三峡库区不同稻田分布格局下农业小流域径流磷排放特征

于2012年3月21日—2013年3月20日期间对三峡库区涪陵段两个毗邻集水域汇出口径流水质进行了高频(每日)采样监测,以对比分析稻田空间分布格局对径流磷浓度和输出强度的影响。两集水域气候地理条件相似,农耕方式相同,单位面积施肥量相近,但其中一个(记为集水域A)稻田分布零散,破碎度高,而另一个(集水域B)稻田连片分布在其末(底)端,破碎度低。结果显示,集水域A在全年和不同作物生长季的径流总磷平均浓度都相应地高于集水域B。同样,前者的径流产流量(1431 m3·hm~(-2)·a-1)也显著高于后者(840 m3·hm~(-2)·a-1),因而前者径流总磷的年输出通量(210 g·hm~(-2)·a-1)远大于后者(72 g·hm~(-2)·a-1)。按季节计算,两集水域水稻/玉米季总磷浓度皆高于榨菜季,集水域A在水稻/玉米季的径流总磷输出通量(147 g·hm~(-2)·a-1)是榨菜季(63 g·hm~(-2)·a-1)的1.9倍,集水域B在水稻/玉米季的径流总磷输出通量(58 g·hm~(-2)·a-1)是榨菜季(14 g·hm~(-2)·a-1)的3.6倍。从研究中看,这些差异很有可能是两集水域的土地利用,特别是水稻田布局差异所导致的,因此实现水稻田的合理布局是三峡库区径流磷排放负荷减控的有效措施。

Characterization of runoff phosphorus export from small agricultural catchments with different spatial distribution patterns of rice paddies in the Three Gorges Reservoir Area

A high frequency(daily) monitoring campaign was carried out in two adjacent catchments in Fuling of the Three Gorges Reservoir for one whole year with the aims of analyzing comparatively the impact of spatial distribution pattern of rice paddies on phosphorus(P) concentration and export fluxes in runoff. The two catchments were subjected to the same climate conditions, tillage and cropping practices, and received the equivalent fertilization rates in terms of per unit of land area. Nevertheless, the rice paddies in one catchment(marked A) were scattered and higher in fragmentation index, and those in the other(marked B) were mainly distributed at the bottom of the catchment and lower in fragmentation index. Comparing the two catchments, the average runoff concentration of total P in A was correspondingly higher than that in B all over the year and in the different crop growing seasons. Similarly, the amount of runoff from the outlet in A(1431 m³·hm^-2·a^-1) was significantly higher than that in B(840 m³·hm^-2·a^-1). As a result, the total P export flux from A(210 g·hm^-2·a^-1) was much higher than that from B(72 g·hm^-2·a^-1). For both the catchments A and B, the runoff P concentration during the rice/maize season far exceeded that of the mustard season, and the total loss of runoff P during the former season was 1.9 and 3.6 times higher than that of the latter season, respectively. The differences in the runoff concentration and loss of P between the two studied catchments might be attributed to the different spatial distribution patterns of the rice fields within them. This indicates that the reasonable configuration of rice paddies can serve as an effective measure to reduce runoff P discharge in the Three Gorges Reservoir Area.