Spatiotemporal Characteristics And Ecological Effects Of Halogens In Terrestrial Soil,in China

In the early 1990 s,China's soil environmental quality geochemical monitoring network systematically obtained the national soil environmental quality status for the first time.Due to the lack of large-scale,more detailed and high-quality soil monitoring data,little is known about the change of soil quality in China in the past 20 years.It was not until 2015 that the latest national geochemical monitoring network for land quality was established based on the original monitoring network,and more reliable new data were obtained.In order to understand the characteristics of geochemical changes of halogens in land soils in China in the past two decades and the soil environmental problems caused by them.Based on 741 comparable surface soil data(5-25cm)obtained by the national land quality geochemical monitoring network in 1992 and 2015,this paper analyzed the change of halogens content and the spatial distribution of halogens in China's land soil during 1992-2015,and discussed 13 major geochemical landscape areas and ten first-class river basins by using the method of classification and zoning.Based on the above monitoring results,the problems and driving mechanism behind the changes were explored.The results showed that: 1)at the national level,the content of Br and I increased,but the content of Cl decreased,and the content of F remained almost unchanged in the surface soils from 1992 to 2015,with the change rates of 26.9%,18.6%,-19.4% and 1.20% respectively;2)The spatial distribution of Br and I changes were the same,and the areas with decreased content included the northeast region,and the northern semi-arid area;the area with increased content is southwest area,and the area with increased content of I element also includes southeast coastal area;Cl element is opposite to the former element;3)In the 13 geochemical landscape areas,there are 5 landscape areas with the increase of halogens content,4 landscape areas with the decrease of halogens content,and the other landscape areas have little change;4)There are 3 basins with the increase of halogen element content and 2 basins with the decrease of halogen element content in the top ten first level basins;5)the land quality problems reflected by the monitoring changes of halogen elements are mainly soil erosion,soil desertification and soil salinization,respectively corresponding to the Songhua River Basin in the northeast of China,the semi-arid middle and low mountain and mausoleum landscape area in the north of China,the southeast coastal area of China,especially the southeast rivers;6)The above changes in the content of halogens and the land quality problems reflected may be related to the content of organic matter,changes in oil and gas resources,seawater intrusion and other aspects.Strictly speaking,the specific reasons need to be further determined.