Earth Science Frontiers ›› 2026, Vol. 33 ›› Issue (1): 14-24.DOI: 10.13745/j.esf.sf.2025.10.35

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Adsorption-desorption behavior and release flux of nitrogen and phosphorus in sediments of the reservoir drawdown zone under water level fluctuations

WU Mohan1,2,3(), SU Xiaosi1,2,3, SONG Tiejun1,2,3,*(), HAO Yuan1,2,3   

  1. 1. College of New Energy and Environment, Jilin University, Changchun 130021, China
    2. Laboratory of Groundwater Resources and Environment of the Ministry of Education, Jilin University, Changchun 130021, China
    3. Institute of Water Resources and Environment, Jilin University, Changchun 130021, China
  • Received:2025-06-20 Revised:2025-09-12 Online:2026-01-25 Published:2025-11-10

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Abstract:

The drawdown zone, formed by water-level fluctuations in reservoirs, represents a critical terrestrial-aquatic interface. The release of nitrogen and phosphorus from its sediments significantly influences reservoir water quality. However, the alternating redox conditions caused by periodic water-level fluctuations lead to poorly understood mechanisms governing the release of these nutrients and their contribution to water quality. This study was conducted in a large-scale reservoir in Jilin Province. Water and sediment samples from the drawdown zone were collected during the pre-flood, flood, and post-flood periods to investigate the release patterns of nitrogen and phosphorus in response to water-level fluctuations and their impact on reservoir water quality. The results showed that during the water-level fluctuation cycle, the concentrations of ammonia nitrogen (${\mathrm{NH}}_{4}^{+}$-N) and phosphate (${\mathrm{PO}}_{4}^{3-}$-P) in the reservoir water first increased and then decreased. In the sediments, ammonia nitrogen content initially decreased and then increased, while inorganic phosphorus content showed an opposite trend. Adsorption-desorption experiments revealed that at pH 5, the sediments had a high adsorption capacity for both ammonia nitrogen and phosphate. In contrast, at pH 9, the desorption of nitrogen and phosphorus was enhanced. Notably, during the post-flood period, the sediments exhibited significant desorption behavior. Mass balance calculations indicated that the release fluxes of nitrogen and phosphorus from the sediments were 324.15 t and 8.18 t, accounting for 47.22% and 57.72% of the variations in inorganic nitrogen and phosphorus concentrations in the surface water, respectively. This study provides crucial scientific evidence for identifying internal pollution mechanisms in reservoirs, predicting water quality risks, and supporting sustainable water resource management and drinking water safety.

Key words: reservoir drawdown zone, water level fluctuation, nitrogen and phosphorus contents, release flux, adsorption-desorption

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