Abstract
This study aims to simulate and predict the nitrate nitrogen (NO3−-N) concentration in groundwater using a Gaussian function model combined with the Groundwater Modeling System (GMS) identification model. Additionally, the components of dissolved organic matter (DOM) in groundwater were measured using fluorescence spectroscopy to analyze their variation characteristics and effects on NO3−-N. The results demonstrated that the Gaussian curve fitting method accurately simulates NO3−-N concentration. For the southwest karst wetland, coupling the Gaussian function model with the GMS model effectively simulates and predicts changes in groundwater NO3−-N concentrations. The simulation indicates that NO3−-N concentrations are lower in the northern region and higher in the central area, with peak values at lower elevations reaching 20.732 mg/L. NO3−-N is primarily concentrated in the southwestern region of the study area and the upper part of Mudong Lake, showing a diffusion trend from west to east. Analysis of DOM characteristics reveals significant contributions from autochthonous sources, primarily endogenous metabolic products of microbial decomposition. The total fluorescence intensity and its components generally increase downstream, being lowest at the source and highest at river confluences. The humification index (HIX) indicates that groundwater with lower NO3−-N concentrations has lower HIX values, while higher NO3−-N concentrations correspond to higher HIX values. In summary, this study provides new insights into the simulation and prediction of NO3−-N in groundwater and the characteristics of DOM, serving as a reference for the protection of groundwater systems in the southwest karst basin.