentration of Cd ranged from 0.019 microg x L(-1) to 0.3265 microg x L(-1) and the concentration of Pb ranged from 0.217 microg x L(-1) to 3.886 microg x L(-1). Mn concentrations were highest in May and December, while Fe concentrations were highest in spring and Zn concentrations were highest in March and August. According to environmental quality standards for surface water, stream water quality in the Huoditang forest region met the requirements for water quality standard I. Water quality was best in autumn and poorest in winter and spring.