种植方式对高原湖区集约化农田浅层地下水中氮浓度及其NO_(3)-来源的影响

Effects of Planting Methods on Nitrogen Concentration and Nitrate Sources in Shallow Groundwater of Intensive Croplands Around Plateau Lakes

种植方式影响着集约化农田种植过程中的水肥投入,进而改变着农田区浅层地下水氮浓度和水中硝酸盐(NO_(3)-)来源及其贡献。为明确不同种植方式对地下水氮浓度及其水中NO_(3)-来源的影响,利用水化学、δ^(15)N-NO_(3)-和δ18O-NO_(3)-、稳定同位素源解析模型(SIAR),研究了杞麓湖周边露天蔬菜种植区和滇池周边设施蔬菜花卉种植区(简称“设施种植区”)浅层地下水中氮浓度和NO_(3)-来源的差异及其影响因素。结果表明:①露天蔬菜种植区旱季地下水NO_(3)^(-)-N浓度高于设施种植区,雨季则低于设施种植区;NO_(3)^(-)-N是两类种植区农田地下水中主要的氮形态,旱、雨季超过50%的样点NO_(3)^(-)-N浓度超过GB/T 14848-2017《地下水质量标准》Ⅲ类水质要求(20 mg/L)。②露天蔬菜种植区旱、雨季地下水化学类型均以HCO_(3)^(-)-Ca^(2+)·Mg^(2+)和SO_(4)^(2-)·Cl^(-)-Ca^(2+)·Mg^(2+)型为主,而设施种植区旱季以HCO_(3)^(-)-Ca^(2+)·Mg2和SO_(4)^(2-)·Cl^(-)-Ca^(2+)·Mg^(2+)型为主,雨季以SO_(4)^(2-)·Cl^(-)-Ca^(2+)·Mg^(2+)型为主。③露天蔬菜种植区旱、雨季地下水氮的转化以反硝化为主,设施种植区旱季以硝化为主,雨季以反硝化为主。氮转化过程差异也影响着地下水NO_(3)-的来源,露天蔬菜种植区旱、雨季地下水NO_(3)-主要来源为土壤有机氮(分别占45.8%和30.9%)、粪肥和污水氮(分别占27.2%和32.2%)、化肥氮(分别占23.8%和27.1%);设施种植区旱季地下水NO_(3)-主要来源为粪肥和污水氮(占59.1%),雨季为土壤有机氮(占38.8%)和化肥氮(占34.1%)。研究显示,不同种植方式主要影响着地下水氮浓度水平和NO_(3)-主要来源的贡献率,而对浅层地下水中NO_(3)-主要来源(土壤有机氮、粪肥和污水氮、化肥氮)的影响不大。地下水NO_(3)-污染防治应合理施用化学氮肥,减少土壤氮流失,加强生活污水管控和科学利用畜禽养殖粪便。

The planting method affects the water and fertilizer inputs during crop cultivation in intensive agricultural areas,thereby changing the nitrogen concentration,nitrate(NO_(3)-)sources and their contributions in shallow groundwater in cropland areas.To assess the-effects of different planting methods on the nitrogen concentration and NO_(3) sources in shallow groundwater,the hydrochemistry,-δ^(15)N-NO_(3) andδ18O-NO_(3)-,and stable isotope source analysis model(SIAR)were used to study the differences and influencing factors of-nitrogen concentration and NO_(3) sources in shallow groundwater in the open-air vegetable planting areas around Qiluhu Lake and the facility vegetable and flower planting areas around Dianchi Lake.The results showed that:(1)In the dry season,NO_(3)^(-)-N concentrations in groundwater in open-air vegetable planting areas were higher than those in facility planting areas,while in the rainy season it was lower than that in facility planting areas.NO_(3)^(-)-N was the main nitrogen form in the groundwater of cropland in both types of planting areas.More than 50%of groundwater samples from both types of planting areas in both dry and rainy seasons exceeded the ClassⅢwater quality standard(20 mg/L)for NO_(3)^(-)-N of the Standard for Groundwater Quality(GB/T 14848-2017).(2)The groundwater hydrochemistry in open-air vegetable planting areas during the dry and rainy seasons was mainly HCO_(3)^(-)-Ca^(2+)·Mg^(2+)and SO_(4)^(2-)·Cl^(-)-Ca^(2+)·Mg^(2+)types,respectively.In facility planting areas,the HCO_(3)^(-)-Ca^(2+)·Mg2 and SO_(4)^(2-)·Cl^(-)-Ca^(2+)·Mg^(2+)types were mainly present in the dry season,while in the rainy season,the SO_(4)^(2-)·Cl^(-)-Ca^(2+)·Mg^(2+)types dominated.(3)Nitrogen transformation in groundwater in open-air vegetable planting areas was mainly through denitrification in the dry and rainy seasons,while in the facility planting areas,nitrification was the main process in the dry season and denitrification was the main process in the rainy season.The difference in nitrogen^(-)-transformation process also affected the source of NO_(3) in groundwater.The main sources of NO_(3) in groundwater in open-air vegetable planting areas in the dry and rainy seasons were soil organic nitrogen(45.8%and 30.9%),manure and sewage nitrogen(27.2%and-32.2%),and chemical fertilizer nitrogen(23.8%and 27.1%).The main sources of NO_(3) in the groundwater in facility planting areas in the dry season were manure and sewage nitrogen(59.1%),while in the rainy season,it was soil organic nitrogen(38.8%)and chemical fertilizer nitrogen(34.1%).This study showed that different planting methods mainly affected nitrogen concentration level in groundwater^(-)-and the contribution rate of NO_(3) as the main source,and had little impact on the main sources of NO_(3) in shallow groundwater(soil-organic nitrogen,manure and sewage nitrogen,chemical fertilizer nitrogen).To prevent and control groundwater NO_(3) pollution in the study area,strategies should include reasonable application of chemical nitrogen fertilizer,reducing soil nitrogen loss,strengthening the control of domestic sewage,and scientifically utilizing livestock and poultry manure.