| Resource & environmental sciences |
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| Phosphorus adsorption characteristic of sediments in drainage ditch of paddy field in southern hilly tea field watershed |
| Yang Shaohui, Yang Jingping, Wang Hua, Zhao Xing |
| (Institute of Environmental Science and Technology, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China) |
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Abstract Excess nutrients, especially phosphorus, running off from agricultural lands have contributed greatly to the eutrophication of water bodies in China. Drainage ditches are important conduits for drainage flows and unavoidably receive the discharge of nutrients, particulate matters, and other chemicals. Thus, more and more attention has been focused on the role of agricultural drainage ditch in water pollution control. However, few of the research were reported on drainage ditches of paddy field in southern hilly tea field watershed.
In this paper, sediment samples collected from drainage ditch of paddy field in southern hilly tea field watershed were analyzed, according to the water discharging distance. The physicochemical properties of sediments were determined and phosphorus isothermal experiments were also conducted.
The result showed that water discharging distance had a significant influence on ditch soil properties. The concentrations of total phosphorus (TP), oxalateextractable ferric iron (Feox), Alox and Pox increased with the discharging distance. The accumulation of P in the ditch soil was significantly correlated with total organic matters (TOM) and Alox, and the existence of TOM enhanced the activity of soil phosphorus. The degree of phosphorus saturation (DPSox) ranged from 1.50%-2.69%, much lower than the threshold value of P release. Both Langmuir equation and Freundlich equation could well describe the phosphorus adsorption behavior of ditch sediments, and the maximum P adsorption (Smax) ranged from 646.62 mg/kg to 754.17 mg/kg; Freundlich’s adsorption constant (Kf) ranged from 271.81 L/kg to 338.74 L/kg. The sediments sampled from the end of the ditch had the maximum values of 338.74 L/kg and 754.17 mg/kg for Kf and Smax, respectively, which suggested that the sediment had the highest P adsorption capacity. The parameters calculated from the Freundlich and Langmuir isotherms ranged from 0.000 to 0.004 mg/L. In isothermal adsorption experiment, the adsorbed P amounts raised with the water discharging distance, but no significant differences were observed among P adsorption amounts of different ditch soils.
In conclusion, for the studied ditch, sediment properties change as water discharging distance increasing, but not for P adsorption capacity. Besides, the sediments have large intrinsic P adsorption capacities and low risk of P release, which indicate that the ditch can be improved as ecological ditch to further P retaining.
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Published: 20 July 2015
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南方丘陵茶园集水区稻田排水沟渠底泥磷的吸附特性
以南方丘陵茶园集水区水塘和稻田排水沟渠为研究对象，探讨沿着排水方向，沟渠底泥属性及磷吸附特性的变化.从靠近水塘一端开始取样，每隔100 m取混合样作为样品，分别标记为渠1、渠2、渠3、渠4.结果表明：从渠1到渠4，底泥总磷（total phosphorus，TP）、草酸提取态的活性铁（oxalate-extractable ferric iron，Feox）、活性铝（Alox）和活性磷（Pox）含量均呈增加趋势.底泥磷含量与相关理化性质的相关性分析及多重线性回归表明：底泥TP及Pox含量与Alox及总有机质（total organic matters，TOM）含量呈显著正相关；有效磷（Olsen-P）含量主要受TOM的影响。朗格缪尔（Langmuir）和弗罗因德利奇（Freudlich）拟合方程参数表明，底泥最大磷吸附量（Smax）在646.62~754.17 mg/kg之间，Freudlich方程吸附能参数（Kf）范围为271.81~338.74 L/kg。渠4底泥的Kf和Smax最大，分别为338.74 L/kg和754.17 mg/kg，对磷的吸附能力相对较强。底泥磷释放风险低，零平衡磷质量浓度（zero equilibrium phosphorus concentration,EPC0）在0.000~0.004 mg/L范围内，磷饱和度（degree of phosphorus saturation，DPSSox）范围为1.50%～2.69%；且沟渠底泥在等温吸附实验中对磷的吸附量具有一定的稳定性，彼此之间差异无统计学意义（P>0.05）.研究表明茶园集水区的稻田排水沟渠能够承担起削减排水中磷的功能，没有改造的必要性，但具有改造成生态沟渠的条件.
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