RESUMO
With the rapid development of industry and agriculture, nitrate pollution in surface water has become one of the serious environmental problems in the Loess Plateau region. In this study, Yanwachuan watershed, a typical suburban watershed in the gully region of a loess plateau, was selected as the research area. Using hydrochemical data and nitrogen and oxygen bistable isotopes, combined with the SIAR model, the contribution rates of different pollution sources of nitrate in surface water in the dry season and wet season were quantitatively identified, and the main reasons for seasonal differences in different pollution sources were clarified. The results showed that inorganic nitrogen mainly existed in the form of NO3--N and NO2--N, and the average concentration of NO3--N and NO2--N in the wet season was higher than that in the dry season, whereas NH4+-N showed the opposite characteristics. Nitrification was the main process of nitrate transformation in the surface water of the basin. In the wet season, the main sources of nitrate were manure and sewage, whereas in the dry season, manure, sewage, and soil N leaching were the dominant sources, followed by ammonium fertilizer. The contribution proportion of different pollution sources to nitrate in surface water of the watershed showed significant seasonal differences. The sewage had the highest contribution, accounting for 31.40% and 65.66% in the dry season and rainy season, respectively, and the contribution of sewage to NO3- in the wet season was much higher than that in the dry season. The increase in residential water consumption in summer led to a large amount of sewage discharge into the watershed.
RESUMO
Understanding the changes of runoff, sediment transport, and hydrodynamic parameters of slopes under the influence of landscape patch coverage and connectivity is of great significance for revealing the hydrodynamic mechanism and hydrological connectivity of slope soil erosion process. In this study, the changes of runoff, sediment transport and hydrodynamic parameters of downhill surface in different coverage levels (0%, 20%, 40%, 60%, 90%) and different connectivity modes (vertical path, horizonal path, S-shaped path, random patches) of shrublands were analyzed by field artificial simulated rainfall test. The results showed that, with the increases of shrub cove-rage, runoff yield and sediment yield decreased exponentially. When the coverage increased to more than 60%, the capacity of shrubs to reduce runoff and sediment became stable. With the increases of shrub coverage, flow velocity, flow depth, Reynolds number, Froude number, stream power, and flow shear resistance significantly decreased, while Manning's roughness coefficient and Darcy-Weisbach resistance coefficient increased significantly. When shrub coverage increased to more than 60%, there was no significant difference in the eigenvalues of hydraulic parameters. The runoff rate under the four connectivity modes followed the order of vertical path > S-shaped path > horizonal path > random patches. The sediment rate was the largest in the vertical path, followed by the S-shaped path, and the horizonal path was not significantly different from the random patches. The path with poor connectivity (horizonal path, random patches) exhibited stronger resistance of hydraulic transmission and poor hydraulic sedimentation capacity than the well-connected path (vertical path, S-shaped path). Our results could provide important theoretical basis for soil erosion control on the Loess Plateau and high-quality development of the Yellow River basin.
