中国不同纬度现代表层土壤水氢同位素分布特征及其影响因素

Hydrogen isotope ratios of modern soil water from different latitudes parts of China: characteristics and effect factors

关键词:  氢同位素  土壤水  大气降水  纬度

Key words:  hydrogen isotope  soil water  precipitation  latitude

摘要:

土壤水的氢氧同位素组成是开展环境示踪和土壤水文学研究的重要基础。目前的研究集中在对大气降水的氢同位素组成的相关信息认识上，关于大区域范围的环境因素对于土壤水和大气降水的氢同位素组成影响的报道很少。2016年9月从中国南部地区一直到东北地区（北纬20°—51°）采集了43个表层土壤样品，并测定表层土壤水δD值。结果表明：不同纬度表层土壤水的δD值与降水δD值存在正相关关系（ R²=0.40， P＜0.01），表明表层土壤水δD值总体响应大气降水的δD值变化，但可能也受其他因素影响。大气降水的δD值与表层土壤水δ D值均有明显的纬度效应，但它们的δD值随纬度变化的程度并不相同，表明虽然表层土壤水主要的来源是降水，但环境变化对表层土壤水的氢同位素组成产生了一定影响，这是利用表层土壤水δD值示踪环境或者与植物中的生物标志物的氢同位素组成结合来示踪环境的基础。

Abstract:

Background, aim, and scope Soil water is the critical matter in crops and plant recovering, thus is has significant value in environment research. In previous study, rain water has been proved that it is one of main sources of soil water and rain water, which can be used to measure the procedure of infiltration, evaporation and mixture of soil water in soil. In recent years, there are many studies which claim that the biomarker δD in geological carrier (such as soil and lake sediment) can be used to reconstruct palaeoenvironment and paleoecology etc., especially it is important for rebuilding the ancient precipitation. In addition, recent studies are mainly focused on the relationship between leaf wax δD and precipitation δD, few of them concern with soil water δD. Soil water δD generally comes from precipitation, nevertheless, it has differences comparing with precipitation δD. Therefore, the research of soil water δD may cause significant influences to the comprehension of the constitution changes of leaf wax hydrogen isotope from terrestrial plants. The propose of this study is to analyze soil δD from precipitation and other factors (such as latitude) by investigating the topsoil water δD from different latitude systematically. Also to provide understanding of environmental effects to the research of leaf wax hydrogen isotope of terrestrial plant in mechanism aspect. Materials and methods We collected 43 topsoil samples from south to northwest parts of China (20°N—51°N) in the rain season, 2016. Following that, we analyzed the soil samples to obtain the soil water δD. Soil water samples were collected by using vacuum distillation. Stable isotopic composition of liquid water was determined by using a Liquid Water Isotope Analyzer Picarro L2130-I (Picarro, Inc., Sunnyvale, CA, USA). Results (1) Precipitation δD has latitude effects, in comparison, soil water δD also has latitude effect. (2) The soil water δD and precipitation δD in different latitudes have positive correlation ( R ²=0.40, P ＜0.01). Discussion (1) Soil water δD and precipitation δD have positive linear correlation ( R²=0.40). It proves that precipitation is the one of main sources of soil water, which is consistent with previous studies. (2) Previous studies illustrate that soil water δD and altitude have negative correlation. (3) The isotope constitution of soil water has correlation with plant cover and soil water evaporation. (4) It is more effective to rebuild paleoenvironment by comparing plant δD and soil water δD. Conclusions (1) The change of soil water δD can record the signal of precipitation, their δD both have negative correlation with latitude. (2) Precipitation is one of main sources of soil water. Precipitation water δD and soil water δD have good linear fitting but there are also some other factors which affect the data. Our study shows that altitude, evaporation and plant cover are the major influence factors, which is consistent with previous study. There are still some other factors are waiting for further research. (3) It is more effective to rebuild paleoenvironment by comparing plant δD and soil water δD. Recommendations and perspectives (1) Our samples were collected in August and September, which belong to rain season (June to September). Consequently, this result shows the relation between precipitation and soil water in rain season in some extent. In addition, it has shortcomings since we lack of the data from June and July. The characteristic of whole rain season is planning to be completed in the future study. (2) In future research, focusing on the comparison of the δD value of leaf wax and the δD value of soil water will help to reduce the error.