Characteristics of nitrogen and phosphorus release from different depths of sediment in typical small lakes——the Jiaolv Lake as an example

Endogenous release of bottom mud from small lakes can cause nitrogen and phosphorus concentrations in the overlying water body to exceed the standard, but the lack of related research affects the improvement of treatment technology. In this study, we took the Jiaolv Lake, a typical small lake with serious nitrogen and phosphorus pollution, as the object to investigate the effect of nitrogen and phosphorus release from the bottom mud on water quality. The study stratified the 90 cm surface sediment and carried out a simulation experiment on the release of nitrogen and phosphorus from the sediment, and investigated the effects of different depths of the sediment and different environmental conditions (temperature, pH and dissolved oxygen) on the release of nitrogen and phosphorus. The results showed that the TP concentration in 0-30 cm sediment ranged from 996.47 to 1083.69 mg/kg, and with the increase of sediment depth, the TN concentration ranged from 2097.24 to 2169.89mg/kg; both TP and TN concentrations in the 30-90 cm sediment decreased with increasing depth. In addition, the surface substrate at 0-30 cm had the greatest influence on the water quality of the overlying water body, with the release of TP decreasing with depth and the release of TN basically unchanged with depth. Higher temperatures favored the release of nitrogen and phosphorus from the substrate; both TN releases decreased with increasing pH, while TP releases diminished as pH tended to be neutral. Low dissolved oxygen is favorable to the release of TN and TP. The above characteristics of nitrogen and phosphorus release from the bottom sediment provide an important reference for the management of small eutrophic lakes.