[Characteristics and the Relationship of Nitrogen and Phosphorus in Soil and Water of Different Land Use Types of a Small Watershed in the Three Gorges Reservoir Area].

Long-term field monitoring data was analyzed regarding the characteristics of nitrogen and phosphorus in the soil and shallow groundwater of different land use types in a typical small watershed of the Three Gorges Reservoir area. Furthermore, the relationships among soil nitrogen and phosphorus contents, concentrations of nitrogen and phosphorus in shallow groundwater, and slope surface runoff were analyzed. The results showed that the average contents of TN and NO-N in terrace soil were significantly higher than those in sloping upland soil (< 0.05), for which the average content of paddy terrace was highest (1.49 g·kg). The average contents of TP in the soil of sloping upland and mulberry-sloping upland were significantly higher than those in the soil of other land types. The average content of NO-N in the soil of dryland terrace was highest of all land use types and its discrete degree was also largest. The slope land use type had greater impact on the concentrations of TN and NO-N in shallow groundwater, but it had little influence on TP concentration. In addition, the shallow groundwater TN concentration and NO-N concentration had significant positive correlation, and the average contribution rate of NO-N to TN in five wells ranged from 67.82% to 78.51%. The monthly average concentration of TN and NO-N in shallow groundwater changed little, only showing a significant upward trend after the fertilization stage of the two crops in spring and autumn. The average contents of TN and NO-N in the slope soil were significantly correlated with the TN and NO-N concentrations in the shallow groundwater, but there was no significant correlation between the TN and NO-N concentrations in the surface runoff. When the slope surface runoff TP concentration was>0.1 mg·L, the average content of TP had a significant linear correlation with it. There was a significant power function relationship between the concentrations of TN and NO-N in the surface runoff and concentrations of TN and NO-N in the shallow groundwater, with higher correlation of NO-N concentrations between surface runoff and shallow groundwater.