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| Effects of dry excavation dredging on the nitrogen species and diffusion flux of ammonia nitrogen in the sediments of ditches in the Nanhan Embankment, China |
| Received:June 14, 2019 |
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| KeyWord:Dongting Lake;Nanhan Embankment;dredging;nitrogen species;sediment;ammonia nitrogen;diffusion flux |
| Author Name | Affiliation | E-mail | | GONG Li-ling | Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China | | | WANG Dan-yang | College of Environmental Science and Engineering, Hunan University, Changsha 410082, China | | | QU Wei | Changsha Environmental Protection College, Changsha 410004, China | | | QIAN Zhan | Research Center of Dongting Lake, Hunan Hydro & Power Design Institute, Changsha 410007, China | | | FAN Qing-yuan | Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China | | | YANG Yu-xin | Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China | | | TAN Shi-yang | Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China | | | DU Chun-yan | Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China | | | CHEN Hong | Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China | chenh@hnu.edu.cn | | YU Guan-long | Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, China | |
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| Abstract: |
| The aim of this study is to investigate the nitrogen species and diffusion flux of ammonia nitrogen in the Nanhan Embankment in the Dongting Lake area, which has been dredged using the dry excavation method. For this, sediments and overlying water were sampled and analyzed from ditches located in typical areas, including the areas around farmland irrigation, a domestic sewage outlet, a duck farm, a pig farm, and aquaculture. Fick's law was used to estimate the nitrogen diffusion flux at the sediment-water interface, and sequential extraction methods were employed for determining the nitrogen content in the sediments. Results showed that the dry excavation dredging method could improve the quality of the overlying water and the endogenous pollution load could be suppressed to a certain extent in the Nanhan Embankment during a short period. The diffusion flux of ammonia nitrogen at the sediment-overlying water interface ranged from-11.43 mg·m-2·d-1 to 16.19 mg·m-2·d-1, while the total nitrogen content in the sediments ranged from 403.66 mg·kg-1 to 1 120.23 mg·kg-1. The total nitrogen and four nitrogen species, including free nitrogen(FN), exchangeable nitrogen(EN), hydrolysable nitrogen(HN), and residual nitrogen(RN), in the sediments increased with time. After 36 months of dredging, the CTN in the sediments of ditches from different functional areas ranked as:duck farm > pig farm > aquaculture > domestic sewage outlet > farmland irrigation. The diffusion flux of ammonia nitrogen was significantly correlated with the FN in the sediment(P<0.05). External inputs, including livestock/poultry pollutants and aquaculture/domestic sewage discharge, were the main culprits for the nitrogen increase in both the ditch sediments and overlying water. After dry excavation dredging, the release of nitrogen pollutants from the sediments decreased significantly in the short term, which improved the quality of the overlying water in ditches in the Nanhan Embankment. It is necessary to enhance regular management and dredge works to secure the connectivity of the ditches and maintain good quality for overlying water. |
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