Phosphorus adsorption on the surface sediments of ditches in Hetao irrigation

In order to understand the role of sediments in the phosphorus transformation in the north China. Overlying water and surface sediments samples were took from up, middle and down sample sites of Main canal, Huangji Tributary canal, Main drainage ditch and Second tributary drainage ditch. Then the concentration of soluble phosphorus and total phosphorus of overlying water were determined and the phosphorus fractions of sediments were analyzed. Moreover, adsorption kinetic and adsorption isotherm of the sediments were obtained. It found that phosphorus in the drainage ditch did not raised obviously. The content of phosphorus fractions ranged sequentially Calcium bound phosphorus > Residual phosphorus > Reductant Soluble phosphorus > Aluminum bound phosphorus > Soluble and Loosely bound phosphorus > Iron bound phosphorus. Especially, the content of Soluble and Loosely bound phosphorus, Iron bound phosphorus and Aluminum bound phosphorus, which were easy to release to water, were very low and they were positively correlative with each other. It conclude that ditches are helpful in the phosphorus reduction, the risk of releasing phosphorus form sediment is high and the adsorption capacity of drainage ditch sediments is larger than that of canal sediments.