Characteristics of nitrogen transportation in Castanea mollissima forest around the Fushi Reservoir watershed in north Zhejiang Province, China.

Abstract

In this study, through setting runoff plots in Chinese chestnut (Castanea mollissima) fo-rest, the runoff water samples were collected and tested from January to October, 2013. Combining with soil nitrogen data before and after the rainy season, we analyzed the characteristics of soil nitrogen transportation in chestnut forest around the Fushi Reservoir watershed in north Zhejiang Pro-vince, China. The results showed that among the 10 surface runoff events of Chinese chestnut fo-rest, there exhibited a significant difference in runoff water volume of each runoff plot, and the maximum amount was 0.51 m3. Nitrogen was the major element associated with nutrient loss in the study region. The concentrations of nitrate nitrogen (NO3--N), ammonium nitrogen (NH4+-N), total nitrogen (TN) andchemical oxygen demend (CODMn) in the runoff water ranged from 0.02-1.87, 0.04-3.53, 1.69-5.33 and 5.30-14.07 mg·L-1, respectively. The water quality indexes were greatly affected by the runoff volume, and the relationship between the amount of nitrogen loss and runoff could be well fitted by using a linear equation. The difference in nitrogen contents of the soil in the upper, middle and lower part of the runoff plots was evident both before and after the rainy season. Moreover, the nitrogen content increased with the increasing altitude, but this trend decreased with increasing soil depth. Comparison of the difference between the four forms of soil nitrogen (NO3--N, NH4+-N, TN and hydrolyzable nitrogen Hydro-N of soil) before and after the rainy season showed that there existed significant differences in Hydro-N and TN, and the average diffe-rence values were 20.21 and 307.49 mg·kg-1, respectively. In this area, there was a great risk of nitrogen loss with runoff, and the potential non-point source pollution in Fushi Reservoir should be concerned.