| The excessive nutrient, especially phosphorus, losses from agricultural lands has made a great contribution to the eutrophication of water body and lakes in China. Land-use change of agricultural cropping system with cash and economic crops such as ornamental flowers and nursery stock planting area increase has led to the increase of N and P application, phosphorus loss and leaching from cropping field changed the situation of water quality and sediment at the same time. Thus, more and more attention has been focused on the role of drainage ditch in water pollution control, so analyzing the physicochemical properties and phosphorus adsorption capacities of different drainage ditches and providing a theoretical basis for ditch transformation have a significant meaning for effective use of drainage ditch to reduce the loads of phosphorus losing from agricultural lands.In this study, sediment samples were collected from drainage ditches of Southern hilly watershed paddy field, potted flowers and grass & and seeding tree nursery base cropping field. To examine the effects of crop planting and to further clarify the relationship between soil properties and soil phosphorus adsorption capacity, the sediment physicochemical properties were determined and phosphorus isothermal experiment was conducted; at the same time, the influence of water discharging distance of paddy field drainage ditch on sediment properties and phosphorus adsorption capacity were studied. The main research conclusions were as following:Sediments in paddy field drainage ditch had a lower pH, mean of 5.87, showing existence of sediment acidification. While pH of sediments in drainage ditches of potted flowers and nursery stock were higher with means 7.37 and 7.21, respectively. Total Phosphorus (TP), Olsen-P and oxalate-extractable phosphorus (Pox) concentrations of sediments in paddy field ditch were the lowest, with means of 402.07mg/kg,16.91mg/kg,166.93mg/kg, respectively; While the values of the corresponding properties of sediments in potted flowers were the highest, with means of 2140.23mg/kg,105.95mg/kg,1693.11mg/kg, respectively. Paddy field drainage ditch had a mean of 4.0% phosphorus saturation (DPSox), much lower than the threshold value of P release; the DPSox values of drainage ditch sediments in potted flowers and nursery stock were similar, about 28%, which is relatively high at the risk of phosphorus release and could become the "source" of phosphorus.The results indicated that studied sediments in paddy field drainage ditch had the maximum amounts of adsorbed phosphorus, followed by the potted flower, and nursery stock had the minimum. Both Langmuir equation and Freundlich equation can well describe the adsorption of phosphorus behavior of ditch soils, and the maximums P sorption (Smax) ranged from 399.51 mg/kg to 853.30mg/kg; Freundlich adsorption constant (Kf) ranged from 77.1L/kg to 338.74 L/kg. The adsorption capacity of ditch soils had the following orders:paddy filed> potted flowers> nursery stock. The Pearson’s correlation analysis showed significant correlations of oxalate-extractable aluminum (Alox) with key parameters of P adsorption capacity, such as Smax and Kf; while oxalate-extractable iron (Feox) showed significant correlations with the equilibrium phosphorus concentration (EPCo) and oxalate-extractable phosphorus (Pox). The results also showed elevated pH could increase the risk of P release from ditch soils, besides, high phosphorus concentrations could also contribute to P release.The study on ditch soils from different sampling points in paddy field drainage ditch indicated that water discharging instance made a significant influence on ditch soil properties. The concentrations of TP, Pox, Alox, Feox increased as the discharging instance increase. The accumulation of P in ditch soils significant correlated with total organic maters (TOC) and Alox, and the existence of TOC enhances the activity of phosphorus. In isothermal adsorption experiment, the adsorbed P amounts were on the rise as the water discharging distance increasing, but there were no significant differences between P adsorption amounts of different ditch sediments.In summary, the sediments in drainage ditches of flowers & grass, seeding planting base zone had higher phosphorus concentrations and high risk of P release, so it is necessary to reconstruct the ditches. Reduce the risk of P release and enhance the P adsorption capacity of ditch soils by appropriately increasing the active aluminum concentration, organic matter or decrease the sediment pH et al. The main measures include reseeding plants, setting up gates, dams to intercept drainage and soon. |
PDF Full Text Request