Experimental simulation of nitrogen and phosphorus release during marine dumping of dredged sediment

Wei Liu,Jing Zhang,Junjian Ma,Bin Zhou,Qingfeng Chen,Pibo Wang,Qing Li,C.-H Weng,R Weerasinghe,J Wu

doi:10.1051/e3sconf/201911803031

Abstract

Marine dumping of dredged sediment results in the release of considerable amounts of nitrogen and phosphorus into the seawater. In this study, we evaluated the release pattern of nitrogen and phosphorus during sediment dumping through experimental simulation under different mixing ratios and temperatures. The concentration of NO3-N, PO4-P, and total phosphorus (TP) in seawater quickly increased in less than 1 h after mixing of sediment and seawater and remained stable thereafter. The concentration of NH4-N increased and peaked at 0.25 h, but quickly decreased thereafter. The concentration of NO3-N, NH4-N, PO4-P, and TP in seawater showed a positive correlation with the mixing ratio. The contribution of NO2-N from sediment to water was negligible and there was no obvious difference in the release amount among different mixing ratios. The release amount of each measured nutrient at 25°C was marginally higher than that at 15°C, suggesting that marine dredging and dumping should be performed in winter rather than in summer. The release amount of NO3-N, NO2-N, NH4-N, PO4-P, and TP in a 5000-m3 vessel reached 26.5, 17.6, 0.28, 1.68, and 1.68 kg, respectively. This study provides a detailed evaluation of nitrogen and phosphorus release pattern in marine sediment dumping process, which will be helpful for the conservation and selection of marine dumping areas.

Highlights

Dredging and dumping of dredged sediment are regular operations in harbors worldwide, especially in estuaries where sedimentation is severe[1]
Simulation experiments were performed in lab for the release of NO3-N, NO2-N, NH4-N, PO4-P, and total phosphorus (TP) from sediment into the seawater under different variables
This suggests that the release of NO3-N from sediment into the seawater occurs at the beginning of dumping of dredged sediment in real world marine dumping process

Summary

Introduction

Dredging and dumping of dredged sediment are regular operations in harbors worldwide, especially in estuaries where sedimentation is severe[1]. The dredging and dumping practices result in the release of large amounts of sediments into the sea, significantly increasing the concentration of suspended particles in seawater and affecting marine organisms both physically and chemically[2,3]. Biogenic elements and contaminants including heavy metals and organic pollutants released from dredged sediment may cause serious environmental problems such as eutrophication and excessive pollution in coastal areas[5,6]. Studies have showed that nitrogen and phosphorus can be released from re-suspended sediment by both natural and artificial sources[7,8]. Several studies have investigated the release of nitrogen and phosphorus via sediment resuspension in natural lakes and gulfs especially caused by natural reasons including current, wave, and bioturbation[9,10,11,12]. Information on the release pattern of nitrogen and phosphorus during the marine dumping process of dredged sediment is limited

Methods

Results

Conclusion