Evaluation of Distribution Properties of Non-Point Source Pollution in a Subtropical Monsoon Watershed by a Hydrological Model with a Modified Runoff Module

Abstract

Non-point source pollution (NPS) is difficult to manage for watersheds, due to the scattering of pollution sources and uncertainty over the time it takes to accumulate. Since local agriculture and poultry rearing prevail, NPS occupies a large proportion of local pollution. In this paper, we modified the runoff module of the Soil and Water Assessment Tool (SWAT) to study the distribution properties and the effect of control of NPS in the Binjiang watershed in Southern China. The model was run from 2005 to 2014. The runoff simulation’s accuracy had apparently improved compared to the original model, as the Nash coefficient (Ens) had improved from 0.72 to 0.89, and the determination coefficient (R2) had improved from 0.75 to 0.91, an improvement in accuracy of 23.61% (Ens) and 21.33% (R2). Thus, the modified model (SWAT-m) is more adaptable for the simulation of extensive non-urban watersheds in subtropical monsoon climates. The validated model was used in further analysis. The results show that 82–90% of total nitrogen and 83–89% of total phosphorus were concentrated in the period from April to September annually. Through the introduction of the pollution generation potential parameter Φi, we obtained the descending order of all sub-basins in terms of their pollution generation potential. The critical source areas (CSAs) were found to be the northeast sub-basins in lower terrain that is used mainly for agricultural applications, accounting for 53% of the total watershed. The accumulation time is April to July, occupying 69% of annual generation. The simulation of management measures showed that NPS control has a good effect, with a 15 m filter strip in CSAs. Ammonia nitrogen and total phosphorus can be reduced apparently by 32% and 43%, respectively. The results may provide support for the management of NPS in watersheds under similar conditions.

An Urban Water Pollution Model for Wuhu City

“…where W pp is the pollution emissions from livestock and poultry breeding; N p is the number of poultry raised; X 1 is the daily manure production of individual livestock and poultry; T is the feeding period; α 1 is the average content of pollution in manure; X 2 is the daily urine production of individual livestock and poultry; and α 2 is the average content of pollutants in the urine. The values of α 1 and α 2 refer to the handbook of the pollution source census production and emission coefficient [19].…”

“…Jiang et al [18] built a coastal water pollution load model using system dynamics coupled with water pollution load and the "concentration loss" model. In 2019, Zhang et al [19] modified the runoff module of SWAT to study the distribution properties and NPS control in the Binjiang watershed, southern China. The northeast sub-basins in lower terrain, used mainly for agricultural applications, were the critical source areas (CSAs).…”

Water Resource Risk Assessment Based on Non-Point Source Pollution

“…For the assessment of basin pollution risk caused by NPS pollution, comprehensive impact factors need to be considered [37]. By examining the literature and taking into consideration the process of pollutant production and reduction, in this study we select nitrogen, phosphorus, soil erosion intensity, distance, slope, and rainfall levels as the main factors contributing to NPS in order to evaluate the risk of NPS pollution in watersheds [38][39][40].…”

A Combination Model for Quantifying Non-Point Source Pollution Based on Land Use Type in a Typical Urbanized Area

“…Urban rainstorm events are often the focus of attention in urban areas; for this purpose, models such as SWMM and STORM are commonly used [18,26,28]. Additionally, some models, such as SWAT and HSPF, are well suited to the evaluation of NPS pollution in a watershed or farmland [17,27,29], but are not applicable to urbanized areas. These NPS evaluation models generally encounter problems with insufficient water quantity or quality modules.…”