摘要：Core Ideas High NO 3 − concentrations were detected in an area with developed conduit networks and sinkholes. Stable isotopes of water and NO 3 − were used to identify their transport. Isotopic composition of NO 3 − was affected by denitrification, particularly in the wet season. Water management should consider the linkage between N flux and rainfall. A typical mixed‐land‐use karst catchment in Guizhou Province, southwestern China, with well‐developed conduit networks was studied to understand the spatiotemporal variability of nitrate sources and transformation processes. High nitrate concentrations were detected in the karstic study area, which is particularly vulnerable to anthropogenic pollution and is considered a representative catchment to understand the surface–underground system in southwestern China. The stable isotopes of water and nitrate (δD water , δ 18 O water , δ 15 N nitrate , and δ 18 O nitrate ) were used to identify nitrate sources and to assess seasonal variations in hydrological processes affecting nitrate levels. Monthly sampling indicated that nitrate flux is strongly related to agricultural activities and the intensity of rainfall, which can accelerate transport between the surface water (SFW) and underground water (UGW) systems. Nitrate in water samples showed nitrification characteristics and was mainly derived from the oxidation of reductive fertilizers including organic N fertilizer. The isotopic composition of nitrate was affected by denitrification, particularly in the wet season. Isotopic signatures indicate that moderate evaporation occurs during the dry season. Denitrification in underground conduits appears to be relatively minor compared with that in SFW. The results of this study suggest that rainfall is an important factor influencing N flux, which has implications for water management.
关键词：HRB; Houzhai River Basin; SFW; surface water; UGW; underground water.
