Spatial distribution and driving factors of sediment net nitrogen mineralization in riparian zone of the Three Gorges Reservoir

Inorganic nitrogen (N) loss through sediment N mineralization is important for eutrophication surrounding riparian zone. Sediment physicochemical properties have been changed at water-level elevation in riparian zone of the Three Gorges Reservoir (TGR) due to differences in hydrological stress and human activity intensity. However, spatial distribution and driving factor of net N mineralization rate (N_min) and its temperature sensitivity (Q₁₀) based on the changes in sediment physicochemical properties are still unclear at water-level elevation in the riparian zone. A total of 132 sediment samples in the riparian zone were collected including 11 transections and 12 water-level elevations on basin scale of the TGR during drying period, to conduct a 28-day incubation at 15℃, 22℃, 29℃ and 36℃. N_min, total N (TN) and substrate quality (SQ) increased with water-level elevation, while Q₁₀ showed an opposite trend (P < 0.001). Results of the structural equation model showed that water-level elevation had direct positive effects on TN and SQ (P < 0.01). In addition, TN was the major factor that had a direct positive effect on N_min, and SQ was the crucial factor that had a direct negative effect on Q₁₀ (P < 0.001). In conclusion, increases in TN and SQ were major driving factors of N_min and its Q₁₀ at water-level elevation, respectively, in riparian zone of the TGR during drying period.