Finite Element Simulation of Total Nitrogen Transport in Riparian Buffer in an Agricultural Watershed

Xiaosheng Lin,Jie Tang,Zhaoyang Li,Haiyi Li

doi:10.3390/su8030288

Abstract

Riparian buffers can influence water quality in downstream lakes or rivers by buffering non-point source pollution in upstream agricultural fields. With increasing nitrogen (N) pollution in small agricultural watersheds, a major function of riparian buffers is to retain N in the soil. A series of field experiments were conducted to monitor pollutant transport in riparian buffers of small watersheds, while numerical model-based analysis is scarce. In this study, we set up a field experiment to monitor the retention rates of total N in different widths of buffer strips and used a finite element model (HYDRUS 2D/3D) to simulate the total N transport in the riparian buffer of an agricultural non-point source polluted area in the Liaohe River basin. The field experiment retention rates for total N were 19.4%, 26.6%, 29.5%, and 42.9% in 1,3,4, and 6m-wide buffer strips, respectively. Throughout the simulation period, the concentration of total N of the 1mwide buffer strip reached a maximum of 1.27 mg/cm3 at 30 min, decreasing before leveling off. The concentration of total N about the 3mwide buffer strip consistently increased, with a maximum of 1.05 mg/cm3 observed at 60 min. Under rainfall infiltration, the buffer strips of different widths showed a retention effect on total N transport, and the optimum effect was simulated in the 6mwide buffer strip. A comparison between measured and simulated data revealed that finite element simulation could simulate N transport in the soil of riparian buffer strips.

Highlights

Agricultural non-point source pollution has emerged as a major source of pollution in water environments worldwide
By using the finite element (FE) method, we elucidated the patterns of total N transport and pollutant retention in the soil of buffer strips characteristic to the Liaohe River Basin
The results indicate that riparian buffers play a role in the retention of soil pollutants

Summary

Introduction

Agricultural non-point source pollution has emerged as a major source of pollution in water environments worldwide. Surface and subsurface runoff is a major mechanism for transporting sediments, fertilizers and pesticides to ground or surface water [1]. Organic forms and inorganic forms of N are transported with sediments and debris. Once released into the soil, N is transported with water and is discharged into rivers, leading to the eutrophication of rivers [2]. Use of fertilizers adds nitrate, ammonium, or various forms of organic N, including urea, to agricultural watersheds. Total N is often adopted to indicate N load in water bodies that are being investigated [3]

Results

Discussion

Conclusion