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

¹ Qilu University of Technology (Shandong Academy of Sciences), Shandong Analysis and Test Center, 250014 Jinan, P.R. China
² Shandong Provincial Key Laboratory of Marine Ecology and Environment&Disaster Prevention and Mitigation, 266061 Qingdao, P.R. China
³ Marine Engineering Prospecting Institute of North China Sea, State Oceanic Administration, 266061 Qingdao, P.R. China

^* Corresponding author: ll_liuwei@163.com ; chensdcn@163.com

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.