The Effects of Disturbance on the Release of Nitrogen and Phosphorus from Sediment in Rural Ditches

Reduced nitrogen (N) and phosphorus (P) released from sediments in rural areas pose a significant challenge to residential sewage treatment and management. Under different disturbance velocities, simulation experiments were undertaken to investigate the effect of disturbance on the release of N and P from rural ditch sediments into the water at the water-sediment interface. No significant difference in the release characteristics of N and P was found among different disturbance velocities. The release fluxes of TN and NH4+-N in the non-disturbance water body were significantly higher than in the disturbance water body, which suggests that increasing water flow influences the release of TN and NH4+-N from sediment into the water. The release fluxes of TP and PO43--P were significantly lower in non-disturbance than the disturbance water body, which suggested that disturbance increased the release of TP and PO43--P in sediments. For both disturbance and non-disturbance conditions, TN and NH4+-N in the sediment were rapidly released into the water body at 0-10 days, and TP and PO43--P steadily rose in the disturbance water body until stabilizing after 20 days. TN, NH4+-N, TP, and PO43--P concentrations all had a negative correlation with DO, and the correlations between TN and NH4+-N were substantial. The percentages of a certain N or P speciation fraction in sediments did not alter between disturbance and non-disturbance conditions, implying that disturbance had no effect on N or P speciation.