[Endogenous Release of Nitrogen and Phosphorus in the Danjiangkou Reservoir]

In situ sediments were collected at different sites of the Danjiangkou Reservoir using a columnar sediment sampler, and the release rate of N and P at the sediment-water interface was determined through static incubation experiments and the diffusion model of interstitial water molecules. The results showed that there was a significant difference in the release rate for N and P from sediments collected at five sampling sites. The release rates of NH₄⁺-N and PO₄^3--P under static incubation conditions were 13.07-24.88 mg·(m²·d)^-1 and 3.06-6.02 mg·(m²·d)^-1, whereas those estimated by Fick's Fist Law were 2.67-7.25 mg·(m²·d)^-1 and 0.04-0.18 mg·(m²·d)^-1, respectively. Overall, the release rates of N and P in the tributaries were 1.48 and 1.57 times higher than that in the reservoir, respectively, and they tended to decrease from the north to the south. The R/F values of NH₄⁺-N and PO₄^3--P were 3.43-4.98 and 29.67-72.88, respectively. The highest release rates of N and P were observed in the Guojiashan tributary for both methods. However, it was found that the release rates of N and P estimated by Fick's Fist Law were significantly lower than those obtained by the simulation method, indicating that the static incubation experiment with intact sediments allowed the release rates of N and P to be closer to the actual situation compared to the interstitial water molecule diffusion model.