太湖流域丘陵地区暴雨条件下农田氮素随地表径流迁移特征

Effects of Rainstorm on the Export of Farmland Nitrogen with Surface Runoff in Hilly Area of Tai Lake Basin

通过流量和水质的同步监测,在流域尺度上研究了暴雨对农田氮素随地表径流迁移的影响。结果表明,次降雨量介于69.85～110.8mm及降雨历时持续7.5h以上的暴雨过程,流域出口处径流过程线一般呈单峰形态,径流峰值滞后于最大降雨强度,但滞后时间受降雨条件影响存在较大差异;流域3次暴雨事件的综合径流系数达0.305;总氮迁移量介于651.5～858.4g·hm-2,其中硝氮与氨氮是氮素迁移的主要类型,平均输出负荷分别为303.7和270.0g·hm-2,占总氮的41.9%和37.2%,亚硝态氮迁移量最小,仅占总氮的3.3%;溶解态氮是氮素迁移的主要形态,其迁移量介于579.1～582.2g·hm-2,与悬浮态氮输出比为3.2∶1。氨氮以悬浮态迁移为主,但受施肥状况影响较大。

In this study, watershed scale experiments were conducted to study the characteristics of nitrogen losses with surface runoff from farmlands under rainstorm conditions in hilly areas around Tai Lake. Results showed that the change of surface runoff hydrographs usually appeared in single-peak form. Generally, the peak of surface runoff lagged behind the maximum intensity of rainfall, but the delay time had big differences because of the different rainfall conditions, when precipitation was within 69.85-110.8 mm and lasted more than 7.5 h, the runoff coeffcient was 0.305 in Meilin catchment. Effects of rainstorm on the export of farmland nitrogen with surface runoff mainly presented as incipient scour and accumulation in later period. During the initial stage of surface runoff, the concentration of TN was relatively high and decreased as a hackly shape. At the later stage, the concentration of TN increased differently. At the same time, changes of the concentration of nitrate nitrogen, ammoniacal nitrogen and nitrite nitrogen in runoff indirectly reacted their conversions in farmland ditch and river channel. Under rainstorm conditions, the transport fluxes of TN was within 651.5-858.4 g·hm^-2 and the average transport fluxes of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen was 303.7, 270.0 g·hm^-2 and 50.0 g·hm^-2, which accounted for 41.9%, 37.2% and 3.3% of total nitrogen respectively. Dissolved nitrogen was the main export form of nitrogen within 579.1-582.2 g·hm^-2. And dissolved nitrate nitrogen was the main export form of dissolved nitrogen which accounted for 31.7%. Due to adherence to soil particle, the losses of ammonia nitrogen were particularly in suspended state and were affected by different fertilizer applications.