Pollution characteristics of nitrogen in surface sediments of the perennial backwater area of the Three Gorges Reservoir

HAN Chang; YANG Wenjun; BI Sheng; HU Man; TENG Sufen; HU Yu; CAO Huiqun

doi:10.3969/j.issn.1000-1123.2026.02.005

Abstract：To clarify the nitrogen pollution status and endogenous release potential of sediments in the Three Gorges Reservoir,this study focused on the perennial backwater area,where nine typical sampling sites were set up to collect 0–30 cm sediment cores.The contents of nitrogen in various forms and nitrogen transformation rates were determined,and the key influencing factors were analyzed.The results show that:①The average total nitrogen(TN)content in the sediments is 792.13 mg/kg,which is much lower than the heavy pollution threshold and the levels in major lakes in the middle and lower reaches of the Yangtze River,indicating an overall low level of nitrogen pollution.②Nitrogen is mainly in the form of total organic nitrogen(TON),and the proportion of residual nitrogen(RN)in TON exceeds 96%.The nitrogen mineralization rate is low,suggesting high nitrogen stability.③The content of active nitrogen is relatively low,implying a low risk of large-scale nitrogen release in the short term.④Spatially,the TN content in the deep sediments of the upper reservoir area is higher than that in the surface sediments,while in the lower reservoir area,the TN content in the surface sediments is higher than that in the deep sediments,indicating a potential risk of local TN accumulation.⑤pH(ranging from 8.03 to 8.95)is a key influencing factor,showing a significant negative correlation with most nitrogen forms and ammonification rate.Excessively high pH will inhibit nitrogen transformation.In conclusion,the current level of nitrogen pollution in the reservoir sediments is low,and the risk of endogenous nitrogen release is low.However,the accumulation of TN in the surface sediments of the pre-dam section requires more attention.Additionally,pH can be used as a key entry point for regulating nitrogen cycling.This study can provide a scientific basis for the prevention and control of nitrogen pollution in the Three Gorges Reservoir.