Risk Assessment Based on Nitrogen and Phosphorus Forms in Watershed Sediments: A Case Study of the Upper Reaches of the Minjiang Watershed

Hongmeng Ye, Hao Yang, Nian Han, Changchun Huang, Tao Huang, Guoping Li, Xuyin Yuan and Hong Wang
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Hongmeng Ye: School of Geography Science, Nanjing Normal University, Nanjing 210023, China
Hao Yang: School of Geography Science, Nanjing Normal University, Nanjing 210023, China
Nian Han: College of Environmental, Hohai University, Nanjing 210098, China
Changchun Huang: School of Geography Science, Nanjing Normal University, Nanjing 210023, China
Tao Huang: School of Geography Science, Nanjing Normal University, Nanjing 210023, China
Guoping Li: Fujian Provincial Key Laboratory of Eco-Industrial Green Technology, College of Ecology and Resource Engineering of Wuyi University, Wuyishan 354300, China
Xuyin Yuan: Fujian Provincial Key Laboratory of Eco-Industrial Green Technology, College of Ecology and Resource Engineering of Wuyi University, Wuyishan 354300, China
Hong Wang: School of Geography Science, Nanjing Normal University, Nanjing 210023, China

Sustainability, 2019, vol. 11, issue 20, 1-21

Abstract: In order to achieve effective eutrophication control and ecosystem restoration, it is of great significance to investigate the distribution characteristics of nutrient elements in sediments, and to perform ecological risk assessments. In the current grading criteria for nutrient elements in sediments, only the overall or organic components of carbon, nitrogen and phosphorus are considered, while the specific species distributions and bioavailability characteristics are rarely taken into account. Hence, using the current grading criteria, the differences in the release, migration and biological activity of nutrient elements in sediments cannot be accurately reflected. Taking the upper reaches of the Minjiang River watershed as an example, we analyzed the overall distributions and the ratio of nutrient elements in sediments, the spatial changes of nitrogen and phosphorus forms, the bioavailability, and the environmental significance. The ecological risk of nitrogen and phosphorus in sediments was assessed using an evaluation method based upon the biological effective parameter. The results were compared with the results of the evaluation methods based on the single pollution index, and then these evaluation methods were confirmed accordingly. From the results, the following conclusions can be obtained: (1) The spatial distributions of nutrient elements in sediments in the upper reaches of the Minjiang River Watershed (including the Jianxi Basin, Futunxi Basin, and Shaxi Basin) were significantly affected by the local ecology and the urban sewage discharge system. (2) The maximum average contents of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in sediments were observed in the Jianxi Basin, the Futunxi Basin and the Shaxi Basin, respectively. (3) According to the contents of nitrogen and phosphorus in sediments, the bioavailable nitrogen (TTN) accounted for 35.49% of the total contents of TN. The components of TTN can be sorted from high to low as follows: Nitrogen in organic sulfide form (SOEF-N) > nitrogen in iron-manganese oxide form (SAEF-N) > nitrogen in ion exchange form (IEF-N) > nitrogen in weak acid leaching form (WAEF-N). Inorganic phosphorus (IP) was the main component of TP. The components of IP can be sorted from high to low as follows: Metal oxide bound phosphorus (NaOH-P) > calcium bound phosphorus (HCl-P) > reduced phosphorus (BD-P) > weakly adsorbed phosphorus (NH 4 Cl-P). Meanwhile, bioavailable phosphorus (BAP, BAP = NH 4 Cl-P + BD-P + NaOH-P) accounted for 36.94% of TP. According to the results of the single pollution index method, the risk level of TOC pollution in the sediments was relatively low in the whole area, while the risk level of TN pollution was low or moderate in most zones, and severe in certain ones. The risk level of TP pollution was low to moderate. (4) From the results of the bioavailability index evaluation method, based on the total amounts and forms of N and P, the risk level of N pollution was moderate, while the risk of P pollution was negligible. In addition, the results of the bioavailability index evaluation method were more consistent with the actual situation and reflected the overall environmental effects of nitrogen and phosphorus.

Keywords: sediment; nutrient element; nitrogen forms; phosphorus forms; risk assessment (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2019
References: View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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