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随着社会经济与城市化的快速发展,人类活动造成的水体污染已成为全球重要的环境污染问题之一。面源污染是水体污染的主要表现形式之一,而农业面源污染是面源污染的主要来源[1]。作为农业大国,中国化肥使用量逐年增长。据统计,2015年全年使用量已高达6 022.6万t,农用化肥单位面积平均施用量已达458.6 kg·hm-2,是安全上限(225 kg·hm-2)的2.04倍,但化肥利用率仅为30%~40%[2],导致化肥中大部分营养元素进入水体,造成水体氮、磷污染。因此,如何治理农业面源污染已成为目前环境治理的重难点问题。许多研究表明:位于水陆交界处的河岸植被缓冲带可以有效截留和清除面源污染中的氮磷[3-6],被认为是控制非点源污染的最佳管理措施之一[7]。河岸植被缓冲带通过沉积、土壤吸附、植物吸收、反硝化作用和微生物固定等途径,有效截留和清除氮等面源污染物质。目前,国内外学者在河岸缓冲带氮素截留方面已做了诸多研究。SPRUILL[8]对小流域的河岸植被缓冲带进行研究时,发现其能移除地表水中95%以上的氮元素,其中反硝化作用去除的氮元素占65%~70%;KOVACIC等[9]研究发现:森林和草地河岸缓冲带对浅层地下水中硝态氮的截留率达90%以上,其中森林河岸缓冲带对硝态氮的截留转化能力高于草地河岸缓冲带;WANG等[10]研究表明:林地和草地缓冲带主要通过显著减少土壤表面径流量有效去除水分和养分。国内研究起步虽然较晚,但也取得了一些成果。陈金林等[11]研究发现:农田与沟渠间的缓冲林带有利于截留和净化土壤径流中的氮、磷等物质,不同林带宽度对农业非点源污染的防治效果不同;王庆成等[12]研究表明:农田背景下的森林河岸带土壤反硝化强度最大,硝态氮消失率的变化范围为46.79%~91.13%,且河岸带表层土壤的反硝化强度大于底层;林晓晟[13]在流域尺度上利用有限元数值模技术构建了HYDRUS2D/3D模型,提出丘陵区河岸缓冲带的宽度为15~60 m,平原区河岸缓冲带宽度为5~20 m,可有效截留氮、磷污染物。总体而言,学者大多基于景观甚至流域尺度上研究河岸植被缓冲带的功能及其影响因素,很少在林分水平上开展缓冲带削减面源污染的研究。且在有关湖泊周围地势较为平坦的河岸缓冲带截留养分和沉积物的研究较少[14]。因此,本研究以太湖不同宽度的林地河岸缓冲带为对象,研究其对径流水及土壤中氮素截留效果的影响,以期为适宜河岸缓冲带宽度的设计提供参考。
Removing nitrogen with trees planted in the riparian vegetation buffer strips of Taihu Lake
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摘要: 为研究河岸植被缓冲带对氮素的截留效率,以太湖流域平缓坡地上人工林河岸缓冲带作为研究对象,分析了不同河岸缓冲带宽度(5,15,30,40 m),不同植物类型(‘南林95’杨Populus×euramericana ‘Nanlin 95’林、中山杉Taxodium hybrid ‘Zhongshanshan’林、南林杨95-中山杉混交林)对不同深度径流水及土壤中氮素的截留效果。结果表明:15 m宽的河岸缓冲带即能很好地截留各形态氮素,40 m缓冲带对径流水中硝态氮、铵态氮、总氮的截留率分别达68.8%,68.7%和66.0%;同一宽度条件下,缓冲带对40 cm深径流水中铵态氮、总氮的截留率较高,分别达71.4%和69.1%,对20 cm深径流水中硝态氮截留率较高,达70.6%;森林土壤对铵态氮和硝态氮的截留主要在中层土壤,对总氮截留主要在表层土壤;杨树林缓冲带对径流水中铵态氮和硝态氮的截留率较高(P < 0.05),达77.4%和66.3%;杨树-中山杉混交林缓冲带对总氮的截留率较高(P < 0.05),达73.0%;植物叶片(r=-0.53)全氮和土壤总氮(r=-0.59)均与径流水中总氮呈负相关关系。Abstract: In the Taihu Lake area many riparian vegetation buffer strips have been built to alleviate the input of eutrophic nutrients into the lake. To provide a scientific basis for determining a suitable width and components of these riparian buffer strips, the effects of riparian vegetation buffer strips with widths of 5, 15, 30, and 40 m and vegetation types of a Populus×euramericana 'Nanlin 95' plantation, an Taxodium hybrid 'Zhongshanshan' plantation, and a mixed plantation with the two tree species on total nitrogen, ammonia nitrogen, and nitrate nitrogen removal rates for different depths of runoff water and soil were studied. Results showed that the buffer strips of 15 m width effectively removed various fractions of N and removal rates in runoff water of 40 m width of 68.8% for NO3-, 68.7% for NH4+, and 66.0% for total N. Removal rates of NH4+ and total N in runoff water at 40 cm below ground level were higher, reached 71.4% and 69.1%, but NO3- removal rate in the 20 cm depth of runoff water was higher, reached 70.6%. The interceptions of NH4+ and NO3- in plantation soils were mainly in the middle soil layer, and total N was trapped mainly in surface soils. The poplar plantation had a higher removal rate of NH4+ and NO3- in runoff water(P < 0.05), reached 77.4% and 66.3%, but the mixed forests of the poplar plantation and Taxodium hybrid 'Zhongshanshan' plantation had a higher removal rate of total N(P < 0.05), reached 73.0%. Also, total N in runoff water was negatively correlated to total N in the soil (r=-0.59) and total N in the leaves (r=-0.53) of plants.
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Key words:
- forest ecology /
- riparian vegetation buffer strip /
- width /
- vegetation type /
- nitrogen /
- removal rate
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链接本文:
https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2019.03.018