Effect of Flow Disturbance Intensity on Nitrogen Release from Bottom Muddy of Plateau Rural Ditches

To investigate the effect of hydrodynamic disturbance on endogenous nitrogen (N) release in plateau mountainous rural ditches, N concentrations in overlying water under various flow disturbance intensities (0, 5, 15, 30, 60 L·h^-1) were analyzed by a simulation experiment. The results show that: (1) Sediment N can be released into overlying water by the initial hydrodynamic disturbance and reaches the highest values of NH₄⁺-N and TN at 5 and 60 L·h^-1 flow disturbance intensity, respectively. After 30 days, N concentration in the undisturbed water was higher than that in the disturbed water; (2) Sediment TN contents increased with the increasing of disturbance intensity, which however were lower than the background values, showing 0 < 5 < 30 < 15 < 60 L·h^-1; (3) The contents of different forms of transformable nitrogen (TTN) were in the order of strong oxidant extractable-N (SOEF-N) > strong alkali extractable-N (WAEF-N) > ion exchange-N (IEF-N) > weak acid extractable-N (SAEF-N), with releasing tendentiousness of IEF-N > WAEF-N > SAEF-N > SOEF-N. All N fractions of the sediment were at the lowest values under undisturbed treatment, indicating that the disturbance of flow benefits the N settlement in sediments, thus decreasing the risk of N to the surrounding environment.