摘要
Phosphorus (P) is the limiting factor for eutrophication in most freshwater ecosystems. In China, Ptransported from intensively cultivated land has been reported as an important source of P in surface waters.In this study, we investigated P concentration and forms in surface and subsurface drainage from wetland ricefields in the Shaoxing plain, Zhejiang Province, China. From selected rice fields, surface drainage sampleswere collected at rice-growing, non-growing and fertilization periods, and subsurface drainage samples atdrought and rewetting (irrigation or precipitation after 5～10 d drought period in the surface soils) and wet(drainage under long-term wet soil condition) periods. Water samples were characterized for their totalreactive P (TRP), dissolved reactive P (DRP) and particulate reactive P (PRP). Concentrations of the TRPand DRP in the surface drainage ranged from 0.08 to 1.50 and 0.06 to 1.27 mg L-1, respectively. The TRPand DRP were dependent on field operation activities, and decreased in the order of fertilization period ＞rice-growing period ＞ non-growing period. Phosphorus concentration of runoff receiving P fertilizer can bean environmental concern. The PRP concentration in the surface drainage, ranging from 0.01 to 0.57 mgL-1, accounted for 8%～78% of the TRP. Concentration of the TRP in the subsurface drainage was from0.026 to 0.090 mg L-1, consisting of 29%～90 % of the DRP and 10%～71% of the PRP. In the droughtand rewetting period, the PRP accounted for, on average, 63% of the TRP, much higher than in the wetperiod (23%), suggesting that there was transport of P in preferential flow during drainage events after ashort-term drought period in the surface soils. Therefore, P losses in particulate form may be importantin the subsurface drainage from rice fields when surface soils form cracks and favor rapid flow downwardthrough the soil profiles, suggesting the important role of water-dispersible colloid particles in mediating andco-transporting P in the subsurface drainage of rice fields.
Phosphorus (P) is the limiting factor for eutrophication in most freshwaterecosystems. In China, P transported from intensively cultivated land has been reported as animportant source of P in surface waters. In this study, we investigated P concentration and forms insurface and subsurface drainage from wetland rice fields in the Shaoxing plain, Zhejiang Province,China. From selected rice fields, surface drainage samples were collected at rice-growing,non-growing and fertilization periods, and subsurface drainage samples at drought and rewetting(irrigation or precipitation after 5～10 d drought period in the surface soils) and wet (drainageunder long-term wet soil condition) periods. Water samples were characterized for their totalreactive P (TRP), dissolved reactive P (DRP) and particulate reactive P (PRP). Concentrations of theTRP and DRP in the surface drainage ranged from 0.08 to 1.50 and 0.06 to 1.27 mg L^(-1),respectively. The TRP and DRP were dependent on field operation activities, and decreased in theorder of fertilization period > rice-growing period > non-growing period. Phosphorus concentrationof runoff receiving P fertilizer can be an environmental concern. The PRP concentration in thesurface drainage, ranging from 0.01 to 0.57 mg L^(-1), accounted for 8%～78% of the TRP.Concentration of the TRP in the subsurface drainage was from 0.026 to 0.090 mg L^(-1), consisting of29%～90 % of the DRP and 10%～71 % of the PRP. In the drought and rewetting period, the PRPaccounted for, on average, 63% of the TRP, much higher than in the wet period (23%), suggesting thatthere was transport of P in preferential flow during drainage events after a short-term droughtperiod in the surface soils. Therefore, P losses in particulate form may be important in thesubsurface drainage from rice fields when surface soils form cracks and favor rapid flow downwardthrough the soil profiles, suggesting the important role of water-dispersible colloid particles inmediating and co-transporting P in the subsurface drainage of rice fields.
基金
Project supported by the National Natural Science Foundation of China (No.49601013).
