桂林寨底地下河农业系统氮流失估算

Nitrogen Losses of Zhaidi Underground River Agricultural System in Eastern Guilin

为评价岩溶区面源污染对漓江的影响,通过对地下径流、氨挥发和农产品等途径输出氮的计算,估算了桂林寨底地下河农业系统氮流失量。结果表明,寨底地下河农业系统年流失氮1.03×105kg,其中地下河水土流失损失氮4.37×104kg,氨挥发逸失氮3.91×104kg,农产品输出氮2.06×104kg。随地下河水流失的溶解态氮为2.62×104kg,且其中99%为硝态氮,比30年前增加了约8倍,而泥沙吸附态氮为1.75×104kg;地下河水土流失损失氮90%以上出现在雨季,且上半年以化肥源氮为主。受石灰土酸碱度的影响,56.5%氨挥发主要发生在稻田。鲜桃输出了农产品中39.8%的氮,这是系统内大力发展桃种植产业的结果。该系统流失氮的80%最终以水溶态、气态进入地表水和大气环境,因而加剧了漓江的环境压力。

In order to evaluate non-point pollution of agriculture in karstic area, nitrogen losses via subterranean runoff, ammonia volatiliza-tion and farm product exports were estimated in Zhaidi karst underground river agricultural systems in Lijiang River watershed situated in Guilin City, Guangxi Zhuang Autonomous Region. Results showed that 1.03 ×105 kg of nitrogen was lost every year in Zhaidi karst under-ground river agricultural ecosystem. Of which 4.37×104 kg N was removed through soil and water loss of underground river, 3.91×104 kg N escaped by ammonia volatilization, and 2.06×104 kg N output as farm products. Soluble N, with 99%of NO-3-N, amounted to 2.62×104 kg, 8 times more than 30 years ago. Sediment-adsorbed N was 1.75×104 kg. More than 90%of N losses via water and soil occurred in rainy days, which was mostly caused by chemical fertilizer N in the first half year and by the excreta of animal and human(including manure)or sewage mixed with dung in the second half year. Fresh peach fruits exported 39.8%of N outputs of agricultural produce. Rice field contributed to 56.5% of ammonia volatilization, which was caused by high pH of calcareous soil. Therefore, about 80% of lost N in Zhaidi karst under-ground river agricultural system entered into surface water and atmospheric environment through water-soluble and gaseous forms, increas-ing environmental pressure on the Lijiang River.