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高标准农田建设中排水沟塘系统改造对排水水质的影响

Effects of drainage ditch and pond system renovation on drainage water quality in high standard farmland construction

  • 摘要: 平原河网区稻麦轮作高标准农田建设中,除了对农田排水系统升级改造提高麦作期田间排水降渍能力外,还需根据区域排水和机械作业要求对沟塘系统进行调整。这些措施不仅会加大稻作期排水及污染物输出量,而且会降低沟塘系统的水质净化能力。为了评价上述排水系统改造措施可能带来的负面影响并提出相应的对策,该研究基于江苏省扬州市稻麦轮作农田排水过程及周边沟塘水质的6 a监测数据,利用田间水文模型(DRAINMOD)模拟了满足高标准农田麦作期降渍要求的田间排水布局,分析了排水布局变化对排水量较大的稻作期氨氮输出的影响;并结合沟塘湿地的分布及水力特性,探讨了不同改造情形对氨氮污染物削减效果的影响。结果表明,研究区现有排水沟(深60 cm,等效间距50 m)降渍能力较差,若要满足高标准农田90%降渍保证率要求,则需采用暗管排水埋深90 cm、间距20 m的浅密型布局,或是埋深120 cm、间距30 m的深宽型布局;在这2种排水布局下,稻作期采取干湿交替的节水灌溉模式与控制排水措施,农田排水氨氮输出量分别为19.23 和18.13 kg/hm2,相较于现有排水布局分别增加了21.7%和14.7%。研究区现有沟塘面积与农田面积比为11.9%,可有效改善排水水质;未来在保留沟塘/农田面积比不小于3.8%的情况下,稻田排水中的氨氮浓度可维持在地表水III类水质标准。因此,建议在高标准建设过程中对农田排水系统进行改造时,应结合地区特点和水质保护目标,在提高排水工程标准的同时,积极利用和保护当地沟塘湿地资源,实现粮食生产和生态环境保护的双赢。

     

    Abstract: The Farmland drainage system can be upgraded to enhance the waterlogging control capacity in the wheat growing period, particularly in the high-standard farmland construction of the rice and wheat rotation area in the plain river network region. It is also necessary to adjust the ditch and pond to fully meet the requirements of the regional drainage and mechanical operation. The drainage and pollutant output can be promoted to reduce the water purification of the ditches and ponds in the rice cultivation period. This study aims to evaluate the potential negative impact of the renovation measures. An appropriate countermeasures were also proposed, according to the 6-year monitoring data of the drainage and water quality of a rice-wheat rotation area in Yangzhou, Jiangsu Province, China. The field hydrology model-DRAINMOD was applied to determine the field drainage layout in order to fully meet the control requirements of the regional waterlogging in the wheat growing period of the high-standard farmland. There was a variation in the influence of the drainage system on the nitrogen losses in the rice growing period. Furthermore, a systematic analysis was carried out to examine the effect of the variable ditch and pond redistribution, thus considering their distribution features and hydraulic functions. Finally, the investigation was also made to explore the influence of the different distributions on the reduction of the agricultural pollutants in the ditches and ponds system. The results showed that the existing drainage ditches in the study area (with 60 cm depth and 50 m equivalent spacing) were insufficient for the required field drainage for wheat production. The required probability of 90% waterlogging control was achieved by using a 'shallow-narrow' subsurface drainage layout with the drain depth of 90 cm and spacing of 20 m, or a 'deep-wide' layout with the drain depth of 120 cm and spacing of 30 m. It was very necessary to adopt controlled drainage and Alternate Wetting-Drying irrigation in the rice growing season. The output values of the ammonia nitrogen in the field drainage were 19.23 and 18.13 kg/ha, respectively, which increased by 17.82% and 12.84%, respectively, compared with the existing drainage ditches. The existing ditches and ponds also covered 11.9% farmland area, in order to improve the drainage water quality. In the process of land consolidation, the ammonia nitrogen concentration of the paddy field drainage was kept under Class III of the surface water quality standards of China, when the ditch/field area ratio was no less than 3.8%. Therefore, the field drainage system was improved for land consolidation. Their regional distribution and water quality protection should be considered jointly; The drainage systems should be upgraded to fully utilize the local wetland resources of the ditches and ponds. A win-win situation can be achieved in food production and environmental protection.

     

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