[Spatial-temporal Variations and the Regulators of Nitrate Status in Shallow Groundwater of the Typical Mountainous Agricultural Watershed in the Upper Reaches of the Yangtze River].

Shallow groundwater is the main drinking water supply for the mountainous area in the upper reaches of the Yangtze River, while its quality is often degraded by nitrate (NO-N) pollution due to intensive agricultural production activities. In the present study, we selected a mountainous agricultural watershed in the upper reaches of the Yangtze River to investigate the land use, management, and hydrogeological conditions, aiming to clarify the spatial-temporal variations in NO-N concentration of shallow groundwater, thereby exploring the key regulators. The results showed that the NO-N concentrations of the groundwater ranged from 0.40 to 12.51 mg ·Lin the study area, and the exceeding ratio was nearly 30%. On an average, NO-N concentrations for the wet season were higher than that for the dry season, indicating great variations in NO-N concentration across different seasons. In addition, the spatial variations of NO-N concentration in groundwater were also significant among different sub-catchment, which was mainly due to variations in the groundwater table depth and land uses. Furthermore, the significant correlations between the NO-N concentrations and concentrations of Cl, NH-N, DOC, and SO in the shallow groundwater were also explored in this study, suggesting that the NO-N concentrations were likely to depend on the chemical factors of the shallow groundwater in the study area. Overall, our current study highlights that the characterization of spatial-temporal variations of NO-N status in shallow groundwater and illustration of key regulators are essential to mitigate NO-N pollution and prevent quality degradation of shallow groundwater in mountainous rural areas of the upper Yangtze River watershed.