• 标题：Coupled hydrological and biogeochemical modelling of nitrogen transport in the karst critical zone
• 关键词：Nitrogen transport,Distributed water-N model,Karst critical zone,Tracer-aided
• 作者：Zhicai Zhang, Xi Chen, Qinbo Cheng, Siliang Li, Fujun Yue, Tao Peng, Susan Waldron,David M Oliver , Chris Soulsby

Transport of nitrogen (N) in karst areas is more complex than in non-karst areas due to marked heterogeneity of hydrodynamic behaviour in the karst critical zone. Here, we present a novel, distributed, coupled hydrologicalbiogeochemical model that can simulate water and nitrogen transport in the critical zone of karst catchments. This new model was calibrated using integrated hydrometric, water stable isotope, and nitrogen-N concentration data at the outflflow of Houzhai catchment in Guizhou province of Southwest China. Hydrological dynamics appears to control N load from the study catchment. Combining flflow discharge and water stable isotopes signififi- cantly constrained model parameterisation and mitigate the equififinality effects of parameters on the simulated results. Karst geomorphology and land use have functional effects on spatiotemporal variations of hydrological processes and nitrogen transport. In the study catchment, agricultural fertilizer was the largest input source of N, accounting for 86% of the total. Plant uptake consumed about 45% of inputs, primarily in the lowlying valley bottom areas and the plain covered by relatively thick soils. Thus, a large amount of N released from soil reservoirs to the epikarst (via fractures or sinkholes) is then exported to the underground channel in the limestone area to the south. This N draining into groundwater could lead to extensive, potentially long- term contamination of the karst system. Therefore, improving the effificiency of fertilization and agricultural management in valleys/depressions is an urgent need to reduce N losses and contamination risk.

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