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山核桃Carya cathayensis是中国特有的高档干果和木本油料植物,主要分布在浙西天目山脉一带,70%生长于土层浅薄、岩石裸露、生态脆弱的石灰岩山地[1-2]。长期以来,林农为增加产量,减少虫害,进行大量施肥,喷施灭蝇胺、啶虫脒等杀虫剂,同时为了方便采摘,使用克无踪等除草剂。山核桃林地的这种不合理经营管理导致严重的土壤侵蚀和水土流失。同时,山核桃林生长在坡地上,汇流、径流流速较快,不利于泥沙的沉积。农业非点源污染中的降雨径流是造成受纳水体水质恶化的主要原因之一,而不同形态存在的氮磷是农业径流中的重要污染物[3-4]。目前,国内外许多学者以农田为单位,在自然或人工模拟降雨条件下,通过径流小区试验来量化农田土壤侵蚀和养分流失。RAMOS等[5]在西班牙北部的一个葡萄园中通过模拟降雨试验监测不同降雨事件下的径流氮磷养分流失总量,所设径流小区面积为0.06 m2。鲁耀等[6]在云南省丘陵缓坡地上设置了18个面积为32 m2的径流小区来定位监测坡耕地红壤地表径流氮磷流失。大多数径流小区都是根据WISCHMEIER等[7]的小区标准或相近的坡长尺寸建造的,降低了小区规模的变异性。然而,径流小区不能完全反映整个研究区域的真实氮磷流失量。有学者[8]研究发现,在规模1~20 m2的径流小区中测定,会低估土壤流失量,而在20~500 m2的径流场中,土壤流失量又会被高估。STROOSNIJDER[9]的研究也表明,土壤流失率可在中小型径流小区中测定,但评估土壤泥沙量应该在更大规模的径流场中进行。可见,修筑径流小区对土壤扰动性大,因此利用径流小区来定位监测土壤径流、泥沙氮磷流失与实际情况存在一定的误差。有鉴于此,不少学者以流域为研究单位,比如DAI等[10]以中国抚仙湖流域为单位,探讨了土地利用类型和空间的变化对水质的影响,分析了河岸缓冲区保护建设对非点源污染和营养物质的输入和保护作用;GALOT[11]在延河流域研究黄土高原丘陵沟壑地区在降雨条件下造成的土壤和水的氮磷流失负荷特征。农田、河流均不是闭合式小区,影响小流域非点源污染的因子复杂多样,如径流、农村生活、人为耕作、养殖等,缺乏固定的污染源,变动大,河流总量不能估测。此外,以往的研究侧重于利用人工降雨试验或者利用典型降雨月份,如吴希媛等[12]和彭圆圆等[13]进行野外人工模拟降雨,分析坡面降雨径流中氮磷流失过程。张洋等[14]研究三峡库区农桑配置对地表氮磷流失的影响,所采集的样品为2014年3月22日、8月13日、9月20日3次径流。吴东等[15]在兰陵溪小流域采集2015年5-9月水样监测土地利用结构变化对氮素输出控制效应,而对自然降雨条件下土壤-径流-泥沙三者动态变化过程及其年际养分流失研究较为少见。本研究选择浙江省杭州市临安区山核桃林闭合区作为研究对象。这是一个天然集水区,在林间沟壑地带设置特殊的径流监测卡口站,研究1 a常规经营管理的山核桃林中自然降雨对径流的影响,观测径流氮磷年际动态变化过程,分析泥沙、土壤有效养分与径流氮磷流失的关系,解析山核桃经济林氮磷养分流失特征,为经济林氮磷流失负荷模拟及控制研究提供依据。
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2016年6月至2017年5月整个水文年中,山核桃林闭合区降雨量和径流量的动态变化见图 2。整个观测期间,降雨主要集中在2016年6-9月和2017年3-5月;径流量的年际变化趋势与降雨量相似,7月20日至8月9日,9月12-30日。径流量随着降雨量的增加而增加,3月下旬降雨量连续下降,径流量也随之下降。9月30日降雨量达到最大值233.1 mm,此时径流量也达到了峰值2 000.0 m3,2017年5月13日的降雨量仅为17.5 mm,监测到的径流量也出现了低谷,仅为383.4 m3。
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径流总氮、硝态氮和铵态氮质量浓度的年际变化趋势基本一致。径流总氮、硝态氮和铵态氮质量浓度在1 a中的高值分别出现在7月1日,8月3日和9月12日,质量浓度分别为3.600,3.047和0.271 mg·L-1。10月以后,不同形态的氮质量浓度趋于平稳。2017年2月后,又呈现增加趋势,并在3月26日和3月21日出现第2次高峰(图 3)。整个试验期间,总氮、水解氮、硝态氮和铵态氮的平均质量浓度分别为2.860,1.740,1.110和0.050 mg·L-1。水解氮、硝态氮和铵态氮分别占总氮的60.7%,38.9%和1.8%(表 1)。
表 1 山核桃闭合区径流不同形态氮磷的平均质量浓度及占比
Table 1. Average concentration and proportion of N and P in different forms of runoff in the closed zone of a Carya cathayensis stand
成分 ρ/(mg·L-1) 比例/% 氮素 铵态氮 0.05 1.8 硝态氮 1.11 38.9 水解氮 1.74 60.7 总氮 2.86 磷素 水解磷 0.01 35.2 总磷 0.03 -
山核桃林闭合区径流磷质量浓度的动态变化见图 4。在2016年6月中旬至9月下旬期间总磷质量浓度的波动较大。此后,2016年10月至2017年5月变化较为平稳,而水解磷质量浓度在整个水文年中变化趋势一直较平稳。在整个观测期间,总磷质量浓度的变化范围为0.01~0.11 mg·L-1,2016年9月至2017年5月,质量浓度在0~0.02 mg·L-1间小幅度变动。水解磷的平均质量浓度为0.01 mg·L-1,占总磷质量浓度的35.20%(表 1)。
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2016年6-12月土壤闭合区有效氮磷质量分数和径流氮磷质量浓度的回归分析表明:山核桃林地径流中总氮质量浓度与土壤的碱解氮无显著的相关性(P>0.05,图 5)。山核桃林闭合区径流总磷质量浓度与土壤有效磷质量分数呈显著线性正相关(P<0.05,图 6)。
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由图 7可知,山核桃林径流1 a中氮磷流失负荷的变化趋势大致相同:2017年9-12月,2017年3-5月,总氮和总磷的流失负荷均呈现逐月下降趋势。径流水中总氮的最大流失量(1 832 g·hm-2)出现在9月,而总磷的最大流失量(47.0 g·hm-2)出现在6月。2016年11月至2017年2月,总氮的月流失量相对较少(<600 g·hm-2),2016年10月至2017年5月,总磷的月流失量均在10 g·hm-2以下。在整个观测期内,总氮、总磷流失负荷总量分别为11.01 kg·hm-2和133.70 g·hm-2。
整个观测期间,山核桃林闭合区共收集冲积物170.9 kg,其中未通过1 mm筛孔的石块占总质量的83.7%。全氮和全磷的总量分别为73.51和7.20 g,林地土壤随泥沙流失的全氮和全磷的年际负荷分别为11.49和1.12 g·hm-2。径流水中,总氮和总磷的年际流失量(不包括泥沙中的氮和磷)分别为11.01 kg·hm-2和133.70 g·hm-2。因此,山核桃林闭合区随径流泥沙流失的氮磷年际流失总量(包括径流和泥沙中的氮和磷)分别为11.02 kg·hm-2和134.82 g·hm-2。
Nitrogen and phosphorus loss in runoff and sediment for a closed zone of a Carya cathayensis stand
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摘要: 为研究自然降雨条件下整个水文年中山核桃Carya cathayensis林闭合区内径流-土壤-泥沙氮磷流失特征,以杭州市临安区山核桃林闭合区作为研究对象,测定总氮、总磷和水解氮等指标。结果表明:降雨是影响径流的重要因子,径流量和降雨量存在显著正相关(P < 0.05);在2016年6月至2017年5月的观测期间,山核桃林径流水中氮素平均质量浓度较高(2.86 mg·L-1),水解氮是氮素流失的主要形式,占总氮的60.7%;径流水中磷素平均质量浓度较低(0.01 mg·L-1)。径流氮质量浓度与土壤碱解氮之间不存在显著的相关性(P>0.05),而径流磷质量浓度与土壤有效磷质量分数之间呈显著相关(P < 0.05);径流中总氮和总磷的年累积流失量分别为11.01 kg·hm-2·a-1和133.70 g·hm-2·a-1,泥沙中全氮和全磷的年累积流失量分别为11.49和1.12 g·hm-2·a-1,山核桃林氮磷流失严重。Abstract: This study was designed to determine the characteristics of nitrogen (N) and phosphorus (P) losses in runoff and sediment with only natural rainfall in a Carya cathayensis stand for a whole hydrological year. The closed zone of a C. cathayensis stand in Lin'an District of Hangzhou setted up a monitoring station for location monitoring was selected to measure total nitrogen (TN), total phosphorus (TP), and dissolved nitrogen (DN) from June 2016 to May 2017 and analyzed. Results showed a significantly positive linear correlation (r=0.940 6, P < 0.05) between runoff and rainfall. During the observation period, the average concentration of N in runoff water was far higher (2.86 mg·L-1) than mass concentration of eutrophication in water. DN in the runoff was a main form of N loss accounting for 60.7% of TN; whereas, the average concentration of P was lower (0.01 mg·L-1) than concentration in other economic forest runoff. There was no significant relationship (P>0.05) between N concentration from runoff and soil available N, but P concentration from the runoff was significantly linearly related to available P (P < 0.05). Accumulated loss of TN in the runoff was 11.01 kg·hm-2·a-1 and TP was 133.70 g·hm-2·a-1; whereas, accumulated loss of TN in the sediment was 11.49 g·hm-2·a-1 and TP was 1.12 g·hm-2·a-1. Thus, in the C. cathayensis stand, rainfall was an important factor affecting runoff with losses of N and P serious.
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Key words:
- forest ecology /
- Carya cathayensis stand /
- closed zone /
- runoff /
- soil /
- sediment /
- nitrogen (N) and phosphorus (P) /
- loss
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表 1 山核桃闭合区径流不同形态氮磷的平均质量浓度及占比
Table 1. Average concentration and proportion of N and P in different forms of runoff in the closed zone of a Carya cathayensis stand
成分 ρ/(mg·L-1) 比例/% 氮素 铵态氮 0.05 1.8 硝态氮 1.11 38.9 水解氮 1.74 60.7 总氮 2.86 磷素 水解磷 0.01 35.2 总磷 0.03 -
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2018.05.003