Environmental dynamics of nitrogen and phosphorus release from river sediments of arid areas

摘要: Human activities lead to the accumulation of a large amount of nitrogen and phosphorus in sediments in rivers. Simultaneously, nitrogen and phosphorus can be affected by environment and re-enter the upper water body, causing secondary pollution of the river water. In this study, laboratory simulation experiments were conducted initially to investigate the release of nitrogen and phosphorus from river sediments in Urumqi City and the surrounding areas in Xinjiang Uygur Autonomous Region of China and determine the factors that influence their release. The results of this study showed significant short-term differences in nitrogen and phosphorus release characteristics from sediments at different sampling points. The proposed secondary kinetics model (i.e., pseudo-second-order kinetics model) better fitted the release process of sediment nitrogen and phosphorus. The release of nitrogen and phosphorus from sediments is a complex process driven by multiple factors, therefore, we tested the influence of three factors (pH, temperature, and disturbance intensity) on the release of nitrogen and phosphorus from sediments in this study. The most amount of nitrate nitrogen (NO3–-N) was released under neutral conditions, while the most significant release of ammonia nitrogen (NH4+-N) occurred under acidic and alkaline conditions. The release of nitrite nitrogen (NO2–-N) was less affected by pH. The dissolved total phosphorus (DTP) released significantly in the alkaline water environment, while the release of dissolved organic phosphorus (DOP) was more significant in acidic water. The release amount of soluble reactive phosphorus (SRP) increased with an increase in pH. The sediments released nitrogen and phosphorus at higher temperatures, particularly NH4+-N, NO3–-N, and SRP. The highest amount of DOP was released at 15.0°C. An increase in disturbance intensity exacerbated the release of nitrogen and phosphorus from sediments. NH4+-N, DTP, and SRP levels increased linearly with the intensity of disturbance, while NO3–-N and NO2–-N were more stable. This study provides valuable information for protecting and restoring the water environment in arid areas and has significant practical reference value.