摘要
我国北方蔬菜种植过程中大量施用化学肥料和人畜粪肥,引起区内浅层地下水硝酸盐(NO_(3)^(-))浓度急剧升高,但高浓度NO_(3)^(-)来源及在浅层地下水环境中转化的过程尚缺乏同位素证据,特别是强降雨事件对其影响尚不清楚。化学肥料中铵盐(NH_(4)^(+))转化为NO_(3)^(-)是造成蔬菜种植区浅层地下水中NO_(3)^(-)浓度升高的重要原因,强降雨事件导致浅层地下水水位升高,土壤和包气带中剩余NH 4+氧化为NO_(3)^(-)造成地下水NO_(3)^(-)浓度升高。为验证上述假设,选择豫北某蔬菜种植基地浅层地下水作为研究对象,通过对比分析枯水期(2021年4月)和丰水期(2021年10月)浅层地下水NO_(3)^(-)浓度及同位素组成(δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)),结合水化学以及水的氢氧同位素组成(δD-H_(2)O和δ^(18)O-H_(2)O),辨识浅层地下水高浓度NO_(3)^(-)来源及其对强降雨事件的响应。结果表明:(1)丰水期浅层地下水中ρ(NO_(3)^(-))范围较枯水期更大,中间值更高,分别为177.47和114.68 mg·L^(-1);(2)丰水期浅层地下水中δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)范围较枯水期更宽泛,δ^(15)N-NO_(3)^(-)中间值升高,丰水期和枯水期分别为7.8‰和7.3‰,但δ^(18)O-NO_(3)^(-)中间值降低,丰水期和枯水期分别为5.1‰和6.4‰;(3)丰水期浅层地下水δ^(18)O-H_(2)O范围较枯水期变窄,中间值升高,分别为-8.8‰和-9.2‰。氘盈余值(d_(e)=δD-8×δ^(18)O)范围变小,中间值降低,丰水期和枯水期分别为6.9‰和9.5‰;(4)强降雨洗脱包气带中富集15 N的NH_(4)^(+)转化为NO_(3)^(-),导致浅层地下水ρ(NO_(3)^(-))升高,δ^(15)N-NO_(3)^(-)值升高,但δ^(18)O-NO_(3)^(-)值降低;(5)贝叶斯同位素混合模型的解析结果表明,丰水期浅层地下水中NO_(3)^(-)来自于粪肥贡献率较枯水期增加,来自于土壤有机氮贡献率降低,化肥中铵态氮贡献率变化不大,但硝态氮肥贡献率增加,同时大气降水硝酸盐贡献率
In the vegetable cultivation regions of northern China,intensive use of chemical fertilizers and various types of manure has led to a significant rise in nitrate concentration in shallow groundwater.Despite this,there remains a deficiency in comprehensive isotope-based evidence regarding the origins and transformation pathways of elevated nitrate levels in these environments,coupled with an incomplete understanding of the impacts of heavy rainfall events on this matter.The oxidation process of ammonium salts within chemical fertilizers to nitrate is a key factor contributing to elevated nitrate levels in the shallow groundwater.During heavy rainfall,elevated water tables prompt the oxidation of residual ammonium in the soil and unsaturated zones into nitrate.This process will increase the concentration of nitrate in groundwater.To verify this hypothesis,we investigated the shallow groundwater in a vegetable plantation in northern Henan Province.Through the analysis concentrations and isotopic compositions(δ^(15)N-NO_(3)^(-)andδ^(18)O-NO_(3)^(-))during the dry season(April 2021)and the wet season(October 2021),as well as hydrochemistry and hydrogen/oxygen isotopes of water(δD-H_(2)O andδ^(18)O-H_(2)O),the sources of high concentration nitrate in shallow groundwater and their responses to heavy rain events were studied.Our findings shows that:(1)Nitrate levels during the wet season exhibited a broader range and a higher median(177.47 mg·L^(-1))compared to the dry season(114.68 mg·L^(-1));(2)Isotopic values(δ^(15)N-NO_(3)^(-)andδ^(18)O-NO_(3)^(-))showed wider ranges during the wet season,with a medianδ^(15)N-NO_(3)^(-)increase from 7.3‰to 7.8‰and aδ^(18)O-NO_(3)^(-)decrease from 6.4‰to 5.1‰;(3)δ^(18)O-H_(2)O range in shallow groundwater was narrower during the wet season,with a higher median(-8.8‰vs.-9.2‰).Deuterium excess(d e)values also exhibited a narrower range but a lower median of 9.5‰vs.6.9‰during the dry season and wet season,respectively;(4)Heavy rainfall events resulted in the wa
作者
陈昊
李艳利
高振朋
张琮
张东
CHEN Hao;LI Yan-li;GAO Zhen-peng;ZHANG Cong;ZHANG Dong(Institute of Resources&Environment,Henan Polytechnic University,Jiaozuo 454003,China;College of Oceanography and Ecological Science,Shanghai Ocean University,Shanghai 201306,China)
出处
《生态与农村环境学报》
CAS
CSCD
北大核心
2024年第7期943-953,共11页
Journal of Ecology and Rural Environment
基金
国家自然科学基金(42073009,41573095)。
关键词
蔬菜种植区
浅层地下水
硝酸盐来源
同位素混合模型
强降雨事件
vegetable cultivation area
shallow groundwater
nitrate source
isotope mixing model
heavy rainfall event
