Author(s): Yuan Bo

Linked Author(s):

Keywords: Cascade Reservoirs; Sediment; Nitrogen speciation; The Lancang River;

Abstract: In order to reveal the effect of nitrogen forms in sediments on nitrogen cycling in overtying water of reservoirs, the distribution characteristics of total nitrogen and bioavailable nitrogen form was analyzed by chemical sequential extraction method in ten representive sediment samples collected in three cascade canyon reservoirs along Lancang River, China. The factors that influence the release of nitrogen form and its potential risk to the overlying water were discussed. The result indicated that there were abrupt changes in the contents of nitrogen speciations between the upstream and downstream of the cascade dams, and the single reservoir also shown obvious spatial gradient characteristics. The concentrations of total nitrogen (TN) ranged from 829.8 mg/kg to 2013.2 mg/kg and the relative concentrations of different nitrogen form ranked according to the following sequence: the non-transferable N (NT-N, 39.19%-62.36%)>organic matler-sulflde fraction N (OSF-N, 23.79%-44.56%)>ion exchangeable N (IEF-N, 6.57%-12.18%)>carbonate fraction N (CF-N. 2.24%-4.22%)>iron-manganese oxides fraction N (IMOF-N, 1.53%-3.87%) IEF-N, CF-N, IMOF-N and OSF-N were the transferable nitrogen forms The highest content of transferable nitrogen in the sediments from the front of dam of reservoirs (Xiaowan, Manwan, Dachaoshan) was consistent with the reservoir age and pollution degree. The nitrogen concentration in the overlying water was closeJy related to the distribution of IEF-N from the sediments. OSF-N was an important source of nitrogen in the overlying water. Moreover, NH4+-N was the mam component of IEF-N, CF-N and JMOF-N However, the concentrations of NH4+-N were relatively higher in the sediments from the front of dams where water bodies flow slowly, indicating that the coupling relationship between eutrophication risk and the cycle of nitrogen in the sediments.

DOI: https://doi.org/10.3850/38WC092019-0850

Year: 2019